GARP+ Erythroid Regulatory Cells (G-ERCs) define spatially organized immunosuppressive niches that restrain anti-tumor immunity

Introduction/Rationale: Erythroid precursors have emerged as regulators of tumor immunity, yet their suppressive mediators and spatial context remain unclear. We identified a distinct population of GARP+ Erythroid Regulatory Cells (G-ERCs) that express the TGFβ docking receptor GARP (encoded by LRRC32). Given GARP’s known role in immune regulation, we hypothesized that these erythroid-derived cells create immunosuppressive niches within the tumor microenvironment (TME) that dampen antitumor responses.

Methods: Erythroid-specific Garp-knockout (KO) mice (EporRCreLrrc32fl/fl) bearing MB49 bladder tumors were analyzed by high dimensional flow cytometry, validated by adoptive co-transfer of Pmel CD8+ T cells with Garp-KO or WT G-ERCs. 10x Visium transcriptomics were used to identify Lrrc32+ regions with positive signature defining G-ERCs. Multiparametric immunofluorescence (mIF) and immune deconvolution validated G-ERC localization and surrounding immune composition.

Results: Tumor growth was significantly slower in erythroid-specific Garp-KO mice compared to WT controls, and in tumor-bearing mice receiving Pmel cells co-transferred with Garp-KO ERCs versus WT G-ERCs. Spatial transcriptomics revealed organized G-ERC enriched regions, enriched for TGFβ, hypoxia, and oxidative-stress pathways. Integrated mIF and deconvolution confirmed that G-ERC niches were surrounded by areas with reduced dendritic cells and B cells, increased myeloid cells, and lower cytotoxic and interferon-response activity. Garp deletion remodeled the TME, increasing CD8+ infiltration and effector activation, enhanced CD8+ T-cell effector differentiation while reducing exhaustion programs, as also validated by flow cytometry. Circulating G-ERC like cells were also detected in patients with cancer.

Conclusion: G-ERCs represent a regulatory erythroid subset forming spatially organized niches suppressing T-cell immunity. Targeting erythroid GARP enhances antitumor responses and represents a novel link between erythropoiesis and cancer immunity.