B7-H1 Influences the Accumulation of Virus-Specific Tissue Resident Memory T Cells in the Central Nervous System.

Therapies that target the PD-1/B7-H1 axis have revolutionized cancer treatment, yet precise knowledge of how this pathway provides benefit continues to evolve. Here, we report a novel role for the immune checkpoint ligand B7-H1 in the accumulation of tissue-resident memory CD8 ⁺ T-cells (T _RM ). After intracranial infection, Theiler's murine encephalomyelitis virus (TMEV) generates T _RM that are maintained in the central nervous system (CNS) tissues of B7-H1 ^WT animals. Although no differences in acute T-cell responses between B7-H1 ^WT and B7-H1 ^KO are observed, at long-term periods post-infection the maintenance of CD8 ⁺ T _RM is diminished in B7-H1 ^KO animals. This is accompanied by redistribution of the resident CD8 ⁺ population from primarily CD103 ⁺ T _RM to a diminished population of T _RM and a preponderance of non-specified PD-1 ⁺ CD103 ^- CD8 ⁺ T-cells. T-cell transfer studies demonstrate that host B7-H1 is necessary for maintaining T _RM and limiting accumulation of PD-1 ⁺ CD103 ^- CD8 ⁺ T-cells. The lack of host B7-H1 results in compromised control of a heterologous virus re-challenge demonstrating a functional defect in T _RM mediated virus control. This study reveals a new role for B7-H1 in T _RM and pro-inflammatory PD-1 ⁺ CD103 ^- CD8 ⁺ T-cell accumulation in the CNS and gives insight for using B7-H1/PD-1 blockade in modulating long-term T-cell protection.