Long-lived central memory γδ T cells confer protection against murine cytomegalovirus reinfection
The involvement of {gamma}{delta} TCR-bearing lymphocytes in immunological memory has gained increasing interest due to their functional duality between adaptive and innate immunity. {gamma}{delta} T effector memory (TEM) and central memory (TCM) subsets have been identified, but their respective roles in memory responses are poorly understood. In the present study, we used subsequent mouse cytomegalovirus (MCMV) infections of {beta} T cell deficient mice in order to analyze the memory potential of {gamma}{delta} T cells. As for CMV-specific {beta} T cells, MCMV induced the accumulation of cytolytic, KLRG1+CX3CR1+ {gamma}{delta} TEM that principally localized in infected organ vasculature. Typifying T cell memory, {gamma}{delta} T cell expansion/proliferation in organs and blood was higher and more efficient after secondary viral challenge than after primary infection. Viral control upon MCMV reinfection involved the T-cell receptor, and was associated with a preferential amplification of private and unfocused TCR {delta} chain repertoire as evidenced by next generation sequencing. The {gamma}{delta} T cell secondary response to MCMV was composed by a combination of clonotypes expanded post-primary infection and, more unexpectedly, of novel expanded clonotypes. Finally, Long-term-primed {gamma}{delta} TCM cells, but not {gamma}{delta} TEM cells, protected T cell-deficient hosts against MCMV-induced death upon adoptive transfer, probably through their ability to survive and to generate TEM in the recipient host. Overall, our study uncovered memory properties of long-lived TCM {gamma}{delta} T cells that confer protection in a chronic infection, highlighting the interest of this T cell subset in vaccination approaches. AUTHOR SUMMARYCytomegalovirus (CMV) is a widespread, latent virus that can cause severe organ disease in immune-compromised patients. Anti-CMV memory immune responses are essential to control viral reactivation and/or reinfection events that commonly take place in solid organ transplantation. The role of {gamma}{delta} T-cell receptor bearing lymphocytes could be crucial in this context where immunosuppressive/ablative treatments cause suboptimal and/or delayed {beta} T cell responses. Here we asked whether {gamma}{delta} T cells could compensate for the absence of {beta} T cells in the long-term control of mouse CMV infection. Three months post-primary viral challenge in {beta}-T cell deficient mice, {gamma}{delta} T cells displayed similar features as cytolytic, CMV-specific {beta} CD8 T cells. We showed that previous priming with CMV endowed {gamma}{delta} T cells with an enhanced antiviral potential and that long-term maintenance of {gamma}{delta}-mediated antiviral protection was dependent on {gamma}{delta} central memory T cells (TCM). The {gamma}{delta} T cell response to a secondary CMV challenge was dependent on {gamma}{delta} TCR-signaling and generated a private TCR {delta} repertoire as observed in human. Our results sustain the adaptive-like properties of these unconventional T cells and reveal the interest of targeting {gamma}{delta} TCM subset in novel antiviral vaccination approaches.