Low frequency of somatic mutation in β-chain variable region genes of human T-cell receptors

We have cloned three pairs of rearranged and germ-line variable region (V(β)) genes of the β chain of the human T-cell receptor from the cell lines ATL2, ATL12, and MT-1 of patients with adult T-cell leukemia (ATL). The pairs were derived from the same (for ATL2 and ATL12) and different (for MT-1) individuals. Comparison of the nucleotide sequences showed no somatic mutation in V(β·ATL2) and V(β·ATL12-2). Although one nucleotide change was found in V(β·MT1-1), the possibility of polymorphism was not excluded. These results indicate that the frequency of somatic mutation in the V(β) gene of the T-cell receptor is 1/10th or less than that in the immunoglobulin gene. Both alleles of the rearranged T-cell receptor gene were analyzed for ATL12 and MT-1. In both, only one of the two rearranged J(β) alleles was an active variable-diversity-joining (V-D-J) complex. The results suggest that allelic exclusion occurs in the T-cell receptor gene.