Tumor cell-released autophagosome (TRAP) programs inflammatory CAFs to drive the immune-excluded TIME through C3a.

The immune-excluded tumor immune microenvironment (TIME) limits responses to ICIs. Cancer-associated fibroblasts are the most abundant stromal population and key regulators of immune suppression; however, the upstream cues that program pathogenic CAF states and the mechanisms of the immune-excluded TIME remain poorly defined. Here, by combining single-cell RNA sequencing and functional validation, we report that tumor cell-released autophagosome (TRAP) programs inflammatory CAFs (iCAFs) and triggers cathepsin L-dependent intracellular cleavage of C3 into C3a via the HSP70-TLR4-MyD88-ERK/p38 pathway. iCAF-derived C3a affects C3a on TAMs, promotes TAM accumulation in the iCAF-rich stroma, limits TIL trafficking into tumor nests, and reinforces an immune-excluded TIME. Disrupting the TRAP-iCAF-C3a/C3aR axis remodels the immune-excluded TIME and sensitizes tumors to anti-PD-L1 therapy. In clinical cohorts, plasma TRAP and C3a levels increased with disease stage, and their combination improved the discrimination of patients with breast cancer from controls (AUC = 0.96). These data define a TRAP-driven stromal-immune circuit that promotes immune exclusion and suggest that the C3a-C3aR axis is a potential target for enhancing ICI efficacy.