HIV-exposed uninfected (HEU) children are at increased risk of morbidity during the first years of life. Although the immune responses of HEU infants in early-life are relatively well described, studies of natural killer (NK) cells in older HEU children are lacking. NK cell subsets were analysed in HEU children and compared to those in HIV unexposed uninfected (HUU) children aged ~ five years.

The proportions of total NK cell, CD56bright and CD56dim NK cells, NK cells inhibitory and differentiation surface marker expression and cytolytic granule-positive cells were similar between HEU and HUU children. These data suggest that early-life HIV/ART exposure may not result in major changes in NK cell subsets at 5 years of age.

Multi-parametric flow cytometry was used to characterize peripheral blood-derived NK cell CD56, CD16, CD57, NKG2A and KIR3DL1/KIR2DL2/L3 expression, including intracellular perforin and granzyme B. NK cell subsets were compared between HEU children exposed to prenatal antiretroviral therapy (ART) from conception [long-term (HEULT)]; those exposed to ART during pregnancy [medium-term (HEUMT)] with continued exposure throughout the breastfeeding period and HUU peers. Furthermore, clinical data of the children, including sick clinic visits and hospitalizations documented in morbidity diaries from birth to 5 years were compared between HEU and HUU groups. Frequencies of CD56bright and CD56dim NK cell were correlated with these clinical parameters.

139 children were enrolled however, 133 comprising 43 HEULT, 38 HEUMT and 52 HUU were included in the main analyses. Total NK cell, CD56bright nor CD56dim NK cell proportions differed between HEU and HUU children. However, HEULT children had lower frequencies of CD56dim NK cells compared to HEUMT children, (p = 0.002) which maintained significance after controlling for preterm birth, p = 0.012. No differences were observed between HEULT and HUU. The expressions of NKG2A, KIR3DL1/KIR2DL2/L3 and CD57 on CD56bright and CD56dim NK cells were similar between the three groups. Furthermore, the frequencies of granzyme B and perforin double positive NK cells were similar between the HUU with HEULT and HEUMT children. CD56dim NK cell counts had a significant moderate negative correlation with recurrent respiratory infections (rho=-0.38; p = 0.010) in HUU children and negatively correlated with total sick clinic visits in HEUMT (rho=-0.40, p = 0.064).