Background:  CD160 is a glycosylphosphatidylinositol (GPI) -anchored protein member of the Ig-superfamily and expressed on cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. Engagement of CD160 on activated CD4 cells provides negative signals to CD4 lymphocytes and inhibits proliferation. The interplay between co-stimulators (CD28, LIGHT) and attenuators (BTLA, PD-1) ultimately determines the downstream functions of responding lymphocytes. Therefore our study aims to characterize the expression levels of CD160 on HIV and cytomegalovirus (CMV) tetramer-specific cells during different stages of HIV disease and relate its expression to markers of T cell exhaustion such as PD1

Methods:  We analyzed the relative expression of PD1 and CD160 on HIV- and CMV-specific cells from 45 HIV-infected individuals and 8 seronegative controls. We subdivided the population into 5 groups:  acute infection (n = 12; infected for <6 months), chronic infection (n = 9; infected for >6 months), successfully treated (n = 12; undetectable viremia under HAART), and elite controllers (EC; n = 12; undetectable viremia without treatment). Multiparametric flow cytometry was used to analyze the memory phenotype (CM, TM, EM, naïve, and Temra cells) and expression levels of CD160 and PD1 on tetramer-positive cells and on total CD8 and CD4 T cells.

Results:  Our results show that the frequency of CD8 T cells expressing CD160 is higher in HIV infection (33.7%) than in seronegative controls (24.3%). Interestingly, we found 3 phenotypically distinct populations of HIV-specific CD8 lymphocytes. EC expressed significantly higher frequencies of PD1^–CD160⁺ T cells (21.0%) than acute (14.9%), chronic (14.5%), and successfully treated (12.7%) patients (p <0.05). However, CD8⁺PD1⁺CD160^– lymphocytes were found at higher frequencies in acutely infected individuals. Similarly, the frequency of PD1^–CD160⁺-expressing HIV-specific tetramer cells from EC (25.4%) was significantly higher than from acute (7.1%), chronic (10.2%), and successfully treated (12.3%) individuals (p <0.05, t test). We found an inverse correlation between the expression of CD160 and PD1 on HIV-specific tetramers (r = –0.26, p = 0.02) and the frequency of PD1⁺CD160^–-expressing T cells positively correlated with viral load, whereas PD1^–CD160⁺ CD8 T cells inversely correlated with viral load (p <0.05, Spearman rank).

Conclusions:  Taken together, our results show that CD160 is preferentially expressed on HIV-specific cells isolated from individuals who spontaneously control viremia and, unlike PD1, seems to be a marker of effective T cell responses