Isolation of the CD7 gene from the DNA of transfected L cells

Using DNA from L cells which expressed high levels of the CD7 (Leu-9 or HuLy-m2) antigen obtained after two cycles of transfection, a genomic library was constructed in the lambda phage Charon 4A. Recombinant clones containing the gene coding for this antigen were identified by first screening the library with both the HSVtk gene and a probe detecting the human repetitive (Alu) sequences. DNA from 10 tk⁺ and 12 Alu⁺ recombinant clones was used to transfect L cells which were analyzed for the cell-surface expression of CD7 either early (48–72 h posttransfection) or later when hypoxanthine aminopterin thymidine-resistant colonies were obtained. Transfection with either Alu⁺ or tk⁺ recombinant phages led to transient early expression of CD7, and stable CD7⁺ transfectants were also established. Thus the CD7 gene has been isolated in a number of clones in association with either the Alu repetitive sequence or with the HSV-tk gene; the insert size in one of the genomic clones was 13.5 kb.