RIG-I Stimulation Enhances the Effector Function and Proliferation of Primary Human CD8+ T Cells.

Cytotoxic CD8 T lymphocytes are crucial in antiviral immune responses. However, their recruitment to infection sites renders them at risk of viral infection, which could affect their effector activity. CD8 T lymphocytes express RIG-I, which detects cytosolic viral RNA and subsequently induces antiviral gene expression. We investigated how Influenza A virus infection and synthetic triphosphorylated double-stranded RNA, a specific RIG-I ligand, influence TCR-dependent effector responses in primary human CD8 T cells. Cells were isolated from healthy donors and either infected with the reassortant virus RG-PR8-Brazil78 (H1N1) or transfected with the synthetic RNA. Proliferation, degranulation, and cytokine production upon anti-CD3/CD28 stimulation were assessed using flow cytometry and intracellular cytokine staining. Type I IFN production and downstream signaling were measured using IFN-I reporter assay and Western blotting. CRISPR/Cas9 gene editing was employed to knock out RIG-I and STAT2 to evaluate their roles in antiviral responses. Influenza A virus infection of CD8 T cells stimulated RIG-I and activated downstream pathways, including TBK1 and NF-κB, resulting in type-I interferon secretion. Transfection of cytotoxic CD8 T lymphocytes with synthetic RIG-I ligands not only stimulated these pathways but also enhanced the proliferation of CD8 T cells in vitro and protected them from influenza A virus infection. In line with a positive effect on CD8 effector function, both influenza A virus infection and RIG-I ligand transfection enhanced CD8 T cell degranulation and cytokine secretion. Conversely, activation of CD8 T lymphocytes via CD3/CD28 crosslinking increased their susceptibility to influenza A virus infection. We demonstrated that RIG-I stimulation by virus infection or RIG-I ligand transfection promotes intrinsic antiviral pathways and enhances CD8 T-cell effector functions and proliferation. This suggests that RIG-I agonists could enhance and prolong the effector function of cytotoxic CD8 T lymphocytes in immunotherapy.