Lentiviral vectors containing the green fluorescent protein gene have been 
successfully used to select transgenic embryos before transfer to a surrogate 
mother. However, there are apparently no reports regarding early detection of 
transgenic embryos using a lentiviral vector carrying an additional 
transcription unit for tissue-specific expression of a valuable protein. In this 
study, two HIV-based lentiviral vectors were constructed. The first one 
contained the green fluorescent protein (GFP) coding sequence driven by the 
early SV40 promoter (Lv-G), whereas the other contained an additional 
transcription unit for the expression of E2 glycoprotein from classical swine 
fever virus, driven by a 1.5 kb αS1casein promoter from water buffalo 
(Lv-αS1cE2hisG). Microinjection of single-cell mouse embryos with Lv-G 
lentiviral vector rendered embryos which were GFP-positive, beginning at the 
four-cell stage. Of 33 mice born, 28 (81%) carried the transgene DNA and 15 
(55.5%) were GFP-positive. Microinjection of Lv-αS1cE2hisG lentiviral vector 
yielded 28 mice born; although 24 (85%) carried the transgene DNA, none were 
GFP-positive, suggesting that the tissue-specific expression cassette interfered 
with expression of the ubiquitous trancriptional unit. In Lv-αS1cE2hisG 
transgenic mice, E2his was expressed in milk as a homodimer (at concentrations ≤ 
0.422 mg/mL). This was apparently the first report of expression of a 
recombinant protein in the milk of transgenic animals generated by lentiviral 
transgenesis.