A Phase 2, Single-Arm, Multicohort, Open Label, Multicenter Trial of Off-the-Shelf Natural Killer Cells (SAR445419) in Patients with High-Risk Myeloid Malignancies Undergoing Allogeneic HSCT

Background and Significance: Relapse remains the leading cause of treatment failure for patients with high-risk acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Although the risk depends on parameters such as age and conditioning intensity, relapse is experienced in 30-50% of patients after conventional HSCT in high-risk AML/MDS. Initial safety and post-HSCT relapse risk reduction results were reported in a phase I study of haploidentical (haplo) donor-derived natural killer (NK) cells expanded ex vivo on feeder cells expressing IL-21 and 4-1BBL in conjunction with haplo-HSCT (Ciurea et al, Leukemia, 2022). This study supported exploring SAR445419 (SAR'419), an off-the-shelf (OTS) product, derived from universal donor NK cells and expanded ex vivo in a feeder cell-free system using plasma membrane particles bearing membrane-bound IL-21 and 4-1BBL. Here, we aim to test whether SAR'419 can mediate an effective anti-leukemia response and reduce post-transplant relapse rate when administered in the peri-transplant period.

Study Design and Methods: In this multicenter, multicohort, phase 2, single-arm trial (NCT05726682), patients with high-risk AML/MDS planned for allo-HSCT from matched sibling, matched unrelated or haplo donors will be enrolled in 2 cohorts. Cohort A will comprise patients aged 18‒65 years undergoing myeloablative conditioning with hematopoietic cell transplantation comorbidity index ≤3 and cohort B will comprise patients aged 18‒75 years undergoing reduced intensity conditioning. Patients with prior allogeneic transplantation or AML beyond first complete remission will be excluded from the study.

Patients will undergo HSCT conditioning starting on Day ‒7 and will receive a peripheral blood stem cell graft on Day 0. Prophylaxis for Graft-versus-host disease (GVHD) using cyclophosphamide, mycophenolate mofetil, and tacrolimus will start on Day +3. SAR'419 will be administered as adjunctive therapy to the HSCT on Day ‒2, Day +7, and Day +28. To confirm the anticipated safety profile of SAR'419, a safety run-in will be conducted in 6‒12 patients in each cohort prior to open enrollment. Patients will be enrolled until 51 and 44 patients in cohorts A and B, respectively, receive at least the first 2 doses of SAR'419 at the target dose confirmed during safety run-in. In total, approximately 107 patients will be enrolled.

The primary endpoint, relapse free survival (RFS), will be assessed at 12 months post-HSCT. Additional primary endpoints include frequency of graft failure, life-threatening infusion-related reactions or cytokine release syndrome, tumor lysis syndrome, immune cell-associated neurotoxicity syndrome, acute GVHD, overall mortality at 100 days post-HSCT, non-relapse mortality, and cytomegalovirus reactivation/infection. Secondary endpoints are safety, tolerability, and the impact of SAR'419 on HSCT outcomes, stem cell engraftment, GVHD, infection, and quality of life. Exploratory assessments include evaluation of the impact of SAR'419 on immune reconstitution, cytomegalovirus seroconversion, minimal residual disease, resource utilization, SAR'419 immunogenicity and persistence and their impact on outcomes in whole blood (including serum and plasma) and bone marrow aspirates.

RFS will be reported as the percentage of patients who are relapse free and alive at 12 months from the date of HSCT and who received at least the first 2 planned doses of SAR'419. Adverse events will be graded by the National Cancer Institute Common Terminology Criteria for Adverse Events v5.0 and will be summarized using descriptive statistics.