Preferential expansion of NK cells lacking NKR-P1A (CD161) receptor expression during human cytomegalovirus infection

Natural killer (NK) cells are essential for immunity against human cytomegalovirus (HCMV). NK cell receptors (NKR) play a key role in anti-HCMV responses, and HCMV infection selectively shapes the NKR repertoire. NKR-P1A (CD161) is an inhibitory receptor, whose expression is lost during HCMV infection, but its role in NK cell responses during HCMV infection is not known. We analyzed peripheral blood mononuclear cells (PBMCs) from healthy individuals and hematopoietic stem cell transplant (HSCT) patients with latent and active HCMV infections, respectively, to assess the impact of NKR-P1A on NK cell function. Our findings reveal a significant increase in NKR-P1A‒ NK cells, particularly in clonally expanded NKG2C+ and CD57+ memory NK cells, but not in NKG2C‒ or CD16+ subsets. A larger proportion of NKR-P1A‒ NK cells from HCMV-infected individuals exhibited an activated (granzyme B+) and proliferating (Ki-67+) phenotype compared to NKR-P1A+ NK cells. However, NK cells maintained their ability to activate and proliferate in response to in vitro stimulation regardless of NKR-P1A expression. Additionally, HCMV infection did not impair cytokine-induced NKR-P1A upregulation. Analysis of publicly available single-cell RNA sequencing datasets showed that only NKR-P1A‒ NK cells in HCMV-seropositive individuals exhibited transcriptomic signatures associated with adaptive NK cells that expand during HCMV infection. These findings suggest that lower activation and proliferation of NKR-P1A+ NK cells contribute to the accumulation of NKR-P1A‒ NK cells, highlighting the inhibitory role of NKR-P1A during HCMV infection and further demonstrating how HCMV shapes the NK cell repertoire.