DNA-PCR analysis of TCRβ gene rearrangements. DNA was isolated from sorted CD34⁺CD1a⁻, CD34⁺CD1a⁺, CD4 ISP, and CD4⁺CD8⁺β⁻ human thymic subsets were sorted as indicated in Materials and Methods and subjected to PCR. Primer combinations were used specifically recognizing TCRβ D-J (first panel), Vβ8-DJ (second panel), and Vβ9-DJ (third panel) as described in Materials and Methods. Amplification of the RAG2 gene was performed to control for the amount of DNA used in the PCR (DNA control, fourth panel). DNA isolated from total thymocytes was used as a positive control and from an EBV-B cell line as a negative control. PCR products were blotted onto nylon filters, and hybridized with endlabeled oligoprobes recognizing sequences different from the primers used for PCR. Filters were washed with 2X SSC, 0.1% sodium dodecyl sulfate and exposed to an autoradiographic film.