Synergistic Reversal of Intrahepatic HCV-Specific CD8 T Cell Exhaustion by Combined PD-1/CTLA-4 Blockade

Abstract

Viral persistence is associated with hierarchical antiviral CD8 T cell exhaustion with increased programmed death-1 (PD-1) expression. In HCV persistence, HCV-specific CD8 T cells from the liver (the site of viral replication) display increased PD-1 expression and a profound functional impairment that is not reversed by PD-1 blockade alone. Here, we report that the inhibitory receptor cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) is preferentially upregulated in PD-1+ T cells from the liver but not blood of chronically HCV-infected patients. PD-1/CTLA-4 co-expression in intrahepatic T cells was associated with a profound HCV-specific effector dysfunction that was synergistically reversed by combined PD-1/CTLA-4 blockade in vitro, but not by blocking PD-1 or CTLA-4 alone. A similar effect was observed in circulating HCV-specific CD8 T cells with increased PD-1/CTLA-4 co-expression during acute hepatitis C. The functional response to combined blockade was directly associated with CTLA-4 expression, lost with CD28-depletion and CD4-independent (including CD4+FoxP3+ Tregs). We conclude that PD-1 and CTLA-4 pathways both contribute to virus-specific T cell exhaustion at the site of viral replication by a redundant mechanism that requires combined PD-1/CTLA-4 blockade to reverse. These findings provide new insights into the mechanisms of virus-specific T cell dysfunction, and suggest that the synergistic effect by combined inhibitory receptor blockade might have a therapeutic application against chronic viral infection in vivo, provided that it does not induce autoimmunity.

Is autoimmunity the Achilles' heel of cancer immunotherapy?

“…Moreover, PD-1 blockade seems to reactivate effector T cells through the targeting of certain transcriptional factors (i.e., nuclear factor kappa-light-chainenhancer of activated B cells, interferon regulatory factors 1 and 2, orphan nuclear receptor NR4A1, and B-lymphocyte-induced maturation protein 1) that cause a reengagement of the effector mechanisms in the epigenome of exhausted T cells 59 . CTLA-4 has also been found to have a clear role in multiple chronic infections, including HBV, HCV, and HIV, and its inhibition can increase the function of pathogen-specific T cells 60,61 . Epigenetic and transcriptional mechanisms determine the functional plasticity of T cells to switch between their exhausted and effector states 62 , and so altering the transcriptional landscape-for example, by manipulating transcription-factor and gene-enhancer expression-and epigenetic landscape-for example, by manipulating the activity of histone-modifying methylation or demethylation enzymes, histone acetylases, and DNA demethylases-of adoptively transferred T cells may yield a more specific anti-tumor response than generalized PD-1 and CTLA-4 blockade.…”

Premature Terminal Exhaustion of Friend Virus-Specific Effector CD8+ T Cells by Rapid Induction of Multiple Inhibitory Receptors

“…PD-1 has been identified as a major cell-surface inhibitory receptor capable of regulating CD8 + and CD4 + T cell exhaustion in mice, as well as in humans and nonhuman primates (50). Tim-3 and CTLA-4 were recently found to be overexpressed on HIV-and hepatitis C virus-specific CD8 + and CD4 + T cells and to act to suppress effector functions of activated T cells (11)(12)(13)51). Upregulation of LAG-3 was also shown to correlate with the impaired effector functions and exhaustion of CD8 + T cells (10,52,53).…”

“…In addition to these inhibitory receptors, it was demonstrated that a variety of other inhibitory receptors were expressed on exhausted CD8 + T cells in chronic virus infections, and the increased levels of expression were critically associated with the severity of infection and the lower functionality of CD8 + T cells (10). Although the precise inhibitory mechanisms of each individual pathway are unclear, some inhibitory receptors, such as Tim-3, LAG-3, and CTLA4, are known to negatively regulate CD8 + T cell function cooperatively with PD-1, because combined blockade of these inhibitory receptors, along with the PD-1/PD-L1 pathway, synergistically improved CD8 + T cell responses (10)(11)(12)(13). Based on the present observations, Ag-specific effector CD8 + T cells in FV-infected mice seemed to be undergoing unusually rapid and extremely severe exhaustion.…”

“…A recent study using the lymphocytic choriomeningitis virus (LCMV) provided a likely explanation for the relatively limited effect of the PD-1 blockade: exhausted CD8 + T cells are coregulated by multiple inhibitory receptors during chronic infection (10). Thus, targeting the precise inhibitory receptors for blockade (10)(11)(12)(13), the timing and duration of treatment, and combination with additional therapeutic vaccination and/or antiviral drugs (14) must be considered to establish the optimal therapeutic strategy that can improve/restore the function of virus-specific CD8 + T cells without enhancing immunopathology.…”

T cell differentiation in chronic infection and cancer: functional adaptation or exhaustion?

“…The strongest evidence that exhausted cells retain the ability to mount a potent effector response comes from the many studies in which strong anti-tumor or anti-viral immunity could be restored by blocking PD-1/PD-L1 interaction alone or in combination with targeting other receptors [46][47][48][49][50][51][52] . This approach of antibody-mediated "checkpoint blockade" is now increasingly used to treat patients with cancer and its impact on chronic infections in humans is being evaluated (Box 1).…”