Combination Agonist And Antagonist Antibody Therapy Enhances Vaccine Induced T Cell Responses In Non-Immunogenic Cancers

A hallmark of many non-immunogenic cancers is the lack of tumor infiltrating lymphocytes (TIL) and/or failure to mount a robust anti-tumor T cell response via multiple mechanisms. The presence of T regulatory cells and myeloid derived suppressor cells (MDSCs) serve to dampen the immune response, and furthermore, tumor antigen-specific T cell tolerance limits the efficacy of therapeutic cancer vaccines. CD40 signaling is critical to the decision of whether cytotoxic T lymphocytes become primed or tolerized. Administration of monoclonal CD40 agonistic antibody (Ab) has been shown to promote CD8 activation in vivo, and likely alters the myeloid component of the tumor microenvironment. Our study asks the question of whether combining a T cell inducing vaccine and PD1 inhibition with CD40 agonistic Ab can induce T cell priming and TIL activation in non-immunogenic solid malignancies. We utilized mouse models of pancreatic ductal adenocarcinoma (PDAC) and breast cancer to assess the effects of drug combinations on intratumoral immune responses. Tumor-bearing mice were treated with a GM-CSF secreting vaccine (GVAX) + anti-PD1 Ab alone or in combination with CD40 Ab, or isotype control Ab, and monitored for survival. A separate cohort of mice were analyzed by immunohistochemistry and multi-color flow cytometry to assess T cell infiltration/activation and myeloid maturation. In a hemisplenectomy model of PDAC in which tumor cells were surgically implanted into wild-type recipients, mice treated with isotype control Abs succumbed to disease with extensive liver and peritoneal metastases at 35-70 days. GVAX + anti-PD1 Ab treatment displayed some efficacy, although 70% of mice eventually developed fatal liver metastases. In contrast, CD40 Ab was highly active, with 90% long-term survival afforded by a single administration of Ab, and mice treated with GVAX + anti-PD1 Ab + CD40 Ab had 100% survival. Similar trends in treatment efficacy were observed following subcutaneous tumor implantation of PDAC tumor cells in the lower limb. In an orthotopic model in which HER2/neu-expressing breast tumor cells were implanted into the mammary fat pad of syngeneic neu-N mice, we demonstrated delayed tumor progression and increased median survival in mice treated with GVAX + anti-PD1 Ab + CD40 Ab relative to either therapy alone. Further characterization of immune populations was carried out by high dimensional flow cytometric analysis utilizing PhenoGraph clustering and visualized by t-SNE. Changes were observed in monocytic and dendritic cell infiltration and maturation in the tumors of combination-treated mice. A significant decrease in granulocytic MDSCs was associated with response, as well as an increase in mature antigen presenting cells. In conclusion, GVAX, anti-PD1 and CD40 agonist Ab have potential synergy in modulating anti-tumor immunity in non-immunogenic cancers. Citation Format: Hayley S. Ma, Evanthia Roussos Torres, Bibhav Poudel, Tara Robinson, Brian Christmas, Kayla Cruz, Skylar Woolman, Christine Rafie, Blake Scott, Valerie Wall, Todd Armstrong, Elizabeth Jaffee. Combination CD40 agonist and PD-1 antagonist antibody therapy enhances vaccine induced T cell responses in non-immunogenic cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4936.