Resident memory T cells (TRM cells) are an important first-line defense against respiratory pathogens, but the unique contributions of lung TRM cell populations to protective immunity and the factors that govern their localization to different compartments of the lung are not well understood. Here, we show that airway and interstitial TRM cells have distinct effector functions and that CXCR6 controls the partitioning of TRM cells within the lung by recruiting CD8 TRM cells to the airways. The absence of CXCR6 significantly decreases airway CD8 TRM cells due to altered trafficking of CXCR6−/− cells within the lung, and not decreased survival in the airways. CXCL16, the ligand for CXCR6, is localized primarily at the respiratory epithelium, and mice lacking CXCL16 also had decreased CD8 TRM cells in the airways. Finally, blocking CXCL16 inhibited the steady-state maintenance of airway TRM cells. Thus, the CXCR6/CXCL16 signaling axis controls the localization of TRM cells to different compartments of the lung and maintains airway TRM cells.

Infection with HIV persists despite suppressive antiretroviral therapy (ART) and treatment interruption results in rapid viral rebound. Antibody-mediated CD8+ lymphocyte depletion in simian immunodeficiency virus (SIV)-infected rhesus macaques (RMs) shows these cells contribute to virus control in untreated animals. However, the contribution of CD8+ lymphocytes to maintaining virus suppression under ART remains unknown. We showed that in SIV-infected RMs treated with short-term ART (i.e., 8-32 weeks), depletion of CD8+ lymphocytes resulted in increased plasma viremia in all animals, and that repopulation of CD8+ T cells was associated with prompt reestablishment of virus control. Although the number of SIV-DNA-positive cells remained unchanged after CD8 depletion and reconstitution, the frequency of SIV-infected CD4+ T cells pre-depletion positively correlated with both peak and area-under-the-curve of viremia post-depletion. These results suggest a role for CD8+ T cells in controlling virus production during ART, thus providing rationale to explore immunotherapeutic approaches in ART-treated HIV-infected individuals.

Resident memory CD8 T (TRM) cells in the lung parenchyma (LP) and airways provide heterologous protection against influenza virus challenge. However, scant knowledge exists regarding factors necessary to establish and maintain lung CD8 TRM. Here we demonstrate that, in contrast to mechanisms described for other tissues, airway and LP CD8 TRM establishment requires cognate antigen recognition in the lung. Systemic effector CD8 T cells could be transiently pulled into the lung in response to localized inflammation, however these effector cells failed to establish tissue residency unless antigen was present in the pulmonary environment. The interaction of effector CD8 T cells with cognate antigen in the lung resulted in increased and prolonged expression of the tissue retention markers CD69 and CD103, and increased expression of the adhesion molecule VLA-1. The inability of localized inflammation alone to establish lung TRM resulted in decreased viral clearance and increased mortality following heterosubtypic influenza challenge, despite equal numbers of circulating memory CD8 T cells. These findings demonstrate that pulmonary antigen encounter is required for the establishment of lung CD8 TRM and may inform future vaccine strategies to generate robust cellular immunity against respiratory pathogens.

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