S110: A NOVEL AND SUCCESSFUL CD7 GENE KNOCKOUT CAR-T CELL THERAPY FOR RELAPSED OR REFRACTORY T-CELL HEMATOLOGIC MALIGNANCIES

Abstract

Background: T cell malignancies represent a group of hematologic cancers with high relapse and mortality rates. The shared expression of target antigens between chimeric antigen receptor (CAR) T cells and malignant T cells has limited the development of CAR-T due to unintended CAR-T fratricide. Here, we develop a fratricide-resistant anti-CD7 CAR-T modified by CD7 ablation through CRISPR/CAS9 gene editing (KO7CAR). Aims: In a phase I clinical trial, we explored the efficacy and safety of KO7CAR T-cells for relapsed or refractory (R/R) T-cell malignancies (NCT04916860 & NCT04938115). Methods: Peripheral blood mononuclear cells were collected from patients (n=13) or the transplant donor (n=2) by leukapheresis. CD7-ablated CAR T cells (KO7CAR) were derived by electroporation of bulk T cells with CD7-targeting Cas9-gRNA RNP 24 hours before 7CAR transduction. This KO7CAR is a second-generation CAR-T with the co-stimulatory domain of 4-1BB and CD3ζ targeting CD7. Intravenous fludarabine (30mg/m2/d) and cyclophosphamide (300mg/m2/d) were given to all patients on day -5 to day -3 prior to KO7CAR-T cells infusion. Results: From Oct. 2020 to Oct. 2021, 15 patients with T-cell acute lymphoblastic leukemia (n=10), T-cell lymphoblastic lymphoma (n=3), and mixed phenotype acute leukemia (n=2) were enrolled and received KO7 CAR-T cells (Table 1). The median age was 28 (8-46) years old. Four patients had prior hematopoietic stem cell transplantation (HSCT). At enrollment, 10 patients had bone marrow (BM) blasts >5% by morphology, and 10 patients had the extramedullary disease (EMD, diffuse involvement, n=8, and bulky mediastinal masses, n=2). Both patient- and donor-derived KO7CAR-T cells were successfully generated with a transduction efficiency of 59.0% (22.5%-97.4%). A single dose of KO7CAR-T cells was infused to patients at low dose (1.5~5x105 cells/kg, n=8), medium dose (1x106 cells/kg, n=6) or high dose (2x106 cells/kg, n=1). On day 28, 15/15 (100%) patients achieved minimal residual disease (MRD) negative complete remission (CR). Among the 10 patients with EMD, 7 achieved EMD CR on day 30, 2 achieved partial response (PR), and 1 who relapsed post 2nd transplant had no response on day 35 then withdrew. Up to data cutoff Feb.10, 2022, the median follow-up time was of 309 days (35~407 days). About 2 months post KO7CAR, 12 patients bridged into allogeneic HSCT, and all remained progression-free after a median time of 253 (30~388) days after HSCT except for 1 who relapsed on day 147 then died from intracerebral hemorrhage on day 249. The other 2 patients without subsequent HSCT (all had a prior transplant) died from infection on day 78 and GVHD on day 103, respectively, post KO7CAR. Mild cytokine release syndrome (CRS, ≤grade II) occurred in 10/15 (66.7%) patients, and 5/15(33.3%) patients had grade III CRS. One patient had grade I neurotoxicity, and 2 had grade III/IV neurotoxicity. All was controlled after the administration of corticosteroids and/or tocilizumab. Following infusion, the median peak of circulating KO7CAR-T cells was 1.77×105 (0.279~14.3×105) copies/μg genomic DNA which occurred around day 20 (day10~ day25) and 63.47% (23.1%~94.18%) occurring on day15 (day 9~day25) by q-PCR and flow cytometry respectively. Image:Summary/Conclusion: This study demonstrated KO7CAR-T therapy had a high efficacy for CD7+ T-cell malignancies even for those who relapsed post-transplant. Safety was manageable, however, more data on additional patients and longer observation time are needed to evaluate the efficacy of KO7 CAR-T products further.