Flow cytometric assay for hCD4 expression in fetal liver (A through D) and fetal blood (E through J). (A) Viable liver cells at E12.5 from a vav-hCD4 fetus (unbroken line) or a nontransgenic littermate (dotted line and shading). (B) Transgenic E14.5 liver, also analyzed for Mac-1. (C) Nontransgenic and (D) transgenic cells at E14.5, also analyzed for Ter119. (E, G, and I) Nontransgenic and (F, H, and J) transgenic blood (unbroken lines), superimposed on the nontransgenic profiles (dotted lines and shading). d indicates the presumptive definitive erythroid population and p the primitive one. In (E), the unidentified second, very small peak (∼2% of cells) probably represents larger, nonerythroid cells. Results in (A) are representative of analyses on more than 15 of each genotype, (B through D) on at least 3 transgenic and 5 nontransgenic littermates, and (E through J) on 15 to 27 mice. All analyses were performed on mice of 1 HS21/45 and 2 HS321/45 lines. Exceptions were E12.5 fetal liver and blood, studied in 1 line for each transgene, and cell surface marker analysis, which was performed on mice of 1 HS21/45 line.