TGF beta-derived immune modulatory vaccine: targeting the immunosuppressive and fibrotic tumor microenvironment in a murine model of pancreatic cancer

BackgroundPancreatic ductal adenocarcinoma (PDAC) is associated with very poor survival, making it the third and fourth leading cause of all cancer-related deaths in the USA and European Union, respectively. The tumor microenvironment (TME) in PDAC is highly immunosuppressive and desmoplastic, which could explain the limited therapeutic effect of immunotherapy in PDAC. One of the key molecules that contributes to immunosuppression and fibrosis is transforming growth factor-beta (TGF beta). The aim of this study was to target the immunosuppressive and fibrotic TME in PDAC using a novel immune modulatory vaccine with TGF beta-derived peptides in a murine model of pancreatic cancer.MethodsC57BL/6 mice were subcutaneously inoculated with Pan02 PDAC cells. Mice were treated with TGF beta 1-derived peptides (major histocompatibility complex (MHC)-I and MHC-II-restricted) adjuvanted with Montanide ISA 51VG. The presence of treatment-induced TGF beta-specific T cells was assessed by ELISpot (enzyme-linked immunospot). Changes in the immune infiltration and gene expression profile in tumor samples were characterized by flow cytometry, reverse transcription-quantitative PCR (RT-qPCR), and bulk RNA sequencing.ResultsTreatment with immunogenic TGF beta-derived peptides was safe and controlled tumor growth in Pan02 tumor-bearing mice. Enlargement of tumor-draining lymph nodes in vaccinated mice positively correlated to the control of tumor growth. Analysis of immune infiltration and gene expression in Pan02 tumors revealed that TGF beta-derived peptide vaccine increased the infiltration of CD8(+) T cells and the intratumoral M1/M2 macrophage ratio, it increased the expression of genes involved in immune activation and immune response to tumors, and it reduced the expression of myofibroblast-like cancer-associated fibroblast (CAF)-related genes and genes encoding fibroblast-derived collagens. Finally, we confirmed that TGF beta-derived peptide vaccine actively modulated the TME, as the ability of T cells to proliferate was restored when exposed to tumor-conditioned media from vaccinated mice compared with media from untreated mice.ConclusionThis study demonstrates the antitumor activity of TGF beta-derived multipeptide vaccination in a murine tumor model of PDAC. The data suggest that the vaccine targets immunosuppression and fibrosis in the TME by polarizing the cellular composition towards a more pro-inflammatory phenotype. Our findings support the feasibility and potential of TGF beta-derived peptide vaccination as a novel immunotherapeutic approach to target immunosuppression in the TME.