Antileukemic Activity Research Articles

Updated Efficacy and Safety Results of Lisaftoclax (APG-2575) in Patients (Pts) with Heavily Pretreated Chronic Lymphocytic Leukemia (CLL): Pooled Analyses of Two Clinical Trials

*Drs. Keshu Zhou, Mingyuan Sun, and Wei Xu are co-first authors; Drs. Jianyong Li, Jianxiang Wang, and Yifan Zhai are co-corresponding authors. Introduction Investigational lisaftoclax is a selective BCL-2 inhibitor that has demonstrated antileukemic activity and favorable tolerability in pts with CLL. We report updated efficacy and safety data of pts with CLL treated with lisaftoclax in phase 1b/2 studies APG-2575-CN001 (NCT03913949) and APG-2575-CC101 (NCT04494503) after a 14-month follow-up. Methods Lisaftoclax (100, 200, 400, 600, and 800 mg) was administered orally once daily to pts with relapsed/refractory (R/R) CLL in repeated 28-day cycles. A daily ramp-up schedule and close monitoring was used for prevention and early detection of tumor lysis syndrome (TLS). Lisaftoclax continued until disease progression, intolerable toxicity, death, or any other reason for termination. Adverse events (AEs) were reported per NCI CTCAE v5.0, and response was evaluated per 2008 iwCLL NCI-WG criteria. Flow cytometry was used to analyze minimal residual disease (MRD) at individual sites in pts who achieved complete response (CR)/CR with incomplete marrow recovery (CRi) and partial response (PR) based on investigator judgement. MRD negativity was defined as a threshold of < 10 -4. Results As of April 27, 2023, a total of 47 pts went through a daily ramp-up of lisaftoclax treatment at an assigned dose, ranging from 100 to 800 mg daily (100 [n = 3], 200 [2], 400 [12], 600 [14], and 800 [16] mg). The median (range) follow-up period was 14.06 (0.70-30.2) months, and the median (range) age was 58 (34-80) years (male, 68.1%), with an ECOG PS of 0-1. At enrollment, 53.2% of pts were in Rai stage III/IV, and 48.9% Binet stage C. A total of 66.0% and 44.7% of pts had been treated with ≥ 2 or 3 lines of systematic treatment, 23.4% > 1 Bruton tyrosine kinase (BTK) inhibitor, and 55.3% a CD20 antibody. A total of 36 (76.6%) pts experienced grade (Gr) 3/4 treatment-emergent AEs (TEAEs), and 13 (27.7%) had serious AEs (SAEs). Incidences of TEAEs were not dose related. Common (> 30%) TEAEs were decreased neutrophil (all Gr, 72.3%; Gr 3/4, 44.7%), platelet (all Gr, 59.6%; Gr 3/4, 31.9%), and leukocyte (all Gr, 51.1%; Gr 3/4, 14.9%) counts; anemia (all Gr, 48.9%; Gr 3/4, 10.6%); hypertriglyceridemia (all Gr, 44.7%; Gr 3/4, 4.3%); hyperuricemia (all Gr, 42.6%); hypokalemia (all Gr, 34.0%); diarrhea (all Gr, 34.0%); and hyperbilirubinemia (all Gr, 31.9%). TRAEs were observed in 45 (95.7%) pts, of whom 32 (68.1%) experienced Gr 3/4 AEs and 7 (14.9%) SAEs. One TLS was reported. Thirty-two (68.1%) pts discontinued the study due to disease progression (51.1%); withdrawal (6.4%); and AEs, investigator decision, poor compliance, protocol deviation, and other reasons (2.1% each). The median (range) time to first response was 2.07 (1.94-3.94) months. The overall response rate (ORR) was 73.3% (33/45), and the CR/CRi rate was 24.4% (11/45). The rate of CR/CRi seemed to be dose-dependent (16.7% at 400, 23.1% at 600, and 33.3% at 800 mg). Furthermore, the pt who achieved a CR in the 200-mg cohort showed systemic exposure (C max and AUC) to lisaftoclax comparable to that observed in the 600-mg cohort. One patient in the 400-mg cohort achieved a CR in response to a dose escalation (per investigator) to 600 mg. MRD negativity was observed in 7 of 18 (38.9%) pts tested with peripheral blood (PB) MRD assessment, and 4 of 6 (66.7%) pts tested negative for MRD with MRD assessment of bone marrow (BM; Table 1). Median progression-free survival (PFS) was 18.53 (95% CI, 9.13-24.05) months, and 12- and 24-month PFS rates were 58.0% (95% CI, 41.9-71.2) and 39.4% (95% CI, 24.4- 54.0), respectively, as shown in Figure 1. The median (range) duration of response was 20.24 (95% CI, 14.75-NR) months. Median overall survival (OS) was NR. OS at 12 and 30 months was 94.8% (95% CI 80.6-98.7) and 86.3% (95% CI 66.1-94.9), respectively. Conclusions Lisaftoclax demonstrated significant efficacy at 400, 600, and 800 mg, and potentially 200 mg, in pts with R/R CLL who were heavily pretreated and had been exposed to BTK inhibitors. CR/CRi exhibited a trend of positive correlation with escalating dose levels. No significant new or unmanageable safety findings were observed.

Update of Olverembatinib (HQP1351) Overcoming Ponatinib and/or Asciminib Resistance in Patients (Pts) with Heavily Pretreated/Refractory Chronic Myeloid Leukemia (CML) and Philadelphia Chromosome-Positive Acute Lymphoblastic Leukemia (Ph + ALL)

Background Olverembatinib, a novel, potent BCR::ABL1 tyrosine kinase inhibitor (TKI), shows strong antitumor activity in pts with CML and Ph + ALL. Here, we report on the safety, efficacy, and pharmacokinetic (PK) profiles of olverembatinib in pts with CML (all phases) and Ph + ALL outside of China, particularly in pts previously treated with ponatinib and/or asciminib. Methods Olverembatinib was administered orally once every other day (QOD) in continuous 28-day cycles. In the monotherapy cohort, pts were enrolled after treatment failure on at least 2 prior TKIs and randomized to olverembatinib QOD 30, 40, or 50 mg. In the combination cohort, pts with Ph + B-cell precursor (BCP) ALL or lymphoid CML-BP (CML-LBP) resistant to at least 1 TKI were enrolled and received olverembatinib (30 or 40 mg) QOD in combination with blinatumomab. Results As of June 30, 2023, 76 pts were enrolled, including 57 with CML-CP and 19 with advanced Ph + leukemia. The median (range) age was 54.5 (21-80) years, and 56.6% of pts were male. In all, 11 (14.5%), 23 (30.3%), and 39 (51.3%) pts had received 2, 3, and ≥ 4 prior TKIs, respectively. A total of 52.6% of pts were previously treated with ponatinib, of whom 67.5% were resistant and 25.0% intolerant to the drug, and 7.5% experienced treatment failure for other reasons. A total of 27.6% of pts were previously treated with asciminib, of whom 71.4% were resistant and 19.1% intolerant to the agent, and 9.5% experienced treatment failure for other reasons. At baseline, 32% of pts had T315I mutations, 38% hypertension, and 17.1% other cardiovascular comorbidities. Median (range) treatment duration was 24.1 (0-134) weeks, and PK profiles were similar to historical PK data on Chinese pts. Twelve pts with CML-CP and 7 with advanced Ph + leukemia discontinued treatment: 4 because of AEs, 7 disease progression, and 8 other reasons. A total of 54 of 65 (83.1%) pts who received ≥ 1 dose of olverembatinib experienced any-grade TRAEs. Grade ≥ 3 AEs occurring in ≥ 3 pts (≥ 4.6% incidence) included thrombocytopenia (17%); neutropenia (13.8%); elevated blood creatine phosphokinase (13.8%); leukopenia (7.7%); and anemia and elevated lipase (4.6% each). Ten (15.4%) pts experienced olverembatinib treatment-related serious AEs, of which each were experienced by 1 (1.5%) pt. Two (3.1%) pts discontinued the study because of TRAEs. No TRAE-associated deaths were reported. Olverembatinib showed sustained antileukemic activity in pts with CML and Ph + ALL (Table 1). Among 50 efficacy-evaluable pts with CML-CP, the rate of complete cytogenetic response (CCyR) was 57% (25/44) and major molecular response (MMR) 43% (21/49). Efficacy improved over time; the MMR rate in pts with CML-CP treated for 6 months was 66% and 88% in pts treated for 12 months. Among pts whose disease failed ≥ 4 prior TKIs, CCyR and MMR rates were 57% (13/23) and 42% (11/26), respectively. In pts with CML-CP harboring the T315I mutation, rates of CCyR and MMR were 60% (9/15) and 44% (7/16), respectively, and 55% (16/29) and 42% (14/33) in pts without the T315I mutation. Among evaluable ponatinib-failed pts, 8/15 (53%) achieved CCyR and 6/16 (38%) MMR. Among pts who failed asciminib therapy, 3/7 (43%) achieved CCyR and 3/8 (38%) MMR. Of 8 pts with CML-CP who had prior exposure to both ponatinib and asciminib, 2 (25%) achieved MMR. At 24 months, PFS was 75% (95% CI, 56.1-86.7) and OS was 97.6% (95% CI, 90.8-99.4). Thirteen pts with advanced Ph + leukemia were efficacy-evaluable, of whom 3 (23%) achieved MMR; only 1 of 3 pts with the T315I mutation achieved MMR; the other 2 were also resistant to ponatinib treatment. The median (95% CI) PFS of efficacy-evaluable pts with advanced leukemia was 12.7 (4-19.5) months. In the combination cohort, 2 pts with Ph + BCP ALL received olverembatinib 30 mg QOD with blinatumomab; both achieved CCyR and 1 achieved a negative MRD status after 1 treatment cycle. Conclusions Olverembatinib alone or combined with blinatumomab was efficacious and well tolerated in pts with heavily pretreated CML or Ph + ALL . Olverembatinib monotherapy was potent in pts who were either resistant or intolerant to ponatinib and/or asciminib, regardless of T315I mutation status. Olverembatinib may provide an effective new treatment option for pts after failure of 2 or more TKIs. Internal study identifier: HQP1351-CU101. Clinicaltrials.gov identifier: NCT04260022.

