Soluble BCMA Research Articles

Next-generation BCMA-targeted chimeric antigen receptor CARTemis-1: the impact of manufacturing procedure on CAR T-cell features.

CAR therapy targeting BCMA is under investigation as treatment for multiple myeloma. However, given the lack of plateau in most studies, pursuing more effective alternatives is imperative. We present the preclinical and clinical validation of a new optimized anti-BCMA CAR (CARTemis-1). In addition, we explored how the manufacturing process could impact CAR-T cell product quality and fitness. CARTemis-1 optimizations were evaluated at the preclinical level both, in vitro and in vivo. CARTemis-1 generation was validated under GMP conditions, studying the dynamics of the immunophenotype from leukapheresis to final product. Here, we studied the impact of the manufacturing process on CAR-T cells to define optimal cell culture protocol and expansion time to increase product fitness. Two different versions of CARTemis-1 with different spacers were compared. The longer version showed increased cytotoxicity. The incorporation of the safety-gene EGFRt into the CARTemis-1 structure can be used as a monitoring marker. CARTemis-1 showed no inhibition by soluble BCMA and presents potent antitumor effects both in vitro and in vivo. Expansion with IL-2 or IL-7/IL-15 was compared, revealing greater proliferation, less differentiation, and less exhaustion with IL-7/IL-15. Three consecutive batches of CARTemis-1 were produced under GMP guidelines meeting all the required specifications. CARTemis-1 cells manufactured under GMP conditions showed increased memory subpopulations, reduced exhaustion markers and selective antitumor efficacy against MM cell lines and primary myeloma cells. The optimal release time points for obtaining the best fit product were > 6 and < 10 days (days 8-10). CARTemis-1 has been rationally designed to increase antitumor efficacy, overcome sBCMA inhibition, and incorporate the expression of a safety-gene. The generation of CARTemis-1 was successfully validated under GMP standards. A phase I/II clinical trial for patients with multiple myeloma will be conducted (EuCT number 2022-503063-15-00).

Serum Soluble B Cell Maturation Antigen Level as a Prognostic Marker for Low Grade Lymphoma

Abstract Background Despite the Indolent lymphoma is a slowly growing tumor that has many therapeutic options and good initial response, it is usually incurable. Relapses and HT to aggressive form may occur and some patients die from their disease. For the RR iNHL Several novel targeted therapies may be recommended such as antibody–drug conjugates (ADC) and bispecific T cell engagers (BiTE). B cell maturation antigen is a transmembrane glycoprotein that regulate B cell proliferation, survival, maturation and differentiation into PCs. IT is expressed in multiple myeloma and B cell neoplasms. The effects of BCMA have been studied in multiple myeloma and a new BCMA-targeted immunotherapy has been approved for the treatment RRMM patients. Few studies done to detect BCMA in other Hematologic malignancies as a diagnostic or prognostic tool and a therapeutic potential of antiBCMa targeted therapy in these malignancies. In this study we detect sBCMA in the serum of iNHL patients. Aim of the Work To measure the levels soluble BCMA (sBCMA) in the serum of adult patients with indolent non Hodgkin lymphoma (iNHL). Patients and Methods A case control study conducted on adult patients of iNHL attending hematology department of Ain Shams university with a participant of 40 cases of newly diagnosed and RR iNHL plus 40 control. Results In the present study we found that there was no statistically significant difference between the studied groups as regard sex, TLC, Hb, platelet counts and tumor subtypes in relation to BCMA level . While there is a statistically significant correlation between Age, stage and LDH to the BCMA level. The results suggest that the BCMA level is significantly higher in patients with iNHL than the healthy controls. Conclusion This study suggest that the BCMA level is significantly higher in patients with iNHL than the healthy controls. By increasing the Age ≥ 40 years the risk of iNHL is increased by 1.71 folds than otherwise healthy controls. The BCMA level was positively correlated to LDH implying that BCMA could be related to iNHL proliferation rate and possibly lymphoma aggressiveness. The level of BCMA more than 430 ng/dL correlated with a more than a 4.5-fold rise in the risk of higher disease stage with borderline significance. Further studies are needed to detect the relation between The BCMA level and the disease prognosis that may be useful for a promising AntiBCMA targeted therapy for RR patients.

Correlative biomarker analyses for optimal therapeutic dose determination of ABBV-383, a B-cell maturation antigen (BCMA) x CD3 bispecific antibody, in patients with relapsed/refractory multiple myeloma (RRMM).

7532 Background: ABBV-383 is a BCMA x CD3 bispecific antibody with 2 high-affinity BCMA-binding domains and a low-affinity CD3 engaging arm that has been shown to decrease the negative impact of soluble BCMA (sBCMA) and drive sustained T-cell activation with reduced cytokine release in preclinical models of MM. Here, we describe correlative biomarker results of baseline and longitudinal sBCMA levels and immune profiles in the ongoing first-in-human trial that supports 60 mg Q4W as the optimal therapeutic dose of ABBV-383 monotherapy. Methods: Peripheral blood and serum samples from patients with RRMM enrolled in the phase 1 open-label, dose-expansion study (NCT03933735) who received ABBV-383 at 20, 40, or 60 mg Q3W or 60 mg Q4W were collected at baseline (post-dexamethasone, pre–ABBV-383), on treatment, and at disease progression. Samples were analyzed by flow cytometry for immune cell populations, Luminex for cytokines, and electrochemiluminescence ligand binding for sBCMA. Results: Median sBCMA levels at baseline were highly variable among patients, but did not associate with clinical response (≥ partial response [PR]) to ABBV-383 at the selected optimal dose level of 60 mg Q4W (&lt;PR: 244.7 ng/mL; ≥PR: 52.2 ng/mL; P=0.13). Reduction in sBCMA levels over time associated with clinical response (Cmin at cycle 5: &lt;PR, 244.7 ng/mL; ≥PR, 4.7 ng/mL; P=0.04). ABBV-383 treatment led to a rapid and transient increase of proinflammatory cytokines, including IL-6, IL-8, IL-10, TNF-α (Cmax within cycle 1: 29, 349.5, 1375, 456.5 pg/mL, respectively), and promoted T-cell redistribution (89% reduction of CD8+ T cells from periphery), activation (1.9-fold increase in CD69+CD8+ T cells), and proliferation (2-fold increase in Ki67+CD8+ T cells) within cycle 1 in 60-mg Q4W-treated patients. The frequency of baseline CD8+ T-cell exhaustion (PD-1/TIM3) did not impact clinical response at the optimal dose level of 60 mg Q4W ABBV-383 (&lt;PR: 3.5%; ≥PR: 3.9%; P=0.9). Peak induction levels of proinflammatory cytokines during cycle 1 correlated with occurrence of cytokine release syndrome (≥G1) as well as clinical response across dose levels. Conclusions: High-avidity BCMA binding coupled to low-affinity T-cell engagement distinguishes the resulting mechanism of action for ABBV-383. Responses to 60 mg Q4W ABBV-383 were independent of baseline sBCMA levels and resulted in rapid and transient proinflammatory cytokine production that promoted robust T-cell redistribution, activation, and proliferation, indicating that the optimal dose of ABBV-383 maximizes its clinical potential as a convenient, safe, and effective therapy for MM. Clinical trial information: NCT03933735 .

