Feasibility and preclinical efficacy of CD7-unedited CD7 CAR T cells for T cell malignancies

Abstract

Chimeric antigen receptor (CAR)-mediated targeting of T lineage antigens for the therapy of blood malignancies is frequently complicated by self-targeting of CAR Tcells or their excessive differentiation driven by constant CAR signaling. Expression of CARs targeting CD7, a pan-T cell antigen highly expressed in Tcell malignancies and some myeloid leukemias, produces robust fratricide and often requires additional mitigation strategies, such as CD7 gene editing. In this study, we show fratricide of CD7 CAR Tcells can be fully prevented using ibrutinib and dasatinib, the pharmacologic inhibitors of key CAR/CD3ζ signaling kinases. Supplementation with ibrutinib and dasatinib rescued the exvivo expansion of unedited CD7 CAR Tcells and allowed regaining full CAR-mediated cytotoxicity invitro and invivo on withdrawal of the inhibitors. The unedited CD7 CAR Tcells persisted long term and mediated sustained anti-leukemic activity in two mouse xenograft models of human Tcell acute lymphoblastic leukemia (T-ALL) by self-selecting for CD7-, fratricide-resistant CD7 CAR Tcells that were transcriptionally similar to control CD7-edited CD7 CAR Tcells. Finally, we showed feasibility of cGMP manufacturing of unedited autologous CD7 CAR Tcells for patients with CD7+ malignancies and initiated a phase I clinical trial (ClinicalTrials.gov: NCT03690011) using this approach. These results indicate pharmacologic inhibition of CAR signaling enables generating functional CD7 CAR Tcells without additional engineering.