Protein Kinase C-η Deficiency Does Not Impair Antiviral Immunity and CD8+ T Cell Activation

We reported that protein kinase C-η (PKCη) forms a novel (to our knowledge) signaling complex with the checkpoint inhibitory protein CTLA-4 in regulatory T cells (Tregs). This complex is required for the contact-dependent suppressive activity of Tregs, including suppression of antitumor immunity. However, the importance of PKCη in protective immunity mediated by T effector cells remains unclear. We used mice with germline or conditional Treg-specific deletion of Prkch , the PKCη-encoding gene, to explore CD8 + T cell-dependent antiviral immunity using the lymphocytic choriomeningitis virus Armstrong strain acute infection model as well as the in vitro activation of murine or human CD8 + T cells. Five days following infection, germline Prkch -/- mice displayed enhanced viral clearance compared with control mice. Similarly, Prkch Treg-specific conditional knockout mice also showed improved viral clearance and displayed enhanced expression of granzyme B and IFN-γ by both virus-specific and total CD8 + T cells, demonstrating that enhanced viral clearance in germline Prkch -/- mice is caused by PKCη deficiency in Tregs and the resulting functional defect of Prkch -/- Tregs. In addition, purified Prkch -/- mouse CD8 + T cells as well as PRKCH knockdown human CD8 + T cells displayed intact, or even enhanced, T cell activation in vitro as measured by proliferation and expression of granzyme B and IFN-γ. Thus, global PKCη deletion does not impair overall CD8 + T cell-mediated immunity, including antiviral immunity, implying that selective pharmacological PKCη inhibition could be safely used in vivo to inhibit undesired contact-dependent suppression by Tregs and, thus, enhance tumor-specific and, likely, virus-specific immunity.