Optimization of a flow cytometry test for routine monitoring of B cell maturation antigen targeted CAR in peripheral blood.

Chimeric antigen receptor (CAR) modified T cell therapies targeting BCMA have displayed impressive activity in the treatment of multiple myeloma. There are currently two FDA licensed products, ciltacabtagene autoleucel and idecabtagene vicleucel, for treating relapsed and refractory disease. Although correlative analyses performed by product manufacturers have been reported in clinical trials, there are limited options for reliable BCMA CAR T detection assays for physicians and researchers looking to explore it as a biomarker for clinical outcome. Given the known association of CAR T cell expansion kinetics with toxicity and response, being able to quantify BCMA CAR T cells routinely and accurately in the blood of patients can serve as a valuable asset. Here, we optimized an accurate and sensitive flow cytometry test using a PE-conjugated soluble BCMA protein, with a lower limit of quantitation of 0.19% of CD3+ T cells, suitable for use as a routine assay for monitoring the frequency of BCMA CAR T cells in the blood of patients receiving either ciltacabtagene autoleucel or idecabtagene vicleucel.

Deciphering the Exact Sequence of Endogenous Soluble B Cell Maturation Antigen and Unbiased Quantitation in Multiple Myeloma Patient Samples by LC-MS.

B-cell maturation antigen is a pivotal therapeutic target for multiple myeloma (MM). Membrane-bound BCMA can be cleaved by γ-secretase and shed as soluble BCMA (sBCMA). sBCMA can act as a neutralizing sink to compete with drug, as well as serve as a diagnostic/prognostic biomarker for MM. Antibody-capture based methods, such as enzyme-linked immunosorbent assay (ELISA) and immunoaffinity-liquid chromatography-multiple reaction monitoring (IA-LC-MRM), have been reported and well adopted to measure sBCMA in clinical samples. However, both methods are biased by capturing antibodies. We have used various LC-MS workflows to characterize and quantify endogenous sBCMA in MM patient samples, including bottom-up peptide mapping, intact analysis, IA-based, and reagent-free (RF)-LC-MRM quantitation. We have confirmed that sBCMA contains a variable N-terminus and a C-terminus that extends to the transmembrane domain, ending at amino acid 61. Leveraging an in-house synthesized G-1-61 sBCMA recombinant standard, we developed a RF-LC-MRM method for unbiased sBCMA quantitation in MM patient samples. By comparing the results from RF-LC-MRM with ELISA and IA-LC-MRM, we demonstrated that RF-LC-MRM measures a more complete pool of endogenous sBCMA compared to the antibody-based methods. This work fills the knowledge gap of the exact sequence of endogenous sBCMA for the first time, which differs from the current commercially available standard. Additionally, this work highlights the necessity of identifying the actual sequence of an endogenous soluble target such as sBCMA, both for bioanalytical purposes and to underpin pharmacodynamic measurements.

Plasma levels of BCMA-positive extracellular vesicles correlate to response and side effects in myeloma patients treated with belantamab-mafodotin.

In myeloma patients, high levels of soluble BCMA (sBCMA) can limit the efficacy of BCMA-directed therapies. Belantamab-mafodotin is a BCMA antibody-drug conjugate and shows good overall response rates in heavily pretreated patients but progression-free survival data are poor. As the drug induces apoptosis, we hypothesized that sBCMA includes extracellular vesicles (EV) and thus evaluated numbers of BCMA-EV before and during belantamab therapy in 10 myeloma patients. BCMA-EV were significantly higher in patients prior to Belantamab (median: 3227/μl; p = .013) than in other myeloma patients before therapy (n = 10; 1082/μl) or healthy volunteers (n = 10; 980/μl). During therapy, BCMA-EV showed a significant increase to a maximum of 8292/μl (p = .028). Maximal changes in BCMA-EV (Δmax = BCMA-EV at C1/maximal BCMA-EV) showed a strong inverse, logarithmic correlation (r = -.950; p < .001) with FLC ratio changes (Δmax = FLC ratio at C1/minimal FLC ratio) and BCMA-EV peaks often preceded FLC progression. Correlating increase of LDH and BCMA-EV levels, together with clinical symptoms, point to a mafodotin-induced eryptosis. In summary, BCMA-EV are a part of sBCMA, peak levels precede progression, and their measurement might be helpful in identifying resistance mechanisms and side effects of BCMA targeted therapies.

Initial Results from a Phase 1 Dose-Escalation Study of WVT078, a BCMA×CD3 Bispecific Antibody, in Combination with WHG626, a Gamma-Secretase (GS) Inhibitor, in Patients with Relapsed and/or Refractory Multiple Myeloma

