In situ cancer vaccines represent an emerging strategy in cancer immunotherapy; however, the local immunosuppressive microenvironment within tumors limits their immune activation and therapeutic efficacy. The CXCL12/CXCR4 axis is a critical mediator of this immunosuppressive environment. In this study, siCXCR4 (S) was employed as an "immune adjuvant" and co-delivered with hydroxycamptothecin (HCPT) to construct an in situ cancer nanovaccine (HCPT/S@CaP/HA) aimed at synergistically inhibiting the growth, recurrence, and metastasis of triple-negative breast cancer (TNBC). HCPT/S@CaP/HA actively targeted orthotopic TNBC cells and cancer-associated fibroblasts (CAFs), inducing immunogenic cell death of TNBC cells and promoting dendritic cell (DC) maturation. Concurrently, HCPT/S@CaP/HA reduced CXCL12 secretion by CAFs and silenced CXCR4 expression in TNBC tissues, thereby bidirectionally blocking the CXCL12/CXCR4 axis. This dual action synergistically reversed the immunosuppressive microenvironment, enhanced infiltration and activity of cytotoxic T lymphocytes in TNBC tissues, and inhibited tumor growth. Furthermore, HCPT/S@CaP/HA prevented TNBC recurrence by increasing memory T lymphocyte populations in mouse spleen tissue and suppressed spontaneous lung metastasis by enhancing tumor antigen presentation and activating TNBC-specific immune responses. Overall, HCPT/S@CaP/HA shows potential as an effective in situ nanovaccine for TNBC immunotherapy.
