Cooperative CAR targeting to selectively eliminate AML and minimize escape.

Abstract

Acute myeloid leukemia (AML) poses a singular challenge for chimeric antigen receptor (CAR) therapy owing to its phenotypic heterogeneity and similarity to normal hematopoietic stem/progenitor cells (HSPCs). Here we expound a CAR strategy intended to efficiently target AML while minimizing HSPC toxicity. Quantification of target expression in relapsed/refractory patient samples and normal HSPCs reveals a therapeutic window for gated co-targeting of ADGRE2 and CLEC12A: We combine an attenuated ADGRE2-CAR with a CLEC12A-chimeric costimulatory receptor (ADCLEC.syn1) to preferentially engage ADGRE2^posCLEC12A^pos leukemic stem cells over ADGRE2^lowCLEC12A^neg normal HSPCs. ADCLEC.syn1 prevents antigen escape in AML xenograft models, outperforms the ADGRE2-CAR alone and eradicates AML despite proximate myelopoiesis in humanized mice. Off-target HSPC toxicity is similar to that of a CD19-CAR and can be mitigated by reducing CAR T cell-derived interferon-γ. Overall, we demonstrate the ability of target density-adapted cooperative CAR targeting to selectively eliminate AML and potentially obviate the need for hematopoietic rescue.