Molecular analyses of in vivo hprt mutations in human t‐lymphocytes: IV. Studies in Newborns

Abstract

In order to characterize in vivo gene mutations that occur during fetal development, molecular analyses were undertaken of mutant 6‐thiogua‐nine resistant T‐lymphocytes isolated from placental cord blood samples of 13 normal male newborns. These mutant T‐cells were studied to define hypoxanthine‐guanine phosphoribosyl‐transferase (hprt) gene structural alterations and to determine T‐cell receptor (TCR) gene rearrangement patterns. Structural hprt alterations, as shown by Southern blot analyses, occurred in 85% of these mutant clones. These alterations consisted mostly of deletion of exons 2 and 3. These findings contrast with the 10–20% of gross structural alterations (i.e., those visible on Southern blots) occurring randomly across the entire gene previously reported for T‐cell mutants isolated from normal young adults. Iterative analyses of hprt structural alterations and TCR gene rearrangement patterns show that approximately one‐third of the newborn derived mutants may have originated as pre‐ or intrathymic hprt mutations. This too contrasts with previous findings in adults where the background in vivo hprt mutations appeared to originate in post‐thymic T‐lymphocytes.