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

## TL;DR

This study explores how different types of cancer-associated fibroblasts affect the success of anti-PD-1 immunotherapy in breast cancer patients.

## Contribution

The study identifies four CAF subtypes and their roles in immunotherapy response through single-cell RNA sequencing and spatial transcriptomics.

## Key findings

- Four CAF subtypes were identified: vascular, myofibroblastic, inflammatory, and antigen-presenting CAF-like cells.
- Stromal remodeling in responders involves pro-inflammatory CAFs and reduced vCAF/myCAF populations.
- Resistance is linked to stromal fortification via apCAF-like and vCAF-derived molecular axes.

## Abstract

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.

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.

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.

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.