Clofarabine and High-Dose Melphalan Reduced Intensity Conditioning Regimen with Methotrexate-Based GvHD Prophylaxis

Introduction: Reduced-intensity conditioning (RIC) allogeneic stem cell transplant (allo-SCT) remains a curative option for elderly and/or unfit patients with hematologic malignancies. Fludarabine-containing regimens make up the cornerstone of RIC regimens, however, during the nation-wide fludarabine shortage in 2022, many institutions used fludarabine-free RIC regimens out of necessity though data was extremely limited. Clofarabine is a second-generation purine analog with more potent anti-leukemic activity and a different adverse effect profile compared to fludarabine. We report our experience with clofarabine-based RIC conditioning for adult patients with non-Hodgkin's lymphoma (NHL) and myeloid malignancies. Methods: In this retrospective single-center matched cohort study at Stanford Health Care, we compared adult RIC allo-SCT patients receiving clofarabine and melphalan (CloMel) with a matched cohort receiving fludarabine and melphalan (FluMel) from January 1, 2022 to December 31, 2022. CloMel consisted of clofarabine 30 mg/m 2 on days -6 to -2 followed by melphalan 140 mg/m 2 on day -1, while FluMel consisted of fludarabine 30 mg/m 2 on days -5 to -2 followed by melphalan 140 mg/m 2 on day -1. Clofarabine dose adjustments were made in patients with renal dysfunction according to the following institutional guidelines based on creatinine clearance (CrCl): 22.5 mg/m 2 for CrCl 60 to 79 mL/min, 15 mg/m 2 for CrCl 30 to 59, and avoiding clofarabine for CrCl less than 30 mL/min. Dose modifications for fludarabine and melphalan due to renal dysfunction were at the discretion of the care team. Patients received graft versus host disease (GvHD) prophylaxis with tacrolimus and methotrexate. Efficacy and safety outcomes were assessed. Data were analyzed using Mann-Whitney U and chi-square tests. Results: We identified 9 matched pairs for a total of 18 patients. Most patients received an allo-SCT for a myeloid malignancy (8 patients with AML, 8 patients with MDS, and 2 patients with NHL). All patients received a peripheral blood stem cell transplant, with 89% receiving a matched unrelated donor and 11% receiving a matched related donor transplant. Baseline characteristics were balanced between groups. There was no difference in time to neutrophil engraftment (mean 14 vs 14 days; p=0.42), time to platelet engraftment (mean 16 vs 24 days; p=0.33), or 100% donor whole blood chimerism (71% vs 78%; p=0.32) at 6 months in the CloMel and FluMel groups, respectively. No statistically significant difference was observed for the number of patients who experienced acute (2 vs 0; p=0.13) and chronic GvHD (0 vs 4, p=0.09) at 6 months between groups. At 6 months, 2 patients in the CloMel group and no patients in the FluMel group experienced early non-relapse mortality (p=0.13). Both patients who died experienced acute renal failure secondary to conditioning chemotherapy with a median onset of renal dysfunction 6 days after initiation of clofarabine, followed by sepsis and multi-organ failure. Both patients required initiation of external renal replacement therapy and ultimately passed 12 days and 29 days post-transplant, prior to engraftment. Notably, both patients had a history of kidney dysfunction prior to transplant, one patient with chronic kidney disease (CKD) stage 3 and the other patient with lymphomatous involvement of the kidneys, and received appropriate clofarabine renal dose adjustments per institutional standards. Conclusion: CloMel demonstrated similar efficacy outcomes at 6 months and represents a feasible alternative to FluMel as a RIC regimen. However, given the notable occurrence of renal failure and early death in the CloMel arm, careful consideration and particular caution in administering to patients with a prior history of renal disease is recommended.

Identification of Vulnerabilities for Pharmacological Inhibition of PIP4K2s in Acute Myeloid Leukemia

Introduction and aims: Proteins of the PIP4K2s family (PIP4K2A, PIP4K2B and PIP4K2C) participate in the generation of PIP 4,5P 2 (PIP 2), which acts as a secondary messenger in signal transduction, substrate for metabolic processes or has structural functions. In patients with AML, high expression of PIP4K2A and PIP4K2C is an independent marker of worse prognosis. Recently, our research group reported that THZ-P1-2 (pan-inhibitor of PIP4K2s) exhibits anti-leukemic activity by disrupting mitochondrial homeostasis and autophagy in AML models. In the present study, we describe the expression profile of PIP4K2s in normal and leukemic myeloid cells, as well as identify the association between PIP4K2s expression and the ex vivo response to several antineoplastic agents in AML. Material and methods: PIP4K2A, PIP4K2B and PIP4K2C expression data in different hematopoietic cell populations were obtained from the study GSE24759. The expression of PIP4K2s in the different AML subgroups was obtained from the TCGA cohort and visualized by BloodSpot. Gene and protein expression of PIP4K2s was investigated in a panel containing twelve AML cell lines and a sample of normal CD34 + cells. Data from ex vivo treatments in patients with AML were obtained from BEAT AML. Kasumi-1, NB4 and U-937 cells were treated with vehicle or increasing concentrations of THZ-P1-2 and/or venetoclax for 48h. Cell viability was assessed by MTT, apoptosis by flow cytometry (annexin V/PI) and cell signaling by Western blot. Correlation analyzes and comparison between groups were performed by Spearman, Mann-Whitney or ANOVA tests, as appropriate. A p value <0.05 was considered significant. Results: In myeloid cells, PIP4K2A expression was higher in erythroid and megakaryocytic cells ( p < 0.05). PIP4K2B expression was higher in hematopoietic stem cells ( p < 0.05). PIP4K2C expression was lower in common myeloid progenitors and erythroid cells ( p < 0.05). In patients with AML, PIP4K2A and PIP4K2C expression was higher in complex karyotype groups, whereas PIP4K2B expression was higher in del(5q)/5q- and t(8;21)+others groups. In cell lines, PIP4K2A expression was higher in K-562, KU812, HEL and SET2 cells. The expression of PIP4K2B and PIP4K2C was similar between the evaluated cells. In ex vivo assays, the expression of PIP4K2s was related to sensitivity and resistance to several drugs, highlighting the association between high expression of PIP4K2A and resistance to venetoclax in AML ( p < 0.05). The combination of THZ-P1-2 and venetoclax showed potentiating effects in reducing viability and inducing apoptosis in Kasumi-1, NB4 and U-937 cells ( p < 0.05). In the molecular setting, the combination of THZ-P1-2 and venetoclax induced higher levels of cleaved PARP1 (marker of apoptosis) and γH2AX (marker of DNA damage) compared to monotherapies. Discussion and conclusion: Our study characterized the expression of PIP4K2s in the myeloid compartment of hematopoietic cells, as well as in different molecular subsets of AML. The identification of the correlation between the expression of PIP4K2s and the response to antineoplastic agents in ex vivo assays in AML exposed vulnerabilities that can be exploited in combined therapies, which could result in better therapeutic responses. Support by FAPESP, CNPq, and CAPES.

Dual-Targeting CD33/CD123 NANOBODY ® T Cell Engager Targeting Leukemia Blasts and Stem/Progenitor Cells in Relapsed AML

