T-cell Engager Research Articles

Bispecific T-Cell Engagers for B-Cell NON-Hodgkin Lymphoma Patients before Allogeneic Stem Cell Transplantation. a Study on Behalf Od Geth-TC

Background: Bispecific T-cell engagers antibodies (BiTEs) have shown promising efficacy across B-cell non-Hodgkin lymphoma (BCL) subtypes. If a response is observed, consolidation with allogeneic hematopoietic cell transplantation (alloHCT) could be reasonably pursued for high risk patients. To date, no data are available regarding BiTEs exposure prior to an alloHCT. Our aim was to describe patient characteristics, response, survival outcomes and treatment-related toxicities of patients treated with anti CD20-CD3 BiTE before alloHCT. Methods: We performed a multicentric, retrospective study including adult patients (>18 years old) who received an alloHCT as consolidative therapy following anti-CD20-CD3 BiTE treatment for relapsed/refractory (R/R) BCL between February 2018 and March 2023. The primary endpoint was non-relapse mortality (NRM). Secondary endpoints were overall survival (OS), progression-free survival (PFS), relapse/progression of disease (Rl/POD), cumulative incidence of acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD), and hematological recovery. Probabilities of OS and PFS were calculated using Kaplan-Meier estimator method, and NRM, RI/POD, GVHD and hematological recovery as cumulative incidences. Results: A total number of 29 patients were included in the analysis. Patient's characteristics are described in Table 1. Median age was 57 (range 22-67) and 62.1% of patients were males. Twenty-four (82.8%) patients had stage III-IV at diagnosis and 21 (72.4%) were primary refractory. Nine (31%) patients had received an autologous transplant and 10 (34.5%), anti-CD19 CART prior to BiTE. Median number of lines at alloHCT were 4 (range 3-11). Median time from diagnosis to alloHCT was 39 (range 9 -208) months. Epcoritamab (n=16) was administered in monotherapy. Glofitamab (n= 13) was given in either monotherapy (n=2) or combination with either atezolizumab (n=2), polatuzumab (n=3) or englumafusp (n=6). The median number of BiTE's administered doses was 10 (range 4-20). The median time between BiTE's last dose and alloHCT was 44 (range 13 - 203) days. Median follow-up among survivors was 21.9 months (range 3.3 - 52.6 months). At 18-months, OS, PFS, NRM and RI/POD were 66% (95% confidence interval [CI]: 45-81%), 62% (95% CI: 40-78%), 33% (95% CI: 15-53%), and 4% (95% CI: 0-12%), respectively. Causes of death were 1 relapse and 9 transplant toxicities (7=infections, 1=cGVHD, 1=cerebrovascular disease). Fifty-five percent of toxicity-related deaths were observed during the first 3 months from transplant. The cumulative incidence of neutrophil and platelet engraftment at day +30 was 90% (95% CI, 78-100%) and 68% (95% CI, 50-86%), respectively. The cumulative incidence of all grade and grade II-IV aGVHD at day +100 was 31% (95% CI: 13-49%) and 22% (95% CI: 7-37%), respectively. The cumulative incidence of all grade cGVHD at 18 months was 16% (95% CI: 2-30%), with only 1 patient presenting with moderate cGVHD. On univariate analysis, no prognostic factors were found in terms of OS, PFS, RI/POD and NRM. A comparison with a contemporary cohort of alloHCT recipients for BCL (N=101) from the Grupo Español de Trasplante y Terapia Celular (GETH-TC) who were not exposed to BiTE was performed ( figure 1). Propensity score matching using most significant patient, disease and alloHCT characteristics was performed to reduce cohort's heterogeneity ( Table 1). In the final 1:1 matched population (n=58; 29 patients treated with BiTE prior alloHCT and 29 patients who did not receive BiTE prior alloHCT), no differences in terms of OS, PFS, RI/POD and NRM at 18 months were observed (66% [95% CI, 45-81%] vs 48% [95% CI, 29-65%] [p=0.18]; 62% [95% CI, 40-78%] vs 45% [95% CI, 27-62%] [p=0.17]; 33% [95% CI, 14-52%] vs 41% [95% CI, 22-60%] [p=0.35] and 4% [95% CI, 0-10%] vs 10% [95% CI, 0-20%] [p=0.24]. Conclusions: We describe for the first time the results of BiTE exposure before alloHCT in terms of safety and efficacy. AlloHCT as consolidation therapy is feasible and does not seem to be detrimental for transplant outcomes in patients with R/R BCL with expected toxicity and surprisingly low relapse rate.

Patterns of Cytokine Release Syndrome with Teclistamab in Relapsed/Refractory Multiple Myeloma with or without Prior T-Cell Redirection Therapy

Introduction: Numerous therapeutic options with novel mechanisms of actions are currently available for treating patients with relapsed/refractory multiple myeloma (RRMM). Teclistamab (Tec) is a first-in-class BCMA X CD3 bispecific T-cell engager antibody that was recently approved for patients with RRMM who have received at least 4 lines of therapy (LOT). In the landmark MajesTEC-1 study, cytokine release syndrome (CRS) with Tec was reported at a rate of 72% (Usmani S, et al. Lancet 2021, Moreau P, et al. N Engl J Med 2022); however, patients who were previously treated with T-cell redirection therapies (TCRT) were excluded from the study [TCRT: chimeric antigen receptor (CAR) T-cells and/or other bispecific antibodies]. Given this knowledge gap, we investigated whether prior TCRT exposure impacts CRS rates with Tec in a real-world setting. Methods: Our institutional plasma cell disorders database was queried to identify RRMM patients who received commercial Tec from November 2022 to July 2023. Patients who completed the Tec step-up dosing phase (first step-up, second step-up and first full doses) were divided into two cohorts based on prior TCRT exposure before treatment with Tec (prior TCRT exposure: cohort 1 and no prior TCRT exposure: cohort 2). Data collection included patient demographics, disease characteristics, prior LOT, and rates/grades of CRS and immune effector cell-associated neurotoxicity syndrome (ICANS). The Chi-square/Fisher exact test was used to compare differences in CRS rates between the two cohorts. Univariate and multivariate logistic regression analyses were performed to assess impact of prior TCRT exposure on CRS rates with Tec. The results were presented as odds ratios (ORs) with 95% confidence intervals (CIs). For cohort 1, the Mann-Whitney U-test was used to compare the median time elapsed from the last prior TCRT dose until the first Tec step-up dose between patients who developed CRS with Tec compared to those who did not. All statistical analyses were performed using SPSS software (version 29). Results: 50 patients (cohort 1: 25 and cohort 2: 25) were included in the final analysis. Baseline characteristics were comparable between the two cohorts except for prior LOT, where patients in cohort 1 represented a more heavily pretreated population (Table 1). The CRS rates were significantly lower in cohort 1 (40%, n=10) compared to cohort 2 (76%, n=19, p=0.02; Figure 1). CRS grades 1 and 2 occurred in 32% (n=8) and 8% (n=2) of patients in cohort 1 and 48% (n=12) and 28% (n=7) of patients in cohort 2, respectively (p=0.40). Among the CRS events, 60% (6/10) and 68% (13/19) occurred following the first Tec step-up dose in cohorts 1 and 2, respectively. In univariate logistic regression analysis, no prior exposure to a TCRT was associated with about a 5-fold increase in the incidence of CRS with Tec (OR= 4.8, 95% CI: 1.5-17.1.2, p=0.02). After adjusting for age, extramedullary disease (EMD) and elevated LDH levels, the impact of prior exposure to TCRT remained significant with an OR of 4.5 (95% CI: 1.3-18.6, p=0.01). In cohort 1 (prior TCRT exposure), the median time elapsed between the last TCRT dose and the first Tec step-up dose was 321.5 days (range: 50-808 days) in patients who developed CRS with Tec compared to 265 days (range: 41-1617 days) in those who did not (p=0.90). Conclusion: In our study, prior exposure to a TCRT was associated with a significantly lower incidence of CRS during the Tec step-up dosing phase, which may be suggestive of T-cell exhaustion. This observation will allow for optimization of CRS prophylactic strategies for RRMM patients receiving Tec treatment.

In-Depth Immune Profiling in Children with BCP-ALL within the AIEOP-BFM ALL 2017 Study

The international multicenter frontline therapy trial AIEOP-BFM ALL 2017 prospectively randomizes CD19-targeting T-cell engager blinatumomab (BLN) against standard of care (SOC) to improve outcomes in pediatric patients (pts) with B-cell precursor acute lymphoblastic leukemia (BCP-ALL) stratified for high (HR) and medium (MR) risks of relapse. In HR arm BLN is given earlier, directly after intensified HR therapy block, while in the MR arm, it is given towards the end of chemotherapy, before maintenance. The immune composition prior to BLN might thus differ between both treatment groups (HR vs MR) which may impact BLN-mediated anti-leukemic activity. Within the Germany-wide immune monitoring program accompanying the AIEOP-BFM ALL 2017 trial we addressed this question and studied a total of 1056 longitudinal peripheral blood samples collected between 11/2018 and 05/2022 from 381 BCP-ALL pts. Samples were prospectively analyzed with multicolor flow cytometry to study immune cell composition (Panel 1) at the time of BLN application (d0) and under ongoing immunotherapy within first 24h (d1), at day 14 (d14), at the end of the cycle I (d28) and end of cycle 2 (day28_II), if applicable (Figure 1A). In-depth T-cell profiling was performed in the BLN arm, utilizing 4 additional 12-color panels concentrated on markers associated with T-cell functionality (measured with standardized cytometer settings). Data were analyzed using classical 2D-manual gating strategies (> 2000 variables) and completed with R-based machine learning algorithms; namely partial Least-Squares Discriminant Analysis (PLS-DA), a multivariate dimensionality-reduction tool for identifying HR- and MR-defining immune signatures and PhenoGraph algorithm for unsupervised T-cell cluster detection. T-cell receptor excision circles (TRECs) and TR-repertoire analysis were also performed among paired samples of 117 BLN-treated pts. Baseline immune composition differed notably between HR and MR pts directly prior to BLN therapy, as shown by PLS-DA analysis on manually gated immune subsets. HR pts showed higher neutrophil counts and lower lymphocyte and monocyte counts compared to MR pts. Interestingly, MR pts had higher levels of B- and T-cells, which are crucial for BLN-mediated T-cell activation. HR pts displayed an elevated CD4+/CD8+ ratio, shifted naïve/memory T-cell phenotypes and increased proportions of immunosuppressive T-regulatory cells. These results suggest that more intensive therapy protocols directly prior to BLN influence the immune composition towards compromised states in the HR arm, potentially affecting BLN-mediated T-cell leukemia control. BLN effectively depleted CD19+ cells in 221 out of 224 pts. We observed significantly stronger T-cell activation/expansion in MR pts compared to HR pts under BLN therapy. This expansion that was primarily attributed to naïve CD8+ T-cell populations, resulting from clonal T-cell proliferation independent of thymic contribution, as supported by TREC and TR-repertoire analysis. The PhenoGraph clustering also identified this expanding naïve CD8+ T-cell populations, surprisingly marked by loss of adhesion molecule DNAM1 (panel 1), normally involved in NK and T-cell mediated cytotoxicity and by gaining the expression of TIM-3 (panel 3), an inhibitory molecule usually co-expressed with PD1 on exhausted T-cells with memory phenotypes. In this setting however, TIM3 was not co-expressed with PD1 (Figure 1B) and its expression was correlated with the B-cell levels at baseline and was strongest in MR pts under BLN therapy. Our data suggest an until now undescribed association between DNAM1 and TIM3 with BLN-mediated T-cell activation, hinting that they may serve as a measure of T-cell activation strength or an early T-cell exhaustion marker. In conclusion our study provides clinically relevant insights in how chemotherapy prior BLN might affect the patients´ immune system, possibly influencing the BLN anti-leukemic activity, and helps to determine the optimal place of immunotherapy with BLN in multimodal treatment schedules. Here, we report until know undescribed effect of BLN on T-cell compartment. Upcoming clinical data, which will be correlated with obtained immune profiles will answer the open question regarding the clinical relevance of these findings, and shed light into the mechanisms determining response to BLN, for its maximum benefit in childhood ALL.

