Abstract 2613: Combination agonist and antagonist antibody therapy enhances vaccine induced T cell responses in non-immunogenic cancers
Authors: Ma Hayley S. , Torres Evanthia Roussos , Christmas Brian , Scott Blake , Robinson Tara , Armstrong Todd , Jaffee Elizabeth 
Published: July 2017

Abstract
Immune tolerance by multiple mechanisms is a major obstacle in the implementation of successful immunotherapy. T regulatory cells (Tregs) and myeloid derived suppressor cells (MDSCs) suppress the immune response, and the presence of extensive stromal networks within the tumor microenvironment (TME) can prevent T cell infiltration in many tumor types. Furthermore, tumor antigen-specific T cell tolerance limits the efficacy of therapeutic cancer vaccines. CD40 is expressed on antigen presenting cells, and 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 TME. Our study asks the question of whether combining a T cell inducing vaccine and PD-1 inhibition with CD40 agonistic Ab can induce T cell priming and tumor infiltrating lymphocyte (TIL) activation in non-immunogenic solid malignancies. We utilized an orthotopic transplant model in which HER2/neu-expressing breast tumor cells were implanted into the mammary fat pad of syngeneic neu-N mice to assess the effects of drug combinations on intratumoral immune responses. Tumor-bearing mice were treated with a granulocyte macrophage colony-stimulation factor secreting vaccine (GVAX) + anti-PD-1 Ab alone or in combination with CD40 agonistic Ab, and monitored for tumor clearance and survival. A separate cohort of mice were analyzed by IHC and multi-color flow cytometry to assess T cell infiltration and activation, myeloid maturation, and MDSCs after one week of treatment. We demonstrated delayed tumor progression and increased median survival in mice treated with GVAX + anti-PD-1 Ab + CD40 Ab relative to CD40 Ab alone, although endogenous T cell infiltration remained low across treatment groups. However, adoptive transfer of neu-specific TCR transgenic cells revealed 100% tumor clearance in the combination-treated mice, along with significant T cell infiltration and activation as measured by IFNγ, Granzyme B and TNFα-secreting CD8+ T cells. In contrast, only 20% of mice treated with GVAX + anti-PD-1 Ab were able to clear tumor, and none of the mice receiving vehicle or CD40 Ab alone had long-term survival. Trends were also observed in monocytic and dendritic cell infiltration and maturation in the tumors of combination-treated mice, and warrant further investigation. In conclusion, GVAX, anti-PD-1 Ab and CD40 agonist Ab have potential synergy in modulating anti-tumor immunity in breast cancer. These results support further studies more broadly in non-immunogenic solid tumors.
Citation Format: Hayley S. Ma, Evanthia Roussos Torres, Brian Christmas, Blake Scott, Tara Robinson, Todd Armstrong, Elizabeth Jaffee. Combination agonist and 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 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2613. doi:10.1158/1538-7445.AM2017-2613