Acute myeloid leukemia (AML) is the most common adult hematologic malignancy. Relapse is common and salvage treatment with cytotoxic chemotherapy is rarely curative. Immunotherapy targeting surface antigens expressed in leukemia cells has emerged as an effective approach for AML treatment for patients who are older/unfit for or relapsed from/refractory to current regimens (Isidori A, et al. Frontiers Oncol. 2021). CD123 and CD33, two clinically validated targets in AML, are jointly expressed on blasts and leukemic stem cells (LSC) in >95% of AML patients. However, their expression is heterogenous between subclones and between patients which may impact the efficacy of single-targeting agents in certain patient populations. We recently reported a novel dual-targeting CD33/CD123 NANOBODY® T-cell engager (CD33/CD123-TCE) and demonstrated the anti-leukemia activity of CD33/CD123-TCE in AML with good safety profile in vivo (Dullaers M, et. al, JITC. 2022). Here we showed that CD33/CD123-TCE effectively targets AML blasts and LSC in relapsed AML. The cell surface expression profiling of samples from 55 patients with relapsed/refractory AML showed that all samples were positive for CD123 and CD33. The frequency of subpopulations in all samples co-expressing CD33 and CD123 is the most prominent, followed by single expression of CD123, and CD33. CD33-CD123- subset represented a minority. To investigate the anti-leukemia effect of CD33/CD123 TCE, we treated 18 primary samples for 7 days and assessed apoptosis by flow cytometry. Treatment of CD33/CD123 TCE at 2.5nM (low dose) and 25nM (high dose) induced more than 50% specific apoptosis in majority of bulk AML, with no significant difference between low and high dose of CD33/123 TCE. Analysis of cytotoxicity towards CD34+ AML-LSC revealed that CD33/CD123 TCE at low and high doses resulted in similar specific apoptosis of CD34+ cells, half of samples reached higher than 50% of apoptosis. Colony-forming assay in 2 primary samples further confirmed that CD33/CD123 TCE effectively inhibited the clonogenicity of primary AML cells expressing CD123 and CD33. While the average activity of CD33/CD123 TCE was comparable to single-targeting CD33-TCE and CD123-TCE reagents, in a subset of patient samples (11% of all samples), the dual-targeting CD33/CD123-TCE induced higher apoptosis in bulk and CD34+ AML cells compared to single-targeting controls, supporting utility of dual targeting. Concomitantly, CD3+ T cell expansion was observed in all dual- and single treatment groups, with a trend toward stronger amplification by CD33/CD123-TCE. Next, we examined AML and T cell phenotypes using mass cytometry (CyTOF) to characterize the impact of the TCE treatments. UMAP plus FlowSOM analysis revealed heterogenous subsets of LSC within samples and across patients. LSC subsets defined by CD34+ are known to co-express various surface markers associated with LSC-drug resistance and disease relapse including CD135 (FLT3), CD117 (c-kit), CLL-1, PD-L1 and TIM-3. These subsets were found highly sensitive to CD33/CD123-TCE, with subset CD34+CD38+CD117+PD-L1+CD123+ and CD34+CD38- showing greater sensitivity to CD33/CD123-TCE. Despite diverse expression of leukemic markers, CD33/CD123-TCE depleted CD34+ AML-LSC in all 3 samples tested by CyTOF, whereas single-targeting CD123-TCE and CD33-TCE were only effective in 2/3 samples. Analysis of T cell subsets revealed that dual- or single- targeting TCE expanded CD4+ helper and CD8+ cytotoxic subsets in all samples compared to control. CD4+ and CD8+ cells co-expressing CD69, TIM-3 or PD-1 were expanded by TCE in all three samples. Expansion of central and effector memory T cells defined by CCR7+CD45RA- and CCR7-CD45RA- in CD4+ and CD8+ subsets were seen in all treatment groups in 2 samples, whereas the highest expansion of CCR7-CD45RA-CD4+ effector memory subsets by CD33/CD123-TCE was seen in 1 sample. Taken together, the CD33/CD123 dual-targeting NANOBODY® TCE exhibits potent anti-AML activity and offers a broad patient coverage. Immunophenotypic profiling confirmed the effectiveness of CD33/CD123-TCE in eliminating various blast- and LSC-subsets, activating CD4+ and CD8+ T cells or expanding central/effector memory CD4+ and CD8+ T cells. These dual-targeting immune engagers may constitute an effective treatment option for patients who are older/unfit for or relapsed from/refractory to current regimens.

Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16/NKG2D Immune Modulating TriNKET ® BMS-986357 (CC-96191)

CD33 is widely expressed by myeloid cells and is a validated drug target in acute myeloid leukemia (AML), as shown by the benefit of some patients from the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO). However, GO is often ineffective and toxic, prompting interest in more potent CD33-directed therapies. Success of T cell-engaging bispecific antibodies in lymphoid malignancies has raised enthusiasm for similar agents targeting CD33, but toxicities from activated T cells cause significant challenges for their use and provide a strong rationale to explore drugs engaging natural killer (NK) cells. Here, we investigated BMS-986357, a TriNKET ® that activates NK cells via CD16 and NKG2D receptors while targeting CD33. This format was chosen because simultaneous engagement of multiple activating NK cell receptors yields greater cytotoxic activity against neoplastic cells than engagement via a single activating receptor. Surface plasmon resonance analyses showed BMS-986357 simultaneously binds CD33, NKG2D, and CD16a, and co-engagement of NKG2D and CD16a increases the avidity. In the presence of primary human NK cells from healthy donors or a human NK cell line, the TriNKET ® demonstrated broad cytolytic anti-leukemia activity in a strictly CD33-dependent manner using a panel of CD33-expressing or CD33-deficient/deleted acute leukemia cells. Consistent with this, removing the CD33 binding domain rendered BMS-986357 ineffective against CD33+ AML cells. Drug-induced cytotoxicity was greater with BMS-986357 than with monoclonal CD33 antibodies, including lintuzumab and an afucosylated antibody with enhanced NK function, demonstrating the benefit of the TriNKET ® format. Compared to BMS-986357, substantially less cytotoxicity was observed with an Fc-mutant variant of BMS-986357 that abrogates binding to CD16a or an NKG2D dead-arm TriNKET ®, and cytolytic effects were reduced with a CD16-deficient NK cell line vs. a CD16-expressing subline, indicating maximal efficacy of BMS-986357 required co-engagement of CD16a and NKG2D. Using sublines of OCI-AML3 and KG-1 cells (both cell lines with low endogenous CD33 expression) to overexpress wild-type CD33 at increasing levels, we found low abundance of CD33 curtailed BMS-986357-induced cytotoxicity. Flow cytometric binding studies identified BMS-986357 to recognize the membrane-distal V-set domain of CD33. Unlike GO, BMS-986357-mediated cytolysis was not affected by over-expression of ABC transporter proteins by AML cells. The potency but not maximal activity of BMS-986357 was reduced by super-physiologic concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact TriNKET ® activity. In the presence of CD33+ AML cells, BMS-986357 activated NK cells but not T cells from healthy donor peripheral blood mononuclear cells and produced similar levels of maximum cytolysis as a CD33/CD3 bispecific antibody. Despite this, BMS-986357 elicited 10 to >100-fold lower soluble cytokine levels including IFN-γ, TNF, IL-6, and GM-CSF than a CD33/CD3 bispecific antibody, suggesting BMS-986357 has the potential for CD33/CD3 bispecific-like efficacy without the associated risk of cytokine release syndrome. Finally, in bone marrow specimens from patients with AML, BMS-986357 killed AML cells but not normal monocytes, suggesting selectivity of drug-induced cytotoxicity toward neoplastic cells, consistent with the notion NK cells are capable to differentiate between healthy and leukemic CD33+ cells. This selectivity suggests BMS-986357 may produce less myelosuppressive toxicity than what has been observed with CD33 targeting antibody-drug conjugates. In summary, our findings demonstrate that BMS-986357 TriNKET ® has potent CD33-dependent cytolytic activity in vitro against human AML cells, supporting the drug's exploration in early phase clinical trials. One such trial (NCT04789655) has opened accrual for adults with relapsed/refractory AML.

Towards Automated Engineering of Donor-Derived T Lymphocytes into CRISPR/Cas9-Mediated CAR T Cells in a Closed-System

Chimeric antigen receptor (CAR)-expressing T cells have revolutionized immunotherapy of cancer. However, some patients derive no benefit from approved CARTcell therapies due to limitations such as toxicity and use of autologous cells which are sometimes unfit and risk manufacturing failures. Additional or more effective CARTcell therapies are needed. Harnessing the endogenous homology-directed DNA repair pathway via precision genome editing based on Cas9RNP/rAAV6, we and others have demonstrated the feasibility of targeting transgene(s) integration into specific gene site(s) including their incorporation under endogenous regulatory elements. Using this strategy, we aimed to engineer healthy donor-derived CAR T cells from αβ+ T lymphocytes. For enhanced safety, we metabolically reprogrammed the CAR T cells by inactivating the UMPS gene needed for uridine biosynthesis. The UMPS-/-CAR T cells become dependent on exogenous uridine thereby serving as a cell control mechanism. We hypothesized that donor-derived αβ+ T lymphocytes can be engineered using the Cas9RNP-rAAV6 strategy in an automated closed-system into controllable CAR T cells. We inactivated TRAC and UMPS gene loci in αβ+T lymphocytes using Lonza4D nucleofector. Electroporated cells were simultaneously transduced with CD19CAR-containing rAAV6 DNA vector. We obtained TRAC gene knockout up to 97% with knock-in up to 89%. Disruption of the UMPS gene would transform the cells to being auxotrophic and depend on uridine supply for viability and growth. To evaluate the CART cells' antitumor potency, we cocultured the CD19CART cells with GFP-expressing Nalm6 leukemia cell lines. The CD19CART cells eradicated the leukemia cells within 72 hours. To mimic relapse, we re-challenged cocultured CART with Nalm6 cells and the tumor cells were again depleted within 72 hours. Expectedly, IL-2 production was elevated in CD19CART cells challenged with Nalm6. Next, we tested the ability to control the cytotoxicity of the CD19CART cells by coculturing them with Nalm6 cells in separate groups with/without exogenous uridine. Interestingly, the CD19CART cells cocultured without uridine eradicated the target cells within 72 hours but lost their potency upon subsequent challenge (Figure 1). In contrast, CD19CAR T cells supplied with uridine remained potent and repeatedly eradicated target cells indicating the ability to turn off the potency of CART cells with uridine supply/withdrawal. To establish an automated closed-system for CART cells, we adopted the Miltenyi CliniMACS Prodigy with in-line electroporator (Elpo) for process engineering. First, we determined optimized parameters for electroporating αβ+ T lymphocytes on Elpo(Table1). Cells electroporated with these settings were (>80% viability) comparable to untreated cells. We first engineered CART cells with Elpo/Miltenyi reagents in an open system(i.e.cultivated Elpo-electroporated cells in culture vessels/incubators). We obtained 95% of TRAC and UMPS gene knockouts and up to 90% CD19CAR transgene knock-in to the TRAC locus - an efficiency slightly higher than using Lonza 4D nucleofector. To scale up the Cas9-based T cell engineering into a single automated process on the CliniMACS Prodigy, the Cas9 and guide RNA reagents would be scaled up 1000fold. To make the process cost-effective, we tested AZD7468, a small molecule DNAPKcs inhibitor. We optimized/reduced the amounts of reagents upto 90% less of Cas9RNP used without any significant reduction in gene editing outcomes. AZD7648 reduced the MOI needed for viral transduction by 50% while maintaining 80% or higher levels of transgene knock-in efficiency. Next, we commenced pilot studies to automate the CAR T cell engineering process in closed-system. Currently, we have achieved an automated TRAC gene knockout of over 90% and CAR transgene knock-in of slightly >10%. Further optimization studies are underway to improve automated gene knock-in efficiency. We have engineered donor-derived αβ+ T lymphocytes into potent/controllable CD19CART cells. The UMPS-deficient CD19CART cells lose antileukemia activity without uridine. We show that metabolic reprogramming can be combined with precision genome editing to generate controllable CART cells. Finally, our data demonstrate the feasibility of automating CRISPR/Cas9-mediated engineering of CAR T cells within closed-system.

