Characterization of SPP1 + macrophages and their correlation with resistance to neoadjuvant chemotherapy in colorectal cancer liver metastasis.

Neoadjuvant chemotherapy (NAC) for colorectal cancer liver metastasis (CRLM) remains a major clinical challenge, with outcomes varying widely among patients, yet the mechanisms that drive therapeutic resistance remain incompletely understood. In this study, we integrated single‑cell RNA‑sequencing and spatial transcriptomics of patient tumor specimens to dissect the interplay between the hepatic tumor microenvironment and chemotherapy resistance. We identified a specific macrophage subpopulation marked by elevated expression of Secreted Phosphoprotein 1 (SPP1) that is significantly enriched in insufficient responders to NAC. Mechanistically, these SPP1 + macrophages exhibit a pro‑tumoral transcriptomic profile and directly suppress CD8 + T cell cytotoxic function through the SPP1‑CD44 signaling axis, as demonstrated by in vitro co‑culture assays, a large‑scale tissue microarray, and multiple syngeneic mouse models. Spatially, they are scattered throughout the tumour and form dense barriers that sequester CD8 + T cells and drive their exhaustion. Strikingly, this spatial configuration inversely correlates with cytotoxic activity and adaptive immune signatures and thereby reinforces a local immunosuppressive niche that sustains chemoresistance. These data provide the missing link: effective chemotherapy requires an immune‑active hepatic microenvironment, and SPP1 + macrophage infiltration actively disrupts this state, which in turn promotes clinical resistance. In a preclinical CRLM model, SPP1 blockade synergised with anti‑PD‑1, inducing significant tumour regression and restoring T‑cell function. Collectively, our findings position SPP1 + macrophages as central drivers of NAC resistance in CRLM and highlight the spatial immune barrier they create as a promising therapeutic target for overcoming chemoresistance and improving immunotherapy responses.