**2.2.3 Production of recombinant proteins**

The mammary gland and blood of transgenic domestic animals, including sheep, goats, cows, pigs and rabbits, have been successfully used as bioreactor to produce numerous recombinant proteins, such as antibodies (Grosse-Hovest et al., 2004), growth factors (Schnieke et al., 1997) and pharmaceuticals (reviewed by Melo et al., 2007). Using various mammary gland-specific or blood-specific promoters to drive the expression of specific protein-coding genes, transgenic domestic animals can continuously produce the recombinant proteins in large quantities in their milk or blood. Recombinant proteins, including human von Willebrand factor (Lee et al., 2009), human erythropoietin (Park et al., 2006), human insulin-like growth factor-I (Monaco et al., 2005), human factor VIII (Paleyanda et al., 1997) and bovine alpha-lactalbumin (Bleck et al., 1998) have been produced in the milk of transgenic pigs. Transgenic goats, capable of synthesizing human butyrylcholinesterase (Huang et al., 2007) and human longer acting tissue plasminogen activator (Ebert et al., 1991) in their milk have also been created. Human salmon calcitonin in milk of transgenic rabbits (McKee et al., 1998); human factor IX (Schnieke et al., 1997) and alpha-1-antitrypsin (Wright et al., 1991) in milk of transgenic sheep; and human lactoferrin (van Berkel et al., 2002; Yang et al., 2008), human growth hormone (Salamone et al., 2006) and human α-lactalbumin (Wang et al., 2008) in milk of transgenic cows are all additional examples of using transgenic domestic animals and the mammary gland as a bioreactor for production of recombinant proteins. Table 2 summarizes some recombinant proteins expressed in milk or blood of cloned transgenic domestic animals. One of the major advantages of using domestic animals for this purpose is that the produced protein is thought to undergo more accurate posttranslational processing to ensure their biological activity. While this application of transgenic technology to produce recombinant protein products is rapidly developing, research efforts exploring the efficacy of these products are still needed.

### **2.2.4 Biomedical models of human diseases**

Another important application of genetically modified domestic animals is to create better and novel biomedical models of human diseases. Pig models of different human diseases, including retinitis pigmentosa, cardiovascular disease, diabetes, Huntington's disease, cystic fibrosis and Alzheimer's disease have been well discussed by Prather et al. (2008). Many of these biomedical models created by SCNT are listed in Table 2.
