The cellular immune system holds much potential for mediating antitumor responses in cancer patients. Melanoma is particularly appealing to study immunotherapy, since several melanoma-specific antigens recognized by T cells have been identified over the past decade. In recent clinical trials, metastatic melanoma patients receiving ex vivo- expanded tumor-reactive T cells have demonstrated encouraging clinical responses, particularly when combined with a lymphodepletion regimen prior to adoptive cell transfer (ACT). However, in many patients, the infused T cells did not proliferate or survive long after cell transfer and no tumor regression was observed. This observation has suggested that increasing T cell persistence in vivo will improve clinical responses following ACT.In our preliminary studies, we have assessed tumor antigen-pulsed dendritic cells (DCs)as an immunization strategy to improve adoptive T cell responses. Using a murine model, we found that DC immunization resulted in significant proliferation of adoptively transferred T cells which mediated enhanced immune responses against large subcutaneous tumors. While the role of DCs in mediating strong stimulation of endogenous naive and resting T cells is well documented, their ability to increase the efficacy of adoptively transferred activated T cells constitutes a novel use of DCs.We hypothesize that this principle will hold true in patients, and that the combination of antigen-specific, adoptively transferred T cells with tumor antigen peptide-pulsed DCs will result in enhanced persistence of the transferred T cells in vivo, increased activation and function, and improved trafficking to tumor sites, ultimately leading to improved clinical responses. Within the context of a clinical trial, we are proposing in this application to investigate the role that specific DC immunization plays in shaping the persistence, function, and phenotype of adoptively transferred antigen-specific T cells. The goals of this proposal are to acquire knowledge about the influence of DCs on ACT and to use this information to improve adoptive immunotherapy of patients with metastatic cancer. The specific aims of this proposal are:(1) Determine if peptide-pulsed DC immunization can alter the persistence, cell surface phenotype, and function of adoptively transferred, antigen-specific T cells in the peripheral blood; (2) Assess whether peptide-pulsed DC immunization enhances the ability of adoptively transferred, antigen- specific T cells to infiltrate and function at the tumor site: and (3) Determine patient clinical responses and assess whether response correlates with T-cell persistence, phenotype, function, and degree of tumor infiltration. These studies may uncover principles regarding the interaction between dendritic cells and adoptively transferred T cells in vivo which may allow the design of improved immunotherapy strategies for patients. i