Abstract B117: Allogeneic tumor-lysate loaded dendritic cells induce anti-tumor immunity and tumor responses in pre-clinical models of pancreatic adenocarcinoma: Towards clinical trials

Abstract

Abstract Although immunotherapy yields striking results in various malignancies, results in pancreatic cancer have been disappointing. Pancreatic cancer has been characterized as a non-cytotoxic T-cell infiltrated tumor, and this may explain the low response rate of immune checkpoint antibodies. A highly immunosuppressive tumor microenvironment and dense desmoplastic stroma in established pancreatic tumors are considered to be the main reasons. Dendritic cells (DCs) are the most potent activators of the immune system and DC vaccination have been shown to successfully induce immune responses in various non-immunogenic malignancies. DCs loaded with an allogeneic mesothelioma tumor cell lysate has proven to be safe, feasible and clinically active in mesothelioma patients. Mesothelioma and pancreatic cancer share tumor characteristics and tumor antigens. We therefore argue that this off-the-shelf vaccine may be beneficial for the treatment of pancreatic cancer. In a murine model we assessed the effectiveness of mesothelioma-lysate loaded DCs against pancreatic adenocarcinoma. C57BL/6 mice were vaccinated with bone-marrow derived DCs both prior to and subsequent to inoculation with subcutaneous syngeneic pancreatic tumor cells (KPC3). DCs were generated with a GM-CSF bone marrow culture and stimulated overnight with CpG along with either pancreatic (KPC3) or mesothelioma tumor (AE17) lysate. Lysates were generated by freeze-thawing and sonification. Mice were challenged with KPC3 tumors and tumor sizes were monitored over time. Immune responses were determined by flow-cytometry of cells in peripheral blood, spleen and tumor. Tumor-specific T-cell responses were investigated by co-culturing purified splenic CD8+ T-cells with IFNg-treated pancreatic cancer cells. DC vaccination preceding tumor challenge led to a significant increase of systemic CD4+ and CD8+ T-cells frequencies in treated mice compared to untreated mice and were persistent over time (p<0.001). This also holds true for effector memory, activated and proliferating CD4+ and CD8+ T-cells. In addition, treated mice displayed significantly delayed tumor growth accompanied by increased frequencies of intratumoral T-cells compared to untreated mice (p<0.05). No difference in immune activation was observed between mice receiving DCs stimulated with pancreatic cancer or mesothelioma lysate. In both groups, a negative correlation between tumor size and tumor infiltrating lymphocyte frequency was found. No differences in intratumoral regulatory T-cells were measured between groups. Interestingly, vaccination with DCs stimulated with CpG in the absence of tumor lysate did not delay tumor growth. To further denote the induction of a tumor-specific T-cell response of both pancreatic and mesothelioma lysate-DC vaccination, the frequencies of CD69+, IFNg+, CD107a+ and granzyme B+ expressing CD8+ T-cells were increased upon stimulation with pancreatic cancer cells compared to untreated mice (P<0.001). Vaccination in a therapeutic setting also demonstrated identical robust systemic immune responses; however, no retardation in tumor growth or survival benefit was observed. In line with this observation, tumor analysis of treated mice revealed a lack of infiltrating lymphocytes in the tumor microenvironment, explaining the lack of therapeutic efficacy.The results demonstrate the potency of mesothelioma lysate-DC therapy generating a robust tumor-specific response with delay in tumor growth in a pancreatic cancer murine model. These findings warrant further testing of mesothelioma lysate-DC vaccination in a clinical setting, and therefore we are currently setting up a trial starting with resected pancreatic cancer patients having no clinical signs of established tumor. Citation Format: Sai Ping S. Lau, Priscilla P. Kinderman, Melanie M. Lukkes, Floris F. Dammeijer, Heleen H. Vroman, Menno M. van Nimwegen, Thorbald T. van Hall, Sjoerd S.H. van der Burg, Joachim J.G.J.V. Aerts, Nadine A.G. Pronk-van Montfoort, Casper C.H.J. van Eijck. Allogeneic tumor-lysate loaded dendritic cells induce anti-tumor immunity and tumor responses in pre-clinical models of pancreatic adenocarcinoma: Towards clinical trials [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B117.