Abstract 4519: Photochemically-primed immune cell enrichment and anti-tumor responses to pancreatic cancer
Authors: De Silva Pushpamali , Saad Mohammad Ahsan , Camargo Assiris P. , Swain Joseph , Palanasami Akilan , Hasan Tayyaba 
Published: September 2020

Abstract
Pancreatic adenocarcinoma (PDAC) is among the deadliest forms of cancer. Currently, it is the third leading cause of cancer deaths in the United States. 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. The latter condition is making a vast proportion of PDAC tumors being 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 photo-responsive 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 tumour-infiltrating lymphocyte (TIL) infiltration at different time points. Visudyne® 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 the anti-tumour 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 co-culture. Tumor reactivity by CD8+ T cells was evaluated at baseline, 3 days, 7 days and 2 weeks in co-culture 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 co-culture treated with PDT compared to untreated controls demonstrating enhanced PDT priming of T cells, in vitro. In addition, there was an effective tumor cell killing in PDT treated immune-tumour co-cultures. Our data shows 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, Tayyaba Hasan. Photochemically-primed immune cell enrichment and anti-tumor responses to pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4519.