• The human epidermal growth factor receptor 2 (HER2), also known as ERBB2 or Proto-oncogene Neu, is a receptor tyrosine kinase encoded by the ERBB2(HER2) gene located on chromosome 17q12. Unlike other ERBB family members, ErbB2 does not bind to any ligand but serves as the primary signaling partner by forming heterodimers with ErbB1, ErbB3, or ErbB4. Following ligand-induced dimerization, the receptors undergo autophosphorylation at specific tyrosine residues within their cytoplasmic domains. These phosphorylated residues serve as docking sites for phosphotyrosine-binding proteins, which recruit downstream signaling molecules and activate multiple intracellular signaling pathways.
• HER2 is overexpressed in a wide range of cancer types, including bladder, breast, cervical, cholangiocarcinoma, colorectal, endometrial, esophageal, gastric, head and neck, liver, lung, ovarian, and salivary gland cancers. Notably, amplification and overexpression of HER2 occur in 25% to 30% of human breast cancer cases and are associated with poor prognosis. Several HER2-targeting therapies, such as trastuzumab, pertuzumab, T-DM1, DS8201, and RC48, have been approved worldwide for treating HER2-positive tumors.
• The exons 2-17 of mouse Erbb2 gene that encode extracellular domain and transmembrane domain were replaced by human counterparts in B-NDG hHER2 mice. The genomic region of mouse Erbb2 gene that encodes cytoplasmic portion was retained. The promoter, 5’UTR and 3’UTR region of the Erbb2 gene were also retained. The chimeric ERBB2 expression was driven by endogenous mouse Erbb2 promoter, while mouse Erbb2 gene transcription and translation will be disrupted.
• Mouse Her2 mRNA was detectable only in wild-type B-NDG mice. Human HER2 mRNA was detectable only in homozygous B-NDG hHER2 mice but not in wild-type mice.
• Mouse HER2 was detected in the lung, liver, stomach, colon, small intestine, uterus and breast of wild-type mice.
• Human HER2 was detected in the lung, liver, stomach, colon, small intestine, uterus, breast and kidney of homozygous B-NDG hHER2 mice.
• B-NDG hHER2 mice can be used to study the in vivo efficacy of monoclonal antibody, bispecific antibody and ADC drugs targeting human HER2.

Gene targeting strategy for B-NDG hHER2 mice. The exons 2-17 of mouse Erbb2 gene that encode extracellular domain and transmembrane domain were replaced by human counterparts in B-NDG hHER2 mice. The genomic region of mouse Erbb2 gene that encodes cytoplasmic portion was retained. The promoter, 5’UTR and 3’UTR region of the Erbb2 gene were also retained. The chimeric ERBB2 expression was driven by endogenous mouse Erbb2 promoter, while mouse Erbb2 gene transcription and translation will be disrupted.

Immunohistochemical (IHC) analysis of HER2 protein expression in wild-type mice and B-NDG hHER2 mice. Thirteen major tissues were collected from wild-type mice and homozygous B-NDG hHER2 mice and analyzed by IHC with anti-mouse HER2 antibodies (ab214275) and anti-human HER2 antibodies (ab16662). Mouse HER2 was detected in the lung, liver, stomach, colon, small intestine, uterus and breast of wild-type mice (Figure 1). Human HER2 was detected in the lung, liver, stomach, colon, small intestine, uterus, breast and kidney of homozygous B-NDG hHER2 mice (Figure 2).

Strain specific analysis of HER2 mRNA expression in wild-type B-NDG mice and B-NDG hHER2 mice by RT-PCR. Liver, lung and stomach RNA were isolated from wild-type B-NDG mice (+/+) and homozygous B-NDG hHER2 mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human HER2 primers. Mouse HER2 mRNA was detectable only in wild-type B-NDG mice. Human HER2 mRNA was detectable only in homozygous B-NDG hHER2 mice but not in wild-type mice.