Introduction: WVT078, a potent anti-B-cell maturation antigen (BCMA)×anti-CD3 bispecific antibody (BsAb), is being investigated as a single-agent and in combination with a GS inhibitor (GSI), WHG626 (AL102), in patients (pts) with relapsed and/or refractory (r/r) multiple myeloma (MM). Single-agent WVT078 showed an acceptable safety profile in the ongoing first-in-human study with active dose range of 48-250 µg/kg (Raab, Leukemia 2023). Membrane BCMA expressed on surface of MM cells is cleaved by GS. This results in shedding of its extracellular domain (ECD) as soluble BCMA (sBCMA), which may bind to and interfere with activity of BCMA-targeting agents such as WVT078. By preventing this shedding, GSIs are postulated to increase clinical benefit of BCMA-targeting agents. WVT078 combined with WHG626 was shown to enhance anti-myeloma activity of WVT078 in vitro preclinically (Raab, Leukemia 2023), supporting rationale for this combination in r/r MM. Methods: The combination of WVT078 and WHG626 is being investigated as part of above-mentioned phase 1 study (NCT04123418) in pts with MM who are r/r to ≥2 standard-of-care regimens, including an immunomodulatory drug, proteasome inhibitor, and anti-CD38 agent (if available). Pts who received prior BCMA chimeric antigen receptor T-cell therapy or BCMA antibody-drug conjugates therapy are included; pts with prior BCMA×CD3 BsAb treatment are excluded. Primary objectives were to evaluate safety and tolerability and to determine recommended dose for expansion of WVT078 in combination with WHG626. Secondary objectives were to assess preliminary anti-tumor activity and characterize pharmacokinetics (PK) and immunogenicity. Key exploratory objectives included evaluation of sBCMA and characterization of immune-cell activation phenotypes. Dose escalation was guided by Bayesian Logistic Regression Model, and International Myeloma Working Group criteria were used to assess disease response. Flow cytometry was used to study pharmacodynamic (PD) effects on immunophenotype of immune cells. Immunoassay-based platform (Meso Scale Discovery) was used for assessing cytokine production and enzyme-linked immunosorbent assay for quantifying serum sBCMA levels. Results: As of April 29, 2023, a total of 23 pts (median age, 64 years) with r/r MM were treated in dose escalation with intravenous WVT078 at 12-48 µg/kg once weekly, combined with oral WHG626 at 2-4 mg once daily, given 2 days on and 5 days off. Eighteen pts (78.3%) discontinued treatment due to progressive disease (n=15), adverse event (AE), guardian decision and physician decision (n=1 each). Most frequent (≥20%) treatment-related AEs across all doses in the combination were cytokine release syndrome (65.2%; Grade ≥3, n=1), pyrexia (39.1%), diarrhea (34.8%), decreased appetite (26.1%), hypophosphatemia, nausea and neutropenia (21.7% each); 5 pts experienced dose-limiting toxicities (pneumonia, neutropenia, ALT/AST/lipase increase, platelet count decrease, sepsis and shoulder pain). The safety profile is consistent with WVT078 and WHG626 as single agents. A maximum tolerated dose was not reached. The overall response rate (partial response or better; ORR) and overall complete response (CR) rate (stringent CR+CR) across all dose levels tested were 39.1% (n=9; 90% CI, 22.2, 58.3) and 13.0% (n=3; 90% CI, 3.7, 30.4), respectively; ORR at two highest dose levels combined was 57.1% (n=8/14; 90% CI, 32.5, 79.4). PK total (AUC) and maximal (Cmax) exposure to WVT078 in serum increased approximately proportionally to dose in Cycle 1. Evidence of T-cell engagement with WVT078 was demonstrated by upregulated peripheral T-cell proliferation and activation markers. WHG626 decreased serum sBCMA levels by 10% within first 24 hours of treatment prior to WVT078 dosing. WHG626 enhanced WVT078-mediated increases in serum inflammatory cytokine levels, and upregulated T-cell activation phenotype in bone marrow in a dose-dependent manner.Based on preliminary data, cytokine and clinical effects were observed at lower WVT078 doses with WVT078+WHG626 than with WVT078 alone. Conclusions: WVT078 combined with WHG626 has an acceptable safety profile and shows preliminary evidence of clinical activity at highest doses tested. PD biomarker analysis supports postulated mechanism of action of WHG626 combined with WVT078. This is the first clinical report on combination of BCMAxCD3 BsAb and GSI in r/r MM.

Trogocytosis May Attenuate the Efficacy of Anti-BCMA CAR T Cells Administered in Combination with γ-Secretase Inhibitor

Introduction: γ-Secretase inhibitors (GSIs) are proven to reduce shedding and increase BCMA surface density on plasma cells thus enhancing anti-multiple myeloma (MM) efficacy of BCMA CAR T cells in preclinical systems (Pont, Blood 2019). Collectively, our recent findings indicate that BCMA density on malignant plasma cells following GSI administration is predictive of improved responses, progression free survival and overall survival in the Phase I trial. Despite that, most patients eventually relapse and 80% have no evidence of CAR T cells by qPCR at the time of disease progression (Cowan, Lancet Oncology, 2023). Trogocytosis involves stripping of the target antigen and incorporating it into the CAR T cell membrane. This phenomenon has been described as one of the causes of relapse following CAR T cell therapy. In this study, we aimed to investigate the effect of GSI on trogocytosis and determine if trogocytosis facilitates fratricide among anti-BCMA CAR T cells thus contributing to relapse. Material and Methods: Healthy donor T cells were activated and transduced with fully human anti-BCMA lentiviral CAR with 4-1BB/CD3z signaling domain. After 10 days of expansion, CAR T cells were sorted (BD FACSymphony S6) following staining with anti-recombinant BCMA/Fc-allophycocyanin (APC) (Creative Biomart). H929, MM.1R and MOLP 8 (MM cell lines) were obtained from ATCC. Cells were incubated with GSI, LY3039478-crenigacestat (Eli Lilly) 0.1 μM for 24h and mean fluorescence intensity (MFI) of BCMA was defined as previously described (Pont, Blood 2019). To identify trogocytosis, samples were analyzed by flow cytometry (BD Symphony 4, BD Celesta) after combined MM cell line and CAR T cell co-culture for 48 hours (h), 24h, 6h, 2h, 1h, 30 minutes (min), 10 min (effector to target ratio=1:1). For fratricide assays, CAR T cells with trogocytosis were sorted following 6h of co-culture with cell lines and re-plated with fresh CAR T cells and were analyzed by flow cytometry after 24h (effector to target ratio=1:1). Soluble BCMA (sBCMA) ELISA was performed according to the manufacturer's recommendations (R&amp;D) Systems. Results: The BCMA MFI increased ~8-fold in MM cell lines-H929 and MM.1R after GSI incubation. In comparison, MOLP8 BCMA increased 3-fold (Figure 1a). BCMA expression on CAR T cells following 10 min, 30 min, 1h, 2h, 6h, 2h and 48h co-culture was increased in both H929 and MOLP8 cell lines consistent with trogocytosis. After GSI administration, using 30 min (P&amp;lt;0.0001), 1h (P&amp;lt;0.0001), 2h (P=0.001), 6h (P&amp;lt;0.0001), 24h (P=0.0003) and 48h (P=0.02) co-cultures, there was more trogocytosis detected with the high antigen density H929 cell line, whereas with MOLP8 significant trogocytosis was only observed at 30 min (P=0.002), 1h (P=0.0007) and 2h (P=0.002) (Figure 1b). When CAR T-trogo cells were sorted and re-challenged with naive CAR T cells, over 90% fratricidal killing was detected in the high BCMA expressor cell lines-H929 and MM1.R (Figure 1c). On the tumor side of the immune synapse, the expression of surface BCMA on H929 with, or without, GSI was decreased over time consistent with antigen downmodulation. sBCMA levels were significantly lower in the H929 cell line when GSI was added (P=0.001). Confocal microscopy and live imaging studies of the immune synapse are ongoing. Conclusion: GSI increases BCMA surface density on MM cells and promotes CAR T cell trogocytosis which results in fratricide that appears proportional to tumor cell BCMA density. Trogocytosis and the ensuing fratricide following anti-BCMA CAR T cell therapy may contribute to reduced persistence of CAR T cells and relapse. This data may facilitate the optimal timing and frequency of GSI administration after BCMA CAR T-cell administration in future clinical trials.

