Temporal delineation of sequential HPRT mutations arising in vivo in a T-cell clone with a mutator phenotype

Recurrent mutations in vivo in T-lymphocytes identify clonally restricted g enomic instabilities in some individuals. Cell-based assays allow initial r ecognition of clones with mutator phenotypes, but genotypic selection is re quired to determine frequencies and temporal sequences of potentially indep endent mutational events isolated only as complex changes in the same allel e. The present work illustrates how two single-base insertions in the HPRT gene recovered only as a double event in a cell-based assay were shown to a rise as separate in vivo mutations, being individually present at frequenci es of less than or equal to 10(-4) and less than or equal to 10(-5), respec tively, in peripheral blood. Full characterizations of mutator clones will allow elucidation of the earliest events in the emergence of genomic instab ility in human somatic cells. (C) 2001 Elsevier Science B.V. All rights res erved.