References 1 Hammer, R.E. et al. (1985) Production of transgenic rabbits, sheep and pigs by microinjection. Nature 315, 680–683 2 Harris, A. (1997) Towards an ovine model of cystic fibrosis. Hum. Mol. Genet. 6, 2191–2194 3 Denning, C. et al. (2001) Deletion of the a(1,3)galactosyl transferase (GGTA1) gene and the prion protein (PrP) gene in sheep. Nat. Biotechnol. 19, 559–562 4 Nottle, M.B. et al. (2001) Effect of DNA concentration on transgenesis rates in mice and pigs. Transgenic Res. 10, 523–531 5 Wright, G. et al. (1991) High level expression of active human a-1-antitrypsin in the milk of transgenic sheep. Biotechnology 9, 830–834 6 Lavitrano, M. et al. (2002) Efficient production by sperm-mediated gene transfer of human decay accelerating factor (hDAF) transgenic pigs for xenotransplantation. Proc. Natl. Acad. Sci. U. S. A. 99, 14230–14235 7 Wilmut, I. et al. (1997) Viable offspring derived from fetal and adult mammalian cells. Nature 385, 810–813 8 Hofmann, A. et al. (2003) Efficient transgenesis in farm animals by lentiviral vectors. EMBO Rep. 4, 1054–1060 9 Rohll, J.B. et al. (2002) Design, production, safety, evaluation and clinical applications of nonprimate lentiviral vectors. Methods Enzymol. 346, 466–500 10 Lois, C. et al. (2002) Germline transmission and tissue-specific expression of transgenes delivered by lentiviral vectors. Science 295, 868–872 11 Pfeifer, A. et al. (2002) Transgenesis by lentiviral vectors: lack of gene silencing in mammalian embryonic stem cells and preimplantation embryos. Proc. Natl. Acad. Sci. U. S. A. 99, 2140–2145 12 Chan, A.W. et al. (1998) Transgenic cattle produced by reversetranscribed gene transfer in oocytes. Proc. Natl. Acad. Sci. U. S. A. 95, 14028–14033 13 Thomas, C.E. et al. (2003) Progress and problems with the use of viral vectors for gene therapy. Nat. Rev. Genet. 4, 346–358 14 Tiscornia, G. et al. (2003) A general method for gene knockdown in mice by using lentiviral vectors expressing small interfering RNA. Proc. Natl. Acad. Sci. U. S. A. 100, 1844–1848 15 Rubinson, D.A. et al. (2003) A lentivirus-based system to functionally silence genes in primary mammalian cells, stem cells and transgenic mice by RNA interference. Nat. Genet. 33, 401–406 16 Clark, A.J. and Whitelaw, C.B.A. (2003) A future for transgenic livestock. Nat. Rev. Genet. 4, 825–833