# POSTN⁺ cancer-associated fibroblast–CCL3⁺ macrophage crosstalk defines the immune-excluded tumor microenvironment in clear cell renal cell carcinoma

## TL;DR

The study identifies a specific interaction between POSTN-positive cancer-associated fibroblasts and CCL3-positive macrophages that creates an immune-excluded environment in kidney cancer, potentially limiting immunotherapy effectiveness.

## Contribution

The novel contribution is the discovery of a POSTN⁺ CAF–CCL3⁺ macrophage signaling axis that drives immune exclusion in clear cell renal cell carcinoma.

## Key findings

- POSTN⁺ CAFs and CCL3⁺ macrophages colocalize at the tumor invasive front, forming a fibrotic niche that excludes CD8⁺ T cells.
- The POSTN⁺ CAF–CCL3⁺ macrophage axis correlates with poor survival and reduced response to immunotherapy in ccRCC.
- GATA6 is identified as a key regulator of fibroblast differentiation into POSTN⁺ CAFs.

## Abstract

•POSTN⁺CAFs drive immunosuppression via CCL3⁺macrophages in ccRCC.•Spatial mapping confirms POSTN⁺ CAF-CCL3⁺ macrophage colocalization.•POSTN⁺ CAF-CCL3⁺ macrophage axis mediates T-cell exclusion in tumors.•SpaGene analysis reveals ECM-immune programs in TLS⁺/TLS⁻ samples.•Targeting POSTN⁺ CAFs may restore T-cell infiltration for immunotherapy.

POSTN⁺CAFs drive immunosuppression via CCL3⁺macrophages in ccRCC.

Spatial mapping confirms POSTN⁺ CAF-CCL3⁺ macrophage colocalization.

POSTN⁺ CAF-CCL3⁺ macrophage axis mediates T-cell exclusion in tumors.

SpaGene analysis reveals ECM-immune programs in TLS⁺/TLS⁻ samples.

Targeting POSTN⁺ CAFs may restore T-cell infiltration for immunotherapy.

Clear cell renal cell carcinoma (ccRCC) frequently exhibits an immune-excluded tumor microenvironment (TME) that limits the efficacy of immune checkpoint blockade (ICB). However, the stromal–immune interactions responsible for this exclusion remain poorly understood.

We integrated eight single-cell RNA sequencing datasets, two spatial transcriptomic datasets, and bulk transcriptomic cohorts to construct a comprehensive ccRCC TME atlas. Fibroblast subsets were characterized using clustering, trajectory, transcription-factor regulon, and gene-network analyses. Stromal–immune signaling was assessed using CellChat and NicheNet, and spatial colocalization patterns were validated by SpaGene analysis. Prognostic and therapeutic relevance were evaluated in TCGA-KIRC and ICB-treated cohorts.

Seven fibroblast subtypes were identified, among which periostin (POSTN)–positive cancer-associated fibroblasts (CAFs) were selectively enriched in tumors and exhibited strong activation of TGF-β, PI3K–AKT, and extracellular-matrix pathways. Trajectory and regulon inference revealed GATA6 as a key transcriptional regulator driving fibroblast differentiation toward this ECM-remodeling phenotype. Spatial analyses demonstrated that POSTN⁺ CAFs colocalized with CCL3-positive macrophages at the invasive front, forming a hypoxic, fibrotic niche that excluded CD8⁺ T cells. Ligand–receptor mapping identified reciprocal TGF-β, SPP1, and IL-6 signaling that reinforced fibro-myeloid activation. Activation of the POSTN⁺ CAF–CCL3⁺ macrophage axis correlated with poor survival and reduced response to ICB therapy.

This study defines a spatially organized stromal–immune signaling axis that drives immune exclusion and immunotherapy resistance in ccRCC. Targeting the POSTN⁺ CAF–CCL3⁺ macrophage interaction offers a promising strategy to remodel the fibrotic barrier and restore antitumor immunity.

Image, graphical abstract