A novel extracellular vesicle-engineered immunotherapy drug for Her2+ breast cancer

• EVs loaded with a Her2 single-chain variable fragment derived from trastuzumab (EVs/Her2-scFv) showed effective targeting of Her2 + breast cancer. • Compared with trastuzumab, the intrinsic properties of EVs allow EVs/Her2-scFv to penetrate the blood–brain barrier and reduce brain metastases. • EVs/Her2-scFv encapsulated with Rabeprazole (EVs/Her2-scFv/Rabe) showed a remarkable ability to improve TIME and correct aberrant vasculaure associated with Her2 + breast cancer. • EVs/Her2-scFv/Rabe incorporated with CXCL9 (EVs/Her2-scFv/CXCL9/Rabe) further enhanced CD8 + T cell recruitment and infiltration. • The EVs/Her2-scFv/CXCL9/Rabe formulation demonstrated a superior antitumor efficacy compared to liposomal doxorubicin in terms of reduced toxicity. Trastuzumab profoundly improves outcomes of Her2 + breast cancer (BC) patients, but eventual drug resistance is inevitable. Therefore, new treatment options are urgently needed. Here, we modify extracellular vesicles (EVs) with a Her2 single-chain variable fragment of trastuzumab (EVs/Her2-scFv) to target Her2 + BC and found that EVs/Her2-scFv inhibit human Her2 + orthotopic BC comparable to trastuzumab and also uniquely suppress brain metastasies. Moreover, EVs/Her2-scFv loaded with rabeprazole (EVs/Her2-scFv/Rabe) effectively improve tumor immunosuppressive microenvironment and abnormal vasculature of Her2 + BC by reducing tumor EVs. When further anchored with CD8 + T cell chemotactic CXCL9, CXCL9-loaded EVs/Her2-scFv/Rabe (EVs/Her2-scFv/CXCL9/Rabe) facilitate CD8 + T cell recruitment and subsequent activation, thereby exhibiting immunotherapeutic effects on mouse Her2 + BC. In BC patient-derived tumor organoids (PDOs) and peripheral blood mononuclear cell coculture systems, EVs/Her2-scFv/CXCL9/Rabe limit PDO growth by blocking Her2 signaling and activating CD8 + T cells. Besides, EVs/Her2-scFv/CXCL9/Rabe are low-immunogenic with biosafety. Altogether, EVs/Her2-scFv/CXCL9/Rabe hold high potential in Her2 + BC therapy.