Fibroblasts in colorectal cancer: Subtype diversity and immune cell modulation
Dissertation
Datum der mündl. Prüfung:2024-02-13
Erschienen:2024-02-20
Betreuer:Prof. Dr. Philipp Ströbel
Gutachter:Prof. Dr. Philipp Ströbel
Gutachter:Prof. Dr. Frauke Alves
Dateien
Name:2023_DavidA_Dissertation_SUB.pdf
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Description:2023_DavidA_Thesis
Diese Datei ist bis 12.02.2025 gesperrt.
Zusammenfassung
Englisch
Despite significant advances in early detection and treatment, colorectal cancer (CRC) remains one of the deadliest cancers worldwide. In case of advanced disease, immunotherapies, such as immune checkpoint inhibitors (e.g., PD-1 blocking antibodies) hold great promise to improve prognosis. However, mainly tumors with pre-existing immune cell infiltration benefit from such approaches, rendering the majority of patients with metastatic disease ineligible. CRC was shown to be characterized by a heterogeneous tumor microenvironment (TME), substantially consisting of fibroblasts. Studies in CRC and other cancer entities have demonstrated that fibroblasts can promote cancer progression, limit infiltration into the tumor and suppress effective anti-tumor immunity. While this corroborates fibroblasts as attractive targets in the TME, their plasticity and heterogeneity hamper specific targeting. To dissect fibroblast heterogeneity in CRC, we performed single-cell RNA sequencing of approx. 23.000 fibroblasts from both normal human colorectal as well as colorectal cancer tissues. We defined eleven distinct fibroblast clusters, of which three were primarily found in cancer tissue. Several of these clusters have been described in normal human colon or other tissues and cancers before, validating our findings. The identified subpopulations were confirmed at the protein level using spatial proteomic analysis of characteristic proteins corresponding to cluster-specific differentially expressed genes. Among the identified cancer-associated fibroblast (CAF) populations, a novel subtype of CAFs was identified, characterized by expression of immune-modulatory factors including NECTIN2, CD40 and CD248. NECTIN2 belongs to the Nectin family of Ca2+-independent cell adhesion molecules and is a ligand for co-stimulatory and -inhibitory receptors on T and NK cells. Our data showed that NECTIN2 expression is restricted to the stroma in CRC and that NECTIN2+ CAFs are located in close proximity to T cells, but distant to tumor cells. Functional analysis demonstrated that this novel subtype inhibits T cell functionality and increases exhaustion via NECTIN2 signaling, as blocking of NECTIN2 but not CD40 signaling was sufficient to restore T cell functionality. Notably, high expression of characteristic genes for this CAF subtype are poor prognostic factors for relapse-free survival of colon cancer patients, underscoring the involvement of the newly identified population in immunosuppression. Taken together, this study provides a comprehensive classification of fibroblasts in colorectal cancer. In addition, it describes a novel CAF subtype that could potentially serve as target for future immunotherapy.
Keywords: colorectal cancer; cancer-associated fibroblasts; CRC; CAFs; T cell-inhibitory CAFs; TinCAFs
Schlagwörter: CRC; CAFs; TinCAFs; colorectal cancer; cancer-associated fibroblasts; T cell-inhibitory cancer-associated fibroblasts