Naturally Selected CD7-Targeted Chimeric Antigen Receptor (CAR)-T Cell Therapy for Refractory/Relapsed Acute Myeloid Leukemia: Phase I Clinical Trial

Introduction Refractory or relapsed (r/r) acute myeloid leukemia (AML) is associated with a relatively poor prognosis, even in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT), emphasizing the critical need for novel therapies. Approximately 30% of AML patients express CD7 on their leukemic blasts and malignant progenitor cells. Naturally selected CD7 CAR-T (NS7CAR-T) therapy has shown significant efficacy with a favorable safety profile in T-cell lymphoid malignancies. In a phase I clinical study (https://clinicaltrials.gov NCT04938115), we investigated the safety and efficacy of CAR-T therapy for treating r/r AML patients with CD7-positive disease. Methods Peripheral blood mononuclear cells were obtained from either the patients themselves (n=9) or the transplant donor (n=1) in cases of relapse post-transplant. T-cells were then purified using CD3+ magnetic beads. The second-generation CD7CAR with a 4-1BB costimulatory domain was manufactured following the manufacturer's protocol. Before the CAR-T cell infusion, bridging therapies were permitted for patients with rapid disease progression. All patients received intravenous fludarabine (30mg/m 2/d) and cyclophosphamide (300mg/m 2/d) lymphodepletion chemotherapy for three consecutive days (Day -5 to Day -3). The median time from leukapheresis to CAR-T cell infusion was 15 days. Results Between June 2021 and January 2023, we enrolled 10 patients with CD7-positive r/r AML (CD7 expression >50% with good intensity) and administered NS7CAR-T cell infusions, with 4 receiving a low dose (5×10 5/kg) and 6 receiving a medium dose (1×10 6/kg). Table 1 displays the characteristics of the enrolled patients, revealing a median age of 34 years (7-63 years) and median bone marrow (BM) blasts percentage by flow cytometry (FCM) of 17.0% (2.0-72.7%) at enrollment. One patient presented with diffuse extramedullary disease (EMD). Before enrollment, patients had undergone a median of 9 (range: 3-17) prior lines of therapy. Seven patients had a history of allo-HSCT and the median interval period from the prior transplant to relapse was 12.5 months (3.5-19.5 months). Following infusion, the median peak of circulating NS7CAR-T cells was 2.72×10 5 copies/μg (0.671~5.41×10 5 copies/μg) genomic DNA, which occurred around Day 21 (Day 14 - Day 21) based on q-PCR, with 64.68% (40.08%~92.02%) occurring on Day 17 (Day 11 - Day 21) according to FCM. The median transduction efficiency of the products was 95.6% (70.4%-98.5%). At four weeks post NS7CAR-T cell infusion, 7/10 (70%) patients achieved complete remission (CR) in BM, and 6 of them attained minimal residual disease (MRD)-negative CR. Three patients showed no remission (NR), including 1 with EMD who had partial remission (PR) based on PET-CT evaluation on Day 35. All NR patients were found lost CD7. The median observation time was 178 days (28-752 days). Among the 7 patients who achieved CR, 3 who relapsed from prior transplants underwent consolidative 2 nd allo-HSCT about 2 months after CD7 CAR T-cell infusion. Two patients remained in leukemia-free survival on day 752 and day 315, respectively, while 1 patient died on day 241 due to transplant-related mortality. Among the other 4 patients without consolidative allo-HSCT, 3 relapsed on day 47, day 83, and day 115, respectively (all 3 patients were found to have CD7 loss), and 1 patient died from lung infection. Post-infusion, the majority of patients (80%) experienced mild cytokine release syndrome (CRS), with 7 displaying grade I and 1 having grade II CRS, while 2 patients (20%) experienced grade III CRS. None of the patients had neurotoxicity. Among the 7 patients with prior allo-HSCT, 1 who had a relapse approximately 100 days after prior allo-HSCT developed mild skin graft-versus-host disease following CAR-T therapy. Conclusion Our study highlights the NS7CAR-T therapy as a promising approach for achieving a favorable initial CR in CD7-positive AML patients, even in those who have undergone extensive prior treatments and experienced relapse post allo-HSCT. It potentially could serve as a bridging therapy before transplant. CD7 loss is a major issue either in NR patients or relapsed patients. The safety profile of NS7CAR-T therapy was manageable. However, to comprehensively assess the efficacy of NS7CAR-T in treating CD7-positive AML, further data from a larger cohort of patients and longer follow-up time are essential.