Chemotherapy-Sparing Induction Followed By Consolidation and Maintenance with Blinatumomab and Concurrent Oral Tyrosine Kinase Inhibitor Therapy for Newly-Diagnosed Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia: Primary Endpoint Results from the Blissphall Study

Background: Oral ABL-targeted kinase inhibitors (TKIs) have transformed treatment of BCR::ABL+ (Philadelphia chromosome-positive, Ph+) acute lymphoblastic leukemia (ALL). Induction (IND) w/ corticosteroids (CS) and dasatinib (DAS) alone results in morphologic complete response (mCR) rates approaching 100% but low rates of measurable residual disease (MRD) negativity; addition of intensive chemotherapy to TKIs adds risks of myelosuppression. DAS + the CD3/CD19 bispecific T-cell engager blinatumomab (BLIN) is effective consolidation (CONSOL) for Ph+ ALL, though ABL kinase mutations conferring resistance can arise early in therapy (Foà, NEJM, 2020). We designed a phase II study of BLIN as part of a chemotherapy sparing strategy in pts w/ Ph+ ALL (BLISSPHALL), introducing BLIN as early as 6 weeks into treatment for pts in mCR, w/ aim of expediting MRD clearance and suppressing resistant clones early in disease course, and including a maintenance (MAINT) phase of BLIN + TKI for pts in molecular response. Methods: We conducted a multicenter trial of TKI + CS IND and TKI + BLIN CONSOL + MAINT in adults (≥18 yrs) w/ newly-diagnosed (ND) Ph+ ALL (NCT04329325). Study schema is depicted in Figure 1. Pts received CS pre-phase w/ prednisone (PRED) or dexamethasone (DEX) followed by modified GIMEMA LAL1205 IND (DEX + DAS 140 mg/d w/ DAS dose adjustments or TKI change per protocol) w/ intrathecal methotrexate (IT MTX) d22, 43 and bone marrow (BM) MRD assessments including FACS and BCR::ABL1 PCR. Pts in mCR on d43 could proceed to CONSOL w/ 3 cycles (C) of TKI + BLIN 28 mcg/d IVCI, d1-28, w/ 14d off BLIN between cycles and BM MRD assessment/IT MTX after each cycle. TKI was given continuously including between BLIN cycles. Pts in protocol-defined complete molecular response (CMR; MRD negative by FACS and no detectable BCR::ABL1 transcripts) after CONSOL could proceed to MAINT (C4-7 BLIN + TKI, 28d off between cycles). The primary objective is to determine the proportion of evaluable pts achieving CMR by the end of CONSOL (≤ 3C BLIN + TKI). Secondary objectives include safety/toxicity of BLIN + DAS, duration of CMR, incidence of relapse, event-free/overall survival. Toxicities were defined by CTCAE v5.0. Results: 17 pts enrolled (12 women, 5 men) w/ median age 50 yrs (range 22-87); BCR::ABL1 transcript type p190 (n=15) or p210 (n=2). Median follow-up 11.7 months (range 3-24). All began DAS 140 mg/d as initial TKI; 4 changed TKI for DAS intolerance per protocol (bosutinib, n=2; ponatinib [PON], n=2) and remained on study; TKI was changed to PON in 1 other pt to optimize BCR::ABL1 transcript suppression pre-allogeneic transplant (alloHCT) and that pt was withdrawn from study. Two had interruption or delay of BLIN due to toxicity (grade [G] 3 transaminase elevation, n=1; G2 cytokine release syndrome, n=1); BLIN was resumed in both. Figure 2 lists nonhematologic adverse effects (AEs) seen in ≥2 pts at least possibly related to TKI or BLIN while on study. One pt developed G3 pancreatitis after DAS was changed to PON; TKI was changed back to DAS. There were no G4-5 AEs. All pts (100%) achieved mCR during IND (median d22). Ten achieved CMR to date (5 during IND, 5 during CONSOL) and 6 did not achieve CMR; determination pending in 1 pt. By FACS, 16/17 achieved BM MRD negativity; 13/14 evaluable pts had no evidence of malignant clonal IgH rearrangement (IgHR) by next generation sequencing (NGS). Notably, 3 pts w/ persistent low-level BCR::ABL1 transcripts had no evidence of malignant clonal IgHR by NGS but were withdrawn post-CONSOL as protocol required BCR::ABL1 PCR negativity to proceed to MAINT. Two pts relapsed, both after achieving CMR (one declined CONSOL and self-discontinued TKI; one had extramedullary (EM) relapse w/ ABL T315I mutation). Four pts underwent alloHCT in CR1 (rising MRD levels on study leading to change in therapy, n=1; persistent BCR::ABL1 PCR positivity, n=2; IKZF1 plus phenotype, n=1); one underwent alloHCT in CR2 following EM relapse. Conclusions: DAS + CS IND w/ addition of BLIN to TKI in mCR leads to high rates of deep molecular response w/ low risk of early relapse and low rates of severe regimen-related toxicity in pts w/ ND Ph+ ALL. Use of PON (vs DAS) as initial TKI w/ BLIN may further suppress resistant clones. Further f/u is needed to confirm durability of CMR w/ BLIN + TKI CONSOL ± MAINT in absence of alloHCT and whether pts w/ persistent BCR::ABL1 PCR positivity and no malignant clonal IgHR by NGS exhibit similar outcomes to those in CMR.

A CD38/CD28xCD3 Trispecific T-Cell Engager (TCE) As a Potentially Active Agent in Multiple Myeloma Patients Relapsed and/or Refractory (RRMM) to Anti-CD38 Monoclonal Antibodies (mAbs)

Background: Despite great advances in the treatment of RRMM, including anti-CD38 mAbs, patients become resistant and therapeutic options are limited. Some factors involved in resistance to anti-CD38 mAbs have been described. On the one hand, their efficacy is partially dependent on baseline CD38 expression in MM plasma cells (MMPC), but the treatment induces a rapid and sustained CD38 downregulation. On the other hand, their tumor-killing activity relies on NK cells, but its frequency rapidly decreases following initiation of treatment, and persistent NK cells exhibit a dysfunctional phenotype. Given the reduction of CD38 levels in MMPC and the impaired NK-cell activity in resistance to anti-CD38 mAbs, we hypothesized that RRMM patients previously treated with these agents could benefit from T-cell-based immunotherapeutic strategies that depend less on CD38 antigen density and NK cell function. Aim: Evaluate a CD38/CD28xCD3 trispecific TCE (SAR442257) as a potential therapeutic agent in the RRMM setting. Results: CD38 expression in MMPC and NK-cell frequency in bone marrow were significantly reduced in 29 RRMM patients previously exposed to anti-CD38 mAbs vs 45 newly-diagnosed MM (NDMM) patients ( P <.001 and P =.013, respectively). Moreover, the percentage of CD57+ NK cells was significantly lower in RRMM than NDMM patients ( P =.006), suggesting that both CD38 downregulation and a contraction of cytotoxic NK cells may be associated with resistance to anti-CD38 mAbs. By contrast, T cells did not change significantly between stages, which ignited further interest in the preclinical efficacy of the CD38/CD28xCD3 TCE. First, we observed that, contrary to isatuximab and daratumumab, CD38/CD28xCD3 TCE did not reduce surface CD38 levels in the MOLP 8, RPMI 8226 and KMS 12 BM cell lines. Fluorescence microscopy imaging revealed that CD38 was present in cell membrane up to one week of treatment with CD38/CD28xCD3 TCE, while isatuximab induced an internalization of CD38 at 24h. Next, in a co-culture of the OPM-2 cell line with purified T or NK cells from healthy individuals (E:T ratio 2:1), we confirmed that the activity of CD38/CD28xCD3 TCE relied on T but not NK cells. Namely, no direct NK-cell stimulation was found whereas a significant T-cell activation was observed upon CD38/CD28xCD3 TCE treatment. Surprisingly, when OPM-2 were co-cultured with freshly-isolated peripheral blood mononuclear cells (PBMCs, E:T ratio 10:1), CD38/CD28xCD3 TCE induced activation of T- and NK-cells, suggesting a bystander NK-cell activation. This dual stimulation resulted in a significant reduction of OPM-2 cell viability at 48h. Interestingly, we found a comparable tumor-killing activity and T-cell activation in the presence of the CD38 null trispecific isotype (CD3xCD28 ΔCD38) compared with CD38/CD28xCD3 TCE, suggesting that the latter targets CD28 not only in T-cells, but also in OPM-2 cells, which express high CD28 basal levels. Altogether, these data demonstrate the potential dual CD38/CD28 targeting in RRMM patients previously exposed to anti-CD38 mAbs, particularly in those with double positive MMPC. Additionally, CD38 regulation was analyzed in the co-culture system (measured with a non-competing anti-CD38 antibody), and an unaltered and increased CD38 expression was observed in OPM-2 and T-cells, respectively, indicating again T-cell stimulation. We tested the ex vivo efficacy of CD38/CD28xCD3 TCE (48h, 700 pM) in primary bone marrow samples from eight RRMM patients, which were collected after a median of 10 months since the last anti-CD38 treatment (range, 0.5 - 37). T-cell activation and MMPC lysis were found in six and four samples, respectively, which was accompanied by a reduction in the frequency of CD4 T cells (from 100% to 76%; P =.014). A positive and borderline-significant correlation (r = 0.764, P =.057) was found between the response to CD38/CD28xCD3 TCE and the time since last anti-CD38 treatment, and no differences in CD38 expression were observed between CD38/CD28xCD3 TCE responders and non-responders. Conclusions: We observed a reduction in CD38 levels in MMPC and an impaired cytotoxic activity of NK cells in RRMM patients previously exposed to anti-CD38 mAbs. We propose a second targeting of CD38 using T-cell-based immunotherapeutic agents whose efficacy depends less on CD38 antigen density, especially after longer washout periods, as a potential therapeutic strategy in the RRMM setting.

