A push-pull approach to maximize vaccine efficacy: Abrogating suppression with an IL-13 inhibitor while augmenting help with granulocyte/macrophage colony-stimulating factor and CD40L

Although a role for CD4(+) helper cells in CD8(+) cytotoxic T lymphocyte (CTL) induction by vaccines is widely recognized, much less is known about a counterbalancing role of CD4(+) T cells in down-modulating this response, or about ways to optimize vaccine responses through abrogation of this negative regulatory mechanism. Here, we discovered a synergistic enhancement of vaccine-mediated CTL induction and protection by the relief of suppression through depletion of regulatory CD4(+) cells, including CD4(+) NKT cells, or blockade of IL-13 made by these cells, combined with the cytokine granulocyte/macrophage colony-stimulating factor and the costimulatory molecule CD40L. Indeed, in the absence of helper epitopes, granulocyte/macrophage colony-stimulating factor and the helper-mimetic molecule CD40L are not sufficient to replace help to induce CTL without abrogation of CD4+ T cell-mediated suppression, suggesting a role for T cell help in overcoming suppression. The increased CTL induction translated to striking protection against viral infection by a vaccine by using this synergistic combined approach. These results argue for a push-pull approach to maximize vaccine efficacy, especially for HIV and cancer.