Interleukin-2: Developing additional cytokine gene therapies using fibroblasts or dendritic cells to enhance tumor immunity

PURPOSE. Recombinant interleukin (IL)-2 administration can mediate regression of solid tumors in patients with melanoma and renal cell carcinoma. A better understanding of the mechanisms of IL-2-mediated antitumor effects has led to the investigation of novel immunotherapeutic approaches. The rationale for these immunotherapeutic approaches and the results of preliminary clinical studies are presented. PATIENTS AND METHODS. The therapeutic potential of dendritic cells and the role of FLT3 ligand, a potent hematopoietic growth factor, was investigated in a variety of preclinical models. In addition, a clinical study with autologous dendritic cells pulsed with synthetic melanoma peptides derived from the MART1/Melan A, gp100, and tyrosinase proteins was conducted. Twenty-eight human leukocyte antigen (HLA)-A2+ melanoma patients received an average of 10⁶ dendritic cells a week for 4 weeks. RESULTS. In a murine liver metastases model, FLT3 ligand administration alone or in combination with IL-12 or IL-2 had significant antitumor effects and resulted in significant infiltration of the tumor border by lymphocytes and dendritic cells, which was associated with an increased number of apoptotic figures. Administration of melanoma peptide- pulsed dendritic cells to 28 patients with advanced metastatic melanoma produced a complete response in two patients and a partial response in one. Significant infiltration of T cells and dendritic cells into melanoma lesions was observed. CONCLUSION. These studies confirm the feasibility of immunotherapeutic approaches using dendritic cells and FLT3 ligand and demonstrate their potential antitumor activity. These approaches may be effective for patients with metastatic melanoma and other solid tumors and will likely be used to improve the efficacy of IL-2-based immunotherapy.