A Phase 2, Single-Arm, Non-Inferiority Study of Limited-Duration Teclistamab for Relapsed and Refractory Multiple Myeloma (LimiTec)

Background and Significance: Teclistamab, a BCMA-directed T-cell engager (anti-BCMAxCD3 bispecific antibody), is currently approved for relapsed/refractory multiple myeloma (MM) patients with ≥4 prior lines of therapy, including an IMID, proteasome inhibitor, and CD38 antibody. Teclistamab is typically dosed on a regular schedule (every 1-4 weeks) indefinitely until disease progression. Yet continuous exposure, as reported on the phase 1/2 MajesTEC-1 study, was associated with infectious complications in 78% of patients, with 52% grade 3 or 4 events (van de Donk et al, ASCO 2023) and several fatal infections (Moreau et al., NEJM 2022). Sustained off-drug responses have been observed in patients who discontinued teclistamab for reasons other than progression and have also been reported with cevostamab, an anti-FcRH5xCD3 bispecific antibody under investigation as a limited-duration regimen (17 cycles) in MM (Lesokhin et al, ASH 2022). These findings raise the possibility that limited-duration teclistamab might provide comparable efficacy with lower risk compared to continuous therapy. Therefore, we hypothesize that monitored discontinuation of teclistamab in patients with deep response after 6-9 months of continuous therapy, with option to resume upon early sign of MM growth, will be non-inferior to that of historical controls [from the MajesTec-1 trial] who were treated with continuous teclistamab dosing. Study design and methods: This is a single-arm, non-inferiority study in which patients who have achieved a very good partial response (VGPR) or better, according to International Myeloma Working Group (IMWG) response criteria, following 6-9 months of standard-of-care teclistamab, will be offered monitored drug discontinuation. Patients will be monitored monthly off-drug for up to 24 months and will be allowed to resume commercial teclistamab on-study in the event of early disease growth (defined as increase in involved free light chain >20 mg/L with ratio >5) or progression (as defined by IMWG criteria).The primary objective is to preliminarily assess whether the rate of treatment failure of limited-duration teclistamab after 6 months of drug discontinuation is non-inferior to that of historical controls who received continuous therapy, where treatment failure is defined as any of the following events: (1) disease progression after teclistamab re-initiation (for subjects who resume teclistamab for early disease growth), (2) failure to achieve at least minimal response to teclistamab re-initiation (for patients who resume teclistamab for IMWG progression), (3) initiation of non-teclistamab systemic MM therapy, or (4) death due to complications of MM, teclistamab, or infection. Secondary endpoints will evaluate time to progression, rates of re-response, the rate and severity of infections, types of clinical complications with progression, patient reported outcomes, and immune cell subset composition. Analysis of minimal residual disease (MRD), tumor features, and bone marrow microenvironment parameters, which will be pursued as exploratory correlative analyses in this study, may identify factors that predict durable response to limited-duration therapy and thereby enable more precise selection of patients likely to benefit from this approach. A subset of patients will be enrolled in an optional biomarker sub-study for analysis of these exploratory endpoints. We will enroll ~75 subjects to reach the target of 64 evaluable subjects assuming 15% will be not evaluable. The sample size was calculated based on a non-inferiority test for the primary outcome of failure-free probability at six months after the date of discontinuation of teclistamab against the null value of 0.79 that estimated from a historical cohort with 80% power, 0.05 alpha level, and a non-inferiority margin of -0.15. The power was evaluated at the value such that no difference between the historical and early discontinuation values using a one-sided one-sample continuity-corrected Z-test for testing a binomial proportion (normal approximation) with the standard deviation estimated under the null value. Conclusions: This single-arm, phase 2 study is exploring whether limited-duration teclistamab is non-inferior to continuously administered therapy in patients who have received 6 to 9 months of teclistamab and have achieved at least a very good partial response. Accrual started in July 2023.

Unraveling the Mechanism of Action of Bispecific T-Cell Engagers in B-Cell Acute Lymphoblastic Leukemia Using Advanced Single-Cell Multiomics

Background Bispecific T-cell engagers (BiTEs) stimulate T lymphocytes proximate to tumor cells, inducing T-cell stimulation and tumor killing. Blinatumomab, an anti CD3-CD19, was the first to be approved with overall response rates of up to 80% in refractory B-cell Acute Lymphoblastic Leukemia (B-ALL). To overcome resistance and to develop next-generation BiTEs, we need to build on blinatumomab's success and better understand BiTEs mode of action and interaction with the tumor microenvironment (TME). Here, we apply advanced multiomics to examine blinatumomab's activation signatures and the sustained dynamics in the tumor and bone marrow (BM) immune TME. Methods Physically interacting Cells sequencing (PIC-seq) is an advanced multiomics technology deciphering the crosstalk between the cellular components of an immunological synapse (Cohen et al., 2022; Giladi et al., 2020). To assess Immediate activation signatures, we applied PIC-seq on a model of B-ALL cell lines (RS4;11, NALM-6) and lymphocytes obtained from healthy subjects, activated by blinatumomab, compared to no-treatment and activation with anti CD3-CD28 antibodies. To examine the Sustained effects on the immune TME, we performed a longitudinal single-cell RNA sequencing of the bone BM of adult B-ALL patients, before and after treatment with blinatumomab in the Division of Hematology in the Tel Aviv Sourasky Medical Center in 2021-22. Results Immediate activation Applying PIC-seq on n=16,543 CD3 and CD19+ cells, we identified the distinct gene expression of ‘blinatumomab-activated lymphocytes’ (Figure 1). Blinatumomab induced cellular synapses composed of specific T lymphocytes subsets along the activation continuum, namely: effector T cells (CCL5, GNLY, NKG7), early IFN-G activation (IRF1, GBP5), activated cytotoxic (Xcl1-2, IFN-G) and proliferating T cells (CD69, CCND2) . ‘Blinatumomab-activated lymphocytes’ were characterized by a unique activation signature: upregulation of cytotoxicity (Xcl1, IFN-G, GNLY), co-stimulation and B-T cells crosstalk (CD40, CD27, TNFRSF18), immune recruitment (CXCL10, CCL4) and antigen-presentation (TNFSF14, ITGB2) pathways. Late synapses also expressed immunoregulatory molecules (TNFAIP8L2). This signature differed from classical anti CD3-CD28 induced activation and is independent of the donor and the target-cell identity. The malignant cells' response varied: RS4;11 cells manifested cellular senescence, while NALM-6 upregulated INFG-induced apoptotic pathways, suggesting indirect killing in the mechanism of action of BiTEs. Data on the introduction of primary B-ALL patients' cells will be presented at the ASH. Sustained effects We profiled >11,000 cells from three patients: Patient 1, 31-year-old (y/o) female, primary refractory B-ALL (50% BM blasts), attaining transient MRD negativity. Patient 2, 71-y/o male, primary refractory Ph+ B-ALL (74% BM blasts) achieving reduction in MRD following first cycle. Patient 3, 71 y/o, Ph+ B-ALL, treated as consolidation therapy, achieving MRD negativity. Blinatumomab induced a dramatic perturbation in the lymphocytic and myeloid compartments of the BM and was highly patient-specific ( Figure 2). The BM lymphocytic compartment prior to initiation of blinatumomab in molecular remission (patient 3) was characterized by active T and Natural Killer cell states, compared to an abundancy of naïve lymphocytes in active disease (patients 1 and 2). There were no signs of T-cell exhaustion pre or post treatment in all patients. Post-treatment, CD8 T-Central Memory cells proliferated in all patients. Patients treated for active disease (patients 2 and 3), had an expansion of the Tregs population post-treatment. In the myeloid compartment, patients with active disease had more non-classical monocytes, known to correlate with poor prognosis. These were replaced by classical monocytes following treatment, in addition to the emergence of a macrophage-precursor population. Data on the BM and peripheral blood dynamics of an additional six patients will be presented at the ASH. Conclusions We present an advanced single cell dissection of blinatumomab-induced target-effector interaction, providing novel insights into the mechanism of action and TME dynamics to guide patient selection and next generation BiTEs. A larger patients' cohort and introduction of patients' cells to the PIC-seq in vitro model will be presented at the ASH.

