Enhanced antigen cross-presentation in human colorectal cancer-associated fibroblasts through upregulation of the lysosomal protease cathepsin S

Harryvan, T.J.; Visser, M.; Bruin, L. de; Plug, L.; Griffioen, L.; Mulder, A.; Veelen, P.A. van; Noort, G.J.V. van; Jongsma, M.L.; Meeuwsen, M.H.; Wiertz, E.J.; Santegoets, S.J.; Hardwick, J.C.; Hall, T. van; Neefjes, J.; Burg, S.H. van der; Hawinkels, L.J.A.C.; Verdegaal, E.M.E.

doi:doi:10.1136/jitc-2021-003591

Background Cross-presentation of exogenous antigens in HLA-class I molecules by professional antigen presenting cells (APCs) is crucial for CD8+ T cell function. Recent murine studies show that several non-professional APCs, including cancer-associated fibroblasts (CAFs) also possess this capacity. Whether human CAFs are able to cross-present exogenous antigen, which molecular pathways are involved in this process and how this ultimately affects tumor-specific CD8+ T cell function is unknown. Methods In this study, we investigated the ability of human colorectal cancer (CRC)-derived CAFs to cross-present neoantigen-derived synthetic long peptides (SLPs), corresponding to tumor-derived mutant peptides, and how this affects tumor-specific T-cell function. Processing of the SLP was studied by targeting components of the cross-presentation machinery through CRISPR/Cas9 and siRNA-mediated genetic ablation to identify the key molecules involved in fibroblast-mediated cross-presentation....Show moreBackground Cross-presentation of exogenous antigens in HLA-class I molecules by professional antigen presenting cells (APCs) is crucial for CD8+ T cell function. Recent murine studies show that several non-professional APCs, including cancer-associated fibroblasts (CAFs) also possess this capacity. Whether human CAFs are able to cross-present exogenous antigen, which molecular pathways are involved in this process and how this ultimately affects tumor-specific CD8+ T cell function is unknown. Methods In this study, we investigated the ability of human colorectal cancer (CRC)-derived CAFs to cross-present neoantigen-derived synthetic long peptides (SLPs), corresponding to tumor-derived mutant peptides, and how this affects tumor-specific T-cell function. Processing of the SLP was studied by targeting components of the cross-presentation machinery through CRISPR/Cas9 and siRNA-mediated genetic ablation to identify the key molecules involved in fibroblast-mediated cross-presentation. Multispectral flow cytometry and killing assays were performed to study the effect of fibroblast cross-presentation on T cell function. Results Here, we show that human CRC-derived CAFs display an enhanced capacity to cross-present neoantigen-derived SLPs when compared with normal colonic fibroblasts. Cross-presentation of antigens by fibroblasts involved the lysosomal protease cathepsin S. Cathepsin S expression by CAFs was detected in situ in human CRC tissue, was upregulated in ex vivo cultured CRC-derived CAFs and showed increased expression in normal fibroblasts after exposure to CRC-conditioned medium. Cognate interaction between CD8+ T cells and cross-presenting CAFs suppressed T cell function, reflected by decreased cytotoxicity, reduced activation (CD137) and increased exhaustion (TIM3, LAG3 and CD39) marker expression. Conclusion These data indicate that CAFs may directly suppress tumor-specific T cell function in an antigen-dependent fashion in human CRC.Show less

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Enhanced antigen cross-presentation in human colorectal cancer-associated fibroblasts through upregulation of the lysosomal protease cathepsin S