Detection of CB-derived thymocytes in the thymic grafts of CB/Thy-NOD/SCID mice. CB/Thy-NOD/SCID chimeras were generated by BM reconstitution with male human CB followed by transplantation of female thymi. Control Thy-NOD/SCID received human female thymi only. At 6 months post-CB reconstitution, the CD4/CD8 double and single-positive thymic subsets were purified by cell sorting. DNA was extracted and assessed for the presence of Y chromosome–specific sequences by PCR. The resulting products resolved on a 1.2% agarose gel are shown. A strong band with the predicted size of 150 bp is detected in the BM, total thymocytes (Total Thys), as well as double and single-positive thymic subsets of CB/Thy-NOD/SCID mice (SCID no. 1 and no. 2), indicating the colonization of the grafts by BM-derived thymocyte progenitors of CB origin. DNA from total thymocytes of Thy-NOD/SCID mice (SCID controls) is negative. Each lane corresponds to the analysis of 10,000 cells. Control PCR using DNA extracted from male (♂) and female (♀) CB cells are shown on the left. The far left lane represents a 100-bp DNA ladder. The lane on the far right shows a control using Y chromosome–specific primers and no template DNA.