Dose Escalation of ISB 1342, a Novel CD38xCD3 Bispecific Antibody, in Patients with Relapsed / Refractory Multiple Myeloma (RRMM)

Introduction: ISB 1342 is a humanized CD38xCD3 bispecific T-cell engager using Ichnos proprietary Bispecific Engagement by Antibodies based on the T cell receptor (BEAT ®) platform, designed to simultaneously bind CD38 on multiple myeloma (MM) cells and CD3ε on T cells, to induce tumor killing. This mechanism of action is different from existing monospecific CD38 targeting therapies and was designed to overcome resistance to daratumumab in MM. ISB 1342 exhibits potent killing of the primary MM cells and MM cell lines with low sensitivity to daratumumab ( Pouleau B. et al. Blood 2023; 142 (3): 260-273). We report here, the updated findings from the weekly dose-escalations of intravenous (IV) and subcutaneous (SC) injections of an ongoing, single-agent phase 1 study (NCT03309111) of ISB 1342 in patients with RRMM. Methods: Adult patients with RRMM that relapsed after or were refractory to prior therapies, including a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 antibody; received ISB 1342 on a weekly (QW) schedule by IV or SC injection with a priming dose on the first day in 2 parallel dose-escalation schemas. Patients had measurable disease per the International Myeloma Working Group (IMWG) criteria (2016). Dose escalation in the QW schedule began at 0.2/0.3 mg/kg priming/treatment dose and followed a “3 + 3” design. The primary study objectives are to determine the maximum tolerated dose (MTD) and select a recommended phase 2 dose (RP2D) of ISB 1342. Secondary objectives includ evaluation of anti-myeloma activity, pharmacokinetics (PK), pharmacodynamics, and immunogenicity of ISB 1342. Results: As of July 18, 2023, based on ongoing clinical database, 39 subjects had received weekly IV infusions of ISB 1342 in 8 dose-escalation groups from 0.2/0.3 mg/kg to 4.0/16.0 mg/kg as priming/treatment dose; and 7 additional subjects had received weekly SC injections at 2.0/8.0 mg/kg. Two different formulations have been tested in SC group. Median number of cycles administered was 2. The majority were male (57%) and white (74%); 13% were Black or African American. The median age was 69 years (range, 54-76) and the median time since diagnosis was 6.6 years (range, 2.8-22.2). The median number of prior anti-myeloma lines of therapy was 6 (range 1-12). Twenty-one (67%) subjects were considered to be triple-class refractory and 18 (48%) penta-drug refractory. Forty-one (89%) subjects experienced treatment-related adverse events (TRAEs) of any grade. Most TRAEs were grade 1-2, including infusion related reactions (37%), cytokine release syndrome (CRS, 34%, all grade 1or 2), anemia (24%), neutropenia (24%), and thrombocytopenia (17%). Five subjects in SC group (71% of SC) had injection site reaction, all grade 1 or 2. Grade 3 or higher TRAEs occurring in more than 5% of subjects were infusion related reaction (no grade 4), anemia (no grade 4), neutropenia, leukopenia. No Grade 5 TRAE was observed. After QW IV infusion, ISB 1342 serum concentration peaked at the end of infusion and then showed bi-exponential decline. ISB 1342 serum exposures increased in a dose linear fashion across the tested IV infusion dose range. The limited PK data after SC injection suggest slow presentation of ISB 1342 into the systemic circulation leading to lower C max and delayed T max relative to IV. Transient increases in serum cytokines were observed within 24 hours after ISB 1342 dosing, including IFNg, TNFa, IL-2, IL-6 and IL-10. Transient increases in T-cell activation were observed by flow cytometry at 24-48 hours after ISB 1342 dosing at 1.0 / 4.0 μg/kg and above, based on increased expression of CD69 on peripheral blood CD4+ and CD8+ T-cell populations (Figure 1). Comparison of the available data from subjects treated at 2 / 8 μg/kg (Cohort 109) indicated reduced T-cell activation following SC compared to IV administration of ISB 1342. The efficacy signals observed in Cohorts 108 and 109 are consistent with the estimates of the lower boundary of the predicted efficacious dose range using a quantitative systems pharmacology (QSP) model based on preclinical data. Updated clinical data, including response rates and safety data, will be present at the meeting. Conclusions: Treatment with ISB 1342 was well tolerated at higher dose levels evaluated. Observed CRS events were moderate. No increased risk of infection has been observed . Updated safety, efficacy, biomarker and PK data will be presented.

The Effectiveness of Blinatumomab in Clearing Next-Generation Sequencing Measurable Residual Disease in Pediatric Patients with B-Cell Acute Lymphoblastic Leukemia

Introduction Blinatumomab is a bispecific T-cell engager antibody designed to redirect CD3+ T cells to bind to CD19+ target cells in relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). Measurable residual disease (MRD) is a significant prognostic factor for relapse and overall survival in B-ALL. Blinatumomab consolidation therapy has been shown to improve MRD remission (<10 -4), as detected by multiparameter flow cytometry (MFC) or reverse transcriptase-polymerase chain reaction (PCR), and survival outcomes in children with high-risk first relapsed B-ALL. The next-generation sequencing (NGS)-MRD is a highly sensitive technique that can detect very low levels of MRD (<10 -6) in patients who were considered “MRD negative” by less sensitive MFC or PCR technologies. Early achievement of NGS-MRD negativity (<10 -6) can help in identifying patients who have a very low risk of relapse. It has been suggested that blinatumomab treatment could help to attain deeper responses than that measured with a MRD sensitivity level of 10 -4. However, data on blinatumomab clearing MRD with high sensitivity of 10 -6 remain scarce. Hence, we evaluated the effectiveness of blinatumomab in eradicating extremely low level of MRD (<10 -6), as detected by NGS, in children with B-ALL. Methods Pediatric B-ALL patients who were MFC-MRD negative (<10 -4) but NGS-MRD positive (sensitivity of 10 -6) after chemotherapy followed by blinatumomab consolidation therapy between October 2021 and February 2023, were studied retrospectively. At diagnosis, NGS analysis was performed by high-throughput deep level sequencing using the Seq-MRD ® (ImmuQuad Biotech, Hangzhou, China) to detect clonal rearrangements. Genomic DNA was extracted from bone marrow samples using QIAamp DNA Mini kit (Qiagen, Hilden, Germany), amplified by quantitative PCR and sequenced using the Illumina® Novaseq PE150 (Illumina ® Novaseq, San Diego, USA) platform. The sequences of immunoglobulin heavy chain (IGH) variable (V), diversity (D), and joining (J) (IGH -VDJ), IGH-DJ, immunoglobulin kappa light chain (IGK), immunoglobulin kappa deleting element (IGKDE) and immunoglobulin light chain (IGL) were assessed for clonality with dominant index sequence(s). Results Overall, 19 patients were enrolled. The baseline patient characteristics are shown in Table 1. Median age at diagnosis was 4.4 years (range 0.3-10.6), with males accounting for 84% of patients. Eight patients (42%) had at least 1 unfavorable genetic abnormality (i.e., KMT2A rearrangement, E2A-PBX1). Seventeen (89%) patients had ≥2 Ig clonal rearrangement at diagnosis. In total, NGS detected 71 clonal rearrangements, including 27 IGH clonal rearrangements in 15 (79%) patients, 9 IGH-DJ in 6 (32%), 14 IGK in 8 (42%), 6 IGKDE in 9 (32%), and 12 IGL in 8 (42%) patients. All patients achieved hematological complete response (CR) with MFC-MRD <10 -4 after the induction or consolidation chemotherapy. However, all these patients were identified to be MRD positive by NGS, including NGS-MRD >10 -6 and positive but not quantifiable (NGS-MRD <10 -6). Though the patients were MFC-MRD negative, 19 IGH clones, 4 IGH-DJ clones, 8 IGK clones, 7 IGKDE clones and 3 IGL clones were still persisted. After blinatumomab, MRD negativity rate by MFC was 95% (18/19) and the NGS-MRD negativity rate was 68% at 10 -6 (13/19). The rate of MRD clearance after blinatumomab per NGS was 69% and 67% in CR1 and CR2 patients, respectively. The clearance rates of IGH, IGK, IGL, IGH-DJ, and IGKDE were 75%, 67%, 33%, 100%, and 83%, respectively (Table 2). Three NGS-MRD negative patients with available NGS-MRD at pre-, mid-, and post-treatment achieved MRD clearance rapidly after blinatumomab treatment that was maintained durably through day 28. Three of 6 NGS-MRD positive patients relapsed after blinatumomab with 3 being IGH positive and 2 being IGL positive. Conclusion To the best of our knowledge, for the first time it has been demonstrated that blinatumomab could further eradicate MRD in patients achieving MFC-MRD <10 -4. Advanced MRD detection using NGS and blinatumomab made deeper molecular remission in B-ALL patients achievable. Further large-scale studies are warranted to verify the prognostic value of NGS in detecting lower levels of MRD in ALL patients treated in the current immunotherapy era.

Vactosertib, a Novel TGFb Type I Receptor Kinase Inhibitor, Improves T-Cell Fitness:a Single-Arm, Phase 1b Trial in Relapsed/Refractory Multiple Myeloma

The prognosis for Multiple Myeloma (MM) patients (pts) has improved substantially over the past two decades with the success of immunomodulatory drugs (IMiDs), monoclonal antibodies, chimeric antigen receptor (CAR) T-cells and bispecific T-cell engagers (BiTEs) that broke the circulus vitiosus of tumor-induced immunosuppression to reengage the immune system. Functional blockade of the transforming growth factor-beta (TGF) signaling pathway improves the efficacy of cytotoxic and immune therapies, therefore we investigator the impact of TGF-inhibition in an steroid free regimn. Methods: We conducted a phase 1b study to determine the safety, efficacy, and maximal tolerated dose (200 mg po bid) of the potent, orally-available TGF type I receptor kinase inhibitor vactosertib in relapsed and/or refractory multiple myeloma (RRMM) pts who had received -2 lines of chemoimmunotherapy in combination with standard dosage of Pomalidomide without any corticosteroids. Results: Twenty one pts were enrolled in the phase 1b dose escalation cohort and received vactosertib plus pomalidomide as indicated (Fig. 1A). Pts' characteristics are described in Table 1The summary of grade 1-4 adverse events is shown (Table 2). A single grade 4 elevated bilirubin (5%) and a single grade 4 elevated lipase (5%) were observed as well as four grade 4 events of decreased neutrophils (19%). Four pts demonstrated a PR, two had a MR, nine had SD and four had disease progression (Fig. 1B). The median time to response for all pts and the responders eight weeks and median duration of response was ~12 weeks. The best overall response for individual pts to treatment is shown (Fig. 1C). Clinical activity was observed across all four dose levels (Table 3). To probe the tumor intrinsic anti-myeloma activity of vactosertib, we first determined the relative effect of vactosertib compared to the IMiDs pomalidomide and lenalidomide (Fig. 2A, B). The effect of vactosertib was greater than that observed with either lenalidomide or pomalidomide. MMCLs and patient CD138 + cells were then treated with vactosertib in combination with pomalidomide, and importantly, vactosertib with pomalidomide synergistically reduced myeloma viability (Fig. 3A). We next probed the systemic, tumor extrinsic effects of vactosertib by analyzing cytokines immune and tumor cells present within patient BM samples. (Fig. 4A). (Fig. 4B). Therefore, we explored the immunophenotype of CD8 + T-cells isolated from patient BM prior to and at the EOT. The relative percentage of T-cells that expressed the immunosuppressive markers programmed cell death-1 (PD-1), T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3), B and T lymphocyte attenuator (BTLA), and cytotoxic T-lymphocyte associated protein 4 (CTLA-4) was reduced following treatment relative to their expression prior to treatment (Fig. 4C). Results indicated that vactosertib and pomalidomide treatment in vivo reduced PD-1, TIM3, BTLA and CTLA-4 expression on patient CD8 + T-cells. Next, CD8 + T-cells were isolated from patient peripheral blood and cultured in the presence of TGF-1, vactosertib, pomalidomide, or vactosertib plus pomalidomide (Fig. 5B). Treatment of patient CD8 + T-cells with vactosertib decreased PD-1 expression up to 40% and decreased TIM3 expression up to 65%. Pomalidomide alone did not significantly reduce PD-1, TIM3, BTLA, or LAG-3 on patient CD8 + T-cells. Vactosertib and pomalidomide also reduced TIM3 levels on CD8 + T-cells from most pts. (Fig. 5C, D). (Fig. 5 G, H). Results indicated that vactosertib or pomalidomide did not increase CD138 + cell death (Fig. 5I). Conclusion: Vactosertib combined with pomalidomide was well-tolerated at all doses, had a manageable adverse event profile and induced durable responses with 80% progression-free survival (PFS-6) at 6 months, Vactosertib reduced TGF- in patient bone marrow and suppressed PD-1 expression on CD8 + T-cells and lead to reduction of PD-L1/PD-L2 expression on CD138 + cells and enhanced autologous T-cell cytotoxicity. Taken together, our results support the safety and efficacy of vactosertib to treat RRMM and revealed that vactosertib modulates the T-cell immunophenotype and reinvigorates T-cell fitness.