Development of Novel Invariant TCR-Anchored Bispecific Engagers to Enhance Anti-Cancer Activity of iNKT Cells

iNKT are rare, CD1d-restricted, glycolipid-reactive T cells that bridge adaptive and innate immunity. iNKT cells are characterised by an invariant TCRVa24Ja18 chain nearly always pairing with a TCRVb11 chain (iTCR). The ability of allogeneic iNKT to protect from aGVHD makes them ideal candidates for ‘off-the-shelf’ immunotherapy without need for TCR deletion. Indeed, CAR-iNKT show promise in pre-clinical models of blood cancer as well as early clinical development against B cell lymphoma and outperform CAR-T counterparts. Here we aimed to enhance the modularity of adoptive iNKT cell immunotherapy for blood cancers by designing a bispecific iNKT cell engager (biNTe) in which one arm would engage the iTCR while the other arm would engage tumour antigen(s) of interest. As a proof-of-principle we designed and synthesised a mono- and a bi-valent biNTe, one each, against the clinically validated myeloma target BCMA with purities of 90% and 70% respectively. We focused on the bivalent biNTe which we first used to demonstrate its iNKT cell binding specificity. Indeed, in flow-cytometry assays, biNTe followed by fluorescent anti-human Fc Ab, stained purified iNKT and but not T cells while in the presence of the same iTCR-binding mAb used to generate the biNTes, binding of the bivalent biNTe on iNKT cells was abrogated. This shows the iTCR engaging specificity of the bivalent biNTe. To demonstrate BCMA specificity of the other arm of the biNTe, we used it to stain iNKT cells, followed by staining with biotinylated soluble BCMA and fluorescently labelled streptavidin. This, compared to staining without soluble BCMA, showed strong staining of iNKT cells thus validating the BCMA specificity of the bivalent biNTe. Next, we set up co-cultures of pre-expanded iNKT against the BCMA-expressing and -knockout myeloma cell line MM1.S in the presence of varying concentrations of the biNTe. While, as assessed by a flow-cytometric cytotoxicity assay, only background killing of myeloma cells was observed in the absence of biNTe or when BCMA ko cell were used as targets, in the presence of biNTe, BCMA+ MM1S cells were killed, in a dose dependent manner (Figure 1A). Consistent with iNKT specificity of the biNTe similar co-cultures involving T cells showed only background killing of MM1S cells (Figure 1B). The same results were obtained using the BCMA-expressing myeloma cell line H929 and its corresponding BCMA knockout. The overall estimated EC50 for MM1.S and H929 cells were 6.56 and 3.4 nM respectively. Using the EC50 concentrations we show that biNTe very effectively kill and almost eliminate patient-derived bone marrow myeloma plasma cells (n=3). To test whether engagement of the iTCR by biNTe would impact its ability to engage with CD1d, we co-cultured iNKT and MM1.S cells transduced with CD1D in the presence of biNTe and the activating, iNKT-specific, CD1d-binding glycolipid ligand a-galactosylceramide (aGalCer). We found that compared to no biNTe control and at biNTE concentrations lower than the EC50, killing of myeloma targets cells was consistently increased. This suggests that iTCR retains its ability to engage CD1d and the efficacy of future biNTe-based immunotherapy could be enhanced by aGalCer. While in vivo validation experiments are ongoing, we conclude that biNTe constitute a novel therapeutic approach with notable pre-clinical anti-myeloma activity. We envisage that they can be used in conjunction with other therapeutic modalities such as CAR and iTCR to enhance the modularity and the efficacy of iNKT cells as an ‘off -the-shelf’ platform for the treatment of myeloma, other blood or solid tumour cancers.

Bivalent BCMA Binding and Low Affinity CD3 T-Cell Engagement By Abbv-383 Drives Sustained Activation with Reduced T-Cell Exhaustion in Preclinical Models of Multiple Myeloma

Introduction: ABBV-383 is an IgG4-based CD3-bispecific T-cell engager (TCE) that has shown promising efficacy and a favorable safety profile in heavily pre-treated patients with relapsed/refractory multiple myeloma (MM). ABBV-383 possesses a unique combination of a low-affinity CD3δε antibody coupled to a bivalent, high-affinity BCMA engager arm in a 2+1 format. Prior pre-clinical studies demonstrated that ABBV-383 induces potent redirected T-cell killing of MM tumors with reduced cytokine release. Here, we provide additional evidence that bivalent BCMA binding by ABBV-383 reduces the negative impact of soluble BCMA and low affinity CD3 T-cell engagement drives sustained T-cell activation with reduced immune exhaustion. Methods: Structural variants of ABBV-383 were created, including 1) the bivalent BCMA targeting antibody of ABBV-383 replaced by proximal and distal monovalent VH targeting molecules, and 2) BCMA antibody structures coupled to high-and low affinity CD3 variants ( Figure). For functional testing, ABBV-383 and the structural variants were added to PBMCs or T-cells from healthy donors to serve as effector cells in co-culture with BCMA-positive MM tumor cell lines. Tumor cell killing and T-cell activation were determined by flow cytometry, and cytokine production was assessed using Luminex instrumentation. Recombinant soluble BCMA (sBCMA) was utilized in the experimental models to evaluate the extent of BCMA TCE suppression. To define the relationship between CD3-affinity and T-cell exhaustion, multi-dimensional flow cytometry was performed in long-term, 28-day co-cultures with irradiated tumor cells replated every 7 days. Results: T-cell binding was shifted by &amp;gt;100x with substitution of the high affinity CD3 antibody compared to ABBV-383. While all antibody variants tested induced T-cell specific MM cell killing in a BCMA-dependent manner, the negative impact of soluble BCMA on tumor killing was reduced with ABBV-383 due to its bivalent interaction with tumor cells compared to the monovalent TCE formats. In addition, the low CD3 binding affinity of ABBV-383 lowered T-cell activation antigen expression and reduced inflammatory cytokine production but resulted in similar maximal cytotoxicity of tumor cells in co-cultures of healthy and MM patient samples compared to high-affinity CD3 targeting. While maximal tumor cytotoxicity was similar, ABBV-383 was found to significantly delay the induction of a critical exhaustion-inducing transcription factor, TOX, in long-term assays. T-cell population changes were observed as early as 3 days with decreased effector memory cells (CD45RA-CD62L-) and increased naïve T-cell populations (CD62L+CD45RA+) compared to high-affinity CD3 targeting. On day 21, the high-affinity CD3 x bivalent BCMA molecule resulted in 85% of the CD8+ T-cell population expressing the transcription factor TOX compared to only 15% for ABBV-383 co-cultures. TOX induces several gene families with chromatin-modulating capacity that drive the distinct transcriptional trajectory leading to T-cell dysfunction during chronic stimulation. Simultaneous expression of multiple checkpoint inhibitory proteins is indicative of T-cell exhaustion. Triple positive CD8+ T-cells expressing LAG3, PD-1 and CTLA4 were significantly reduced by ABBV-383 versus the high-affinity CD3 variant ( Figure). Conclusions: High avidity BCMA binding coupled to low affinity T-cell engagement distinguishes the resulting mechanism of action for ABBV-383 in MM. Here, we show that the presence of bivalent-BCMA reduced the negative impact of soluble BCMA, reduced inflammatory cytokine production, and dampened the emergence of TOX+ CD8+ T-cells indicating that ABBV-383 structure maximizes its clinical potential as a safe and effective MM therapy.

