Reactive glia promote development of CD103⁺ CD69⁺ CD8⁺ T-cells through programmed cell death-ligand 1 (PD-L1)

Previous work from our laboratory has demonstrated in vivo persistence of CD103⁺ CD69⁺ brain resident memory CD8⁺ T-cells (bT_RM ) following viral infection, and that the PD-1: PD-L1 pathway promotes development of these T_RM cells within the brain. Although glial cells express low basal levels of PD-L1, its expression is upregulated upon IFN-γ-treatment, and they have been shown to modulate antiviral T-cell effector responses through the PD-1: PD-L1 pathway.

We performed flow cytometric analysis of cells from co-cultures of mixed glia and CD8⁺ T-cells obtained from wild type mice to investigate the role of glial cells in the development of bT_RM .

In this study, we show that interactions between reactive glia and anti-CD3 Ab-stimulated CD8⁺ T-cells promote development of CD103⁺ CD69⁺ CD8⁺ T-cells through engagement of the PD-1: PD-L1 pathway. These studies used co-cultures of primary murine glial cells obtained from WT animals along with CD8⁺ T-cells obtained from either WT or PD-1 KO mice. We found that αCD3 Ab-stimulated CD8⁺ T-cells from WT animals increased expression of CD103 and CD69 when co-cultured with primary murine glial cells. In contrast, significantly reduced expression of CD103 and CD69 was observed using CD8⁺ T-cells from PD-1 KO mice. We also observed that reactive glia promoted high levels of CD127, a marker of memory precursor effector cells (MPEC), on CD69⁺ CD8⁺ T-cells, which promotes development of T_RM cells. Interestingly, results obtained using T-cells from PD-1 KO animals showed significantly reduced expression of CD127 on CD69⁺ CD8⁺ cells. Additionally, blocking of glial PD-L1 resulted in decreased expression of CD103, along with reduced CD127 on CD69⁺ CD8⁺ T-cells.

Taken together, these results demonstrate a role for activated glia in promoting development of bT_RM through the PD-1: PD-L1 pathway.