Downregulation of MICA/MICB improves cell persistence and clinical activity of NKG2DL CAR T-cells in patients with relapsed or refractory acute myeloid leukemia or myelodysplastic neoplasia

The NKG2D receptor binds eight ligands (NKG2DL) overexpressed in a wide range of malignancies, but largely absent on non-neoplastic cells. Initial clinical evaluation of NKG2DL chimeric antigen receptor (CAR) T-cells (CYAD-01) in patients with relapsed or refractory (r/r) acute myeloid leukemia (AML) or myelodysplastic neoplasia (MDS) demonstrated low durability of responses and short cell persistence. Two Phase I trials were initiated to evaluate the effect of lymphodepletion prior to a single CAR T-cell infusion in a similar r/r AML/MDS patient population. The DEPLETHINK trial (NCT03466320) evaluated CYAD-01 while the CYCLE-1 trial (NCT04167696) evaluated a next-generation NKG2DL CAR, CYAD-02, where the two main NKG2D ligands MICA and B are downregulated, to increase CAR T-cell persistence. Seventeen and twelve patients were treated in the DEPLETHINK and CYCLE-1 trials, and confirmed the good tolerability of both products with cytokine release syndrome (CRS) grade 3 or 4 reported in 25% and 33.3% of patients, respectively. CYAD-02 presented an higher engraftment and an improved clinical activity (17% objective response rate) compared to CYAD-01 (no objective response). Altogether, our data provide proof of principle that knock-down of MICA/B can enhance CAR T-cell persistence and efficacy while maintaining a good safety profile.