Off-the-Shelf CAR-Engineered Natural Killer Cells Targeting FLT3 Enhance Killing of Acute Myeloid Leukemia.

The majority of patients with acute myeloid leukemia (AML) succumb to their disease or its complications, especially among the elderly. Natural killer (NK) cells have been shown to have anti-leukemic activity in AML patients; however, primary NK cells armed with a chimeric antigen receptor (CAR) targeting antigens associated with AML as an "off-the-shelf" product for disease control have not been explored. We developed frozen, "off-the-shelf" allogeneic human NK cells engineered with a CAR recognizing FLT3 and secreting soluble IL-15 (FLT3 CAR_sIL15 NK) to improve in vivo NK cell persistence and T cell activation. FLT3 CAR_sIL15 NK cells had higher cytotoxicity and IFN- secretion against FLT3+ AML cell lines when compared to activated NK cells lacking a FLT3 CAR or soluble IL-15. Frozen and thawed allogeneic FLT3 CAR_sIL15 NK cells prolonged survival of both the MOLM-13 AML model as well as an orthotopic AML patient-derived xenograft model when compared to control NK cells. FLT3 CAR_sIL15 NK cells showed no cytotoxicity against normal blood mononuclear cells or hematopoietic stem cells. Collectively, our data suggest that FLT3 is an AML-associated antigen that can be targeted by frozen, allogeneic, "off-the-shelf" FLT3 CAR_sIL15 NK cells that may provide a novel approach for the treatment of AML.