Single-Cell and Spatial Transcriptomics Reveal a Tumor-Associated Macrophage Subpopulation that Mediates Prostate Cancer Progression and Metastasis.

Tumor-associated macrophages (TAM) are a transcriptionally heterogeneous population, and their abundance and function in prostate cancer is poorly defined. We integrated parallel datasets from single-cell RNA sequencing, spatial transcriptomics, and multiplex immunofluorescence to reveal the dynamics of TAMs in primary and metastatic prostate cancer. Four TAM subpopulations were identified. Notably, one of these TAM subsets was defined by the co-expression of SPP1+ and TREM2+ and was significantly enriched in metastatic tumors. The SPP1+/TREM2+ TAMs were enriched in the metastatic tumor microenvironment in both human patient samples and murine models of prostate cancer. The abundance of these SPP1+/TREM2+ macrophages was associated with patient progression-free survival. Spatially, TAMs within prostate cancer bone metastases were highly enriched within the tumor region, consistent with their protumorigenic role. Blocking SPP1 in the RM1 prostate cancer mouse model led to improved efficacy of anti-PD-1 treatment and increased CD8+ T-cell infiltration in tumor. These findings suggest that targeting SPP1+ TAMs may offer a promising therapeutic strategy and potentially enhance the effects of immune checkpoint inhibition in advanced prostate cancer. IMPLICATIONS: This study expands our understanding of the diverse roles of macrophage populations in prostate cancer metastases and highlights new therapeutic targets.