Targeted therapeutic remodeling of the tumor microenvironment improves an HER-2 DNA vaccine and prevents recurrence in a murine breast cancer model.

The tumor microenvironment (TME) mediates immunosuppression resulting in tumor cell escape from immune surveillance and cancer vaccine failure. Immunosuppression is mediated by the STAT-3 transcription factor, which potentiates signaling in tumor and immune cells. Because immunosuppression continues to be a major inhibitor of cancer vaccine efficacy, we examined in this study whether therapeutically targeted delivery of a synthetic STAT-3 inhibitor to the TME, combined with an HER-2 DNA vaccine can improve immune surveillance against HER-2(+) breast cancer and prevent its recurrence. To this end, we developed a novel ligand-targeted nanoparticle (NP) encapsulating a CDDO-Im payload capable of specific delivery to the TME, which showed an effective therapeutic inhibition of STAT-3 activation in primary tumors. Furthermore, we showed that treatment with these NPs resulted in priming of the immune TME, characterized by increased IFN-γ, p-STAT-1, GM-CSF, IL-2, IL-15, and IL-12b and reduced TGF-β, IL-6, and IL-10 protein expression. In addition, we found significantly increased tumor infiltration by activated CD8(+) T cells, M1 macrophages, and dendritic cells. These changes correlated with delayed growth of orthotopic 4TO7 breast tumors and, when combined with an HER-2 DNA vaccine, prevented HER-2(+) primary tumor recurrence in immunocompetent mice. Furthermore, antitumor T-cell responses were enhanced in splenocytes isolated from mice treated with this combination therapy. Together, these data show effective protection from cancer recurrence through improved immune surveillance against a tumor-specific antigen.