A Phase 1 Dose-Escalation Study of the Cladribine Added to CPX-351 in Patients with Relapsed/Refractory Acute Myeloid Leukemia (AML) - the Polish Adult Leukemia Group AML-1/2018 Study

AW and AP equally contributed to the study Introduction: There is no standard salvage therapy in relapsed/refractory AML (R/R AML). CPX-351, a dual-drug liposomal encapsulation of daunorubicin (DNR) and cytarabine (AraC) in a synergistic 1:5 molar ratio, shows effective antileukemia activity ( Lancet JE, JCO 2018). Favorable results of cladribine-based salvage regimens (CLAG-M, CLAG) ( Wierzbowska A; Eur J Hematol 2008, Scheckel CJ, Leuk Res. 2020) as well as first-line therapies ( Hołowiecki J, JCO 2012; Kadia TM Lancet Haematol 2021, Kadia TM JCO 2022) confirmed a value of cladribine in the treatment of AML. Aim: This phase I study was designed to explore safety (MTD), toxicity and efficacy of increasing doses of cladribine in combination with standard dose of CPX-351 in R/R AML patients (pts). (EudraCT number: 2020-002535-29). Results: Twelve pts were enrolled with a median age 65 (range 61-69) years. Importantly, 8 pts (67%) were refractory to the former first- or second- line treatment. Nine pts (75%) were in the adverse risk group according to ELN 2022 including 4 pts with TP53 mut. Four pts (33%) were refractory to venetoclax (VEN)-based therapy and 3 pts (25%) had previous alloHCT (Table 1). Three patients (2 in DL1 and 1 in DL2) required two inductions. One patient in DL3 experienced a CNS and GI hemorrhage due to thrombocytopenia refractory to platelet transfusion, which was considered a DLT requiring enrollment of additional 3 pts. No patients discontinued therapy due to intolerance. Toxicities of grade ≥3 during the induction cycle were mainly infections. All patients developed infections during 1-st cycle of treatment. Blood stream infections (n=5; 42%), febrile neutropenia (n=4; 33%), and pneumonia (n=3; 25%) were the most common infectious events. One episode of grade 5 hemorrhage occurred in a patient with thrombocytopenia refractory to platelet transfusions. Cytopenias in responding pts treated with CPX-351 and cladribine were similar to that observed with CPX-351 alone. The composite CR (cCR=CR+CRi+CRp) rate was 50% (6/12 pts), 5 pts (42%) not responded and 1 patient died due to CNS hemorrhage before response evaluation but with significant BM blasts clearance at D14. cCR was achieved in 2 out of 3 pts (66%) with intermediate-risk and 4/9 pts (44%) with adverse-risk according ELN 2022. Within the high-risk population, pts with TP53 mut had lower probability to achieve remission (1/4; 25%) than pts with myelodysplasia related mutations (3/5; 60%). No remissions were observed in pts refractory or relapsed after VEN-based therapy. Measurable residual disease (MRD)-negative cCR assessed via multiparameter flow cytometry was achieved in 60% ( n = 3/5) of MRD-evaluable pts, including all pts (n = 3/3; 100%) in DL3. All pts achieving cCR had post remission therapy with one (n=1; 8%) or two (n=5; 92%) courses of CPX-351+ cladribine consolidation and 3 pts proceeded to alloHCT. After a median (Me) follow-up of 12.8 months (mos), Me overall survival (OS) was 6.6 mos (95% CI, 2.3-not reached [NR]) for all pts and 9.8 mos (95% CI, 8.07-NR) for those who achieved cCR. Median event-free survival (EFS) was 3.28 mos (95% CI, 0.8-NR) for the study population. Conclusions: Combination of cladribine with standard dose of CPX-351 is well tolerated. Cladribine dose 5 mg/m 2 was selected as RP2D. Safety profile does not indicate any significant additional myelosuppression. Cladribine with CPX-351 shows satisfying clinical activity with cCR rate of 50%, cCR-MRD neg of 60% and durable remission in some R/R AML patients. Further evaluation of the efficacy and safety of this regimen is needed.

Bone Marrow Microenvironment-Responsive Nanomedicine Promotes Anti-Leukemia Activity In Vivo

Background: Leukemia escape and relapse is the leading cause of death after allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acute myeloid leukemia (AML). Work over the past decades has demonstrated that the CD47- signal-regulatory protein α (SIRPa) interaction mediated cancer cell immune escape. Although CD47-SIRPα interaction blockade contributes to cancer cell clearance by macrophages, how to deliver the anti-CD47 to bone marrow niche through an efficient drug delivery strategy and improve the cytotoxic activity of macrophages is an important issue that needs to be addressed. Methods: Here, we performed immunohistochemical (IHC) analysis and flow cytometry analysis of TIM-3 expression using samples of bone marrow from patients with or without relapse. In addition, according to the natural “myeloid niche homing” characteristic of AML cells and the low-oxygen microenvironment in bone marrow, we constructed β-cyclodextrin azobenzene linker (AZO-β-CD)-modified fusion protein and amantadine-modified HSA protein (HSA-ADA), followed by the addition of anti-CD47. Furthermore, the nanogel TIM3-targeting antibodies were modified on the surface of the nanogel to finally construct the supramolecular nanogel delivery system. Moreover, we detected the effect of target nanomedicine in a leukemia xenograft mouse model. Results: We demonstrated that in the bone marrow microenvironment of patients with relapse, the expression of TIM-3 significantly increased, especially in the CD34 +CD38 + leukemic progenitors, but not in the HSCs. Furthermore, we verified using nanomedicine could significantly increase the number of macrophages in the bone marrow. Importantly, the blockade of CD47-SIRPα signaling using nanomedicine markedly improved the anti-tumor activity in a leukemia xenograft mouse model. Conclusion: Thus, our findings reveal that nanomedicine could inhibit CD47-SIRPα signaling and contribute to anti-leukemia function effectively, which may be a new strategy for preventing and treating the recurrence of AML after transplantation.

Safety and Tolerability of AZD0466 As Monotherapy for Patients with Advanced Hematologic Malignancies. Results from a Phase I/II Trial

Background: Overexpressionof B-cell lymphoma 2 (BCL-2)-related pro-survival proteins allows cancer cells to evade apoptosis, and targeting these proteins has become important in anticancer therapy. BCL-2 inhibition by venetoclax (VEN) is beneficial in many patients (pts) with acute myeloid leukemia (AML), but resistance is common due to upregulation of other pro-survival proteins such as BCL-extra-large (BCL-xL) and myeloid cell leukemia-1. Dual inhibition of BCL-2/xL has potential for broader activity than agents such as VEN. However, BCL-xL is critical for platelet survival and inhibition can cause dose-limiting thrombocytopenia (Konopleva and Letai. Blood 2018). To broaden therapeutic activity, we developed AZD0466, a drug-dendrimer conjugate in which the BCL-2/xL dual inhibitor AZD4320 is covalently conjugated to a pegylated poly-L-lysine dendrimer and gradually released by hydrolysis. Preclinically, AZD4320 showed greater inhibition of tumor growth than VEN and navitoclax in VEN-resistant xenograft models (Balachander et al. Clin Cancer Res 2020). A first-in-human study (NCT04214093) in pts with advanced solid tumors indicated that AZD0466 is well tolerated with no reported dose-limiting toxicities (DLTs). We present preliminary data from NIMBLE, a Phase I/II trial of AZD0466 in pts with advanced hematologic malignancies (NCT04865419). Methods: Module 1, Part A of NIMBLE is a dose-escalation study of AZD0466 monotherapy investigating its preliminary safety and tolerability, pharmacokinetics (PK), and preliminary efficacy. Dose escalation and de-escalation of AZD0466 follow a modified toxicity probability interval (mTPI-2) design. Eligible pts are ≥18 years old with relapsed/refractory (R/R) AML, acute lymphoblastic leukemia (ALL), or high-risk myelodysplastic syndrome. AZD0466 is administered IV with a dose ramp-up on Days (D) 1, 4, and 8, reaching the target dose on D8 of Cycle 1, with weekly administrations thereafter. Cycle duration is 35 days for Cycle 1 and 28 days for subsequent cycles. Pts remain on study until disease progression, unacceptable toxicity, or withdrawal of consent. Resul ts: As of May 31, 2023, 31 pts (n=25 AML, n=6 ALL; median age 69 years) had received ≥1 dose of AZD0466 at target doses of 300 mg (n=4), 600 mg (n=4), 1200 mg (n=7), 2400 mg (n=5), 3600 mg (n=9), and 5400 mg (n=2). Median treatment duration was 4.1 weeks (range 0.1−29.6). Twenty-two pts (71%) had prior VEN and 11 (35%) had prior hematopoietic stem cell transplantation. Treatment-emergent adverse events (TEAEs) of any grade reported in >10% of pts are displayed in Table 1. One Grade 5 intracranial hemorrhage unrelated to AZD0466 was reported. Four pts experienced a serious adverse event (SAE) possibly related to AZD0466 (alanine aminotransferase [ALT] increase, pneumonia, troponin T increase, and uncoded SAE). Grade ≥3 TEAEs possibly related to AZD0466, reported in 12 pts (39%), included febrile neutropenia (n=3), platelet count decrease (n=2), diarrhea, thrombocytopenia, ALT increase, blood creatinine phosphokinase increase, pneumonia, gamma-glutamyltransferase increase, lipase increased, and troponin T increase (n=1, each). DLTs of asymptomatic troponin increase were observed in two pts (3600 mg [n=1], 5400 mg [n=1]). Evaluation of maximum concentration and area under the concentration-time curve revealed dose-proportional exposure to AZD4320. Released AZD4320 represented 1-5% of total AZD4320 and had a longer half-life than total AZD4320. Preclinical modeling and PK data predicted that 5400 mg may be required to drive efficacy. As a surrogate of BCL-xL on-target activity, transient aggravation of thrombocytopenia post-dosing was observed across all dose cohorts followed by platelet recovery prior to the next dose. Platelet reduction was in line with preclinical models showing a substantial reduction at lower doses with a ceiling effect at higher doses. As of July 6, 2023, no complete responses have been observed. However, preliminary bone marrow (BM) blast reductions of >50% were observed in four pts (1200 mg [n=1], 2400 mg [n=2], 3600 mg [n=1]), indicating antileukemia activity of AZD0466. Conclusions: Given the observed DLTs of asymptomatic increase in troponin levels, and the lack of significant clinical benefit, the study was terminated.

