Thymic lobes from day 14.5 gestation age C57BL/6 fetal mice were cultured for 13 days over transwell membranes containing serum-free media (Stemspan Expansion Medium, StemCell Technologies, Vancouver, CA) with the indicated concentration of rhGH (Serono Inc, Rockland, MA), rhPRL (kindly provided by Genzyme Corp., Cambridge, MA) or 10 ng/ml rhIL-7. At the end of the culture, cells were dissociated from the lobes, viable cells numbers were assessed using the Viacount method (Guava Technologies, Hayward, CA), labeled with CD45-FITC, CD4-PE and CD8-PC5 and analyzed by flow cytometry. A. Representative dotplots demonstrating normal distribution of thymocytes in lobes cultured with rhGH or rhPRL. Cells were gated on CD45+ expression. B. Significant increases in total viable cells in FTOC cultured with 10 ng/ml of rhGH (ANOVA with Dunnett’s post-hoc test p< 0.05).