Updated Safety and Efficacy Results of Abbv-383, a BCMA x CD3 Bispecific T-Cell Redirecting Antibody, in a First-in-Human Phase 1 Study in Patients with Relapsed/Refractory Multiple Myeloma

Updated Safety and Efficacy Results of Abbv-383, a BCMA x CD3 Bispecific T-Cell Redirecting Antibody, in a First-in-Human Phase 1 Study in Patients with Relapsed/Refractory Multiple Myeloma

BMS-986393 (CC-95266), a G Protein-Coupled Receptor Class C Group 5 Member D (GPRC5D)-Targeted Chimeric Antigen Receptor (CAR) T-Cell Therapy for Relapsed/Refractory Multiple Myeloma (RRMM): Updated Results from a Phase 1 Study

Introduction: Despite advances in RRMM therapy, new approaches are needed for patients (pts) that relapse. GPRC5D, an orphan receptor expressed on MM cells with limited expression in other tissues, is a promising therapeutic target for MM. Previously, we presented interim results from the dose escalation and expansion parts of CC-95266-MM-001 (NCT04674813), a phase 1, first-in-human, multicenter, open-label, dose-finding study evaluating BMS-986393 (CC-95266), a GPRC5D-targeted autologous CAR T-cell therapy, in pts with RRMM (Bal S et al. ASH 2022, P364; Bal S et al. EHA 2023, S193). Here, we present updated safety and efficacy data from the study. Methods: Eligible pts received ≥ 3 prior treatment regimens and must have received a proteasome inhibitor, an immunomodulatory agent, an anti-CD38 therapy, and an autologous stem cell transplant (if eligible); prior BCMA-directed and CAR T-cell therapies were allowed. After screening and leukapheresis, pts received bridging therapy, if needed, and underwent lymphodepletion followed by a single infusion of BMS-986393. In dose escalation, BMS-986393 was used at doses of 25, 75, 150, 300, and 450 × 10 6 CAR T cells. In dose expansion, additional pts received 75, 150, 300, or 450 × 10 6 CAR T cells. Safety, tolerability, and determination of maximum tolerated dose and/or recommended phase 2 dose (RP2D) of BMS-986393 were primary objectives; secondary objectives included evaluation of preliminary efficacy. Results: As of May 24, 2023, 70 pts received BMS-986393 at doses of 25 (n = 6), 75 (n = 10), 150 (n = 26), 300 (n = 17), and 450 (n = 11) × 10 6 CAR T cells. 32 pts (46%) had high-risk cytogenetics (del[17p], t[4;14], and/or t[14;16]), 40 (57%) had 1q21amp, and 30 (43%) had extramedullary plasmacytomas; 32 (46%) pts had received prior BCMA-targeted therapy, including BCMA-directed CAR T-cell therapy in 25 (36%) pts. 24 (34%) pts had penta-refractory MM. Grade (G) 3/4 treatment-emergent adverse events (AEs) occurred in 64/70 (91%) pts; the most frequent were neutropenia (69%), anemia (31%), and thrombocytopenia (30%). Any-grade infections occurred in 30 (43%) pts (G 3/4 in 11 [16%] pts). Cytokine release syndrome (CRS) occurred in 59 (84%) pts (G ≥ 3 in 3 [4%] pts, with 1 [1%] G5 event); 3 (4%) pts had hemophagocytic lymphohistiocytosis, all G3. On-target off-tumor treatment-related AEs (TRAEs), all G1/2, included skin (17 [24%]) and nail (11 [16%]) TRAEs and dysgeusia/dysphagia (2 [3%]). Immune effector cell-associated neurotoxicity syndrome (ICANS)-type neurotoxicity occurred in 8 (11%) pts (G3 in 2 [3%] pts). The most frequent non-ICANS neurologic TRAEs were headache (10 [14%]), dizziness (6 [9%]), ataxia (5 [7%]), dysarthria (3 [4%]), neurotoxicity (3 [4%], including events termed cerebellar toxicity in 2 pts), and paresthesia, gait disturbance, and nystagmus (1 pt each [1%]). Aside from headache and paresthesia, incidence of the listed non-ICANS neurologic TRAEs appeared to be dose-related, and reversibility of some events was observed. Overall response rate (ORR) across doses was 86% (55/64) in efficacy-evaluable pts and 75% (21/28) in pts treated with prior BCMA-directed therapies, including CAR T cells. Complete response (CR) rate was 38% (24/64). In pts refractory to prior BCMA-directed therapies, ORR was 85% (11/13), and CR rate was 46% (6/13). Median follow-up for all treated pts was 5.9 mo (range, 0.0-24.0). At the time of data cutoff, 75% of responses (41/55) were ongoing. All 10 pts (100%) with available minimal residual disease (MRD) data and a best overall response of CR were MRD-negative (10 −5 depth) at ≥ month 3. BMS-986393 reduced soluble BCMA levels (indicative of tumor burden reduction) across all dose levels and showed a dose-dependent increase in cellular expansion. Conclusions: In this first-in-human study, BMS-986393 showed a manageable safety profile and deep and durable responses, including MRD negativity, at all tested dose levels, including in pts refractory to prior BCMA-directed therapies. CRS and ICANS-type neurotoxicity were mostly low-grade, with increased G ≥ 3 events at the 300 and 450 × 10 6 CAR T-cell doses. On-target off-tumor TRAEs, all G1/2, occurred in a minority of pts. These data support GPRC5D-directed CAR T-cell therapy with BMS-986393 as a potential treatment in RRMM, irrespective of prior BCMA-directed therapy. Dose expansion is continuing to define the RP2D. Updated data will be presented.

Sequential T-Cell Engagement for Myeloma (“STEM”) Trial: A Phase 2 Study of Cevostamab Consolidation Following BCMA CAR T Cell Therapy

