Conventional CD4+ T cells present bacterial antigens to induce cytotoxic and memory CD8+ T cell responses

Bacterial phagocytosis and antigen cross-presentation to activate CD8 + T cells are principal functions of professional antigen presenting cells. However, conventional CD4 + T cells also capture and kill bacteria from infected dendritic cells in a process termed transphagocytosis (also known as transinfection). Here, we show that transphagocytic T cells present bacterial antigens to naive CD8 + T cells, which proliferate and become cytotoxic in response. CD4 + T-cell-mediated antigen presentation also occurs in vivo in the course of infection, and induces the generation of central memory CD8 + T cells with low PD-1 expression. Moreover, transphagocytic CD4 + T cells induce protective anti-tumour immune responses by priming CD8 + T cells, highlighting the potential of CD4 + T cells as a tool for cancer immunotherapy. Antigen presentation is generally considered the domain of innate immune cells, but CD4 + T cells can transphagocytose bacteria from infected dendritic cells. Here the authors show CD4 + T cells can transphagocytose bacterial and tumour antigens and present them to CD8 + T cells to activate memory and cytotoxic functions.