865 Sugar high: Does the sialic acid profile of cancer-associated fibroblasts induce a more tumour-permissive microenvironment?. (10th December 2020)

• Record Type: Journal Article
• Authors: Egan, Hannah; Treacy, Oliver; Lynch, Kevin; Leonard, Niamh; Nader, Amir; Sheehan, Margaret; Hynes, Sean; Egan, Laurence; Ritter, Thomas; Daly, John; Hogan, Aisling; Michael, O; Ryan, Aideen
• Is Part Of: Journal for immunotherapy of cancer. Volume 8(2020)Supplement 3
• Page Start: A514
• Page End: A515
• Publication Date: 2020-12-10
• Subjects: Cancer -- Immunotherapy -- Periodicals; Cancer -- Immunological aspects -- Periodicals; Tumors -- Immunological aspects -- Periodicals; Immunotherapy -- Periodicals; 616.99406105
• DOI: 10.1136/jitc-2020-SITC2020.0865
• Languages: English
• ISSNs: 2051-1426

Abstract

Abstract : Background: Immunosuppressive tumour microenvironments (TME) inhibit the effectiveness of cancer immunotherapies. Sialic acids, which exist as terminal sugars of glyco-conjugates, are highly expressed on cancer cells and are involved in various pathological processes including increased immune evasion, tumour invasiveness and tumour cell metastasis. 1 Siglecs (Sialic acid-binding immunoglobulin-type lectins) are expressed on immune cell surfaces and bind sialic acid. Siglec binding to hypersialylated tumour glycans blocks immune cell activation to promote immunosuppression. 1 2 Intestinal stromal cells (iSCs), precursors to cancer-associated fibroblasts (CAFs), are a key component of the TME and play a vital role in tumour progression by enhancing a tumour-promoting microenvironment. The aim of this study was therefore to investigate if iSC/CAF sialylation contributes to enhanced immunosuppression in the TME. Methods: iSCs were isolated from colorectal cancer patient biopsies and cultured ex vivo. Informed consent was obtained from all patients prior to sampling. Tumour-derived iSCs were termed CAFs while control iSCs, isolated from tumour-adjacent non-cancerous tissue, were termed normal-associated fibroblasts (NAFs). NAFs/CAFs were then co-cultured with healthy allogeneic PBMCs and their immunosuppressive properties were assessed by flow cytometry. Results: CAFs significantly supressed the proliferation of CD8+ and CD4+ T-cells and induced a more exhausted T-cell phenotype as evidenced by increased expression of the exhaustion markers TIM-3, LAG-3 and PD-1 when compared to co-culture with control NAFs, thereby demonstrating their potent immunosuppressive properties. Strikingly, CAFs also induced significantly higher expression of both Siglec-7 and Siglec-9 receptors on CD8+ T-cells specifically. To elucidate the role of sialylation on CAF-mediated immunosuppression, NAFs/CAFs were treated with the sialyltransferase inhibitor (SI) P-3FAX-Neu5Ac prior to co-culture. Reduction of sialic acid expression on NAFs/CAFs was confirmed by flow cytometry and the SI-treated NAFs/CAFs were then co-cultured with allogeneic T-cells to assess the functional consequences of reduced NAF/CAF sialylation. SI-treated CAFs induced significantly less CD4+TIM-3+ and both CD4+LAG-3+ and CD8+LAG-3+ T-cells compared to their untreated counterparts. Interestingly, SI-treated CAFs also induced significantly less Siglec-7 and -9 receptor-expressing CD8+ T-cells. Conclusions: These results demonstrate that non-haematopoietic stromal cells in the tumour-microenvironment can suppress activated T-cells and that this immunosuppressive effect can be significantly reversed through the modulation of sialylation on the stromal cell surface. These results support the hypothesis that stromal cell sialylation plays a role in their immunosuppressive properties. Understanding how sialylation of stromal cells is regulated and functions to enhance immunosuppression in the TME could uncover novel immune checkpoints to reactivate anti-tumour immunity, allowing for tumour cell clearance. Ethics Approval: This study was approved by Galway University Hospitals' Clinical Research Ethics Committee, approval number C.A 2074. Consent: N/A References: Wang L, Liu Y, Wu L, Sun XL. Sialyltransferase inhibition and recent advances. Biochim Biophys Acta 2016 Jan; 1864(1):143-53. Munkley J, Scott E. Targeting aberrant sialylation to treat cancer. Medicines (Basel) 2019 Oct 13;6(4):102.