Abstract 1266: Downregulation of PD-L1 by NSAID administration augments the effects of a multi-antigen vaccine for the prevention of adenomatous polyps in APC(Min/+) mice
Authors: Disis Mary L. , Corulli Lauren R. , Grubbs Clinton , Lubet Ronald A. , Cowan Paul , Gad Ekram 
Published: August 2018

Abstract
Introduction: We have shown that treatment of APC(Min/+) mice with NSAIDs will inhibit development of adenomatous polyps and induce significant levels of polyp-infiltrating CD8 T-cells. We sought to identify the mechanism of NSAID induced immune stimulation and questioned whether administration of NSAIDs concurrent with vaccination could further reduce polyp formation.
Methods: PD-L1 expression and T-cell infiltrates were assessed by IHC and flow cytometry. MC38 and RKO (murine/human colorectal carcinoma cell lines) were treated with naproxen (200uM-1000 uM) and harvested at 24, 48 and 72h. At 4-6 weeks, APC(Min/+) mice were given a multi-antigen peptide vaccine (COX2, CDC25B, EGFR) with CFA/IFA or adjuvant alone. Two groups received 400ppm naproxen orally 7d/wk for 18 weeks. Polyps were quantified at ≤24 weeks. Spleens and polyps were collected for IFN-gamma ELISPOT, flow cytometry, and IHC.
Results: Polyps from the APC(Min/+) mouse and both cancer cell lines highly express PD-L1. PD-L1 expression was significantly decreased in MC38 (p&lt;0.01) and RKO (p&lt;0.01) as compared to control after incubation with naproxen at all doses. The inhibitory effect of NSAIDs on PD-L1 expression was both time and dose dependent. We evaluated the in vivo effect of combination immunoprevention in the APC(Min/+). Animals receiving vaccine alone showed a 33% inhibition of polyp formation while naproxen alone showed 54% inhibition (p&lt;0.0001) compared to adjuvant alone. Combination treatment demonstrated significantly greater inhibition of polyps than either modality (p&lt;0.001), 81% inhibition vs. adjuvant. Antigen specific T-cells could be detected at higher levels than control antigen in both the vaccine alone (p=0.0001) and combination-treated animals (p&lt;0.0001). The antigen specific responses seen in combination treated animals were nearly two-fold that of vaccine alone (p=0.008). No antigen specific immunity was detected in naproxen and adjuvant only treated mice. The magnitude of the immune response was significantly correlated with lower polyp counts, with a Pearson correlation coefficient of -0.55 (p=0.0014). Detailed immunologic analysis of tumors will be presented.
Conclusions: NSAIDs, via modulation of PD-L1, synergize with vaccines to increase immunogenicity and enhance influx of polyp infiltrating lymphocytes. This synergy results in superior prevention of polyp formation compared to treatment with NSAID or vaccine alone and has high potential for clinical application.
Citation Format: Mary L. Disis, Lauren R. Corulli, Clinton Grubbs, Ronald A. Lubet, Paul Cowan, Ekram Gad. Downregulation of PD-L1 by NSAID administration augments the effects of a multi-antigen vaccine for the prevention of adenomatous polyps in APC(Min/+) mice [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 1266.