Experimental study of tumor-associated macrophage-derived SPP1 inhibit CD8+ T cells to promote Colorectal cancer progression

Colorectal cancer (CRC) progression is strongly influenced by the tumor immune microenvironment, yet the immunoregulatory role of tumor-associated macrophages (TAMs) remains incompletely defined. Using integrated single-cell RNA sequencing and spatial transcriptomic analyses, we identified a distinct TAM subset in CRC characterized by high expression of secreted phosphoprotein 1 (SPP1). In a macrophage-depleted murine CRC model established with clodronate (CL2MDP) liposomes and MC38 cells, macrophage depletion significantly inhibited tumor growth, accompanied by reduced SPP1 expression and increased infiltration of CD8⁺ T cells and type 1 cytotoxic T (Tc1) cells. Supplementation with recombinant SPP1 partially reversed these antitumor effects. Mechanistically, in vitro coculture experiments demonstrated that TAM-derived SPP1 suppressed CD8⁺ T cell differentiation into Tc1 cells through CD44-mediated signaling, resulting in decreased TNF-α and IFN-γ production and impaired activation of the LCK-ZAP70-LAT signaling pathway. These effects were attenuated by SPP1 neutralization or CD44 inhibition. Collectively, these findings elucidated TAM-derived SPP1 as a key mediator of immune suppression in CRC and suggested that the TAM-SPP1 axis is a potential therapeutic target.