Production of Fc-fused receptor agonists for glucagon-like peptide-1/glucose-dependent insulinotropic polypeptide (GLP-1/GIP) in the milk of transgenic mice

Incretin hormones, including glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), play pivotal roles in glucose homeostasis and metabolic regulation. Therapeutic incretin receptor agonists (RAs), such as tirzepatide, are widely used to manage type 2 diabetes and obesity. However, incretin RAs are facing production challenges at present. Therefore, we engineered transgenic (tg) mice to secrete incretin RAs in milk, leveraging mammary gland bioreactors for cost-effective peptide production. The goat beta-casein promoter-driven constructs encoding tirzepatide-derived peptide linked to human IgG4 Fc via a (GGGGS) ₃ spacer were used to produce tg mice. Founders tg-1 and tg-5 exhibited mammary-specific expression, yielding 0.8–1.42 g/L recombinant protein exclusively in milk. Progeny nursed by founders showed sustained hypoglycemia (10−39% reduction; p < 0.05) and marked weight loss (14−49%; p < 0.01) compared to wild-type controls, validating the bioactivity of milk-derived GLP-1/GIP RAs. Moreover, tg-5-nursed offspring experienced high mortality post-Day 16, likely due to overdosing. This proof-of-concept demonstrates the mammary gland bioreactor as a viable platform for incretin RAs production, circumventing complex synthesis and enabling scalable biologics manufacturing.