Cancer-associated fibroblasts (CAFs) have been described as key players in the tumor microenvironment. They have been shown to affect cancer progression and response to treatment in different cancers [1-3]. Moreover, subtypes, such as myofibroblastic (myCAF), inflammatory (iCAF) and antigen-presenting cancer-associated fibroblasts (apCAF), have been identified and shown to have different functional implications [4-6]. Accordingly, their contribution to tumor progression varies. This provides means to specifically target tumor-promoting CAFs and refine therapy approaches. However, for colorectal cancer a comprehensive analysis of fibroblast subtypes has been missing thus far.
In order to address these limitations, we analyzed approx. 23,000 fibroblasts isolated from normal human colon or colorectal cancer tissue from 7 different patients by single-cell RNA sequencing. We identified 11 distinct clusters of fibroblasts, including known subtypes, such as myCAFs, iCAFs, colon crypt and crypt tip fibroblast. Four of the clusters were primarily found in colorectal cancer. We then used spatial proteomics to confirm these findings and to address the spatial organization within colorectal cancer tissue. To identify cell types based on their marker expressions we used the MACSima platform. This technology is based on cyclic staining, enabling immunofluorescent imaging of hundreds of targets on the same sample at subcellular resolution. The erasure mechanism between cycles uses photobleaching of fluorescent labels, or release of binders or labels. With MACSima we identified a close interaction between CAF populations and T cells in the tumor microenvironment of colorectal cancer. In vitro assays confirmed the capacity of CAFs to interact with and suppress T cells.
Our approach demonstrated the utility of spatial proteomics in immune-oncology contexts, and revealed fibroblast heterogeneity in human colon and colorectal cancer. Our data confirmed the presence of known subtypes and suggested the presence of novel types of CAFs. Moreover, spatial proteomics highlighted a close interaction of CAFs and T cells, which was confirmed in vitro. These findings provide an atlas of fibroblast heterogeneity and colorectal cancer and might facilitate identification and targeting of pro-tumorigenic CAFs in colorectal cancer.
Literature:
[1] Glabman, R.A., et al., Cancers (Basel), 2022. 14(16). [2] Mhaidly, R., et al., Immunol Rev, 2021. 302(1): p. 259-272. [3] Shimoda, M., et al., Semin Cell Dev Biol, 2010. 21(1): p. 19-25. [4] Costa, A., et al., Cancer Cell, 2018. 33(3): p. 463-479 e10. [5] Elyada, E., et al., Cancer Discov, 2019. 9(8): p. 1102-1123. [6] Ohlund, D., et al., J Exp Med, 2017. 214(3): p. 579-596.