Aurora Kinase a Inhibition for Gvhd and Relapse Prevention after Allogeneic HCT: Phase I Trial in Combination with Ptcy/Sirolimus

Introduction: With the wider use of post-transplant cyclophosphamide (PTCy) graft-versus-host disease (GVHD) prophylaxis, there is interest in replacing tacrolimus (TAC) with sirolimus (SIR, mTOR inhibitor) to avoid calcineurin inhibitor toxicity, maintain excellent GVHD control, and potentially allow for a greater graft-versus-tumor effect. mTOR and Aurora kinase A (AURKA) mediate CD28 costimulation in alloreactive T cells. SIR can only partially block CD28 costimulation. Adding selective AURKA inhibition to SIR following PTCy fully suppresses CD28 signal transduction, with synergistic GVHD prevention in mice (see ASH 2023 abstract ID 173376). AURKA inhibitors also have direct anti-leukemia activity. Here, we present the phase 1 dose escalation portion of a first-in-human clinical trial of PTCy plus SIR and VIC-1911 (VIC), a selective oral AURKA inhibitor, for GVHD and relapse prophylaxis after myeloablative allogeneic hematopoietic cell transplantation (alloHCT). Methods: This single-arm phase I dose escalation trial (NCT05120570) is designed to evaluate the pharmacodynamic potency of AURKA pathway suppression and the safety of PTCy/SIR/VIC. The primary endpoint of phase I is to identify the lowest biologically active dose of VIC, defined as <54% pH3ser10+ CD4+ T cells at day +21 (the lower confidence interval of the normal, pre-transplant frequency of pH3ser10+ CD4+ T cells - a marker of AURKA activity), that is safe with PTCy/SIR. Patients aged 18-60 years receive myeloablative conditioning of TBI alone at a dose of 1320 cGy. PTCy is given as 50 mg/kg on days +3 and +4, SIR on day +5 with levels targeting 8-12 ng/ml and tapered after day +100, and VIC given on days +5 to +45 at doses of 25, 50, or 75 mg BID. Patients undergoing myeloablative TBI-based alloHCT with PTCy/SIR plus mycophenolate mofetil (MMF), without VIC on a separate protocol, served as a control. Results: Proof-of-concept experiments with PTCy/SIR/alisertib (AURKA inhibitor) demonstrate synergistic protection against xenogeneic GVHD and tumor (Raji cells) in mice, compared to PTCy/TAC (median survival: 45 days v undefined, 9 mice/group, 2 experiments, P<0.0001). Unlike alisertib, VIC-1911 is not myelosuppressive, providing rationale for this trial. In vitro studies show killing of multiple leukemia cells lines at physiologically achievable VIC-1911 concentrations. VIC 75 mg BID is the lowest biologically active dose suppressing AURKA activity below the primary endpoint target of <54%, with reduced mean frequency of day +21 pH3ser10+ CD4+ T cells at 23.7% compared to 58.5% with PTCy/SIR/MMF (Figure 1A, P=0.0091). PTCy/SIR/VIC also suppresses mTOR activity in donor T cells (3.9% v 16.6% pS6+ CD4+ T cells, P=NS; pS6 frequency in healthy donor T cells is ~30-40%), concurrently ablating CD28 signal transduction. Data trends show greater Tregs at day +21 with PTCy/SIR/VIC, compared to PTCy/SIR/MMF controls (40.2% v 10.5%, P=NS). Patient characteristics are detailed in Figure 1B. Neutrophil engraftment occurred in 9/9 evaluable patients at a median of 18 days. Platelet engraftment occurred in 8/9 evaluable patients at a median of 21 days; one patient is awaiting platelet engraftment. No dose-limiting toxicities have been observed during dose escalation. Patient 1 died of non-COVID coronavirus during initial hospitalization; he received high-dose methylprednisolone for ARDS beginning on day +17, which made him unevaluable for the primary pharmacodynamic endpoint. Conclusions: A VIC-1911 dose of 75 mg BID from day +5 to day +45 effectively suppresses AURKA activity as determined by a low frequency of pH3ser10+ CD4+ T cells, ablating CD28 T cell costimulation when combined with sirolimus, resulting in no dose-limiting toxicities. VIC 75 mg BID will be studied further in an expanded phase I cohort to obtain estimates of efficacy in preventing both GVHD and relapse in PTCy-based myeloablative alloHCT.

Identification of vulnerabilities for targeting BCL-2 family members in T-Cell Acute Lymphoblastic Leukemia

T-Cell acute lymphoblastic leukemia (T-ALL) is a disease caused by the malignant transformation of T-cell lineage progenitors. With the use of intensive chemotherapies survival rates have improved, but outcomes particularly of relapsed patients remain poor. In addition, currently used intensive chemotherapies are associated with high rates of treatment-related morbidity and mortality, emphasizing the need to develop new and improved therapies. The intrinsic apoptosis pathway, one of the key pathways controlling cell death, is dysregulated in many cancers and contributes to leukemogenesis and treatment failure. The main steps of this pathway are controlled by proteins of the B-cell lymphoma (BCL-2) family at the outer mitochondrial membrane. Hence, targeting this pathway by BH3-mimetics has emerged as an effective new treatment strategy in different cancers. Venetoclax is a selective BCL-2 inhibitor and is successfully used in CLL and AML, but heterogeneous sensitivity to venetoclax has been described in ALL and inhibitors of other BCL-2 family members including BCL-XL-selective A-1331852 and MCL-1 selective AZD5991 have been developed. Moreover, a dual inhibitor of the anti-apoptotic BCL-2 family members BCL-2 and BCL-XL (AZD4320) with its dendrimer conjugate (AZD0466) has recently shown anti-tumor activity in hematologic cancer models with manageable toxicity. The aims of this study are to evaluate susceptibilities of T-ALL to inhibitors of BCL-2 family proteins, to identify markers of response, to elucidate mechanisms of action and to assess combination effects. First, we analyzed the anti-leukemia activities of inhibitors targeting BCL-2 (venetoclax), BCL-XL (A-1331852) and MCL-1 (AZD5991) and of the dual BCL-2/BCL-XL inhibitor AZD4320 in T-ALL cell lines (N=6) and a series of patient-derived xenograft (PDX) samples (N=8). Inhibition of MCL-1 alone was not effective in the cell lines tested (EC50 >1 µM), but heterogeneous sensitivity was found in PDX samples (EC50 <1µM in 3/8 samples). In cell lines, sensitivity for BCL-2 inhibition was exclusively found in a cell line with an early T-cell precursor ALL phenotype (Loucy). Similar to cell lines, we found insensitivity for BCL-2 inhibition in all PDX samples tested (N=8). For inhibition of BCL-XL, we found heterogeneous sensitivities with 4/6 cell lines and 5/8 PDX samples showing an EC 50 <1 µM. Interestingly, BH3-profiling confirmed BCL-2 dependence in Loucy and BCL-XL dependence in the other cell lines. Importantly, dual inhibition of BCL-2 and BCL-XL showed clear responses in cell lines and PDX samples (median EC 50s 796.1 nM and 721.6 nM). Notably, sensitivity was associated with priming of the BH3-peptide BAD (r s=0.89, p=0.03), providing a marker of response. We next sought to elucidate the molecular mechanisms by which different BH3-mimetics induce cell death in T-ALL. Analyzing protein interactions of BCL-2 family members by co-immunoprecipitation studies, we found that AZD4230 acts on-target by releasing BIM from BCL-2 and BCL-XL, but with compensatory increased protein complexes of BIM and MCL-1. Accordingly, combined inhibition of BCL-2 and BCL-XL with inhibition of MCL-1 leads to release of BIM from all three anti-apoptotic proteins enabling downstream apoptosis signaling. These findings suggest that combined inhibition of BCL-2 and BCL-XL together with MCL-1 may provide synergistic benefits. To further validate these data, we applied dynamic BH3-profiling and determined dependencies of T-ALL samples on BCL-2 family members in response to BCL-2/BCL-XL inhibition. Here, we found that the MCL-1 dependence strongly increases upon BCL-2/BCL-XL inhibition, suggesting MCL-1 as a target for combined inhibition. Based on these results, we performed dose-response matrix analyses to test the effects of combined BCL-2/BCL-XL and MCL-1 inhibition. Most importantly, combined inhibition showed synergism in all cell lines and PDX samples tested (Bliss scores >10), including leukemias being insensitive to single compounds. Taken together, we found vulnerabilities of T-ALL to BCL-2 family inhibition, particularly to dual BCL-2/BCL-XL inhibition by AZD4320, and we demonstrated on-target activities. Using BH3-profiling, we identified BAD-priming as a marker of response for AZD4320 and MCL-1 dependence as a resistance mechanism that can be targeted by combination treatment, suggesting further clinical evaluation.

