Defects in Hoxa-9^−/− adult thymuses. (A) Hoxa-9^−/− thymuses have reduced percentages of TN cells. FACS analysis using antibodies against CD4, CD8, and αβ TCR were performed. Hoxa-9^−/−thymuses showed a twofold reduction in the percentage of CD4⁻CD8⁻ cells (lower left quadrant, middle panels) and significant contraction of TN cells (lower left side panels), with no changes in the percentages of mature populations. The numbers in the CD4⁻CD8⁻panel represent the TN cells expressed as a percentage of total thymocytes. (B) Absolute numbers of T-cell subsets. Based on analyses of 5 litters, there were statistically significant decreases in cell numbers of TN, DN, DP, and SP populations of theHoxa-9^−/− thymuses (*P < .05; **P < .01). (C) Schematic representation of normal T-cell development, correlated with FACScan profiles. Note that the CD4⁻CD8⁺ subset (lower right quadrant) includes both mature and immature (ISP) cells, which can be distinguished by their expression or lack of expression of TCR (A, lower right side panels).