Tissue Resident CD8+T-cells as mediators of protective immunity in breastmilk transmission of HCMV

While the role of breastmilk antibodies to protect infants from CMV has been investigated, the role of T-cells, have received little attention. We compared the frequency of memory T-cell populations in breastmilk between mothers of infants who acquired breastmilk HCMV (transmitters) and those with uninfected infants (non-transmitters). Non-transmitter moms had an increased frequency of CD8+ effector memory T-cells (Tem) in their breastmilk. In addition, we describe tissue resident memory T-cells (Trm) in breastmilk and demonstrate most were Tem. We present data that non-transmitter moms have increased frequency of CD8+ Trm T-cells in their breastmilk when compared to transmitters and that Trm frequency is inversely correlated with breastmilk HCMV VL. Lastly, using scRNA-seq analysis we identified a unique population of T-cells in non-transmitters and demonstrate that these cells comprise CD8+ Trm T-cells. These studies suggest that CD8+ Trm T-cells may play a role in preventing viral transmission via breastmilk to infants.