Alteration of the Tumor Stroma Using a Consensus DNA Vaccine Targeting Fibroblast Activation Protein (FAP) Synergizes with Antitumor Vaccine Therapy in Mice

Abstract

Purpose: Fibroblast activation protein (FAP) is overexpressed in cancer-associated fibroblasts and is an interesting target for cancer immune therapy, with prior studies indicating a potential to affect the tumor stroma. Our aim was to extend this earlier work through the development of a novel FAP immunogen with improved capacity to break tolerance for use in combination with tumor antigen vaccines.

Experimental Design: We used a synthetic consensus (SynCon) sequence approach to provide MHC class II help to support breaking of tolerance. We evaluated immune responses and antitumor activity of this novel FAP vaccine in preclinical studies, and correlated these findings to patient data.

Results: This SynCon FAP DNA vaccine was capable of breaking tolerance and inducing both CD8⁺ and CD4⁺ immune responses. In genetically diverse, outbred mice, the SynCon FAP DNA vaccine was superior at breaking tolerance compared with a native mouse FAP immunogen. In several tumor models, the SynCon FAP DNA vaccine synergized with other tumor antigen–specific DNA vaccines to enhance antitumor immunity. Evaluation of the tumor microenvironment showed increased CD8⁺ T-cell infiltration and a decreased macrophage infiltration driven by FAP immunization. We extended this to patient data from The Cancer Genome Atlas, where we find high FAP expression correlates with high macrophage and low CD8⁺ T-cell infiltration.

Conclusions: These results suggest that immune therapy targeting tumor antigens in combination with a microconsensus FAP vaccine provides two-fisted punch-inducing responses that target both the tumor microenvironment and tumor cells directly. Clin Cancer Res; 24(5); 1190–201. ©2018 AACR.