Anti-CD117 CAR T cells incorporating a safety switch eradicate human acute myeloid leukemia and hematopoietic stem cells

Abstract

Discrimination between hematopoietic stem cells and leukemic stem cells remains a major challenge for acute myeloid leukemia immunotherapy. CAR Tcells specific for the CD117 antigen can deplete malignant and healthy hematopoietic stem cells before consolidation with allogeneic hematopoietic stem cell transplantation in absence of cytotoxic conditioning. Here we exploit non-viral technology to achieve early termination of CAR Tcell activity to prevent incoming graft rejection. Transient expression of an anti-CD117 CAR by mRNA conferred Tcells the ability to eliminate CD117+ targets invitro and invivo. As an alternative approach, we used a Sleeping Beauty transposon vector for the generation of CAR Tcells incorporating an inducible Caspase 9 safety switch. Stable CAR expression was associated with high proportion of T memory stem cells, low levels of exhaustion markers, and potent cellular cytotoxicity. Anti-CD117 CAR Tcells mediated depletion of leukemic cells and healthy hematopoietic stem cells in NSG mice reconstituted with human leukemia or CD34+ cord blood cells, respectively, and could be terminated invivo. The use of a non-viral technology to control CAR Tcell pharmacokinetic properties is attractive for a first-in-human study in patients with acute myeloid leukemia prior to hematopoietic stem cell transplantation.