Stem Cell Utilization in the Era of Novel Therapies for Multiple Myeloma

Introduction: Stem cell collection is recommended for patients with newly diagnosed multiple myeloma (NDMM) deemed eligible for autologous stem cell transplantation (ASCT). Standard practice at most institutions is to collect an adequate number of stem cells for at least 2 ASCTs, but the benefit of maintaining extra stem cells in storage for future use beyond an initial ASCT warrants re-evaluation in the current era of novel therapies and evolving MM clinical practice. To address this, we reviewed the utilization rates and indications for the use of stored stem cells (SSC) at our institution. Methods: We conducted a single-center, retrospective study of 1470 patients with NDMM who collected sufficient stem cells for at least 2 ASCTs and underwent at least one ASCT at Memorial Sloan Kettering Cancer Center between January 2007 and December 2022. From this cohort, we assessed rates of stem cell utilization for second, non-tandem (salvage) ASCT and/or stem cell boost over time and determined progression-free survival (PFS) and overall survival (OS) from the time of salvage ASCT using the Cox proportional hazard model. Results: The median patient age atinitial ASCT was 61 years (range 24-81), with 58% male, 25% International Staging System stage III, and 42% (542/1283) with at least one high-risk cytogenetic alteration. Granulocyte-colony stimulating factor, either with or without plerixafor, was used for stem cell mobilization in 70% (834/1193) of patients, with the remaining patients undergoing chemotherapy-based mobilization, including high-dose cyclophosphamide (15%) or other multiagent chemotherapy regimens (15%). The median total CD34 + cell collection yield was 10.3 × 10 6/kg (interquartile range, IQR, 8-13). During the entire study period, SSC were used for 14.6% (214/1470) of patients, with 11.2% (n=165) for a salvage ASCT and 2.1% (n=31) for a stem cell boost. Seven patients received both a salvage ASCT and a boost. An additional 25 patients had upfront tandem ASCT (none since 2015) and were excluded from this analysis. Notably, from 2019 to 2022, the annual utilization of salvage ASCT increased compared to pre-2019 levels (median=21, range 11-27 vs. pre-2019 median=7, range 4-12), as did stem cell boosts (median=4, range 1-6 vs. pre-2019 median=1, range 0-3), despite a decline in numbers during the COVID-19 pandemic (Figure 1). The median age at SSC use was 61 years (range 29-78). The median number of prior lines of therapy (LOT) before the use of SSC was 4 (IQR: 2-7) for salvage ASCT and 6 (IQR: 1-6.5) for boosts. The median infused stem cell dose (CD34+ cells/kg) was 4.4 × 10 6 (range 3.2-5.7) for salvage ASCT and 3.1 × 10 6 (range 2.2-3.6) for boosts. The median PFS after salvage ASCT was 16 months (95% confidence interval, CI, 12-21), and the median OS was 37 months (95% CI 29 - 53). On multivariable analyses, receipt of fewer lines of therapy was the sole favorable prognostic factor for PFS and OS. Among patients with ≤ 3 prior LOT, the median PFS after salvage ASCT was 32 months (95% CI 22-42), while those with > 3 LOT had a median PFS of 8.0 months (95% CI 5.8-12) (Figure 2). Post-treatment therapy after salvage ASCT or stem cell boost most commonly included various MM triplet regimens, chimeric antigen receptor T-cell therapy, and bispecific T-cell engagers. Conclusion: While overall rates of SSC utilization at our institution remain low, rates have increased in recent years, as both salvage ASCT and stem cell boosts provide effective platforms for treating disease and treatment-related refractory cytopenias as a bridge to next therapy for patients with advanced MM. Ultimately, institutional practices for stem cell collection and storage require optimizing the balance of clinical utility with resource allocation and costs of maintaining SSC.

A CD38/CD28xCD3 Trispecific T-Cell Engager (TCE) As a Potentially Active Agent for the Treatment of Older Patients with Acute Myeloid Leukemia (AML)

Background: Refractory disease is common and the outcome of elderly AML patients unable to receive intensive chemotherapy with acceptable side effects remains dismal. Thus, the identification of effective and safer drugs in AML is warranted. Immunotherapeutic strategies have shown extraordinary efficacy for the treatment of hematological malignancies, such as anti-CD38 monoclonal antibodies (mAbs) in multiple myeloma. Indeed, CD38 could represent a potential therapeutic target for AML too, not only because it is expressed in AML blasts, but also because AML patients with heterogeneous or low CD38 expression could benefit from T-cell based immunotherapies that are less dependent of the density of the targeted antigen. Aims: To evaluate CD38 as a potential therapeutic target in AML, and to determine the mode of action and preclinical efficacy of isatuximab (an IgG1 anti-CD38 mAb) and SAR442257, which is a new CD38/CD28xCD3 trispecific TCE. Results: We evaluated CD38 expression in bone marrow blasts from 241 newly diagnosed elderly AML patients by flow cytometry. Overall, 99.2% of AML patients expressed CD38, 55.6% with homogeneous pattern and 44.6% with heterogeneous pattern. CD38 expression had no impact in the overall survival of AML patients. Interestingly, CD38 expression increased 2-fold in MRD positive leukemic blasts compared with patient-matched blasts at diagnosis (n=10). At 24h and up to 96h, isatuximab (70 nM) decreased CD38 surface level in 3 AML cell lines expressing low (KG-1), intermediate (MOLM-13) and high or similar (OCI-AML3) basal CD38 density as compared to AML patients. Isatuximab (70 nM) did not induce complement-dependent cytotoxicity; by contrast, we observed a trend to an increased antibody-dependent cellular phagocytosis and significant antibody-dependent cellular cytotoxicity (ADCC) only in OCI-AML3 cells in the presence of purified NK cells. In 17 primary samples from AML patients with homogeneous vs heterogeneous CD38 expression, isatuximab (70 nM) showed a median of 19% and 4.5% tumor-cell death, respectively. Altogether, these findings indicated an association between CD38 density and the mode of action triggered by isatuximab and its efficacy. As such, AML patients with heterogeneous CD38 expression are less likely to respond to isatuximab, but might benefit from TCE that are less dependent of the density of the targeted antigen. Contrary to isatuximab, the CD38/CD28xCD3 TCE did not induce a dose- and time-dependent decrease in CD38 surface levels in any AML cell line measured with a non-competing anti-CD38 antibody, regardless of the CD38 antigen density. When we cultured PBMCs from healthy adults (n=6) with MOLM-13 cells (E:T ratio of 10:1) in the presence of isatuximab or the CD38/CD28xCD3 TCE (700 pM), we observed a significantly higher tumor cell lysis at 48h induced by the latter. The same effect of the CD38/CD28xCD3 TCE was observed with purified T-, but not NK-cells from healthy adults (n=3). To identify the immune cells involved in tumor cell lysis, we confirmed that isatuximab only induced NK-cell activation, whereas the CD38/CD28xCD3 TCE induced both T- and NK-cell activation, measured as percentage of CD69+ cells. Co-culture of purified NK- or T-cells with MOLM-13 cells in the presence of the CD38/CD28xCD3 TCE demonstrated a T-cell dependent bystander activation of NK cells. Furthermore, isatuximab downregulated CD38 in a dose-dependent manner, especially in NK cells, while the CD38/CD28xCD3 TCE did not. Surprisingly, the CD38/CD28xCD3 TCE induced CD38 upregulation on T cells, indicating again T-cell activation. The efficacy of isatuximab and the CD38/CD28xCD3 TCE was analyzed in primary AML samples (n=8) and blast lysis was observed in two and three samples, respectively. Notably, two of the three CD38/CD28xCD3 TCE-responders were resistant to isatuximab. CD38/CD28xCD3 TCE-mediated lysis was independent of CD38 expression and induced no significant off-target toxicity. Conclusions: CD38 is widely present in blasts from older AML patients but nearly half show heterogeneous expression. While isatuximab-driven ADCC in AML cell lines and primary samples is dependent on CD38 density in tumor cells, the CD38/CD28xCD3 TCE exerted its anti-tumor efficacy regardless of CD38 density. Thus, AML patients expressing both high and low/heterogenous levels of CD38 could benefit from T cell based immunotherapeutic strategies targeting CD38.

