Hybrid T cell receptor genes formed by interlocus recombination in normal and ataxia-telangiectasia lymphocytes

Abstract

In this paper, using polymerase chain reaction (PCR), we demonstrated the occurrence of hybrid genes formed by interlocus recombination between T cell receptor γ (TCR-γ) variable (V) regions and TCR-β joining (J) regions in the peripheral blood lymphocytes (PBL) from normal individuals and patients with ataxia-telangiectasia (AT). Sequence analysis of the PCR-derived hybrid genes confirmed that site-specific Vγ-Jβ recombination had occurred and showed that 10 of 23 genomic hybrid genes maintained a correct open reading frame. By dilution analysis, the frequency of these hybrid genes was 8 ± 1/105 cells in normal PBL and 587 ± 195/105 cells in AT PBL. These frequencies and the ∼70-fold difference between the normal and AT samples are consistent with previous cytogenetic data examining the occurrence of an inversion of chromosome 7 in normal and AT PBL. We also demonstrated expression of these hybrid genes by PCR analysis of first-strand cDNA prepared from both normal and AT PBL. Sequence analysis of the PCR-amplified transcripts showed that, in contrast to the genomic hybrid genes, 19 of 22 expressed genes maintained a correct open reading frame at the V-J junction and correctly spliced the hybrid V-J exon to a TCR-β constant region, thus allowing translation into a potentially functional hybrid TCR protein. Another type of hybrid TCR transcript was found in a which a rearranged TCR-γ V-J exon was correctly spliced to a TCR-β constant region. This form of hybrid gene may be formed by trans-splicing. These hybrid TCR genes may serve to increase the repertoire of the immune response. In addition, studies of their mechanism of formation and its misregulation in AT may provide insight into the nature of the chromosomal instability syndrome associated with AT. The mechanism underlying hybrid gene formation may be analogous to the mechanism underlying rearrangements between putative growth-affecting genes and the antigen receptor loci, which are associated with AT lymphocyte clones and lymphoid malignancies.