Abstract P031: Enrichment of photodynamically-primed anti-tumor immune infiltrates in pancreatic cancer: Enabling enhanced immunotherapy

Pancreatic ductal adenocarcinoma (PDAC) has a dismal 5-year survival rate of 10%. It poorly responds to conventional cancer treatments. Immune checkpoint blockade (ICB) has revolutionized cancer therapeutics. However, in PDAC, even the modest success of ICB is limited to ~1-3% of patients as the majority of patients' tumors are considered as immunologically ‘'cold'' due to their highly immunosuppressive tumor microenvironment (TME). Photodynamic therapy (PDT) is an FDA approved anti-cancer therapy that utilizes light, a photoresponsive non-toxic chemical called a photosensitizer, and oxygen to generate reactive molecular species that confer direct cytotoxicity or vascular shutdown. PDT alters the TME transiently in a process termed photodynamic priming (PDP), making it more receptive to subsequent therapies, including chemo- and immunotherapy. Previous studies have demonstrated that PDP is capable of affecting both the innate and adaptive immune systems. These immune-stimulatory effects occur through its ability to induce immunogenic cell death via the release of damage-associated molecules (DAMPs) and tumor-associated antigens. In this study, we investigated PDP-induced immunogenicity in PDAC. In an immunocompetent mouse model of PDAC, we evaluated tumor-infiltrating lymphocyte (TIL) enrichment in tumors and ongoing immune responses in mouse spleens/blood from 1h to 120h post-PDP treatment comparing the responses in untreated controls. We observed gradual increases in T and B cell infiltration from 1h to 120h post-PDP where the T cell subset analysis showed an enrichment of CD8+ T cells in PDP-treated tumors. These CD8+ T cells showed temporal increases in PD1, CTLA4 and TIM3 immune checkpoints suggesting PDP-induced immune priming in the TME. This was further evidenced by the upregulation of DAMPs, including high mobility group box protein-1 and calreticulin in PDP treated tumors. Analyzing spleens of mice, we detected a significant increase in CD11C+MHC11hi dendritic cells from 1h to 24h post-PDP. Also, activation of an adaptive immune response in splenic B cell follicles was noted by the presence of proliferating germinal centers by 120h post-PDP. In addition, evaluating the blood of PDP treated mice, we detected expansion of CD8+ effector memory T and natural killer cell populations, signifying PDP-induced systemic immune responses compared to untreated mice. We further investigated how immune cells infiltrate PDP-treated tumors. A reduced formation of blood (CD31+) and lymphatic (Lyve-1+) vessels post-PDP at 120h was observed. However, decreases in PDL1, collagen and fibroblast activation proteins were observed in PDP-treated tumors at 120h, suggesting mitigation of immunosuppressive mechanisms and enhanced tumor permeability, allowing TIL migration. Our data shows converting immunologically silent PDAC tumors into inflamed ‘'hot'' tumors by triggering not only a local immune infiltration but also enhanced systemic immune responses, ultimately enhances the immunogenicity of pancreatic tumors.

Citation Format: Pushpamali De Silva, Mohammad Ahsan Saad, Zhiming Mai, Shazia Bano, Assiris P. Camargo, Tayyaba Hasan. Enrichment of photodynamically-primed anti-tumor immune infiltrates in pancreatic cancer: Enabling enhanced immunotherapy [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P031.

Abstract 4519: Photochemically-primed immune cell enrichment and anti-tumor responses to pancreatic cancer

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.