• Background: MUC4 is a high-molecular-weight transmembrane mucin that is specifically expressed in various epithelial tissues (e.g., respiratory, digestive, and reproductive tracts) under physiological conditions, where it functions primarily in lubrication, protection, and cellular signaling. However, MUC4 is aberrantly overexpressed in multiple epithelial-derived cancers (such as pancreatic, breast, and ovarian cancers), and this upregulation is closely associated with tumor proliferation, invasion, metastasis, and poor prognosis. Due to its cancer-specific overexpression and critical role in oncogenesis, MUC4 has emerged as an attractive therapeutic target. Current research on clinically relevant macromolecular drugs targeting MUC4 is primarily focused on monoclonal antibodies, antibody-drug conjugates (ADCs), chimeric antigen receptor T-cell (CAR-T) immunotherapy, and cancer vaccines.
• Targeting strategy: The mouse Muc4 gene that encode signal peptide and extracellular domain are replaced by human counterparts in B-hMUC4 mice. The genomic region of mouse Muc4 gene that encodes transmembrane domain and cytoplasmic portion is retained. The promoter and 5’UTR region of the mouse gene are replaced by human counterparts. The chimeric MUC4 expression is driven by human MUC4 promoter, while mouse Muc4 gene transcription and translation will be disrupted.
• Validation: Human MUC4 mRNA and protein were detected in the B-hMUC4 mice but not in C57BL/6 mice.
• Application: Tumor cell lines inoculated in B-hMUC4 mice can be used to study the in vivo efficacy and safety evaluation of antibody drugs.

Species specific analysis of MUC4 gene expression in wild-type C57BL/6 mice and homozygous humanized B-hMUC4 mice by RT-PCR. Colon were collected from wild-type C57BL/6 mice (+/+) and homozygous B-hMUC4 mice (H/H). Mouse Muc4 mRNA was detectable only in wild-type C57BL/6 mice. Human MUC4 mRNA was detectable only in homozygous B-hMUC4 mice, but not in wild-type C57BL/6 mice.