Background and significance: The BCMA-targeted CAR T products idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel) are currently approved for relapsed/refractory multiple myeloma (RRMM) patients with ≥4 prior lines of therapy, including an IMID, proteasome inhibitor, and CD38 antibody. However, despite unprecedented response rates, CAR T cells are not curative in these late-line patients, even for those in complete remission. Mechanisms of resistance may include lack of persistence or poor function of persisting CAR T cells, as well as BCMA-low or -negative residual tumor cells that serve as a reservoir for relapse. FcRH5 is another MM cell surface antigen, with expression independent of BCMA. Cevostamab is an FcRH5-targeted, T cell-engaging bispecific antibody (bsAb) with demonstrated activity in RRMM, including in patients with prior BCMA-directed therapies (Trudel et al, ASH 2021, #157). We hypothesize that consolidating BCMA CAR T cell therapy with a bsAb targeting a different antigen may re-invigorate persisting CAR+ T cells against residual BCMA+ tumor cells, while also activating endogenous T cells against FcRH5+, BCMA-low/negative tumor cells, ultimately improving rates of sustained minimal residual disease (MRD)-negativity and durability of response. Study design and methods: This is a single-institution, investigator-initiated study (NCT05801939) sponsored by the University of Pennsylvania, with funding support from Genentech. Targeted population are patients with RRMM who have received a commercially available CAR T cell product (ide-cel or cilta-cel) according to the FDA label, within the past 8 weeks, with stable disease or better. Major inclusion criteria include absolute neutrophil count ≥ 1, hemoglobin ≥ 7, platelets ≥ 50, and creatinine clearance ≥ 30 ml/min. Major exclusion criteria include prior cytokine release syndrome or ICANS ≥ grade 3, or any grade hemophagocytic lymphohistiocytosis (HLH) or Parkinsonism, or any active infection. The study schema is shown in Figure 1. Cevostamab is initiated 8-10 weeks after CAR T cell infusion. This timepoint was chosen to allow recovery from acute CAR T cell-related toxicities, but while CAR T cells may still be detectable in circulation. Cevostamab is given at a step-up dose of 3.6mg intravenously (IV) on Cycle 1, Day 1 (C1D1), followed by full dose of 160mg IV on C1D8. Subjects are hospitalized for 48 hours after each C1 dose to monitor for CRS and ICANS. They then continue cevostamab every 3 weeks for total of 8 cycles. If they are in an MRD-negative complete response (CR) after 8 cycles (Adaptive Clonoseq assay, at 10e-5 sensitivity), they stop therapy and are observed. If not, or if bone marrow results are indeterminate, they get another 8 cycles of cevostamab, then stop and are observed. The primary endpoint is frequency of MRD-negative CR at 12 months post-CAR T cell therapy. Assuming a roughly equal proportion of patients enrolling after ide-cel and cilta-cel, the null hypothesis is that the true MRD-negative CR rate at 12 months is 35%. Twenty-six evaluable subjects will be accrued in a single-stage design. The null hypothesis will be rejected if 14 or more subjects meet the primary endpoint. This design yields a one-sided type I error rate of 0.05 and power of 0.84 for an exact test when the true 12-month MRD-negative CR rate is 60%. Secondary endpoints include feasibility, safety/tolerability, and other efficacy measures (overall and CR rates, PFS, OS). Exploratory endpoints include 1) impact of cevostamab on pre- and post-therapy frequency and phenotype of both CAR+ and CAR-negative T cells in blood and marrow, assessed by multiparameter flow cytometry; 2) pre- and post-therapy expression of BCMA and FcRH5 on myeloma cells (when available), serum concentrations of soluble BCMA and FcRH5, and relationship of these factors to clinical outcome measures, and 3) pre- and post-therapy genotypic and phenotypic make-up of bone marrow microenvironment, assessed by single cell RNA sequencing (scRNAseq) and multiparameter flow cytometry, and relationship of these factors to clinical outcome measures. Conclusions: This phase 2 study is exploring the efficacy, safety, and feasibility of cevostamab consolidation following BCMA-directed CAR T cell therapy for RRMM, with the goal of sequential T cell engagement against 2 different antigens to eliminate residual disease. Accrual started in July 2023.

Immune and Genome Profiling of Myeloma Patients Treated with Sequential Immunotherapies Reveal Differential Non-Overlapping Mechanisms of Resistance

Chimeric antigen receptor T cells (CAR T) or bispecific T cell engagers (TCE) targeting multiple myeloma (MM) antigens result in deep responses in relapsed patients. Nevertheless, resistance invariably emerges requiring salvage treatments. Sequential therapies with CAR T or TCE, in patients with or without prior anti-BCMA therapy exposure, reported durable responses. However the genomic and molecular determinants of response to sequential immunotherapies are poorly defined. To define the molecular determinants of response to sequential immunotherapies we identified patients treated with more than one anti-BCMA or -GPRC5D (n=8) regimens. Bone marrow (BM) and peripheral blood (PB) mononuclear cells from these patients were collected prior to each therapy and at the time of progression. Sorted CD138+ cells were subjected to whole genome sequencing (WGS) or single cell CNV (scCNV) and single cell RNA (scRNA) analysis. CD3+ T cells were subjected to CITEseq and functional in vitro cytotoxicity assays. Patient 1 received anti-BCMA CAR T (Ide-cel) with VGPR lasting 7 months (mos) (Figure 1). He subsequently received elranatamab with no response. CITEseq profiling of T cells at progression post CAR T did not reveal expansion of exhausted cytotoxic or regulatory T cells. However, WGS and scCNV of MM cells identified biallelic TNFRSF17 deletion consistent with antigenic escape as cause of resistance. Patient 2 received Ide-cel (DOR = 3.5 mos) followed by elranatamab with no response. CD138+ MM cells retained BCMA expression and in vitro studies with in-house manufactured anti-BCMA CAR T efficiently eliminated his MM cells. Profiling of T cells showed terminal T cells exhaustion (CD45RA +, TOX +, TIGIT +, PDCD1 + and LAG3 +). In contrast to recipients of CAR T, antigenic loss was commonly observed post TCE therapy. Patient 3 received 3 sequential therapies with Ide-cel (DOR = 3 mos), teclistamab (DOR = 6 mos), and then talquetamab with daratumumab with an ongoing response of 11 mos. While T cell exhaustion was not observed, functional loss of BCMA on MM cells was detected post teclistamab, with 2 coexisting clones harboring TNFRSF17 extracellular domain mutations (p.Pro34del, or p.Ser30del) that abrogated teclistamab binding. Similarly in patient 4 progressing on elranatamab (DOR = 21 mos), there was no evidence of T cell exhaustion but rather acquired BCMA mutation (p.Pro34del) in MM cells. Consistent with fit T cells profile, he has an ongoing response (13+ mos) to talquetamab and daratumumab in his next line of therapy. Patient 5 with penta-refractory disease and high disease burden (&amp;gt; 90% BM infiltration) had no response to elranatamab, however achieved an ongoing sCR (DOR = 30 mos) with talquetamab, daratumumab and pomalidomide (Tal-DP). PB T cells did not show exhaustion at the time of progression on elranatamab. A similar pattern was observed in patient 6 with high disease burden and no response to teclistamab but achieved lasting VGPR to Tal-DP (DOR=24 mos) in the next line followed by an acquired biallelic loss of GPRC5D at progression. Patient 7 had a 17 mos remission to talquetamab and daratumumab and similarly to patient 6, he acquired biallelic loss of GPRC5D at progression. He subsequently received elranatamab with no response with elevated serum soluble BCMA (sBCMA=638 ng/ml) level and phenotypic and functional evidence of T cell exhaustion. Patients 5, 6 and 7 illustrate the impact of disease burden and the ensuing sBCMA sink effect on the efficacy of anti-BCMA TCEs. Lastly patient 8 had lasting remissions to elranatamab (DOR 13 mos) and subsequently to talquetamab (DOR 13 mos) with no evidence of T cells exhaustion but rather antigenic escape with acquired functional antigenic losses with clonal BCMA (p.Arg27Pro) and subsequently GPRC5D (p.Asp239Asn) mutation. Highlighting the lack of cross resistance between anti-BCMA therapies, our in vitro studies showed that while mutant BCMA (p.Ser30del or p.Pro34del) abrogated teclistamab mediated T cell killing, T cells transduced with teclistamab based scFv CAR retained cytolytic activity. Therefore, TCE resistance derived from BCMA mutations does not preclude retreatment with another anti-BCMA TCE or CAR T. We here describe variable non-overlapping mechanisms mediating resistance to sequential TCE and CAR T therapies. Dynamic surveillance for antigenic escape and functional evaluation of T cell fitness will optimize immunotherapy sequencing.

