Both CD8+ and CD4+ T cells have demonstrated roles in antitumor immune response in many animal tumor systems. In many human tumor systems, although abundant literature exists on the evidence of tumor antigen-specific CD8+ CTL response, only limited information is available on tumor antigen-specific CD4+ T-cell response. Using the MART-1/Melan-A (MART-1) antigen system as a prototype human tumor-associated antigen (TAA)- and dendritic cell (DC)-based MART-1 antigen presentation system (i.e., DCs transduced with an adenoviral vector-based construct carrying the MART-1 gene), we explored, in vitro, the feasibility of generating both CD8+ and CD4+ T-cell responses in the same individual. Here, we show that autologous DCs from both HLA-A2-positive melanoma patients and normal healthy individuals that are transduced with an adenoviral vector containing the MART-1 antigen are capable of inducing both MART-1-specific CD8+ and CD4+ T cells in in vitro coculture. After several rounds of stimulation, both the CD4+ and CD8+ T cells synthesized IFN-gamma when they were specifically stimulated. The CD8+ T cells generated in such cocultures also recognized the MART-1(27-35) peptide, AAGIGILTV, in 4-h cytotoxicity assays. These observations, therefore, suggest that Th1-type responses can be generated, in vitro, by stimulation with DCs that are genetically modified to express a TAA. Although the outcome of this type of genetically engineered DC-based stimulation may vary from system to system, this type of in vitro antigen presentation may be very useful in more comprehensive analyses of CD4+ T-cell response to defined TAAs, and such genetically engineered autologous DCs might be better candidates to serve as surrogate cancer vaccines.