The Mammary Gland as a Bioreactor: Expression, Processing, and Production of Recombinant Proteins

A variety of transgenic animal species are beingused to produce recombinant proteins. The generalapproach is to target the expression of the desiredprotein to the mammary gland using regulatory elements derived from a milk protein gene and thencollect and purify the product from milk. Promotersequences from a number of different milk protein geneshave been used to target expression to the mammarygland, although significant problems remain withregard to achieving transgene expression levelsconsistent with commercial exploitation. The mammarygland appears to be capable of carrying out the complexposttranslational modifications, such as glycosylation andγ-carboxylation required for the biologicalactivity and stability of specific proteins. Effectivepurification protocols have been established andproducts produced by this route have now enteredclinical trials.