Abstract 3678: Muc4 nanovaccine and checkpoint blockade based combination immunotherapy for pancreatic cancer

Background: Pancreatic cancer (PC) is a highly metastatic and therapy-resistant malignancy characterized by immunosuppressive tumor microenvironment (TME) mucin overexpression. MUC4 is most differentially overexpressed mucin and functionally contributes to disease aggressiveness and is thus ideal candidate for targeted therapies. Tumor cells are also known to express programmed death ligand 1 (PD-L1) to suppress effector immune cells activity via PD-L1-PD-1 axis. We developed a novel vaccine using recombinant MUC4 fragments and exploiting adjuvant-like properties of amphiphilic polyanhydride-based nanoparticle delivery system. The strong involvement of MUC4 in disease aggressiveness and PD-L1 in immunosuppression makes a compelling case for their combined targeting. We hypothesize that combined overexpression of MUC4 and PD-L1 expression in pancreatic tumor microenvironment contributes to immunosuppressive and aggressive tumor behavior. Methods: Recombinant MUC4β fragment was encapsulated into polyanhydride nanoparticles (20:80 CPTEG:CPH) via nanoprecipitation. Murine PC cell lines (KCT960) derived from spontaneous pancreatic cancer mouse model (KPC mice) were transfected with human MUC4 expressing construct known as KCT960-mini-MUC4 cells for in-vivo studies. Flow cytometry, immunoblotting, PCR and immunofluorescence techniques were utilized to perform to characterize the immune response and target expression. Results: MUC4β nanovaccine immunized mice exhibited slower tumor growth kinetics than unimmunized control mice. We investigated tumor infiltrating lymphocytes (TILs) and necrosis in the tumor bed. We observed a positive correlation between TILs and tumor regression. Accumulation of infiltrating CD8+ and CD4+ T cells was greater in mice receiving the MUC4-Nanovaccine compared to soluble MUC4 delivered with blank nanoparticles, indicating the benefit of sustained availability of antigen via encapsulation. However, we did not observe complete tumor regression and ex vivo studies indicated induction of IFN-gamma by MUC4 vaccine. Based on this, we rationalized that PD-L1 expression by MUC4-expressing tumor cells suppressed and inhibited the therapeutic benefits of the nanovaccine in-vivo. We observed differential surface expression of PD-L1 on endogenously MUC4 expressing and negative PC cell lines. Paired analysis of MUC4 CRISPR knockdown and scrambled Capan-1 cell lines further suggested similar positive correlation. Conclusion: MUC4 nanovaccine suppressed tumor progression in-vivo indicating its potential for immunotherapy of PC. Positive correlation observed between MUC4 and PD-L1 in PC cell lines suggests an underlying molecular mechanism for establishing an immunosuppressive and aggressive PC tumor microenvironment and provides a strong rationale for evaluating MUC4 vaccine in combination with immune checkpoint blockade agents. Citation Format: Kasturi Banerjee, Shailendra Gautam, Waseem Mohd. Nasser, Prakash Kshirsagar, Kathleen Ross, Gaelle Spagnol, Abhijit Aithal, Paul Sorgen, Surinder Kumar Batra, Sushil Kumar, Balaji Narasimhan, Maneesh Jain. Muc4 nanovaccine and checkpoint blockade based combination immunotherapy for pancreatic cancer [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 3678. doi:10.1158/1538-7445.AM2017-3678