Changes in gastrointestinal microbial communities influence HIV-specific CD8+ T-cell responsiveness to immune checkpoint blockade

OBJECTIVES: The aim of this study was to examine the relationship between gut microbial communities in HIV-infected individuals on suppressive antiretroviral therapy (cART), and the peripheral HIV-Gag-specific CD8 T-cell responses before and after ex-vivo immune checkpoint blockade (ICB). DESIGN: Thirty-four HIV-seropositive, 10 HIV-seronegative and 12 HIV-seropositive receiving faecal microbiota transplant (FMT) participants were included. Gut microbial communities, peripheral and gut associated negative checkpoint receptors (NCRs) and peripheral effector functions were assessed. METHODS: Bacterial 16s rRNA sequencing for gut microbiome study and flow-based assays for peripheral and gut NCR and their cognate ligand expression, including peripheral HIV-Gag-specific CD8 T-cell responses before and after ex-vivo anti-PD-L1 and anti-TIGIT ICB were performed. RESULTS: Fusobacteria abundance was significantly higher in HIV-infected donors compared to uninfected controls. In HIV-infected participants receiving Fusobacteria-free FMT, Fusobacteria persisted up to 24 weeks in stool post FMT. PD-1 TIGIT and their ligands were expanded in mucosal vs. peripheral T cells and dendritic cells, respectively. PD-L1 and TIGIT blockade significantly increased the magnitude of peripheral anti-HIV-Gag-specific CD8 T-cell responses. Higher gut Fusobacteria abundance was associated with lower magnitude of peripheral IFN-γ+ HIV-Gag-specific CD8 T-cell responses following ICB. CONCLUSION: The gut colonization of Fusobacteria in HIV infection is persistent and may influence anti-HIV T-cell immunity to PD-1 or TIGIT blockade. Strategies modulating Fusobacteria colonization may elicit a favourable mucosal immune landscape to enhance the efficacy of ICB for HIV cure.