Primate resident memory T cells activate humoral and stromal immunity.

CD8+ resident memory T (Trm) cells comprise a small population of frontline sentinels compared with the large tissues they surveil, making outsized contributions to immune protection from infection. Here, we interrogated mechanisms of Trm cell function in primates. Intravenous immunization of macaques with a simian immunodeficiency virus (SIV)-gag-containing heterologous prime-boost-boost vaccine established memory T cells in >30 tissues, including visceral and mucosal compartments. Upon in vivo reactivation in the reproductive tract, antigen-sensing CD8+ Trm activated local stromal, parenchymal, and innate and adaptive immune cells. Stromal and parenchymal cells accentuated leukocyte migration and antiviral defenses. B and plasma cells mobilized into the vaginal mucosa, and bloodborne CD4+ T cells were recruited and adopted a host-defense program. Our findings demonstrate that systemic vaccination promotes a Trm cell response in barrier compartments and that Trm cells repurpose abundant neighboring stromal, parenchymal, and immune cells to amplify alarm signals and activate diverse host defenses.