Abstract A17: Enhanced immune infiltration and antitumor immune reactivity in response to optical priming in pancreatic cancer

Pancreatic adenocarcinoma (PDAC) is one of the most lethal malignancies with a survival rate of approximately 5% at five years. At diagnosis, the majority of patients present with advanced primary or metastatic disease that is unresectable. PDAC pathophysiology is challenging for current therapies as immunosuppressive desmoplastic stroma limits responsiveness to treatments including immunotherapy. Latter condition is making vast proportion of PDAC tumors immunologically cold as defined by the lack of effective immune infiltration to the tumor. Thus, there is an unmet need for improved treatment strategies. Photodynamic therapy (PDT) is an approved modality that utilizes light, a photoresponsive photosensitizer (PS), and oxygen to generate reactive oxygen species that will kill nearby cells or prime neighboring cells to be more responsive to traditional therapies, and thereby produce a synergistic outcome. We aimed to investigate PDT-induced immunogenicity in PDAC tumors. In this study, we applied PDT in an immunocompetent mouse (C57BL/6 mice), PDAC tumor model and assessed tumor-infiltrating lymphocyte (TIL) infiltration at different time points. Visudyne was used as the PS. Multicolor flow cytometric analysis showed gradual increase of T- and B-cell infiltration at 1h time point to 5 days after PDT. T-cell subset analysis showed a higher infiltration of CD8+ T cells with time. Localization of immune cells using immunofluorescence assays further confirmed latter findings. We observed a presence of proliferating T cells in the T cell zone of spleen B cell follicles 1h after treating with PDT, suggesting an early T-cell activation. Activated dendritic cells were localized in the spleens treated with PDT compared to the untreated control. We further evaluated antitumor immune reactivity of CD8+ T cells treated with PDT in an in vitro 3D system consisting of human PDAC cell line, MiaPaCa2, pancreatic fibroblast, and human peripheral blood mononuclear cell coculture. Tumor reactivity by CD8+ T cells was evaluated at baseline, 3 days, 7 days, and 2 weeks in coculture after PDT by staining for the surface expression of degranulation marker CD107a. There was a continuous CD107a upregulation in CD8+ T cells from day 3 to 2 week in coculture treated with PDT compared to untreated controls, demonstrating enhanced PDT priming of T cells, in vitro. In addition, there was effective tumor cell killing in PDT-treated immune-tumor cocultures. Our data show a possibility of triggering an immediate and effective immune response to PDT in PDAC tumors, enhancing the immunogenicity of this tumor type. Citation Format: Pushpamali De Silva, Mohammad Ahsan Saad, Assiris P. Camargo, Joseph Swain, Akilan Palanasami, Girgis Obaid, Shalin Shetty, Tayyaba Hasan. Enhanced immune infiltration and antitumor immune reactivity in response to optical priming in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A17.