Selective homing of CAR-CIK cells to the bone marrow niche enhances control of the Acute Myeloid Leukemia burden

: Acute myeloid leukemia (AML) is a hematological malignancy derived from neoplastic myeloid progenitor cells characterized by abnormal clonal proliferation and differentiation. Although novel therapeutic strategies have recently been introduced, the prognosis of AML remains unsatisfactory. So far, the efficacy of chimeric antigen receptor (CAR)-T therapy in AML has been hampered by several factors including the poor accumulation of the blood-injected cells in the leukemia bone marrow (BM) niche, where chemotherapy-resistant leukemic stem cells reside. Thus, we hypothesized that overexpression of CXCR4, whose ligand CXCL12 is highly expressed by BM stromal cells within the niche, could improve T cell homing to the BM and consequently enhance their intimate contact with BM-resident AML cells facilitating disease eradication. Specifically, we engineered conventional CD33.CAR-cytokine induced killer cells (CIKs) with the wild-type CXCR4 and the variant CXCR4R334X, responsible for leukocyte sequestration in the BM of WHIM syndrome patients. Overexpression of both CXCR4wt and CXCR4mut in CD33.CAR-CIKs resulted in significant improvement of chemotaxis toward recombinant CXCL12 or BM stromal cell conditioned medium with no observed impairment of cytotoxic potential in vitro. Moreover, CXCR4-overexpressing CD33.CAR-CIKs showed enhanced in vivo BM homing, associated with a prolonged retention for the CXCR4R334X variant. However, only CD33.CAR-CIKs co-expressing CXCR4wt but not CXCR4mut exerted a more sustained in vivo antileukemic activity and extended animal survival, suggesting a non-canonical role for CXCR4 in modulating CAR-CIK functions independent of BM homing. Taken together, these data suggest that arming CAR-CIKs with CXCR4 may represent a promising strategy for increasing their therapeutic potential for AML.