Human growth hormone (hGH) secretion in milk of goats after direct transfer of the hGH gene into the mammary gland by using replication-defective retrovirus vectors.

Mammary-specific promoters have been used in transgenic animals to limit transgene expression to the mammary gland. Gene therapy techniques to target just one organ for introduction of a foreign gene have also been demonstrated. We have directly infused replication-defective retroviruses encoding hGH into the mammary gland of goats via the teat canal during a period of hormone-induced mammogenesis. This resulted in the secretion of hGH into the milk when lactation commenced on day 14 of the regime. Levels of hGH in the milk were highest on the first day of lactation, averaging approximately 60 ng/ml, and declined to a plateau of 12 ng/ml from day 9 to day 15 of lactation. Thus we report targeting of replication-defective retroviruses to the mammary secretory epithelial cells to produce foreign proteins in the milk of ruminants.