Survival Outcomes of Diffuse Large B Cell Lymphoma Beyond the Rituximab Era: Comprehensive Analysis of a Veteran Population within the Veterans Health Administration over 11 Years

Introduction: The standard treatment approach for DLBCL has traditionally relied on chemo-immunotherapy with R-CHOP (Rituximab, Cyclophosphamide, Doxorubicin, Vincristine and Prednisolone) for decades. However, approximately 30-40%, remain refractory or experience relapse with poor outcomes. Since 2017, the landscape for relapsed refractory DLBCL has changed dramatically with the FDA approval of newer monoclonal antibody, chimeric antigen receptor (CAR) T-cell, antibody-drug conjugate, and bispecific T-cell engagers. Nonetheless, a comprehensive analysis of population survival outcomes since the new treatment modalities remains to be evaluated. In this study, we present an extensive demographic analysis of one of the largest DLBCL cohort to date within the VHA, spanning over 11 years, and the survival outcomes before and after 2017 period. By assessing this vast dataset, we aim to provide valuable insights into the changing landscape of DLBCL treatment and its impact on patient survival. Methods: Using the VHA electronic database, 6266 patients with an ICD code for DLBCL were randomly selected for this retrospective chart review from 01/01/2011, to 12/31/2021. Diagnosis outside of these dates or lack of any treatment history were excluded from the study. Patients were separated based on the diagnosis date into pre- and post-2017 era, diagnosis prior to 1/1/2017 vs diagnosis on and after 1/1/2017. Baseline disease characteristics, treatment patterns and outcomes were collected manually by trained abstractors. Finally, we calculated the overall survival (OS) and graphed using Kaplan Meier method comparing the pre- and post-2017 era. P-values were calculated using Log-Rank test or Chi-Square test. Results: 2660 patients were included in the final analysis. Baseline characteristics between the two groups were comparable. Of all patients, 73% achieved complete response (CR) to the first-line treatment. Most of the patients (1968 patients, 74%) received CHOP-based therapy as their first-line regimen with a median of 6 cycles, and this did not differ significantly between the pre- and post-2017 era. Diagnostic lumbar puncture was performed in 19% of all patients, and about 14% of the patients received CNS prophylaxis. Only 4.2% of all patients proceeded with hematopoietic stem cell transplantation (HSCT). Notably, patients diagnosed post-2017 had fewer HSCT than pre-2017, 2.7% vs 5.1% respectively. The median overall survival of all patients in the pre-2017 group was 96 months whereas post-2017 was not reached yet (P-value 0.011). Further analyzing the outcomes of the veterans who experienced refractory or relapsed disease, based on the date refractory or relapsed disease diagnosis, we identified improved OS for an extended period in the post-2017 group. The median OS of pre-2017 was 21 months vs post-2017 was 28 months (P-value 0.013). The OS rate at 12 months and 60 months was 66% vs 76% (P-value 0.003) and 25% vs 32% (P-value 0.034) in the pre-2017 and post 2017 era respectively. However, the OS rate at 96 months was 17% vs 19% was not different statistically (P-value 0.48). Conclusions: This is the most extensive DLBCL population-based data set existing, encompassing survival outcomes over a decade. Our study shows improved OS in patients diagnosed with refractory and relapsed disease on 1/1/2017 and beyond compared to the pre-2017 era, highlighting the available newer treatments outside the rituximab-based chemo-immunotherapy and refined supportive care. The improved survival extends to over 5 years. However, the overall survival remains similar after 8 years, irrespective of treatment era. This finding suggests that other factors, such as comorbidities, appear to play a role in mortality, rather than the disease itself or its treatment. The limitation of the study includes limited follow up period for patients diagnosed post 2017 era and the predominantly male population found in the VHA system, which represents a restricted view of a real-world population.

Dose Reduced Chemotherapy in Sequence with Blinatumomab for Newly Diagnosed Older Patients with Ph/BCR::ABL Negative B-Precursor Adult Lymphoblastic Leukemia (ALL): Preliminary Results of the GMALL Bold Trial

Older patients (pts) with newly diagnosed ALL are ineligible for unmodified pediatric-based therapies. Although results are improved with age-adapted, dose-reduced regimens including MRD-based treatment modification, there is much space for further improvement.Therefore, the GMALL study group developed a trial to evaluate Blinatumomab, a CD19 directed bi-specific T-cell engager, in sequence with chemotherapy in this patient population with high medical need (NCT 03480438). Importantly, Blinatumomab replaced three cycles of standard consolidation chemotherapy.Pts aged 56 - 76 years (yrs) with CD19-positive, Ph-neg B-precursor ALL wereeligible. The primary endpoint was complete hematologic remission (CR) afterinduction (1 cycle chemo, 1 cycle Blinatumomab) and the key secondary endpoint was molecular response (table 1). The efficacy population included pts treated with dose reduced and shortened induction I (IP1) and Blinatumomab 1 or early death (ED). Induction was followed by 3 further Blinatumomab cycles alternating with age adapted consolidation cycles (HDMTX/ASP, HDAC, reinduction and maintenance) according to GMALL protocols for older pts (Gökbuget et al, ASH 2021). The median age was 66 (56-76) yrs. 21% had pro-B-ALL and 79% c/preB subtype. 40% had comorbidities according to the Charlson Score; most frequent were diabetes (13%) myocardial infarction (10%) or vascular diseases (10%). 50 pts were evaluable for IP1: 76% achieved CR/CRu and 2 pts (4%) died due to infections. 33% (N=11) had a molecular response and 18% MolCR (table 1). 47 pts were evaluable for the primary endpoint after Blinatumomab 1: CR/CRu was observed in 85%; 2 experienced ED (4%; those mentioned above; no additional ED). 88% of the CR pts had a molecular response (82% MolCR). The median follow-up is 757 (61-1584) days. Overall Survival (OS) after 1 and 3 yrs was 80% and 67% for the efficacy population (figure 1). The resp results for the total population were 82% and 65%. The 3y OS was 69% for c/pre-B-ALL and 58% for pro-B-ALL (p>.05). 3y OS was 81% for pts aged 55-65 yrs and 53% for those older than 65 yrs (p=.025). Only three pts received an allogeneic stem cell transplantation in CR1. 6 pts relapsed, 2 pt developed a secondary malignancy (Colon Ca, MDS) and 3 pts died in CR (1 HLH, 1 arterial disease, 1 Covid19). EFS was 60% at 3 yrs. We compared the results with those of the current GMALL standard therapy for older pts with B-precursor ALL (N=186) (Gökbuget et al, ASH 2022). Patient characteristics were similar. CR rates after induction were 85% vs 78% for BOLD vs standard (p>.05). Molecular CR rates in pts with hematologic CR were 82% vs 55% (p=.006). OS at 3 yrs was 67% and 49% (p=0.08) and Remission Duration (RD) was 83% vs 58% (p=0.055). Overall tolerability and efficacy of the regimen was very promising with a high hematologic and molecular response rate; mortality in induction and consolidation was low. In comparison with the current standard therapy the MRD response rates were significantly better. OS and RD was superior despite the omission of several chemotherapy cycles in contrast to other trials with unmodified chemotherapy but additional cycles of Blinatumomab. An ongoing randomized trial (NCT04994717) compares an even more dose reduced combination of Blina and chemotherapy with standard of care. This is an independent academic trial initiated by the GMALL Study Group which received free supply of Blinatumomab and financial support by Amgen.

Cardiovascular Toxicities Associated with Bispecific T-Cell Engagers

Background: Bispecific T-cell engagers (BTEs) are a novel class of drugs used to treat hematological malignancies that link endogenous tumor antigens to CD3 on the T-cell receptor, priming circulating T-cells to effectively target tumor cells. Although chimeric antigen receptor T-cell therapies, a closely related class, have been associated with cardiovascular toxicity, little is known about the cardiovascular toxicity of BTEs. As early clinical trials may have been underpowered for the detection of cardiovascular adverse events (CVAEs), we conducted a large-scale post-marketing surveillance study to identify safety signals that may have been missed. Methods: Leveraging the US Food and Drug Administration's Adverse Events Reporting System (FAERS), we identified adverse event (AE) reports in patients who received BTEs from October 2014 to March 2023. Eligible therapies included Blinatumomab (CD3/CD19 bispecific antibody) and Teclistamab (CD3/BCMA bispecific antibody). The primary outcome of the study was the frequency and fatality rates of CVAEs associated with BTEs. CVAEs included bleeding, hypotension or shock, thromboembolic disease, heart failure, conduction abnormalities (including tachyarrhythmia, bradyarrhythmia, QT-prolongation, and premature contractions), myocarditis, pericarditis, sudden death, and vasculitis. Secondary outcomes included the frequency and fatality rates of cytokine release syndrome (CRS), neurotoxicity (seizures, altered mental status [AMS], speech disorders, gait disorders, and tremors), and infections. We used multivariable logistic regression models, adjusting for age, sex, and disease status, to calculate adjusted reporting odds ratios (RORs). RORs represent the likelihood of reporting a given AE with BTEs compared to reporting the same AE with all other drugs in the database. Mortality rates for each AE are also reported. Results: Overall, 1,181 cases were reported to FAERS for BTE-associated AEs. Among these, 148 (12.5%) involved CVAEs. The most common CVAEs (non-exclusive) were bleeding (70 events), hypotension or shock (56 events), thromboembolic disease (37 events), heart failure (23 events), and tachyarrhythmias (11 events). Less common CVAEs included myocarditis (3 events), pericarditis (1 event), sudden death (1 event), and vasculitis (1 event) (Figure 1A). Of these, BTEs as a class were disproportionately associated with shock or hypotension (ROR: 1.37 [95% CI: 1.03 to 1.80]). Blinatumomab was associated with disproportionately high rates of thromboembolic disease (ROR: 1.48 [95% CI: 1.05 to 2.08]), particularly disseminated intravascular coagulation (DIC; ROR: 4.67 [95% CI: 2.85 to 7.63]). Teclistamab was associated with disproportionately high rates of myocarditis (ROR: 35.79 [95% CI: 10.47 to 122.41]), QT prolongation (ROR: 9.85 [95% CI: 1.33 to 73.08]), and sudden death (ROR: 8.62 [95% CI: 1.16 to 63.99]). Compared to non-cardiovascular AEs, CVAEs were associated with a 92% relative increase in mortality (25.9% vs 50.7%; risk ratio: 1.92 [95% CI: 1.53 to 2.42]). Among CVAEs, the highest mortality rates were reported for heart failure (82.4%), myocarditis (66.7%), bleeding (61.5%), shock or hypotension (57.1%), thromboembolic disease (42.3%), and tachyarrhythmias (37.5%) (Figure 1B). Non-cardiovascular AEs such as neurotoxicity (322 events), infection (277 events), and CRS (190 events) were reported more frequently but had lower mortality rates (28.3%, 48.4%, and 40.0% respectively). Blinatumomab was associated with disproportionately high rates of CRS (ROR: 6.54 [95% CI: 5.41 to 7.92]) and neurotoxicity (ROR: 2.94 [95% CI: 2.56 to 3.39]). Neurotoxicity included AMS (ROR: 2.47 [95% CI: 2.01 to 3.04]), seizures (ROR: 2.81 [95% CI: 2.09 to 3.77]), speech disorders (ROR: 5.72 [95% CI: 4.16 to 7.85]), and tremors (ROR: 6.94 [95% CI: 5.15 to 9.34]). Teclistamab was associated with CRS (ROR: 134.35 [95% CI: 74.45 to 242.47]), infections (ROR: 6.83 [95% CI: 4.63 to 10.07]), and neurotoxicity (ROR: 2.75 [95% CI: 1.53 to 4.94]). Conclusion: In the first large-scale post-marketing surveillance study of BTEs, CVAEs were not uncommon and were more likely to be fatal compared to non-CVAE. Heart failure and myocarditis in particular may portend worse outcomes. These safety signals warrant clinical vigilance and further investigation of their mechanisms, optimal surveillance strategies, and treatment options.

