Human Pancreatic Carcinoma-Associated Fibroblasts Promote Expression of Co-inhibitory Markers on CD4+ and CD8+ T-Cells.

Laia Gorchs,Katharina P Kern,Peter Bankhead,Qingda Meng,Elena Rangelova,Helen Kaipe,Imrul Sadeak,Carlos Fernández Moro

doi:10.3389/fimmu.2019.00847

Abstract

Carcinoma-associated pancreatic fibroblasts (CAFs) are the major type of cells in the stroma of pancreatic ductal adenocarcinomas and besides their pathological release of extracellular matrix proteins, they are also perceived as key contributors to immune evasion. Despite the known relevance of tumor infiltrating lymphocytes in cancers, the interactions between T-cells and CAFs remain largely unexplored. Here, we found that CAFs isolated from tumors of pancreatic cancer patients undergoing surgical resection (n = 15) expressed higher levels of the PD-1 ligands PD-L1 and PD-L2 compared to primary skin fibroblasts from healthy donors. CAFs strongly inhibited T-cell proliferation in a contact-independent fashion. Blocking the activity of prostaglandin E2 (PGE2) by indomethacin partially restored the proliferative capacity of both CD4+ and CD8+ T-cells. After stimulation, the proportion of proliferating T-cells expressing HLA-DR and the proportion of memory T-cells were decreased when CAFs were present compared to T-cells proliferating in the absence of CAFs. Interestingly, CAFs promoted the expression of TIM-3, PD-1, CTLA-4 and LAG-3 in proliferating T-cells. Immunohistochemistry stainings further showed that T-cells residing within the desmoplastic stromal compartment express PD-1, indicating a role for CAFs on co-inhibitory marker expression also in vivo. We further found that PGE2 promoted the expression of PD-1 and TIM-3 on T-cells. Functional assays showed that proliferating T-cells expressing immune checkpoints produced less IFN-γ, TNF-α, and CD107a after restimulation when CAFs had been present. Thus, this indicates that CAFs induce expression of immune checkpoints on CD4+ and CD8+ T-cells, which contribute to a diminished immune function.

Highlights

The late diagnosis and the lack of an effective treatment brings pancreatic cancer to the fourth leading cause of cancer-related death, with a 5-year survival rate of only 6% [1]
We found that the expression of T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) (Figures 3A,B), PD-1 (Figures 3A,C) and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) (Figures 3A,D) were higher in the presence of cancer-associated fibroblasts (CAFs) on both CD4+ and CD8+ T-cells in a dosedependent manner (Supplementary Figures S2B–E) compared to the T-cells cultured in the absence of CAFs
Since we found that the immune modulatory activity of CAFs was at least partly mediated by COX-2 (Figure 2), we examined the impact of prostaglandin E2 (PGE2) on T-cell proliferation and expression of coinhibitory markers

Summary

Introduction

The late diagnosis and the lack of an effective treatment brings pancreatic cancer to the fourth leading cause of cancer-related death, with a 5-year survival rate of only 6% [1]. The failure of developing a successful treatment is due in part to the limited understanding of the complex microenvironment in the pancreatic tumor. Pancreatic stellate cells have a limited proliferative capacity and store vitamin A containing lipid droplets in their cytoplasm. In the presence of cancer cells, pancreatic stellate cells acquire an increased contractile ability which promotes the expression of α-smooth muscle actin (α-SMA), podoplanin and the loss of their characteristic cytoplasmic lipid droplets which results in the pathological release of extracellular matrix proteins triggering fibrosis and building a “wall” for therapy delivery [4]. Recent studies suggest that there are several subtypes of CAFs in pancreatic cancer that may play different roles in the tumor microenvironment [6,7,8]

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Results

Conclusion