Use of T-cell receptor gene probes to quantify the in vivo hprt mutations in human T-lymphocytes

T-cell receptor (Ti) gene restriction fragment patterns (RFPs) were determined by Southern blots of genomic DNA obtained from T-lymphocyte colonies isolated from a single normal individual. 4 wild-type colonies and 11 in vivo derived 6-thioguanine-resistant mutant colonies with previously characterized hprt gene structural alterations were studied. Among the hprt mutants, 10 of the 11 showed unique Ti RFPs indicating their origins in different in vivo progenitors. Unique Ti RFPs were also seen among the wild-type T-cell colonies. One, however, shared its Ti RFP with a mutant. These results suggest that mutation in vivo of the hprt gene in human T-lymphocytes occurred after thymic maturation and that the 11 recovered hprt mutants probably resulted from 11 independent mutational events.