Tri-Functional T-Cell Engagers Target Immune Checkpoint Inhibitors Pd-1 And Tigit To Enhance Cd8 Effector T-Cell Functions In Chronically Shiv-Infected Rhesus Macaques

Abstract Checkpoint inhibitors, such as PD-1 and TIGIT, are crucial dysregulators of CD8 T cell function during chronic HIV/SIV infections. Importantly, these checkpoint inhibitors are highly expressed on the surface of CD4 T cells that harbor latent HIV. We have previously demonstrated that an anti-HIV/anti-CD3 bispecific T-cell engager (BiTE) can be used to redirect follicular CD8 (fCD8) T cells to kill HIV infected cells in vitro. Here, we hypothesize that adding an extra specificity to target PD-1 or TIGIT to the BiTE will further enhance the functional activities of CD8 T cells and simultaneously lower the threshold for reactivation of HIV latently infected cells. By using HIV-infected cell lines and primary CD4 T cells isolated from chronically SHIV-infected lymph nodes (LN) as target cells in in vitro and ex vivo killing assays, we found that trifunctional anti-HIV/anti-CD3-anti-TIGIT or anti-HIV/anti-CD3-anti-PD1 increased (1) T-cell specific activation, (2) antigen-specific CD107a degranulation, levels of granzyme B, cytokine/chemokine release by CD8 T cells, and (3) the killing capability of functionally compromised CD8 T cells when compared to the BiTE. When administered at 100 mcg/kg subcutaneously to chronically SHIV-infected animals, we demonstrated that anti-HIV/anti-CD3-anti-TIGIT could safely be used to augment activation and expansion of CD8 effector T cells that further resulted in a better elimination of the SHIV-infected cells as shown by the reduction in cell-associated SHIV gag DNA and RNA. Together, our results indicate that trifunctional T cell engagers targeting checkpoint inhibitors may serve as novel immunotherapeutic strategies to eliminate infected cells in HIV infected individuals.