Single Cell Analysis Reveals the Heterogeneity of Cancer-Associated Fibroblasts in Pancreatic Ductal Adenocarcinoma

Introduction:

Cancer-associated fibroblasts (CAFs) are major players in the progression and drug resistance of pancreatic ductal adenocarcinoma (PDAC). Thus, targeting CAFs is considered a promising approach to sensitize this highly resistant malignancy. However, contradicting results obtained from multiple CAF-targeting methods support the notion that CAFs represent a heterogeneous population of cells, although the precise nature of this heterogeneity remains unknown. We have previously described two distinct CAF subtypes, myofibroblastic CAFs (myCAFs) and inflammatory CAFs (iCAFs) using a three-dimensional co-culture platform of PDAC organoids and fibroblasts. We hypothesized that there are other CAF subtypes in the PDAC microenvironment, and that different CAF subtypes have unique functions during PDAC development, that might incite opposite outcomes for the tumor biology.

Material and Method:

Here we employ single cell RNA sequencing of human and mouse PDAC tumors, to thoroughly decipher the heterogeneity of CAFs and to delineate the different cell populations in this cancer. We also validate the transcriptomics findings using orthogonal methods of flow cytometry and immunohistochemistry.

Results and Discussion:

We describe the different cell types found in PDAC, with an emphasis on the stromal cell populations. We corroborate the existence of myCAFs and iCAFs in mouse and human tumors and define their unique gene signatures in vivo. Importantly, we discover a third CAF population, which is characterized by the unique expression of MHC class II and the invariant chain Cd74, hence termed antigen presenting CAFs (apCAFs). Although limited, apCAFs show some antigen processing capacity in vitro and express low levels of the costimulatory molecule Cd80, suggesting they might be involved in the immunomodulation of PDAC.

Conclusion:

This comprehensive analysis paves the way to investigate the functional role of distinct CAF subtypes in PDAC, and to design effective therapeutic combinations for patient benefit.