HCMV peptide (LFL) presentation drives KIR+NKG2C+ NK cell accumulation and HLA-E+ tumor elimination in vitro

Natural Killer (NK) cells expressing both NKG2C and inhibitory KIRs are promising candidates for targeting HLA-E+ tumors, which often evade conventional T-cell recognition by downregulating other HLA class I molecules. However, efficiently generating and expanding these specific NK cell subsets for therapeutic application remains a challenge. Understanding the mechanisms of their accumulation—whether through expansion or de novo expression of markers—and how these mechanisms relate to an individual's ex vivo NK cell phenotype is crucial for optimizing NK cell-based immunotherapies.

Researchers characterized the ex vivo NK cell phenotype in healthy individuals, focusing on markers like NKG2C, KIR2DL2/3, HLA-DR, and CD57. They then cultured these NK cells in vitro, with or without presentation of the HCMV peptide (LFL), which is known to bind HLA-E. The study analyzed NKG2C and KIR expression de novo, as well as the expansion rates of KIR+NKG2C+ NK cell subsets (both CD57- and CD57+ fractions). Finally, LFL-activated NK cell cultures were tested for their ability to eliminate HLA-E+ tumor spheroids.

The study observed that NKG2C expression de novo was most pronounced in KIR+ NK cells, and this was associated with a higher HLA-DR+ proportion in the ex vivo phenotype. Enhanced LFL-dependent KIR+NKG2C+ cell expansion within the CD57- fraction correlated with a high content of adaptive NK cells ex vivo. Conversely, the CD57+KIR+NKG2C+ expansion rate showed a correlation with a high level of NKG2A ex vivo. These findings suggest distinct mechanisms of KIR+NKG2C+ NK cell accumulation linked to the donor's baseline NK cell profile. Importantly,

LFL-activated NK cell cultures demonstrated more effective elimination of HLA-E+ tumor spheroids compared to control cultures, highlighting their enhanced cytotoxic potential.