CD38-CAR human NK cells in combination with ATRA enhance cytotoxicity against CD38-expressing hematologic malignancies.

CD38 is a metabolically active enzyme broadly expressed on the surface of normal and malignant hematologic cells. It has been targeted clinically with anti-CD38 monoclonal antibodies (mAbs), for which efficacy may be limited by natural killer (NK)-cell fratricide. Isatuximab is an anti-CD38 mAb that uniquely inhibits CD38 metabolic activity. Here, we used CRISPR/adeno-associated virus (AAV) to generate fratricide-resistant and metabolically-enhanced CD38KO/CD38-chimeric antigen receptor (CAR) NK cells using 2 isatuximab-based CD38 single-chain variable fragments (scFvs; reversing heavy and light chain orientation) on the same CD8α/4-1BB/CD3ζ base, and we demonstrate their activity against a range of CD38+ hematologic malignancies (acute myeloid leukemia, multiple myeloma, Burkitt lymphoma, and T-cell leukemia/lymphoma). The cytotoxicity of the CAR NK cells was enhanced by upregulating CD38 expression on the malignant targets with all-trans retinoic acid (ATRA). By generating CD38KO/CD38-CAR T cells using the same engineering approach, we show that the CAR NK cells had higher cytotoxicity than CAR T cells against all hematologic tumor targets. Additionally, AAVS1KO/CD38-CAR NK cells were capable of targeting CD38 without experiencing fratricide and have a similar enhanced metabolic activity via the inhibitory activity of the cis-acting isatuximab-based scFv. Finally, we report fratricide-resistant CD38-CAR NK cells with enhanced metabolism and cytotoxicity toward CD38+ hematologic malignancies, further increased by combination treatment with ATRA.