The distribution of DN subpopulations defined by CD25 and CD44 in the EGFP+ cells was not affected by the infection of day 14.5 fetal thymocytes that were mostly DN1 and DN2 before the culture, with theIAN5 shRNA retrovirus (Figure 5C), whereas the infection of purified DN4 thymocytes with theIAN5 shRNA retrovirus significantly reduced the generation of EGFP+ DP cells but significantly increased the numbers of EGFP+ DN and EGFP+ CD8SP immature cells in 2-d FTOC (Figure 5D). This evidence concerns the gene CD44 and infection.