284: Maturation of cord blood natural killer (NK) cells differs among neonates

Abstract

The source, timing of colonization, and stability of the neonatal microbiome is largely unknown, and it remains unclear how microbes influence early immunity. We and others have recently shown that infant colonization may begin in utero, challenging the notion that neonates are born sterile. However, some neonates are particularly vulnerable to viral infection, which is thought to be due to dampened responses from NK cells and delayed maturation of adaptive immunity. Given the degree of variability in neonatal vulnerability to infection, we hypothesized that intrauterine exposure to microbes in the more common non-sterile environment actually enables a greater diversity of NK cells in the neonates relative to the adult to allow for immune tolerance. Here, we performed the largest multi-parametric flow cytometry analyses to dissect the normal range and expression of human NK cell developmental markers from umbilical cord (UC) blood. UC blood was collected at delivery in a large number of neonates (n=35). Whole blood was stained with NK cell maturation markers and data was acquired by flow cytometry. Data was analyzed using FlowJo X and Cytobank. Spanning analysis density of events (SPADE) analysis was applied to identify NK cell developmental subsets by individual. Diversity between neonates and adults was calculated using Simpson’s Diversity Index. NK cells were identified in UC blood as CD3−CD45+CD56+. UC blood had a lower frequency of mature NK cells than adult peripheral blood (Fig. A) Furthermore, examination of NK cell maturation via SPADE analysis identified highlighted inter-individual diversity of neonatal NK cell subsets (Fig. B). Diversity of NK cells subsets between neonates and adults was significantly different with higher diversity in neonates (Fig. C, p = 0.008). Our findings suggest diversity in stages of NK cell development between individual neonates that may reflect early immune exposure and harken viral susceptibility. Given ours and others recent work demonstrates that the intrauterine environment is not sterile, we speculate that microbial exposures during gestation may be a driving difference in the diversification NK cell populations in human infants and hence enable immune tolerance at the risk of neonatal viral vulnerability.