Differential Inhibitory Receptor Expression on T Cells Delineates Functional Capacities in Chronic Viral Infection

Abstract

Inhibitory receptors have been extensively described for their importance in regulating immune responses in chronic infections and cancers. Blocking the function of inhibitory receptors such as PD-1, CTLA-4, 2B4, Tim-3, and LAG-3 has shown promise for augmenting CD8 T cell activity and boosting pathogen-specific immunity. However, the prevalence of inhibitory receptors on CD4 T cells and their relative influence on CD4 T cell functionality in chronic HIV infection remains poorly described. We therefore determined and compared inhibitory receptor expression patterns of 2B4, CTLA-4, LAG-3, PD-1, and Tim-3 on virus-specific CD4 and CD8 T cells in relation to their functional T cell profile. In chronic HIV infection, inhibitory receptor distribution differed markedly between cytokine-producing T cell subsets with, gamma interferon (IFN-γ)- and tumor necrosis factor alpha (TNF-α)-producing cells displaying the highest and lowest prevalence of inhibitory receptors, respectively. Blockade of inhibitory receptors differentially affected cytokine production by cells in response to staphylococcal enterotoxin B stimulation. CTLA-4 blockade increased IFN-γ and CD40L production, while PD-1 blockade strongly augmented IFN-γ, interleukin-2 (IL-2), and TNF-α production. In a Friend retrovirus infection model, CTLA-4 blockade in particular was able to improve control of viral replication. Together, these results show that inhibitory receptor distribution on HIV-specific CD4 T cells varies markedly with respect to the functional subset of CD4 T cells being analyzed. Furthermore, the differential effects of receptor blockade suggest novel methods of immune response modulation, which could be important in the context of HIV vaccination or therapeutic strategies.IMPORTANCE Inhibitory receptors are important for limiting damage by the immune system during acute infections. In chronic infections, however, their expression limits immune system responsiveness. Studies have shown that blocking inhibitory receptors augments CD8 T cell functionality in HIV infection, but their influence on CD4 T cells remains unclear. We assessed the expression of inhibitory receptors on HIV-specific CD4 T cells and their relationship with T cell functionality. We uncovered differences in inhibitory receptor expression depending on the CD4 T cell function. We also found differences in functionality of CD4 T cells following blocking of different inhibitory receptors, and we confirmed our results in a Friend virus retroviral model of infection in mice. Our results show that inhibitory receptor expression on CD4 T cells is linked to CD4 T cell functionality and could be sculpted by blockade of specific inhibitory receptors. These data reveal exciting possibilities for the development of novel treatments and immunotherapeutics.

Keywords: CD4 T cells; CTLA-4; HIV; PD-1; inhibitory receptors.