Pancreatic ductal adenocarcinoma (PDA) is an aggressive and lethal disease, with current standards of care extending overall survival by only a few months, as observed with the combination of nab-paclitaxel (nP) and gemcitabine (Gem). As such, efforts have begun to focus on the prospect of immune therapy has a new paradigm for patients in PDA. Given the potential synergy between chemotherapy and immune stimulation to create an anti-tumor vaccine, we hypothesized that agonistic CD40 monoclonal antibody with combined Gem/nP chemotherapy can activate the immune response and reverse immunosuppression in the PDA microenvironment. Using the KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) genetically engineered mouse model of PDA, we found that 37.5% of mice treated with Gem/nP/CD40 therapy had tumor regressions or stable disease, compared to only 9% of mice receiving Gem/nP without CD40 (p<0.03). Furthermore, when mice were depleted of CD8 T cells, the tumor regressions were completely ablated. To understand the mechanism by which chemotherapy potentiated CD40 agonist treatment, we injected PDA cell lines generated from KPC tumors subcutaneously into C57Bl/6 mice, and found that more than 50% of mice treated with Gem/nP/CD40 experienced T cell dependent tumor regressions compared to only rare regressions in Gem/nP or CD40 treated mice (p<0.0001). Tumor regressions were dependent on T cells and IFN-gamma, and accordingly, we found the proportions of both CD4 and CD8 T cells producing IFN-gamma to be increased 2- to 4-fold in mice treated with Gem/nP/CD40 as compared to other cohorts. Concurrent with increased effector T cells, the proportion of T regulatory cells in the tumor was reduced 6.9-fold after Gem/nP/CD40 (p<0.05, versus Gem/nP or CD40 alone). The loss of the immunosuppressive tumor microenvironment was detectable 24 hours after Gem/nP/CD40 treatment, when CD11b+ and CD11c+ cells in the tumor reduced production of IL-10 and TGF-beta by 1.3 to 5-fold (compared to Gem/nP treatment), and increased production of IL-12 (35% versus 23% in CD40 treated mice), concurrent with increased expression of both CD86 and MHCII (37% versus 10% in control group). Despite prior results linking MyD88 signaling with immune potentiating effects of chemotherapy, we observed that responses to Gem/nP/CD40 were independent of MyD88, and TLR4 pathways. Tumor regressions with Gem/nP/CD40 were also independent of TRIF, IFNAR, Caspase 1 and 4, TLR3, muMT, TNF-alpha, and Perforin. These studies reveal a novel MyD88- and TLR4-independent mechanism of chemotherapeutic activation of the immune system, and highlight the significant clinical potential of combining Gem/nP with agonistic CD40 stimulation.

Citation Format: Katelyn T. Byrne, Robert H. Vonderheide. Chemotherapy and agonistic CD40 cooperate to regress pancreatic adenocarcinoma independently of TLR4 and MyD88. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1356. doi:10.1158/1538-7445.AM2015-1356

©2015 American Association for Cancer Research.
2015