NK cells maintain licensing status and are subject to KIR/KIR-ligand inhibition following ex vivo expansion

Infusion of allogeneic NK cells is a potential immunotherapy for both hematopoietic malignancies and solid tumors. Interactions between killer immunoglobulin-like receptors (KIR) on human NK cells and KIR-ligands on tumor cells influence the magnitude of NK function. To obtain sufficient numbers of NK cells for infusion, several approaches have been tested. One potent method uses cells from the K562 human erythroleukemia line that have been transfected to express activating 41BB ligand (41BBL) and membrane-bound interleukin15 (mbIL15); co-culture with these cells stimulates NK cell expansion and activation . The functional importance of KIRs on ex vivo expanded NK cells has not been studied in detail. We investigated how KIR/KIR-ligand interactions between expanded NK cells and target cells affect the function of expanded NK cells. After a 12-day co-culture with K562-mbIL15-41BBL cells, expanded NK cells maintained inhibition specificity and prior in vivo licensing status determined by KIR/KIR-ligand interactions. Addition of an anti-CD20 antibody (rituximab) induced NK-mediated antibody dependent cellular cytotoxicity (ADCC) and augmented killing of CD20+ target cells. However, partial inhibition induced by KIR/KIR-ligand interactions persisted. Finally, we found that extended co-cultures of NK cells with stimulatory cells transduced to express various KIR-ligand modified both the inhibitory and activating KIR repertoires of the expanded NK cell product. These studies demonstrate that the licensing interactions known to occur during NK ontogeny also influence NK cell function following NK expansion ex vivo. These findings can help donor selection and guide expansion of specific NK cell subsets for adoptive therapy of cancer.