SPP1+ Macrophages Drive Immune Suppression in Colorectal Cancer Lymph Nodes
A newly identified macrophage-Treg axis in tumor-draining lymph nodes may explain how colorectal cancer evades immune attack.
Summary
Researchers discovered that a specific macrophage subtype, marked by SPP1, promotes the growth of immune-suppressing regulatory T cells in the lymph nodes nearest to colorectal tumors. Using single-cell RNA sequencing on matched patient samples, the team found that these SPP1-positive macrophages drive the maturation of a particularly immunosuppressive T cell subset called CD137+ Tregs. The mechanism involves a signaling chain from SPP1 to CD44 to NF-κB1, which activates genes that entrench immune suppression. When researchers blocked this pathway in mouse models using nanoparticle-delivered gene silencing and an antibody against CD44, lymph node metastasis was reduced and cancer-killing CD8+ T cells became more active. This work identifies a potentially druggable target for improving immunotherapy outcomes in colorectal cancer.
Detailed Summary
Colorectal cancer (CRC) is one of the leading causes of cancer-related death worldwide, and immune evasion is a central reason why tumors persist and spread. Tumor-draining lymph nodes (TDLNs) sit at a critical crossroads: they are the first lymphatic checkpoints the tumor microenvironment influences, and how the immune response is shaped there can determine whether metastasis occurs. Understanding the cellular dynamics within TDLNs is therefore essential for developing better immunotherapies.
This study performed single-cell RNA sequencing (scRNA-seq) on 23 matched tissue samples from seven CRC patients, covering primary tumors, adjacent normal tissue, tumor-free lymph nodes, and tumor-invaded lymph nodes (TILNs). This comprehensive atlas allowed researchers to map the immune landscape with single-cell resolution across disease-relevant compartments.
The key discovery was that TILNs are dominated by an expansion of SPP1-positive macrophages, which actively promote the differentiation of regulatory T cells (Tregs) into a highly immunosuppressive CD137+ subset. Mechanistically, SPP1 binds CD44 on Treg precursors, triggering NF-κB1 to bind directly to the TNFRSF9 promoter and drive CD137 expression. This creates a maturation niche within TILNs that effectively shields the tumor from immune clearance.
To validate therapeutic relevance, the team used lipid nanoparticle-encapsulated siRNA targeting SPP1 combined with an anti-CD44 monoclonal antibody in mouse lymph node metastasis models. The combination reduced metastatic spread, decreased CD137+ Tregs, and restored CD8+ cytotoxic T cell function — a clinically promising result confirmed across multiple patient cohort datasets.
These findings have significant implications for CRC treatment, particularly for patients who respond poorly to checkpoint inhibitors. However, the study is limited by small patient numbers and the use of murine models, which may not fully recapitulate human disease. The abstract-only access also constrains a full methodological appraisal.
Key Findings
- SPP1+ macrophages expand in tumor-invaded lymph nodes and create an immunosuppressive niche favoring Treg maturation.
- The SPP1-CD44-NF-κB1 signaling axis drives differentiation of immunosuppressive CD137+ Tregs in CRC lymph nodes.
- Blocking SPP1 with lipid nanoparticle siRNA plus anti-CD44 antibody reduced lymph node metastasis in mouse models.
- Targeting this axis restored CD8+ T cell cytotoxic function, suggesting potential to enhance immunotherapy responses.
- Findings were validated across in vitro assays, CRISPR knockout models, and independent patient cohort multiomics data.
Methodology
Single-cell RNA sequencing was performed on 23 quadruplet-matched samples (primary tumor, adjacent normal, tumor-free and tumor-invaded lymph nodes) from seven CRC patients. Mechanistic validation used in vitro functional assays, CRISPR knockout in primary Tregs, and in vivo mouse footpad-popliteal lymph node metastasis models with LNP-siSPP1 and anti-CD44 mAb. Findings were cross-validated with independent CRC multiomics cohorts.
Study Limitations
The patient cohort is small (n=7), which limits generalizability despite multiomics validation in independent datasets. Mouse models may not fully replicate the human TDLN immune environment, and translating LNP-siSPP1 delivery to clinical use involves unresolved safety and targeting challenges. This summary is based on the abstract only; full methodology, supplementary data, and statistical details were not accessible.
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