V kappa gene segments rearranged in chronic lymphocytic leukemia are distributed over a large portion of the V kappa locus and do not show somatic mutation

Abstract

The structure of the human V kappa locus has been thoroughly investigated, but how the germ-line V kappa gene segment repertoire is actually sampled in kappa chain gene rearrangements is not known. In order to begin to answer this question we have polymerase chain reaction (PCR) amplified the rearranged V kappa genes from 26 kappa-expressing cases of chronic lymphocytic leukemia (CLL), followed by cloning and sequencing of the PCR product. All four V kappa gene families were represented amongst rearranged genes. In 25 out of 32 cases, the sequence of the rearranged gene matches perfectly that of 1 of 11 different known germ-line V kappa genes, indicating that no somatic mutation has occurred. Of the remaining 7 rearranged V kappa genes, 4 differ from known germ-line genes by only one or two amino acid residues; and 3 differ from each other and from all known sequences by 5 or more residues, suggesting that somatic mutation has occurred in these 3 cases. We conclude that: (a) in at least three-quarters of cases the rearranged genes are unmutated; (b) there is preferential usage of individual V kappa genes but not of V kappa gene families; and (c) the V kappa genes used are widely dispersed in the V kappa locus.