Intratumoral delivery of encapsulated IL-12, IL-18 and TNF-alpha in a model of metastatic breast cancer.

Intratumoral (i.t.) cytokine release through the use of poly-lactic acid microspheres (PLAM) holds tremendous potential for the immunotherapy of breast cancer as it harnesses the immunologic potential of autologous tumor in a clinically feasible and minimally toxic manner. We examined the potential of combinations of i.t. IL-12, IL-18 and TNF-alpha PLAM to generate a tumor-specific immune response and improve outcome in a model of metastatic breast cancer. Balb/c mice with established 4T1 mammary carcinomas were treated with a single injection of BSA, IL-12, IL-18 or TNF-alpha-loaded PLAM alone or in combination after spontaneous metastases occurred. Combined treatment with IL-12 and TNF-alpha PLAM was superior to all other treatments, including the triple combination of IL-12, IL-18 and TNF-alpha in ablation of the primary tumor, eradicating distant disease and enhancing survival. Simultaneous delivery of IL-12 and TNF-alpha was superior to sequential delivery of IL-12 followed by TNF-alpha, but not TNF-alpha followed by IL-12. In vivo lymphocyte depletion studies established that the effects of IL-12 alone are mediated primarily by NK cells, while the combination of IL-12 and TNF-alpha is dependent upon CD8+ T-cells. Only the combination of IL-12 and TNF-alpha results in an increase in both CD4+ and CD8+ T-cells and a reduction in CD4+CD25+ cells. While there was no change in the dendritic cell population, IL-12 and TNF-alpha resulted in a dramatic increase in DC maturation and antigen presentation. Neoadjuvant immunotherapy with simultaneous intratumoral delivery of IL-12 and TNF-alpha PLAM augments DC antigen presentation and increases cytotoxic T-cells without increasing regulatory T-cells, resulting in a T-cell based anti-tumor immune response capable of eradicating disseminated disease. The addition of IL-18 did not improve the efficacy.