Résumé
Abstract CD4 + T cells are important for CD8 + T‐cell priming by providing cognate signals for DC maturation. We analyzed the capacity of CD4 + T cells to influence CD8 + T‐cell responses induced by activated DC. Surprisingly, mice depleted for CD4 + cells were able to generate stronger antigen‐specific CD8 + T‐cell responses after DC vaccination than non‐depleted mice. The same observation was made when mice were vaccinated with MHC class II −/− DC, indicating the presence of a MHC class II‐dependent CD4 + T‐cell population inhibiting CD8 + T‐cell responses. Recently we described the expansion of DX5 + CD4 + T cells, a T‐cell population displaying immune regulatory properties, upon vaccination with DC. Intriguingly, we now observe an inverse correlation between CD8 + T‐cell induction and expansion of DX5 + CD4 + T cells as the latter cells did not expand after vaccination with MHC class II −/− DC. In vitro , DX5 + CD4 + T cells were able to limit proliferation, modulate cytokine production and induce Foxp3 + expression in OVA‐specific CD8 + T cells. Together, our data show an inhibitory role of CD4 + T cells on the induction of CD8 + T‐cell responses by activated DC and indicate the involvement of DX5 + CD4 + , but not CD4 + CD25 + , T cells in this process.