Expression of Foxp3 and β-actin mRNAs in human fetal thymocytes.Foxp3 mRNA and β-actin mRNA were amplified by RT-PCR from sorted CD8^-CD4⁺CD25⁺ and CD8^-CD4⁺CD25^- thymocytes from a 24-month-old child and CD8^-CD4⁺CD25⁺ thymocytes from a 14-WG fetus. Arrows indicate the specific PCR band corresponding to Foxp3 and β-actin mRNA.