Characterization of a novel human T cell receptor β chain variable region family by transspecies DNA hybridization

Abstract

One essential component in the generation of diversity of T cell receptor (TcR) alpha and beta chains is the existence of multiple tandemly arranged variable regions in the germ line which are subsequently rearranged to form functional units. In attempting to establish the extent of the human TcR alpha and beta chain repertoire an approach of randomly sequencing cDNA for rearranged receptors has been generally pursued. So far, 24 human V beta families have been characterized and they encompass some 51 transcriptionally active gene segments. Recently, surveys of several hundred TcR beta cDNA clones have failed to establish further V beta families which suggests that if they exist, they are likely to be poorly represented in the peripheral blood repertoire. It is likely, therefore, that the majority of human V beta regions which are rearranged conventionally and are transcriptionally active have already been described. To investigate whether additional V beta families characterize the human TcR repertoire we have examined V beta sequences from an inverse polymerase chain reaction (PCR) TcR beta cDNA library of the chimpanzee, the most closely related creature to man. One clone which could not be assigned to any human V beta family cross-hybridized with human TcR beta chain cDNA. This new human family has been called V beta 25. Comparison of chimpanzee and human V beta 25 sequences using the Lipman-Pearson method gives a similarity index of 94.6% over a consensus length of 112 amino acids. On the evidence of Southern blotting with cDNA probes, V beta 25 segments in human and chimpanzee appear to represent single member gene families and no restriction fragment length polymorphism was evident with the restriction enzymes used. Equalization of TcR beta cDNA followed by family-specific quantitative PCR showed that the gene is expressed at similar levels in the chimpanzee and the human. The actual level of expression in the human is less that 0.5% of the total TcR beta repertoire. Transspecies DNA hybridization using novel sequences from closely related species may be a powerful tool for establishing the full extent of TcR alpha and beta and immunoglobulin repertoires.