Influenza Training of Granulopoiesis Promotes Long-Term Anti-Leukemia Activity

Abstract Influenza viral infections have the ability to reprogram the immune system of the host and alter its functions to fight infections. However, the exact mechanisms and functions of virus-induced innate immunity in the context of leukemia are not yet fully understood. Our previous research has shown that a patient with refractory acute myeloid leukemia (AML) achieved complete remission (CR) after being infected with the Influenza A virus (IAV, H1N1 subtype), and this was functionally validated in two different animal disease relevant models. Our recent study demonstrates that mice pre-trained with the IAV promotes a long-term anti-leukemia effect. The anti-leukemia activity of IAV-induced trained immunity is due to the transcriptomic rewiring of hematopoietic stem and progenitor cells (HSPCs), resulting in a sustained enhancement of myeloid cells reprogramming toward an antitumor phenotype. This mechanism involves the upregulation of type I interferons (IFNs) and subsequent downregulation of inflammatory proteins. Our findings shed light on the dynamic changes in innate immune cells following viral infections and indicate a novel anti-leukemia facet of appropriate rewiring of granulopoiesis via upregulation of type I IFNs. Statement of significance The study profiles the dynamic changes in immune cells during exposure to the Influenza virus and sheds light on the role of Influenza trained innate immunity in anti-leukemia effect. The study also explores a novel anti-leukemia facet of appropriate rewiring of granulopoiesis via upregulation of the type I IFN pathway. These findings suggest that innate immune training could be a promising adjuvant therapy for cancer and warrant further investigation. Legend for Figure 5 . H1N1 reprogrammed granulopoiesis via up-regulation of type I interferon pathway. (A-C) FCM analyses and absolute counts of BM progenitor cells on day 7 after training with H1N1 or PBS. FCM, flow cytometry; BM, bone marrow; LK, Lin-c-kit+Sac1-; LSK, Lin-c-kit+Sac1+; GMP, granulocyte-monocyte progenitors (Lin-c-kit+Sac1-CD16/32 hiCD34+); CMP, common myeloid progenitors (Lin-c-kit+Sac1-CD16/32 intCD34+); MEP, megakaryocyte-erythroid progenitor cell (Lin-c-kit+Sac1-CD16/32-CD34-). (D) T-SNE plot of top 7 progenitor cells population changes. t-SNE, t-distributed stochastic neighbor embedding. (E) Heatmap visualization of the expression of different genes in HSPCs. The upregulated genes related to the type I IFNs pathway are listed on the right. HSPCs and hematopoietic stem/progenitor cells. (F) The top enriched GO terms of biological processes for upregulated genes in H1N1 trained group. GO, gene ontology. (G-H) Heatmap and t-SNE plot of type I IFN-associated upregulation genes in progenitor cells of HSPCs, GMP, CMP, and MEP. t-SNE, t-distributed stochastic neighbor embedding.

Effect and Mechanism of NL-101 Combined with Bcl-2 Inhibitor Venetoclax in Acute Myeloid Leukemia

Background Acute myeloid leukemia (AML) is a kind of malignant clonal disease originating from hematopoietic stem cells with strong heterogeneity,with the highly recurrence rate and mortality rate.Although the application of hematopoietic stem cell transplantation and new targeted drugs has improved the prognosis of some patients in recent years, chemotherapy is still the most important treatment for AML. 50-80% of AML patients eventually relapsed after CR, with a low remission rate after relapse.There are reports that BCL-2 overexpression is a clinical feature of human hematologic malignancies that exacerbates the malignant state and drives apoptosis resistance phenotypes.Therefore, how to reduce treatment-related toxic and side effects and overcome tumor cell drug resistance is a hot and difficult topic in current AML treatment. Venetoclax (ABT-199) is an oral, selective Bcl-2 inhibitor. It showed strong anti-leukemia activity in preclinical stage, but its clinical efficacy as a single drug for AML was limited.Nl-101 (also known as EDE-S101)is a new small molecule compound formed by covalently linking the DNA damage core group of Bendamustine hydrochloride with the inhibition core group of histone deacetylase of the histone inhibitor Volinostat (also known as SAHA).Our previous study found that NL-101 single drug can reduce tumor load and prolong survival of AML mice in vivo.In this study, we used Venetoclax in combination with NL-101 to understand its efficacy and safety in vitro and in vivo, and to explore the synergies and mechanisms of action between the two drugs, providing new effective options for the treatment of AML patients. Purpose To explore the efficacy of Bcl-2 inhibitor Venetoclax (ABT-199) and a novel small molecule compound NL-101 in the treatment of acute myeloid leukemia（AML） and the related mechanisms. Experimental Design AML cell lines and primary patient samples were collected and used for cell proliferation assay. MTS colorimetric assay was used to determine the effect of Venetoclax alone or in combination with NL-101 on the growth of AML cells，the combination index (CI) was calculated to evaluate the synergistic effect of the two drugs. Cell death induced by Venetoclax alone or in combination with NL-101 was analyzed by Annexin V-FITC/ Propyl -iodide staining and flow cytometry. Western blot was used to analyze the protein expression levels of MAPK/ERK, PI3K/AK/GSK pathway members and BCL-2 family members.The MV4-11-derived xenograft mouse model was used to assess in vivo efficacy of the combination of venetoclax and NL-101. Results Venetoclax alone and in combination with NL-101 can inhibit the growth of AML cell lines and primary cells to a certain extent, and the combination of drugs has a synergistic effect. Venetoclax combined with NL-101 effectively synergistically induced apoptosis in AML cell lines and primary patient samples. Venetoclax combined with NL-101 can down-regulate the expression of pro-survival proteins in the Bcl-2 family, such as McL-1, Bcl-2, and Bcl-XL, and up-regulate the expression of pro-apoptotic proteins, such as BIM, BID, and BAX/BAK. Phosphorylated ERK, AKT, and JNK expressions were eliminated by venetoclax in combination with NL-101. In vivo results suggest that Venetoclax combined with NL-101 has the potential to treat AML. Conclusions Venetoclax combined with NL-101 can synergistically inhibit the growth and promote apoptosis of AML cell lines and primary AML cells. In vivo experiments demonstrated that Venetoclax combined with NL-101 can synergistically reduce tumor load and prolong survival time in AML mice. These results suggest that Venetoclax in combination with NL-101 is effective in the treatment of acute myeloid leukemia.

AML Immunotherapy Using a Novel Tcrm-Based Bispecific Antibody That Targets a Leader Sequence Peptide Derived from Cathepsin G

