Production of recombinant human proinsulin in the milk of transgenic mice

There is a steady increasing demand for insulin worldwide. Current insulin manufacturing capacities can barely meet this increasing demand. The purpose of this study was to test the feasibility of producing human proinsulin in the milk of transgenic animals. Four lines of transgenic mice harboring a human insulin cDNA with expression driven by the goat β-casein gene promoter were generated. The expression level of human proinsulin in milk was as high as 8.1 g/L. The expression of the transgene was only detected in the mammary gland during lactation, with higher levels at mid-lactation and lower levels at early and late lactation. The blood glucose and insulin levels and the major milk compositions were unchanged, and the transgenic animals had no apparent health defects. The mature insulin derived from the milk proinsulin retained its biological activity. In conclusion, our study provides supporting evidence to explore the production of high levels of human proinsulin in the milk of dairy animals.