CD40 cross-linking bypasses the absolute requirement for CD4 T cells during immunization with melanoma antigen gene-modified dendritic cells

Genetic immunization of mice with dendritic cells (DCs) engineered to express a melanoma antigen generates antigen-specific, MHC-restricted, CD4-dependent protective immune responses. We wanted to determine the role of CD4 cells and CD40 ligation of MART-1 gene-modified DC in an animal model of immunotherapy for murine melanoma. CD4 knock-out (CD4KO) or antibody-depleted mice were immunized with DC adenovirally transduced with the MART-1 gene (AdVMART1/DC) with or without CD40 cross-linking. Tumor protection was absent in CD4-depleted mice, but protection was reestablished when the CD40 receptor was engaged using three different constructs. Transduction of DCs with vectors expressing the Th1 cytokines interleukin (IL)-2, IL-7, or IL-12 could not reproduce the CD40-mediated maturation signal in this model. CD8 T-cell depletion in CD4KO mice immunized with CD40-ligated DCs abrogated the protective response. Pooled analysis of CD40 cross-linking of AdVMART1/DC administered to wild-type C57BL/6 mice revealed an overall enhancement of antitumor immunity. However, this effect was inconsistent between replicate studies. In conclusion, maturation of AdVMART1-transduced DCs through the CD40 ligation pathway can promote a protective CD8 T-cell-mediated immunity that is independent of CD4 T-cell help.

Generation of T-cell immunity to a murine melanoma using MART-1-engineered dendritic cells

The murine melanoma B16 expresses the murine counterpart of the human MART-1/Melan-A (MART-1) antigen, sharing a 68.6% amino acid sequence identity. In this study, mice were vaccinated with bone marrow-derived murine dendritic cells genetically modified with a replication-incompetent adenoviral vector to express the human MART-1 gene (AdVMART1). This treatment generated a protective response to a lethal tumor challenge of unmodified murine B16 melanoma cells. The response was mediated by major histocompatibility complex class I-restricted cytotoxic T lymphocytes specific for MART-1 antigen, which produced high levels of interferon-gamma when reexposed to MART-1 in vitro and lysed targets in a calcium-dependent mechanism suggestive of perforin/granzyme B lysis. MART-1 was presented by the dendritic cells used for vaccination and not by epitopes cross-presented by host antigen-presenting cells. In conclusion, dendritic cells genetically modified to express the human MART-1 antigen generate potent murine MART-1-specific protective responses to B16 melanoma.