Cytokine-Induced Memory-Like Differentiation Enhances Unlicensed Natural Killer Cell Antileukemia and FcγRIIIa-Triggered Responses

Cytokine-induced memory-like natural killer (NK) cells differentiate after short-term preactivation with IL-12, IL-15, and IL-18 and display enhanced effector function in response to cytokines or tumor targets for weeks after the initial preactivation. Conventional NK cell function depends on a licensing signal, classically delivered by an inhibitory receptor engaging its cognate MHC class I ligand. How licensing status integrates with cytokine-induced memory-like NK cell responses is unknown. We investigated this interaction using killer cell immunoglobulin-like receptor– and HLA-genotyped primary human NK cells. Memory-like differentiation resulted in enhanced IFN-γ production triggered by leukemia targets or FcγRIIIa ligation within licensed NK cells, which exhibited the highest functionality of the NK cell subsets interrogated. IFN-γ production by unlicensed memory-like NK cells was also enhanced to a level comparable with that of licensed control NK cells. Mechanistically, differences in responses to FcγRIIIa-based triggering were not explained by alterations in key signaling intermediates, indicating that the underlying biology of memory-like NK cells is distinct from that of adaptive NK cells in human cytomegalovirus–positive individuals. Additionally, memory-like NK cells responded robustly to cytokine receptor restimulation with no impact of licensing status. These results demonstrate that both licensed and unlicensed memory-like NK cell populations have enhanced functionality, which may be translated to improve leukemia immunotherapy.