Molecular remodeling of cancer-associated fibroblasts in breast cancer patients receiving anti-PD-1 immunotherapy.

Introduction: Cancer-associated fibroblasts (CAFs) are integral components of the tumor microenvironment that modulate the response to immune checkpoint inhibitors, particularly in breast cancer. However, the specific roles of CAF subtypes in regulating the efficacy of anti-PD-1 therapy remain poorly elucidated. Methods: In this study, we reanalyzed single-cell RNA sequencing data from breast cancer patients treated with anti-PD-1 inhibitors to identify CAF subtypes and characterize their molecular signatures. Identified subtypes were further validated using spatial transcriptomics mapping to assess their anatomical niches. Results: Four distinct CAF subtypes were identified: vascular CAFs (vCAF), myofibroblastic CAFs (myCAF), inflammatory CAFs (iCAF), and antigen-presenting CAF-like (apCAF-like) cells. MyCAFs were localized to fibrotic stromal regions, while iCAFs were found within immune-rich, inflamed areas. In responders, stromal remodeling occurs, characterized by the functional re-education of iCAFs-transitioning to a pro-inflammatory CXCL9-CXCR3 axis-and the concurrent disarmament of vCAF and myCAF populations. Conversely, resistance in non-responders is linked to stromal fortification, driven by the apCAF-like-derived THBS2-CD47 axis and the pathological intensification of the vCAF-derived CXCL12-CXCR4 axis, leading to dysfunctional lymphoid sequestration. Discussion: Collectively, these findings highlight the critical role of CAF heterogeneity and spatial organization in modulating the response to anti-PD-1 therapy. Targeting subtype-specific stromal modules may represent a promising therapeutic strategy to enhance the efficacy of immunotherapy in breast cancer.