Abstract
In situ immunization aims at generating antitumor immune responses through manipulating the tumor microenvironment. On the basis of recent advances in the understanding of antitumor immunity, we designed a three-step approach to in situ immunization to lymphoma: (i) inducing immunogenic tumor cell death with the chemotherapeutic drug doxorubicin. Doxorubicin enhances the expression of "eat-me" signals by dying tumor cells, facilitating their phagocytosis by dendritic cells (DC). Because of the vesicant activity of doxorubicin, microparticles made of biodegradable polymer poly(lactide-co-glycolide) or PLGA can safely deliver doxorubicin intratumorally and are effective vaccine adjuvants, (ii) enhancing T-cell activation using anti-OX40 and (iii) sustaining T-cell responses by checkpoint blockade using anti-CTLA-4. In vitro, doxorubicin microparticles were less cytotoxic to DCs than to B lymphoma cells, did not require internalization by tumor cells, and significantly enhanced phagocytosis of tumor cells by DCs as compared with soluble doxorubicin. In mice, this three-step therapy induced CD4- and CD8-dependent systemic immune responses that enhanced T-cell infiltration into distant tumors, leading to their eradication and significantly improving survival. Our findings demonstrate that systemic antitumor immune responses can be generated locally by three-step therapy and merit further investigation as an immunotherapy for patients with lymphoma.