Phase I Trial of Ex Vivo Expanded Donor Gamma Delta T Cell Immunotherapy to Prevent Acute Myeloid Leukemia Relapse after Allogeneic Transplantation

Background Patients with adverse risk acute myeloid leukemia (AML) by European LeukemiaNet (ELN) risk stratification are at high risk (~50%) of relapse after reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (alloHCT). We developed a novel cellular therapy using ex vivo expanded donor-derived gamma delta T (GDT) cells to prevent post-HCT relapse and cure more patients with adverse risk AML. GDT cells that are rare in circulating blood have MHC-independent potent antitumor cytotoxicity against AML. They cause no graft-versus-host-disease (GVHD) in preclinical studies, which allows the potential for a healthy donor-derived cellular immunotherapy for AML. Methods This first-in-human trial enrolled patients with ELN adverse risk AML who received either HLA-identical sibling donor (MSD) or haploidentical donor RIC alloHCT. The same donor used for HCT underwent non-mobilized leukapheresis for large scale expansion of GDT cells with use of artificial antigen presented cells (Boucher J. Immunother. 2023). Expanded GDT cells were infused to patients between days 60-100 after alloHCT in the absence of uncontrolled infection and/or GVHD requiring systemic steroids. The trial followed a 3+3 design to study the primary endpoint of maximum-tolerated dose (MTD) of donor GDT cell infusion. Three dose levels (DL) of GDT cells were studied where DL1 was 6.25 x 106 cells/kg, DL2 was 3.13 x 107 cells/kg and DL3 was 1.10 x 108 cells/kg. Dose-limiting toxicities (DLT) were evaluated for 42 days following GDT cell infusion and were defined as grade 3-4 cytokine release syndrome (CRS), grade 3-4 immune effector cell-associated neurotoxicity syndrome (ICANS), or any grade 4 organ toxicity by CTCAE 5.0. Results We treated 9 patients with ELN adverse risk AML in morphological complete remission (CR), including 5 patients who had detectable measurable residual disease (MRD) prior to HCT. Median age was 63 years, and all patients received RIC alloHCT prior to GDT cell infusion. MSD was used in 3 and haploidentical donor in 6 patients. GDT cell expansion was successful in all cases with all products achieving >90% GDT cell viability and <0.06% alpha beta T cell contamination. GDT cell infusion was safe and no DLTs were observed at any DL. None of the treated patients experienced any grade CRS, ICANS or acute GVHD. At median follow up of 454 days, all but one patient (DL2) remain in continuous MRD negative CR with 100% donor chimerism after GDT infusion. All patients with pre-HCT MRD positive AML are in MRD negative CR, including 2 patients with TP53 mutation/complex karyotype. All treated patients are alive including the patient with RUNX1 AML who relapsed 8 months after GDT cell infusion. Single-cell RNA sequencing analysis of infused donor GDT products identified predominantly Vγ9Vδ2 T cells with average subset of effector (74.8%), effector memory (23.8%), stem like (0.8%) cells, and only very low proportion of early exhausted (0.6%) cells. Conclusions Large dose ex vivo expanded donor GDT cell infusion was safe and well tolerated with no DLTs. MTD was not reached, and a phase II trial will be conducted with recommended GDT cell dose of 1 x 108 cells/kg. Initial efficacy results are promising with ~90% of the study patients who are at high-risk for AML relapse achieving MRD negative CR, including all cases with pre-HCT detectable MRD and/or TP53 mutation. Finalized phase 1 data, including correlative analysis, will be presented at the annual meeting.