Novel Cancer Immunotherapy Using Cell-Derived Membrane Vesicles Orchestrates Multimodal Antitumor Immunity

Cancer immunotherapy has emerged as a promising therapy for hematological malignancies. Although multiple immunotherapeutics are currently available in the clinic such as chimeric antigen receptor-engineered T-cell therapy (CAR-T cell therapy) and bispecific T-cell engager (BiTE), their long-term efficacy is still insufficient in most of the cases. Simultaneous inputs of multiple signals may provide more optimal T-cell activation and overcome the immunosuppressive tumor microenvironment (TME), which results in a durable therapeutic effect. However, integrating multifaceted immunomodulatory signals into a single drug or cell is technically difficult. To overcome these limitations, we developed nanosized cell-derived membrane vesicles (MVs) that orchestrate multimodal antigen-specific antitumor immunity in endogenous T cells. We isolated MVs with 100-150 nm in size and intact membrane-bound proteins from the HLA-negative leukemia cell line K562 by mechanical homogenization followed by isolation of the plasma membrane fraction using magnetic beads and ultracentrifugation. MVs can be loaded with a desired combination of immunomodulatory molecules on the surface by preparing cells stably transduced with those proteins. First, K562 cells were genetically engineered with a membrane-bound form of the anti-CD3/CD19 BiTE and homogenized to form BiTE-expressing MVs. When co-cultured with T cells and CD19-positive leukemia cell line NALM-6, MVs loaded with anti-CD3/CD19 BiTE induced potent cytotoxic activity in nonspecific T cells in a dose-dependent manner. To provide optimal T-cell activation, we further loaded MVs with a variety of immunostimulatory molecules including costimulatory ligands (CD80 and 4-1BBL) and cytokines (IL-7 and IL-15) on the surface. The generated antitumor MVs simultaneously induced multiple immunostimulatory signals in T cells, resulting in superior proliferation, cytokine production, and cytolytic functions compared with MVs loaded with BiTE alone. Intriguingly, MVs activated T cells only in the presence of target tumor cells, which is considered to provide a safety advantage in clinical settings. Changing the antitumor mAb sequences of the BiTE enabled to generate MVs against any type of antigen including B cell maturation antigen (BCMA), EGFR, and mesothelin. To test functions of our MVs in vivo, NSG mice were transplanted with NALM-6 and then infused with human peripheral blood T cells. While infusion of T cells alone did not contribute to controlling leukemia progression, infusion of anti-CD19 MVs with CD80, 4-1BBL, IL-7, and Il-15 induced potent antitumor response. Repeated infusion of MVs further augmented their therapeutic efficacy. To overcome the immunosuppressive TME, we additionally loaded MVs with immune checkpoint inhibitors (anti-PD-1 and anti-CTLA-4 antibody), TGF-b receptors to trap TGF-b, and inflammatory cytokines (IL-12 and IL-18) that activate both T cells and myeloid cells in the TME. Immunocompetent Balb/c mice were subcutaneously inoculated with colon carcinoma cell line CT26 ectopically expressed with CD19 and treated with MVs targeting CD19. The injected MVs converted tumor-associated M2-type macrophages into an inflammatory phenotype and promoted CD8+ T cell infiltration within the TME, resulting in better control of tumor progression in in vivo solid tumor mouse models. K562 cells are highly sensitive to NK cells because they endogenously express several ligands for NK cell activation receptors such as MIC-A and MIC-B, and lack the expression of HLA class I that represses NK cell activation. K562-derived MVs induced potent cytotoxic activity in NK cells against NK-cell-resistant myeloma cell line MM1S in an antigen-specific manner. In summary, this novel technology enables to deliver desired combinations of antitumor immune signals to not only T cells but also NK cells and other types of immune cells, which can transmit superior therapeutic efficacy against the tumor cells that are resistant to the present immunotherapeutics.

Loss of p53 Impairs Death Receptor Expression and Confers Resistance to CD19-Directed CAR T-Cell Therapy in B-Cell Precursor Acute Lymphoblastic Leukemia

Background In recent years, new therapy strategies such as the antibody-drug conjugate inotuzumab ozogamicin, the bi-specific T-cell engager blinatumomab, and chimeric antigen receptor (CAR) T-cells have been introduced to salvage relapsed precursor B acute lymphoblastic leukemia (ALL). However, recent evidence indicates that these new therapies are ineffective in TP53-aberrant ALL, although the mechanism remains unclear. TP53 is the most frequently mutated gene in cancer, but in ALL, mutations or deletions affecting TP53 are rare, with an incidence of only 3% at diagnosis. However, at relapse, TP53 aberrations are found in approximately 12% of the patients and predict a very poor outcome. Consequently, relapsed TP53 deleted ALL is now classified as ‘very high risk’. Since p53-mediated apoptosis is an endpoint for many (cytotoxic) drugs, loss of p53 function induces therapy resistance to classical chemotherapeutics. Hence, there is a clear clinical need for more effective strategies to treat TP53 aberrant relapsed ALL. Methods Using CRISPR/Cas9, we introduced frameshift mutations in the TP53 gene to generate isogenic wild type and knockout models in TP53 WT ALL cell lines Nalm6 and RCH-ACV. Additionally, we prepared CD19-directed CAR T-cells with a 4-1BB co-stimulatory domain from three healthy donors by isolating, transducing, and expanding CD4+ and CD8+ T-cells separately. With flow cytometry, we assessed survival of p53 WT and p53 KO leukemic cells in the presence of CD4+ and CD8+ CAR T-cells at a 1:1 CD4:CD8 ratio. Moreover, we performed mRNA profiling by qRT-PCR and cell membrane profiling by flow cytometry to determine how loss of p53 affects CAR T mediated killing. Initial findings in cell lines were then validated in patient-derived xenografts. Results We observed that loss of p53 led to up to a 35% decrease in killing by overnight CAR T treatment in both cell line models (Figure 1A). Although loss of p53 has been linked to reduced cell surface expression of CD19 (Pan et al., 2020, Leukemia), no changes in CD19 expression were observed in response to p53 loss. In search for an explanation for the diminished killing, we performed mRNA profiling and found a reduced expression of death receptors CD95/Fas and DR5/TRAILR2 in p53-deficient cells, which was confirmed at the protein level with flow cytometry (Figure 1B). Indeed, CRISPR/Cas9 mediated loss of CD95/Fas expression in p53 wild type cells reduced CAR T mediated cell killing, consistent with a key role for CD95/Fas in T-cell mediated killing. Conversely, treatment of p53 proficient cells with MDM2 inhibitors induced expression of CD95/Fas and DR5/TRAILR2 (Figure 1B), which translated into enhanced killing of target cells. Most of these observations have already been recapitulated in a diagnosis-relapse pair of patient-derived cells in which the diagnosis was p53wild typeand the relapse was p53 deficient (Figure 1A-B). We observed lower baseline mRNA expression of CD95/Fas and DR5/TRAILR2 in p53-deficient cells, accompanied by a 50% reduction in killing relative to the p53 wild type controls. Conversely, MDM2 inhibition increased death receptor expression only in p53-proficient cells. The ongoing experiments validating enhanced killing after MDM2 inhibition in patient-derived cells will be presented during the meeting. Conclusions Loss of p53 impairs expression of CD95/Fas and DR5/TRAILR2, thereby protecting ALL cells from CAR T induced cell death. In addition, our results indicate that the p53-controlled expression of these receptors may be exploited to increase the efficacy of CAR T-cell therapy in p53-proficient patients.

CD155 on Multiple Myeloma Cells Is Epigenetically Regulated, Reduce Patients Survival and Compromises the Action of Novel Immunotherapies

