Single injection of IL-12 coacervate as an effective therapy against B16-F10 melanoma in mice

Melanoma is the deadliest type of skin cancer with one of the fastest increasing incidence rates among solid tumors. The use of checkpoint inhibitors (e.g. alpha PD-1 antibody) has recently emerged as a viable alternative to conventional modes of therapy. However, increasing evidence points towards the need for a tumor priming step to improve intratumoral immune cell infiltration. IL-12 is an immune-activating cytokine with such potential and was explored in earlier clinical trials as a highly concentrated systemic infusion. This unfortunately led to severe adverse effects. From this perspective, the localization and gradual release of such a potent immunotherapeutic agent in the tumor microenvironment is desired. This manuscript reports the use of a heparin-based complex coacervate to deliver IL-12, in which heparin-binding motifs on IL-12 allow for its effective encapsulation. IL-12-encapsulated complex coacervates significantly improved the bioactivity of IL-12 and provided protection from proteolytic cleavage in-vitro. Indeed, a single injection of IL-12 coacervate significantly inhibits the in-vivo growth of treated and untreated, contralateral tumor growth in a syngeneic B16F10 mouse melanoma model. Furthermore, tumors in mice receiving IL-12 complex coacervate treatment displayed increased infiltration by natural killer (NK) cells and CD8 alpha(+) T cells, and a decreased presence of CD4(+) Foxp3(+) regulatory T cells. This study provides proof-of-concept data supporting the use of complex coacervates for sustained delivery of immunostimulatory proteins as an effective therapeutic strategy against disseminated tumors.