We performed a clinical study of five patients with melanoma to evaluate the immunobiological effects of retrovirally transduced autologous tumor cells given as a vaccine to prime draining lymph nodes. Patients were inoculated with both wild-type (WT) and GM-CSF gene-transduced tumor cells in different extremities. Approximately 7 days later, vaccine-primed lymph nodes (VPLNs) were removed. There was an increased infiltration of dendritic cells (DCs) in the GM-CSF-secreting vaccine sites compared with the WT vaccine sites. This resulted in a greater number of cells harvested from the GM-CSF-VPLNs compared with the WT-VPLNs at a time when serum levels of GM-CSF were not detectable. Four of five patients proceeded to have the adoptive transfer of GM-CSF-VPLN cells secondarily activated and expanded ex vivo with anti-CD3 MAb and IL-2. One patient had a durable complete remission of metastatic tumor. Utilizing cytokine (IFN-gamma, GM-CSF, IL-10) release assays, GM-CSF-VPLN T cells manifested diverse responses when exposed to tumor antigen in vitro. In two of two patients, GM-CSF-VPLN T cell responses were different from those of matched WT-VPLN cells. This study documents measurable immunobiologic differences of GM-CSF-transduced tumor cells given as a vaccine compared with WT tumor cells. The complete tumor remission in one patient provides a rationale to pursue this approach further.