It is known that the method of antigen (Ag) delivery is important for the success of DC vaccines, but it remains unclear which method is most effective in producing antitumor responses. Approaches tested clinically include pulsing with HLA-restricted defined peptide Ags, loading with purified proteins, transfecting with mRNA, engineering with Ag-encoding viral vectors, and using autologous tumor cells or allogeneic cell lines directly as sources of Ag. Efficacy can be measured in vivo using surrogate endpoints, such as development of tumor-specific delayed-type hypersensitivity (DTH) reactions. Prolonged survival of vaccinated melanoma patients has been reported to correlate with induction of positive DTH tests. Antitumor activity may also be assessed by ELISpot analysis of the frequency of tumor-Ag specific IFNγ-producing T cells. To assess the quality of the DC vaccines, surrogate markers of DC function including maturation markers, co-stimulatory molecule expression, and IL12p70 production, a critical cytokine in antitumor response, can be measured