Epigenetics, especially DNA methylation, is a key molecular regulator of gene expression. This regulation is important for cytotoxic cell activation (i.e., T-cells and NK cells) and is crucial for the clearance of malignant cells. Immune checkpoint (IC) events mediate cytotoxicity, one IC receptor involved in the process is CD155. Such receptor interacts primarily with TIGIT on cytotoxic cells and induces the inhibition of cytotoxicity. Multiple myeloma (MM) represents the 10% of all hematological malignancies and it has been described that MM cells hinder cytotoxic cell activation by inhibition and exhaustion. Furthermore, novel immunotherapeutic strategies such as Bispecific T-cell Engagers (BiTE) and Chimeric Antigen Receptor (CAR) therapies are being evaluated in MM treatment, with promising results. Nevertheless, they will confront a hostile environment. This is a very active field with frequent descriptions of new targets and therapeutic approaches being studied each day. We investigated whether CD155 is epigenetically regulated in MM and its importance in inducing inhibition of anti-tumor response in the context of novel immunotherapies through the CD155/TIGIT axis. To achieve our objectives, we focused on the promoter region of CD155 (the region up to 1500 base pairs upstream of the TSS) and characterized it at DNA, RNA and protein levels through bisulfite sequencing, quantitative PCR, and flow cytometry. We confirmed CD155 as an epigenetically regulated gene, thus demonstrating an existing correlation between CD155 promoter methylation and gene expression. In vitro treatment with azacytidine was performed to assess the active repression of CD155 expression by DNA methylation. Six different MM cell lines were characterized (two not expressing: AMO-1, KMS-12-BM, four expressing: RPMI-8226, MM.1S, EJM and JJN-3). From there, we created CD155 depletion models on expressing cell lines by short hairpin RNA interference and developed an in vitro coculture system with T-cells (from healthy donors). We observed a loss of expression between the 60% to 90% (when compared with controls). Depletion of CD155 did not significantly impact cell growth, apoptosis, or cell cycle. On the coculture with healthy T-cells, more cytotoxicity was detected against CD155-depleted cells (in RPMI-8226 Mann-Whitney P=0.020; JJN-3 and EJM P<0.001). To incorporate novel immunotherapeutic strategies, we carried out the same cocultures with 100pg/mL of anti-BCMA/CD3 BiTE, against anti-BCMA CAR-T or anti-BCMA CAR-NK cells (for RPMI-8226 and JJN-3 Mann-Whitney P=0.008). Coculture combinations were also performed in the presence of 10μg/ml of neutralizing αTIGIT (RPMI-8226, Mann-Whitney P =0.005; JJN-3 P=0.004) and/or αPD1 antibody. When novel immunotherapy approaches were included in the system, we observed how the depletion of CD155 was related to a cytotoxicity increase in all cases. In the presence of neutralizing αTIGIT, cytotoxicity was increased against CD155-expressing cells, while we observed no difference against CD155-depleted cells. In the presence of αPD1, we saw a significant restoration of T-cell cytotoxicity against both models and the antibody combination showed a synergic effect in CD155 expressing cells. Finally, we analyzed the existence of a correlation between CD155 gene expression and survival in newly diagnosed MM samples from CoMMpass project public data (N= 793). These data supported our results as the newly diagnosed MM patients with higher expression of CD155 had shorter overall survival than lower expressing ones (Logrank test P<0.001). In summary, in the context of MM, the expression of CD155 is regulated by the methylation status of its promoter region. Expression of CD155 effectively reduces cytotoxic cell response, which is mediated by the interaction of CD155 and TIGIT. The addition of αTIGIT and αPD1 validated that the CD155 cytotoxic cell inhibition is mediated in part by TIGIT interaction, independently of PD1/PD-L1 axis. This interaction seems to impact patients treated with current therapies, since their outcome correlates with CD155 expression. Based on our results, novel immunotherapies focused on enhancing immune cytotoxicity will benefit from CD155/TIGIT axis blockade. These results warrant further investigation on CD155 as a biomarker and target for novel immunotherapies for MM and other malignancies.

Real-World Safety and Efficacy of Teclistamab for Patients with Heavily Pretreated Relapsed-Refractory Multiple Myeloma

Background: Teclistamab is a B-cell maturation antigen (BCMA) targeting bispecific T-cell engager approved in October of 2022 for patients with relapsed-refractory multiple myeloma (RRMM) who have received at least 4 prior lines of therapy (LOT) based on the results of the pivotal MajesTEC-1 trial. In this multicenter retrospective study, we evaluated the real-world safety and efficacy of teclistamab, highlighting patterns of utilization and outcomes, including patients who would have been considered ineligible for MajesTEC-1 trial. Methods: Five U.S. academic centers, part of the US Myeloma Innovations Research Collaborative (USMIRC), contributed data to this retrospective analysis, which included 102 patients with RRMM who received teclistamab as of 7/1/2023. Baseline characteristics were outlined by descriptive analysis. Teclistamab was administered in a step-up dosing manner as per the package insert. All patients had received at least the two step up doses and the first full dose of teclistamab. Patients received antimicrobial prophylaxis, supportive care, and toxicity management per institutional protocols. Responses to therapy including overall response rate (ORR), very good partial response (VGPR), and complete response or better (≥CR) were evaluated using the International Myeloma Working group (IMWG) criteria. Adverse events were graded based on the CTCAE v5.0 criteria. The Kaplan-Meier method was used for progression free survival (PFS), duration of response (DOR), and overall survival (OS) calculation. Results: Of the 102 patients included in this analysis, 25% were non-Hispanic Black and 44% had extramedullary disease (EMD); the median number of prior LOT was 6 (range 4-17). More than 80% (83/102) of the patients would not have met the MajesTEC-1 eligibility criteria; main reasons for ineligibility included: prior BCMA-directed therapy (BDT) (55%), ECOG performance status ≥2 (28%), and baseline cytopenias: grade 3-4 anemia (26%), and grade 3-4 thrombocytopenia (20%). All patients were triple class exposed and 92% were triple class refractory, 78% were penta-class exposed and 67% were penta-class refractory. More than half of the patients (55%) were refractory to prior BDT. Baseline characteristics are summarized in Table 1. Cytokine release syndrome (CRS) was observed in 65% of patients, all of which, except one, were grade 1-2 events, while immune effector cell-associated neurotoxicity syndrome (ICANS) was reported in 15% of the patients, with three patients having grade 3-4 events. The most common grade 3-4 hematological toxicities were neutropenia (23%), leukopenia (18%), thrombocytopenia (17%), and anemia (17%). Infections occurred in 28% of the patients, half of which were characterized as severe. The vast majority (80%) of infections involved the respiratory tract and 7% of patients discontinued teclistamab permanently due to recurrent or severe infections. After a median follow up of 3.2 months, the ORR was 64% for the entire cohort; ORR was 57%, 66% and 45% for patients who were BDT-refractory, penta-refractory, or had EMD, respectively. Of those who did respond, responses were found to be deep (72% ≥VGPR; 45% ≥CR). Patients that would have been ineligible for the MajesTEC-1 trial had an ORR of 59%. Detailed responses for the groups of interest are reported separately in Table 1. The estimated 6-month PFS, DOR, and OS of the entire cohort were 38% (95% CI, 26-56), 54% (95% CI, 34-85) and 68% (95% CI, 58-80), respectively (Figure 1). No treatment-related mortality was observed, although 26% of the patients had died at the time of data cut-off, with 89% of the deaths attributed to disease progression. Conclusion: This is the largest real-world experience of the safety and efficacy of teclistamab for RRMM. Overall, teclistamab was well tolerated with no major safety concerns, despite worse performance status and cytopenias than the MajestTEC-1 trial population. Moreover, despite the increased incidence of high-risk features, including penta-refractoriness, BDT refractoriness, and presence of EMD in this heavily pre-treated RRMM patient population, early efficacy assessment of teclistamab in a real-world setting was encouraging.

BCMA-Directed Low Dose Alpha-Emitter Therapy Eliminates Minimal Residual Disease in a Multiple Myeloma Mouse Xenograft Model

BACKGROUND: Unprecedented reductions in multiple myeloma (MM) tumor burden after treatment with B cell maturation antigen (BCMA) directed bispecific T-cell engagers, or chimeric antigen receptor modified T-cells, have translated into improved progression free and overall survival; however, virtually all patients are predicted to ultimately relapse. The mechanisms of resistance to BCMA targeting agents are currently being explored, but presumably reflect persistence of MM cell subpopulations that either lack target antigen or otherwise evade immune-mediated tumor cell killing. Antigen targeted delivery of radiation to tumor cells leverages a unique effector mechanism that capitalizes on the exquisite sensitivity of malignant plasma cells to radiation. The α-emitter astatine-211 ( 211At) has particular promise as it deposits a very large amount of energy (~100 keV/μm) within a few cell diameters (50-90 μm) resulting in irreparable double-stranded DNA breaks. The high energy cell killing mediated by 211At is agnostic to MM cell heterogeneity, facilitates bystander delivery of radiation to target antigen negative clones, and limits radiation exposure to normal cells. We hypothesized that 211At targeting BCMA may be uniquely suited to eliminate residual MM cells. METHODS: We conjugated a human IgG1 anti-BCMA mAb and an isotype matched nonbinding control mAb (ofatumumab), with the amine-reactive labeling agent B10-NCS to enable 211At radiolabeling. In biodistribution studies of 211At-BCMA-B10 and 211At-ofatumumab-B10 using NOD.Cg-Rag1 tm1MomIl2rg tm1Wjl/SzJ (NRG) mice bearing flank MM tumor cell xenografts (MM1R or NCI-H929; n=5 mice/group), we demonstrated tumor-specific uptake of BCMA-B10 relative to control mAb and identified the optimal dose of 211At-mAb-B10 (210μg) for assessing therapeutic efficacy. In subsequent therapy studies, NRG mice (n=7-10/group) received 0.3-0.4e6 NCI-H929 luc tumor cells by tail vein injection 6-7 days prior to administration of 210 µg of 211At-BCMA-B10 or 211At-ofatumumab-B10 or no therapy (non-treatment control). Animal body weight was monitored serially, and disease was tracked using in vivo bioluminescence imaging (IVIS Spectrum) performed at 8 or more timepoints over 150 days. RESULTS: Disease elimination was defined as survival with no measurable disease by IVIS at 150 days following treatment. All mice receiving 6 or 8 µCi of 211At-BCMA-B10 (n=36) were cured (100%) after a single infusion of 211At-BCMA-B10. Mice in the untreated control groups uniformly experienced exponential tumor growth. At the lowest 211At dose (6 µCi), all BCMA targeted mice survived for more than 150 days while no untreated control mice survived beyond day 60 (median duration of survival 49 days [range 42-60 days]). Mice receiving 211At-ofatumumab had expected attenuation in tumor growth relative to untreated controls (presumably a consequence of non-specific radiation exposure); with a median duration of survival of 85 days; no mice survived beyond 108 days (range 65-108 days) [Figure 1, Figure 2]. No significant toxicity was observed in the 211At-BCMA-B10 treated groups. Among mice receiving 8 μCi of 211At-BCMA-B10 median animal body weight on day 14 post-treatment was 106% of baseline (range 97%-109%). Among mice receiving 6 μCi of 211At-BCMA-B10 the median body weight on day 14 was 107% of baseline (range 100% to 111%) and on day 150 the median weight was 123% of baseline (range 116% to 126%). CONCLUSIONS: Tumor responses are encouraging with 100% of mice cured of MM after receiving low doses of BCMA targeted 211At. While we have previously demonstrated that 211At-CD38 could eliminate MM in a similar model system, in that setting fewer than 50% of mice bearing the same NCI-H929 Luc tumors, and treated with 8 μCi of 211At, survived to day 150 [O'Steen S. Blood, 2019]. In contrast, here we show that 100% of mice are cured after receiving 6 μCi of 211At-BCMA-B10. These findings support further evaluation of BCMA targeted 211At in other tumor model systems and in clinical trials aimed at eliminating minimal residual disease.