Cancer immunotherapy with interleukin 12 and granulocyte-macrophage colony-stimulating factor-encapsulated microspheres: coinduction of innate and adaptive antitumor immunity and cure of disseminated disease.

Tumor cells, injected s.c., were maintained until spontaneous metastases to the lungs were established in all of the mice. Mice were then treated with a single dose of cytokine-encapsulated biodegradable microspheres injected directly into primary s.c. tumors to achieve a local and sustained release of interleukin 12 (IL-12), granulocyte-macrophage colony-stimulating factor (GM-CSF), or a combination of these cytokines to the tumor microenvironment. The s.c. tumors were surgically excised 6 days after microsphere injections, and the mice were monitored for recurrence of the primary tumor, survival, and progression of metastatic disease. Combined neoadjuvant treatment with IL-12 and GM-CSF microspheres was superior to all other treatments in reducing the recurrence of primary tumors, enhancing postoperative survival, and suppressing established metastatic disease. Long-term survival analysis demonstrated that intratumoral injection of IL-12 + GM-CSF-loaded microspheres resulted in the complete cure of disseminated disease in the majority of the animals. The addition of systemic low-dose IL-2 therapy to the treatment protocol resulted in the loss of the antitumor activity induced by IL-12 + GM-CSF treatment. In vivo lymphocyte subset depletions established that both T- and natural killer-cell subsets were required for the suppression of primary and metastatic tumors. Long-term, tumor-specific T-cell activity was demonstrated by immunohistochemical analysis of metastatic lesions, IFN-gamma enzyme-linked immunosorbent spot (ELISPOT) assays and tumor challenge studies. These results establish that neoadjuvant in situ tumor immunotherapy with IL-12 + GM-CSF microspheres induces both innate and adaptive antitumor immune responses resulting in the eradication of disseminated disease.

IL-12 + GM-CSF microsphere therapy induces eradication of advanced spontaneous tumors in her-2/neu transgenic mice but fails to achieve long-term cure due to the inability to maintain effector T-cell activity.

A single intratumoral injection of interleukin-12 and granulocyte-macrophage colony-stimulating factor-encapsulated microspheres induced the regression of advanced spontaneous mammary tumors, suppressed additional tumor development, and enhanced survival in her-2/neu transgenic mice. Posttherapy tumor eradication was dependent on both CD4+ and CD8+ T cells and correlated with the tumor infiltration kinetics of a transient effector T-cell response. Upon long-term monitoring, tumor regression was found to be temporary, and disease-free survival was not achieved despite the development of systemic anti-tumor cytotoxic T-cell memory and antibody responses. Repeated immunization of mice enhanced short-term tumor suppression, resulting in the complete regression of primary tumors in up to 40% of the mice, but did not improve long-term survival owing to recurrence. The failure of chronic therapy to achieve complete cure was associated with an inability to maintain the intensity of the posttherapy effector T-cell response in this model.