Bispecific CS1-BCMA CAR-T cells are clinically active in relapsed or refractory multiple myeloma.

Multiple myeloma (MM) bears heterogeneous cells that poses a challenge for single-target immunotherapies. Here we constructed bispecific CS1-BCMA CAR-T cells aiming to augment BCMA targeting with CS1. Sixteen patients with relapsed or refractory (RR) MM received CS1-BCMA CAR-T infusion. Six patients (38%) had cytokine release syndrome, which was of grade 1-2 in 31%. No neurological toxicities were observed. The most common severe adverse events were hematological, including leukopenia (100%), neutropenia (94%), lymphopenia (100%) and thrombocytopenia (31%). Three patients with solitary extramedullary disease (sEMD) did not respond. At a median follow-up of 246 days, 13 patients (81%) had an overall response and attained minimal residual disease-negativity, and six (38%) reached a stringent complete response (sCR). Among the 13 responders, 1-year overall survival and progression-free survival were 72.73% and 56.26%, respectively. Four patients maintained sCR with a median duration of 17 months. Four patients experienced BCMA+ and CS1+ relapse or progression. One patient responded after anti-BCMA CAR-T treatment failure. Lenalidomide maintenance after CAR-T infusion and the resistance mechanism of sEMD were preliminarily explored in three patients. CAR-T cells persisted at a median of 406 days. Soluble BCMA could serve as an ideal biomarker for efficacy monitoring. CS1-BCMA CAR-T cells were clinically active with good safety profiles in patients with RRMM. Clinical trial registration: This study was registered on ClinicalTrials.gov, number NCT04662099.

P-005 Association of baseline soluble BCMA with measures of disease burden and response to linvoseltamab: a comprehensive analysis in patients with relapsed/refractory multiple myeloma (RRMM)

P-005 Association of baseline soluble BCMA with measures of disease burden and response to linvoseltamab: a comprehensive analysis in patients with relapsed/refractory multiple myeloma (RRMM)

Evaluating the efficacy of commercial teclistamab in relapsed refractory multiple myeloma patients with prior exposure to anti-BCMA therapies.

8049 Background: Teclistamab (Tec) is the first CD3 x BCMA bispecific antibody (BsAb) receiving accelerated FDA approval for treatment of relapsed or refractory multiple myeloma (RRMM) in patients who have received ≥4 prior lines of therapy, including a PI, IMiD and an anti-CD38 monoclonal antibody. The approval was based on the results of the MajesTec-1 study (Usmani S et al Lancet 2021, Moreau P et al NEJM 2022), demonstrating a 63% overall response rate in a heavily pretreated RRMM population. Patients with prior exposure to anti-BCMA therapies, such as BCMA targeted ADCs, CAR T-cell products and BsAbs were excluded from this study. Herein, we present our institutional experience with commercial Tec for RRMM including patients with prior BCMA and GPRC5D directed therapies. Methods: We have performed an IRB-approved, retrospective analysis of clinical outcomes of all patients who have received commercial Tec at MSKCC since its approval on 10/26/2022 using the PCD research database. Descriptive analyses were performed for baseline characteristics. The IMWG criteria (Kumar S et al, Lancet Oncol 2016) were used to assess response and define prior therapy refractoriness. Immune profile was assessed via high-dimensional flow cytometry using lineage, exhaustion, and activation markers. Serum soluble BCMA levels were assessed using an immunoassay. Results: As of 2/4/2023, 24 patients have received commercial Tec and 15 are response evaluable with ≥1 month of clinical follow-up. Median age was 66 (51-80), prior lines of therapy was 7 (4-13), time from diagnosis was 7 years (1.5-16), 53% had high-risk cytogenetics, and 40% had EMD. All patients were triple class refractory and 80% were penta-drug refractory. Ten had prior anti-BCMA therapy (7 Belamaf, 8 BCMA CART, 1 BCMA BsAb, 5 with ≥2 anti-BCMA therapies). With a median follow-up time of 1.3 months, the median time to response was 16 days. ORR was 60% (9/15) in all patients and 50% (5/10) in the prior anti-BCMA therapy group. Pts with ≥2 anti-BCMA therapies had a 40% (2/5) response rate to Tec. Clinical benefit rate (CBR) in all patients was 73% (11/15). None of the responders have progressed at this short follow-up time. Cytokine release syndrome was observed in 7/15 patients (41%) during step-up dosing (5/7 with g1 and 2/7 with g2 CRS) and CBR was 100% in patients with CRS (71% ORR). Other notable toxicities include 2 patients with grade 2 neurotoxicity that improved with therapy discontinuation. Conclusions: To our knowledge, this is the first report of commercial Tec in RRMM. Tec remains effective in RRMM despite prior exposure to anti-BCMA therapies, though exposure to multiple prior anti-BCMA therapies may be predictive of diminished efficacy. Clinical data on additional patients will be presented at the meeting. Ongoing translational investigations on soluble BCMA levels and patient-specific immune phenotype will also be presented at the meeting.

LINKER-MM1 study: Linvoseltamab (REGN5458) in patients with relapsed/refractory multiple myeloma.

