CD40 ligand is essential for generation of specific cytotoxic T cell responses in RNA-pulsed dendritic cell immunotherapy

Background. Dendritic cell (DC)-based immunotherapy is a promising form of adjuvant therapy for high-risk tumors. DCs transfected with tumor-associated antigens are capable of stimulating antigen-specific T cells, but cytolytic responses have been disappointing. Activation of DC surface CD40 influences DC cytokine production, particularly that of interleukin (IL)-12, which favors a Th1 (cytotoxic) helper T cell response. This study evaluated the effects of exogenous soluble CD40 ligand (sCD40L) on RNA-transfected DC preparations and their subsequent ability to generate antimelanoma cytolytic T cells. Methods. Human monocyte-derived DCs were cultured and transfected with mRNA encoding full-length melanoma-associated antigen, Mart-1, and matured with and without sCD40L. DC IL-12 secretion and the ability to stimulate naïve T cells were assessed by enzyme-linked immunosorbent assay (ELISA), tetramer analysis, Elispot, and ⁵¹Cr release assay. Results. Mature DCs stimulated with sCD40L secreted higher levels of IL-12 compared with immature DCs and DCs matured without sCD40L (P < .001). DCs treated with sCD40L generated a greater number of antigen-specific T cells (P < .05) by tetramer and Elispot analyses, and yielded specific T cells with significant cytotoxicity against HLA-matched melanoma cell lines. Conclusions. CD40L augments DC IL-12 secretion and is essential to potentiate specific antimelanoma cytolytic responses stimulated by the Mart-1 antigen, sCD40L should be considered a crucial adjuvant in DC preparations for RNA-based DC vaccine therapies.