B7-H3/CD276-specific nanobody T3CL11 enables tumor imaging in murine osteosarcoma and colorectal cancer models

Members of the B7 receptor family regulate immune responses and tumor progression. B7-H3 (CD276) is highly expressed in many solid tumors, where it suppresses immune surveillance and is associated with poor clinical prognosis, making it an attractive diagnostic and therapeutic target. Here, we generated T3CL11, a nanobody specific for the human B7-H3 ectodomain, and report a crystal structure at 2.4-Å resolution of its complex with a single IgV-IgC module of B7-H3. T3CL11 binds the membrane-distal IgV domain on the face opposite the two N-glycosylation sites, with recognition mediated primarily by CDR2 and CDR3. In murine osteosarcoma and colorectal cancer models, T3CL11 enabled tumor imaging and co-localized with the clinically evaluated anti-B7-H3 antibody DS-7300a, confirming specific tumor-surface binding in vivo . These findings establish T3CL11 as a promising candidate for the development of B7-H3-targeted diagnostic imaging and future theranostic applications.