8006 Background: Linvoseltamab is a BCMA×CD3 bispecific antibody with encouraging efficacy and a manageable safety profile in patients (pts) with relapsed/refractory multiple myeloma (RRMM) (Bumma et al. ASH 2022). Two Phase (Ph) 2 full dose cohorts (50 mg and 200 mg) in the LINKER-MM1 (NCT03761108) trial were studied to optimize dose selection. Methods: Ph 2 enrolled adults with MM who progressed on/after ≥3 lines of therapy (LoT) including a proteasome inhibitor (PI), an immunomodulatory drug (IMiD), and an anti-CD38 antibody (Ab), or were at least triple class (IMiD/PI/anti-CD38 Ab) refractory. A protocol amendment permitted pts who progressed during 4–12 wks on 50 mg to dose escalate to 200 mg. Primary endpoint was objective response rate (ORR). Key secondary endpoints included duration of response (DoR) and minimal residual disease status. Results: As of 1 Sept 2022, 252 pts have enrolled (Ph 1: 73; Ph 2: 179 [200 mg: 75; 50 mg: 104]). Median age was 66 yrs (range 37–90), 12% had extramedullary plasmacytomas, 12% high-risk cytogenetics, 37% bone marrow plasma cell percentage (BMPC) ≥50%. Median soluble BCMA concentration (sBCMA) was 0.43 mg/L (range 0–10.2), median prior LoT: 5 (range 1–16), and 81% were ≥triple class refractory. Numerically higher efficacy was observed with 200mg, including in high disease burden subgroups; ORR was 64% (200 mg cohort; n = 58, includes 12 Ph 1 pts) and 50% (50 mg cohort; n = 104). Subgroup analyses showed higher ORR in the 200 mg cohort versus 50 mg for sBCMA ≥0.4 mg/L (52% vs 37%), BMPC &gt; 67% (64% vs 35%) and revised ISS stage III (71% vs 27%). Median DoR was not reached for both cohorts (median follow-up: 2.3 months [200 mg], 4.7 months [50 mg]). Probability of maintaining response at 6 months was 89% (200 mg) and 85% (50 mg). Eight pts dose escalated from 50 to 200 mg; 6 (75%) achieved a response. Treatment-emergent adverse events (TEAEs) occurred in 95% (Grade [Gr] ≥3: 66%) of pts in the 200 mg cohort (n = 87, includes 12 Ph 1 pts) and 100% (Gr ≥3: 80%) in the 50 mg cohort. The most common TEAEs were cytokine release syndrome (200 mg: 37% [Gr 3: 1%]; 50 mg: 53% [Gr 3: 2%]), fatigue (200 mg: 32% [Gr ≥3: 0]; 50 mg: 33% [Gr ≥3: 0]) and anemia (200 mg: 28% [Gr ≥3: 24%]; 50 mg: 40% [Gr ≥3: 36%]). Grade ≥3 ICANS occurred in 2 pts (2%) in the 200 mg cohort and 1 pt (1%) in the 50 mg cohort. TEAEs leading to treatment discontinuation occurred in 7% (200 mg cohort) and 8% (50 mg cohort) of pts. Infections occurred in 43% (Gr ≥3: 26%) in the 200 mg cohort and 59% (Gr ≥3: 31%) in the 50 mg cohort. Conclusions: Linvoseltamab 200 mg showed better efficacy compared with 50 mg, including in pts with high disease burden. The 200 mg dose had consistent efficacy across high-risk subgroups and induced responses in pts who progressed on 50 mg. Safety was consistent across Ph 2 doses. The recommended linvoseltamab dose for further development is 200 mg. Updated data with longer follow-up and complete enrollment of the 200 mg cohort will be presented at the meeting. Clinical trial information: NCT03761108 .

BAFF and APRIL signaling through B cell maturation antigen affects regulatory transitional B cells in multiple sclerosis.

Abstract Multiple sclerosis (MS) is a debilitating neuro-autoimmune disease that can be stratified into relapsing remitting (RR) MS, secondary progressive (SP) MS, and primary progressive (PP) MS. B cells can have both inflammatory and regulatory functions in MS. Transitional B cells are considered to have regulatory functions in MS. BAFF and APRIL, two cytokines, signals through the receptors BAFFR, TACI and BCMA and are thought to drive the regulatory function of transitional B cells. Here, we assessed the frequencies and expression of BAFFR, TACI and BCMA on the surface of regulatory transitional B cells in the blood of RRMS, PPMS and healthy individuals along with soluble versions of these receptors in the plasma. We found that transitional B cells were decreased in both RRMS and PPMS patients. The surface expression of BCMA was significantly lower on transitional B cells from RRMS patients but not PPMS patients compared to healthy individuals with no change in the expression of TACI and BAFFR. In addition, we found elevated levels of soluble BCMA in blood of PPMS patients but not RRMS patients compared to healthy and no difference in soluble BAFFR and TACI. Our data suggests that reduced BCMA signaling is associated with reduced numbers of transitional B cells in RRMS and PPMS. In RRMS, expression of BCMA is reduced on regulatory transitional B cells. In PPMS patients, there are higher levels of soluble BCMA which could act as a blocker of APRIL signaling through BCMA on the surface of transitional B cells. Altogether, our data suggests that reduced BCMA signaling in transitional B cells is contributing to the MS disease and the dysregulation of the BCMA signaling in RRMS and PPMS may be through a different mechanism. This study was supported by grants from the NMSS (RG-1602-07722), the NIH (R01AI137047 and R01EY027346) awarded to R.C. Axtell.

Real-life experiences with CAR T-cell therapy with idecabtagene vicleucel (ide-cel) for triple-class exposed relapsed/refractory multiple myeloma patients

BackgroundChimeric antigen receptor (CAR) T-cell therapy has revolutionized the treatment landscape of relapsed/refractory multiple myeloma (RRMM), leading to unprecedented responses in this patient population. Idecabtagene vicleucel (ide-cel) has been recently approved for treatment of triple-class exposed RRMM. We report real-life experiences with the commercial use of ide-cel in RRMM patients.MethodsWe performed a retrospective analysis of the first 16 triple-class exposed RRMM patients treated with ide-cel at a single academic center. We assessed toxicities, response to treatment, CAR T expansion and soluble BCMA (sBCMA) levels.ResultsWe identified 16 consecutive RRMM patients treated with ide-cel between 06–10/2022. Median age was 69 years, 6 (38%) patients had high-risk cytogenetics, 3 (19%) R-ISS stage III, and 5 (31%) extramedullary disease. Median number of previous treatment lines was 6 (3–12). Manufacturing success rate was 88% (6% required second lymphapheresis, 6% received an out-of-specification product). At 3 months, the overall response rate (ORR) was 69% (44% sCR, 6% CR, 19% VGPR). Cytokine release syndrome (CRS) occurred in 15 (94%) patients (88% G1, 6% G2), immune effector-cell associated neurotoxicity syndrome (ICANS) in 1 (6% G1), febrile neutropenia in 11 (69%), and infections in 5 (31%). Prolonged hematologic toxicity occurred in 4/16 (25%) patients. Other non-hematological toxicities were elevated hepatic enzymes (38%), colitis (6%, G3) and DIC (6%, G2). Responses were more frequent in patients with higher CAR T expansion (100% vs 38%), and lack of decrease or plateau of sBCMA levels was typically observed in non-responders.ConclusionsWe report one of the first cohorts of RRMM treated with commercial ide-cel. The ORR was 69% and safety profile was manageable, but prolonged hematologic toxicity still represents a major challenge. Responses correlated with in vivo CAR T cell expansion, underlining the need of further research to optimize CAR T expansion.