Introduction: Myeloid azurophil granules provide a rich source of intracellular leukemia antigens. Cathepsin G (CG) is a serine protease that has higher expression in AML blasts in comparison to normal myeloid progenitors. Based on the unique biology of HLA-A*0201 (HLA-A2), in which presentation of leader sequence (LS)-derived peptides is favored, we focused on the LS-CG-derived peptide CG1 (FLLPTGAEA). LS peptides are naturally processed and loaded on HLA-A2, providing an abundant source of surface peptide/HLA (pHLA) targets. We eluted CG1 from the surface of primary HLA-A2 + AML blasts and AML cell lines, and demonstrated CG1-targeting immunity in leukemia patients following allogeneic stem cell transplant, hence highlighting the potential for CG1 to be a promising immunotherapeutic target in AML. Numerous platforms have been developed to target cell surface pHLA complexes. T cell receptor (TCR) mimic (m) antibodies are immunotherapeutic antibodies that target pHLA, which are the natural ligands for the TCR. TCRm antibodies have been a breakthrough in immunotherapy, as they: (1) target intracellular antigens expressed on HLA; (2) are engineered to have high affinity for HLA; (3) can elicit their cytotoxic effect independent of the TCR; and (4) can be produced in large quantities providing an off-the shelf-product for patient use. Here we report on the engineering, preclinical efficacy, and safety evaluation of a novel CG1-targeting, T cell-engager, bispecific antibody (CG1xCD3e), which incorporates a novel TCRm construct that recognizes cell surface CG1/HLA-A2 complexes. Methods: To generate the CG1/HLA-A2-binding monoclonal antibodies, H2L2 human transgenic mice were immunized with CG1/HLA-A2 monomers subcutaneously. The resulting paired heavy and light chains were cloned from the antigen-sorted memory B cells into the single pcDNA3.1(+) vector with both human (h) immunoglobulin (Ig)G1 and hKappa for subsequent ExpiCHO high-throughput transient expression. Antibody binding was assessed by Bio-Layer Interferometry (BLI) and T2 cellular binding assays. Xencor anti-CD3e scFv and Knobs-in-holes technology was applied for the bispecific antibody engineering for xMab format. In vitro activity of CG1xCD3e and T cell cytokine secretion was confirmed using flow cytometry-based T cell-dependent cellular cytotoxicity (TDCC). The specificity of CG1xCD3e for leukemia was assessed using colony forming unit assays. In vivo efficacy was evaluated in NSG mice engrafted with AML cell lines and treated with CG1xCD3e with normal donor peripheral blood mononuclear cells (ND-PBMC). Results: Using BLI, binding avidity of the CG1xCD3e to CD3-Fc, KD= 7.52 x 10-10 M, and affinity to CG1/HLA-A2, KD= 1.28 x 10-10 M were calculated. Using flow cytometry, we confirmed high affinity binding of CG1xCD3e to CG1/HLA on the CG1- expressing EM2 HLA-A2 + cell line, and also demonstrated binding of CG1xCD3e to CD3 using jurkat T cell line. After co-culturing GFP/Luciferase + HLA-A2 + AML (U937-A2 and ML-2) or CML (EM2) cell lines with ND-PBMC and different concentrations of CG1xCD3e bispecific antibody for 24 or 48 hours, flow cytometry analysis demonstrated highly specific CG1/HLA-A2 dependent killing of AML cells by T cells cultured with CG1xCD3e bispecific antibody, in comparison with control bispecific antibody with a disabled CG1 binding arm. This correlated with both tumor- and bispecific antibody- dependent T cell activation and cytokine secretion. To study the in vivo anti-leukemia activity of CG1xCD3e, we engrafted NSG mice with the HLA-A2 + ML-2 and U937-A2 AML cell lines, and treated mice after tumor engraftment with ND-PBMC (1 x 107 cells) and weekly intraperitoneal injections of CG1xCD3e bispecific antibody (0.01 mg/Kg, 0.05 mg/Kg, and 0.1 mg/Kg) or PBS. Bioluminescence imaging demonstrated that the mice treated with ND-PBMC + CG1xCD3e had significantly lower levels of leukemia burden compared to the mice treated with ND-PBMC alone (Figure 1). Lastly CFU assays using HLA-A2 + normal donor marrow in a semi-solid matrix of methylcellulose in the presence of T cells and either CG1xCD3e bispecific antibody or isotype antibody, confirmed specificity of CG1xCD3e bispecific antibody for leukemia. Conclusion: Our study provides strong pre-clinical evidence supporting the targeting of LS- derived peptides, specifically CG1, in the setting of AML using a novel TCRm-based bispecific antibody.

Efficacy and Safety of Chimeric Antigen Receptor T Cells Therapy Strategy That Dual Targeting CD19 and CD22 to Treat Relapsed/Refractory Acute Lymphoblastic Leukemia in Adults

Background: Chimeric antigen receptor T-cells (CAR-T) targeting CD19 therapy is reported to induce 83-93% response in relapsed/refractory acute lymphoblastic leukemia (r/r-ALL) in adults. However, 30-60% of patients relapse after CAR-T treatment, of which 14-25% CD19-negative relapse. In spite of CAR-T cells persistence, CD19 absent causing tumors that evade CAR-T cells mediated recognition and clearance. For CD19-negative relapse, it is necessary to explore more effective targets. There are some research proved that compared with single-targeted CARs, CD19/CD22 dual-targeted CARs induce more IFN-γ and IL-2 in vitro and eradicate patient-derived xenografts (PDX) produced with CD19-negative relapse of CD19-directing CAR-T treatment. Therefore, our study explored the efficacy and safety of clinical studies on mixture of CD19 CAR-T and CD22 CAR-T cells in the treatment of r/r ALL in adults. Patients and Methods: CD3 + cells were selected from the apheresis PBMC and activated before lentiviral CAR T cells infection. The cells were transduced with a caspase9-inducible, safety-engineered lentivector CAR containing anti-CD19 or -CD22 scFv fused with multiple intracellular signaling domains: CD28/CD27/CD3z-iCasp9. The quality of apheresis cells, gene transfer and T cell proliferation efficiencies, and effective CAR-T infusion dose were quantitatively scored and documented. All enrolled patients expressed CD19 and CD22 positively. All patients received fludarabine (FLU) and cyclophosphamide (CTX) conditioning chemotherapy (FLU 30mg/m 2, d1-3; CTX 500mg/m 2, d1-3) before CAR-T infusions. Results: The study included 16 r/r ALL patients, median age is 26 years, and median of previous theraples is 6, all of patient details can be found in the table (Fig.1). In the first month after CD19/CD22 CAR-T cells infusion, total of 93.8% (15/16) of patients achieved complete response (CR), 1 case (6.25%) was evaluated as non-remission (NR). In the evaluation of safety, 68.75% (11/16) of patients did not experience cytokine release syndrome (CRS), 25% of patients (4/16) occurred grade 1 CRS and 6.25% (1/16) of patients occurred grade 2 CRS, no case of severe CRS defined as≥grade 3 and no any immune effector cell-associated neurotoxicity syndrome (ICANS) occurred. After a median follow-up of 9.9 months, 4 patients maintained CR, while other 11 patients were relapsed, with a duration of response (DOR) of 25% (4/16), median LFS was 6.1 months and median OS were not reached (Fig.2). Conclusions: In summary, CD19/CD22 exhibited a manageable safety but limited antileukemia activity. Our study showed that mixture of CD19 CAR-T and CD22 CAR-T cells infusion is fail to expected to compensate for the treatment of relapsed in r/r ALL and prolonging the leukemia-free survival of patients. The low-efficacy of dual-targeted CAR-T cells may be caused by the CAR19 and CAR22 cells interfere with each other and weaken the CAR-T amplification in vivo. From our data, it seems that the timing of treatment and tumor burden status may play a more important role rather than new targets CAR-T cells infusion for r/r ALL in adults.

Results of Cynk-001-AML-001: A Phase I Multi-Dose Study Evaluating the Safety, Tolerability, and Persistence of Cynk-001 in Adults with De Novo or Secondary Acute Myeloid Leukemia in Morphologic Complete Remission with Minimal Residual Disease or Relapsed/Refractory AML

Introduction: Acute myeloid leukemia (AML) is a clinically and genetically heterogeneous disease often with suboptimal outcomes. While progress has been achieved in the treatment of AML, relapse remains a significant challenge. Novel therapeutic options aimed at attaining minimal residual disease (MRD) negative complete remission (CR) are expected to reduce the incidence of relapse and prolong survival. Evidence shows that natural killer (NK) cells can exhibit potent anti-leukemia activity against AML. CYNK-001 is a CD56+CD3- enriched, off-the-shelf, unmodified allogeneic NK cells expanded from placental CD34+ cells. Aim CYNK-001-AML-001 is a phase I multi-dose study evaluating the safety, tolerability, and persistence of CYNK-001 with or without recombinant human interleukin-2 (rhIL-2) in adults with de novo or secondary acute myeloid leukemia (AML) in morphologic complete remission (CR) with minimal residual disease (MRD) or relapsed/refractory (R/R) AML. Methods This Phase I, single-arm, dose escalation clinical trial (NCT04310592) enrolled patients 18-80 years with R/R AML or patient in MRD positive CR. Two lymphodepletion regimens were assessed. Patients in cohorts 1-3 underwent standard lymphodepletion with fludarabine (25 mg/m2/day) and cyclophosphamide (300 mg/m2/day) on days -5, -4 and -3. Subsequent cohorts received enhanced lymphodepletion with fludarabine (30 mg/m2/day) and cyclophosphamide (900 mg/m2/day) on days -6, -5, -4 and -3. Escalating doses of NK cells were administered following a standard 3+3 design, with 2 separate arms (MRD+ arm and R/R arm) starting with cohort 4. A starting dose of 600 million cells on days 0, 7, and 14 was escalated to a maximum dose of 1.8 billion cells on days 0, 7, 14 and 21. The primary objective of the study was to determine the maximum tolerated dose (MTD) or maximum planned dose (MPD) of CYNK-001 and to assess the safety of multiple infusions of CYNK-001 administered using a flat, non-weight-based dose as assessed by the frequency and severity of adverse events (AE). The secondary objective was to assess the clinical efficacy of CYNK-001 in AML subjects. Results 28 patients (17 with R/R AML and 11 with MRD-positive AML) were enrolled during dose escalation, and 27 received CYNK-001. The highest dose of NK cells administered was 1.8 billion cells X 4 in cohort 6b (patients with R/R AML). Treatment was well tolerated with no dose limiting toxicities (DLTs) even at the highest dose. No cases of neurotoxicity or GvHD were reported. Four cases of grade 2 CRS were reported but there were no cases of ≥ grade 3 CRS. Two incidences of grade 4 thrombocytopenia and one grade 4 decreased white blood cell count were noted in patients who had received enhanced lymphodepletion. In R/R AML patients treated with the highest dose of CYNK-001, 2 of 4 patients achieved an objective response of Morphologic Leukemia-Free State (MLFS) on Day 28. One of these patients has maintained a response to D120 and is continuing follow up. One of 3 patients with MRD +ve AML treated with 3 doses of 1.8 billion CYNK-001 cells per dose achieved MRD negativity until day 120 at which time a blast count of 1.6% was observed. Conclusion Treatment with CYNK-001 showed biological activity as evidenced by achievement of MLFS in R/R AML patients and eradication of AML MRD positivity in AML patients in morphologic CR. Therapy was generally well-tolerated, with no dose-limiting toxicities observed with even the highest dose of CYNK-001. This trial yielded important insights into the optimal approach to lymphodepletion and the potential clinical efficacy of allogeneic NK cells in R/R AML. Based on these results, this trial is now closed to further enrollment and future development activities will focus on next generation NK cell therapies edited to optimize persistence and efficacy and limit the requirement for enhanced lymphodepletion.

