The role of CD4 T cells in tumor and chronic viral immune responses.

Immunotherapies are mainly aimed to promote a CD8 T cell response rather than a CD4 T cell response as cytotoxic T lymphocytes (CTLs) can directly kill target cells. Recently, CD4 T cells have received more attention due to their diverse roles in tumors and chronic viral infections. In antitumor and antichronic viral responses, CD4 T cells relay help signals through dendritic cells to indirectly regulate CD8 T cell response, interact with B cells or macrophages to indirectly modulate humoral immunity or macrophage polarization, and inhibit tumor blood vessel formation.