CD4+ T lymphocytes: a critical component of antitumor immunity.

Both prophylactic and therapeutic vaccines targeting a wide variety of cancers are being developed. Because of the potency of cell-mediated immunity, many vaccine strategies are focused on activating tumor-specific cytotoxic CD8+ T lymphocytes. CD4+ T lymphocytes are a key element in optimal activation of CD8+ T cells and in the maintenance of immune memory, and therefore their activation is critical for cancer vaccine efficacy. This article reviews the mechanisms by which CD4+ T cells facilitate tumor immunity and the vaccine strategies that enhance CD4+ T cell activity.