The Clinical Menin Inhibitor Ziftomenib and the Nuclear Export Inhibitor Selinexor Synergistically Inhibit the Growth of MLL-r AML

CONCLUSION Menin is a scaffold protein that interacts with oncogenic histone-lysine-N-methyltransferase MLL1 (KMT2A)-fusion protein (FP) complex in MLL-rearranged ( MLL-r) AML. Menin inhibitors that evict menin from this interaction have been shown to be active against MLL-r and NPM1MT leukemia by modulating the expression of the leukemogenic homeobox A9 ( HOXA9) gene and its co-factor, MEIS1. Recent evidence showed that menin inhibitors can activate a tumor-suppressive network via a non-canonical transcriptional program through UTX. On the other hand, selective inhibitor of nuclear export (SINE) against XPO1/CRM1 has been shown to have robust anti-leukemia activity via enrichment of tumor suppressor proteins in the nucleus. In the present study, we hypothesized that menin and nuclear export inhibition would synergistically suppress AML cell proliferation and possibly sensitize menin inhibitor-resistant cells. We have used the clinical-stage menin inhibitor ziftomenib and SINE compound selinexor to simultaneously target menin-KMT2A protein-protein interactions and nuclear export. To assess growth inhibition, an ATP-based cell proliferation assay was used. Combination synergy was determined using CalcuSyn Version 2.0 synergy software. Stem-like progenitor cells were isolated using the StemSpan CD34+ expansion kit (StemCell Tech). Colony formation efficiency was determined using a Methocult assay (StemCell Tech). Gene and protein expression was detected using quantitative real-time PCR and western blotting. Flow cytometric analysis was performed to detect cell death and cell cycle status. We have performed the whole transcriptomic analysis via the RNA sequencing approach. The clinical candidate drug ziftomenib, in combination with selinexor, synergistically inhibited the growth of MLL-r AML cell lines (MV4;11 and MOLM13) (CI<1) [Fig.1A]. The combination of menin and XPO1 inhibitors significantly suppressed colony formation of CD34+ MLL-r progenitor stem cells derived from primary patient samples but was not toxic to normal CD34+ human hematopoietic progenitor stem cells (HPSCs). Menin inhibitor treatment caused the downregulation of menin protein along with its downstream targets HOXA9, MEIS1, and FLT3 in western blot analysis. Interestingly, selinexor also reduced menin, HOXA9, and MEIS1 protein levels. The combination enhanced menin down-expression, suggesting a molecular basis for the synergy between the two compounds. Ziftomenib suppressed the expression of menin in a time-dependent manner, which is evident as early as six hours of treatment. The combination showed increased CD11b, a marker of monocytic differentiation in MV4-11 treated cells. The combination also significantly enhanced both early and late apoptotic cell death in MLL-rearranged AML cells compared to either compound alone. Compared to controls, ziftomenib and selinexor-treated samples individually showed increased apoptotic and decreased G2/M populations, significantly enhanced in the combination. We observed differential expression of certain mRNAs and micro RNAs (miRs) in MV4-11 treated cells. The TMEM191B, SH3TC1, and SULT1C2 mRNAs were upregulated by ziftomenib and selinexor, which are enhanced further in the combination group. On the contrary, CENPK, CKS2, KIF18A, and H2BC4 mRNAs were downregulated by a single agent or combination. Among miRs, hsa-miR-34a-5p, hsa-miR-142-3p, hsa-miR-26b-5p were upregulated, and hsa-miR-33b-3p, hsa-miR-4454, hsa-miR-210-3p and hsa-miR-130b-3p [reported to be an essential lineage-specific codriver of MLL-AF4 leukemia] were downregulated by single agent or combination. Such mRNAs and miRs panels could serve as biomarkers for treatment response. MV4-11 cell line-derived xenografts in NSG mice showed a significant difference in survival in the combination arm compared to any single agent. Metronomic dosing also showed robust improvement in survival in the combination arm. Patient-derived xenografted NSG mice model using human primary MLLr re-transplantable leukemia cells showed improved survival in the combination arm [Fig. 1B]. These preclinical findings demonstrate that simultaneous inhibition of the menin-KMT2A interaction and nuclear export is a viable strategy for the treatment of MLL-r AML. Ongoing experiments with functional proteomic analysis will be presented at the ASH meeting.

CRISPR-Cas9-Based Gene Knockout of Immune Checkpoints in Expanded NK Cells.

Natural killer (NK) cell immunotherapy has emerged as a novel treatment modality for various cancer types, including leukemia. The modulation of inhibitory signaling pathways in T cells and NK cells has been the subject of extensive investigation in both preclinical and clinical settings in recent years. Nonetheless, further research is imperative to optimize antileukemic activities, especially regarding NK-cell-based immunotherapies. The central scientific question of this study pertains to the potential for boosting cytotoxicity in expanded and activated NK cells through the inhibition of inhibitory receptors. To address this question, we employed the CRISPR-Cas9 system to target three distinct inhibitory signaling pathways in NK cells. Specifically, we examined the roles of A2AR within the metabolic purinergic signaling pathway, CBLB as an intracellular regulator in NK cells, and the surface receptors NKG2A and CD96 in enhancing the antileukemic efficacy of NK cells. Following the successful expansion of NK cells, they were transfected with Cas9+sgRNA RNP to knockout A2AR, CBLB, NKG2A, and CD96. The analysis of indel frequencies for all four targets revealed good knockout efficiencies in expanded NK cells, resulting in diminished protein expression as confirmed by flow cytometry and Western blot analysis. Our in vitro killing assays demonstrated that NKG2A and CBLB knockout led to only a marginal improvement in the cytotoxicity of NK cells against AML and B-ALL cells. Furthermore, the antileukemic activity of CD96 knockout NK cells did not yield significant enhancements, and the blockade of A2AR did not result in significant improvement in killing efficiency. In conclusion, our findings suggest that CRISPR-Cas9-based knockout strategies for immune checkpoints might not be sufficient to efficiently boost the antileukemic functions of expanded (and activated) NK cells and, at the same time, point to the need for strong cellular activating signals, as this can be achieved, for example, via transgenic chimeric antigen receptor expression.

NKX101, an Allogeneic Off-the-Shelf CAR NK Cell Therapy Targeting NKG2D-Ls, Has Potent Anti-Leukemic Activity Alone or in Combination with Ara-C

Introduction NKG2D-Ligands (NKG2D-Ls) are a family of immunomodulatory proteins that are upregulated on damaged or transformed cells but have limited expression on normal tissues. Natural killer (NK) cells target and eliminate NKG2D-L + cells through NKG2D receptor binding and subsequent activation. NKX101 is an allogeneic off-the-shelf healthy donor-derived chimeric antigen receptor (CAR) NK cell therapy candidate engineered to express an NKG2D-L targeting CAR and membrane-bound IL-15 for extended persistence. In a clinical trial, NKX101 treatment combined with modified lymphodepletion incorporating cytarabine (Ara-C) has shown promise for the treatment of relapsed/refractory (r/r) AML, including generating complete responses (CR) with MRD negativity (MRD -). To support the rationale of NKX101 combined with modified lymphodepletion, we developed assays to (i) investigate the cytotoxic activity of NKX101 against individual NKG2D-Ls, (ii) determine the effect of Ara-C pre-treatment on NKG2D-L expression on AML cell lines, and (iii) evaluate the combined anti-leukemic activity of NKX101 and Ara-C. Methods NKX101 cells were generated from peripheral blood leukopaks from healthy donors. CHO-K1 cells were engineered to stably express individual NKG2D-Ls or empty vector controls and were combined with NKX101 cells for cytotoxicity experiments. AML cell lines were treated with increasing levels of Ara-C and evaluated for NKG2D-L expression by flow cytometry. To measure NKX101 cytotoxicity against AML cell lines, NucRed™-labeled target cells were pre-treated with Ara-C using IC 50 and IC 90 concentrations and co-cultured with NKX101. Specific cell killing of target cells was measured using an Incucyte® instrument for five days. Assessment of the contribution of each agent was determined using a dose-response matrix of increasing concentrations of NKX101 cells and Ara-C to generate specific cytotoxicity values. Combination effects were analyzed using the SynergyFinder Plus web application. Results Expression of a single NKG2D-L was sufficient to trigger NKX101 cytotoxicity against target cell lines. Flow cytometry analysis revealed that pre-treatment with Ara-C upregulated NKG2D-Ls on AML cell lines in a dose-dependent manner. NKX101 showed enhanced anti-leukemic activity against AML cells pre-treated with Ara-C compared to untreated controls, demonstrating that the combination can enhance NKX101 potency. Assessment of the combination of NKX101 and Ara-C using a dose-response matrix revealed that the two modalities combine to potently kill AML cells. Conclusions In summary, we show that NKX101 potently targets and eliminates AML cells expressing NKG2D-Ls further validating NKG2D-Ls as therapeutic targets. Additionally, we show that the combination of Ara-C and NKX101 leads to increased anti-leukemic activity, supporting continued investigation of NKX101 CAR NK cell therapy after lymphodepletion incorporating Ara-C for the treatment of r/r AML.