Expression of active human blood clotting factor VIII in mammary gland of transgenic rabbits.

Human clotting factor VIII is probably the largest protein to be expressed to date in the mammary gland of a transgenic animal, and it requires extensive posttranslational modification to achieve full biological activity. The mammary gland specific construct mWAP-hFVIII-MT-I was injected into the pronuclei of rabbit zygotes, and three transgenic offspring were obtained. Founder 385 showed germ-line transmission of a single integrated copy, and a homozygous line was established from this animal. The rhFVIII was transcribed and translated exclusively in the mammary gland. The activity of rhFVIII in the rabbit milk ranged from 5 to 8% of that found in normal human plasma. Results indicate the suitability of the transgenic rabbit mammary gland for rhFVIII production.