Long-lived central memory γδ T cells confer protection against murine cytomegalovirus reinfection

The involvement of (c)delta TCR-bearing lymphocytes in immunological memory has gained increasing interest due to their functional duality between adaptive and innate immunity. (c)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 alpha beta T cell deficient mice in order to analyze the memory potential of (c)delta T cells. As for CMV-specific alpha beta T cells, MCMV induced the accumulation of cytolytic, KLRG1+CX3CR1+ (c)delta TEM that principally localized in infected organ vasculature. Typifying T cell memory, (c)delta T cell expansion in organs and blood was higher after secondary viral challenge than after primary infection. Viral control upon MCMV reinfection was prevented when masking (c)delta T-cell receptor, and was associated with a preferential amplification of private and unfocused TCR delta chain repertoire composed of a combination of clonotypes expanded post-primary infection and, more unexpectedly, of novel expanded clonotypes. Finally, long-term-primed (c)delta TCM cells, but not (c)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. This better survival potential of TCM cells was confirmed by a detailed scRNASeq analysis of the two (c)delta T cell memory subsets which also revealed their similarity to classically adaptive alpha beta CD8 T cells. Overall, our study uncovered memory properties of long-lived TCM (c)delta T cells that confer protection in a chronic infection, highlighting the interest of this T cell subset in vaccination approaches. Cytomegalovirus (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 (c)delta T-cell receptor bearing lymphocytes could be crucial in this context where immunosuppressive/ablative treatments cause suboptimal and/or delayed alpha beta T cell responses. Here we asked whether (c)delta T cells could compensate for the absence of alpha beta T cells in the long-term control of mouse CMV infection. Three months post-primary viral challenge in alpha beta-T cell deficient mice, (c)delta T cells displayed similar features as cytolytic, CMV-specific alpha beta CD8 T cells. We showed that previous priming with CMV endowed (c)delta T cells with an enhanced antiviral potential and that long-term maintenance of (c)delta T cell-mediated antiviral protection was dependent on (c)delta central memory T cells (TCM). As observed in human, the (c)delta T cell response to a secondary CMV challenge generated a private TCR delta repertoire. Finally, our gene expression/accessibility single cell analysis revealed that (c)delta TCM shared similar features as their alpha beta T cell counterpart. Our results sustain the adaptive-like properties of these unconventional T cells and reveal the interest of targeting (c)delta TCM subset in novel antiviral vaccination approaches.