CD137 signaling mediates the enhancement of antiviral activity of V[gamma]9V[delta]2-T cells against influenza virus

Abstract

Influenza virus continues leading to a seasonal, pandemic, or zoonotic transmission and affects millions of people worldwide every year with high morbidity and mortality. The efficacy of current therapeutic strategies is restricted to the high mutation rates of the viral genome and the concomitant emergence of drug-resistance strains. In our previous studies, we have proved that pamidronate (PAM)-expanded human Vγ9Vδ2-T cells can control the infection of influenza A virus (IAV), which suggests a novel therapeutic strategy for treating influenza by targeting γδ-T cells rather than viruses themselves. CD137 is an inducible costimulatory molecule and necessary for functional CD8+ T cells. Our preliminary study showed that the cytotoxicity of Vγ9Vδ2-T cells to H7N9 virus-infected monocyte-derived macrophages (MDMs) was impaired significantly after neutralizing with anti-CD137 antagonist antibody. Although one study reported that CD137 costimulation could facilitate the proliferation of human γδ-T cells and enhance their effector function during Listeria monocytogenes infection, our understanding about whether and how the CD137 signaling is involved in γδ-T cells’ anti-influenza activity remains obscure. The objectives of my research are to investigate the function of CD137 signaling in human γδ-T cells and confirm the possibility of improving γδ-T cell-based anti-influenza immunotherapy by targeting CD137.

Firstly, I investigated the mechanisms for the involvement of CD137 signaling in the anti-IAV activity of human Vγ9Vδ2-T cells by in vitro experiments. Using IAV-infected autologous MDMs as the target cells, we demonstrated human Vγ9Vδ2-T cells, as the effector cells, could acquire CD137 costimulation from these target cells. After being blocked by anti-CD137 antagonist antibodies, γδ-T cells exhibited impaired cytotoxicity with the reduced production of INF-γ, Granzyme B, and Perforin. The phenotypes of activated Vγ9Vδ2-T cells indicated that CD137+ γδ-T cell subset was in a superior activation status with a higher expression of CD107a, Fas, FasL, TRAIL, NKG2D, Perforin, and Granzyme B versus CD137- subset, which was consistent with the result that CD137+ γδ-T cells exhibited a higher cytotoxicity to virus-infected MDMs. By generating SA-hCD137L recombinant protein and studying its direct role on human Vγ9Vδ2-T cells, I confirmed that signaling through CD137 could enhance the cytolytic effect of human Vγ9Vδ2-T cells, promote their activation and proliferation, as well as prevent the activation-induced cell death.

Secondly, we explored whether signaling through CD137 could be utilized for improving the γδ-T cell-based anti-IAV immunotherapy in vivo. By adoptive transferring different subsets of PAM-expanded Vγ9Vδ2-T cells to influenza virus-infected Rag2-/-γc-/- mice, we observed that the protection of Vγ9Vδ2-T cells for IAV infection was mainly determined by the CD137+ subset cells. The SA-hCD137L recombinant protein synergized with PAM and significantly improved the PAM-induced therapeutic effect of human Vγ9Vδ2-T cells in IAV-infected humanized mice.

This study develops our understanding about the role of CD137 signaling in human Vγ9Vδ2-T cells and provides proof-of-concept of a novel strategy in improving the γδ-T cell-based immunotherapy for influenza virus infection by targeting CD137.