The human T cell receptor alpha-delta locus: a physical map of the variable, joining and constant region genes

Diversity in recognition and function of human γδ T cells

As interest increases in harnessing the potential power of tissue-resident cells for human health and disease, γδ T cells have been thrust into the limelight due to their prevalence in peripheral tissues, their sentinel-like phenotypes, and their unique antigen recognition capabilities. This review focuses primarily on human γδ T cells, highlighting their distinctive characteristics including antigen recognition, function, and development, with an emphasis on where they differ from their αβ T cell comparators, as well as from γδ T cell populations in the mouse. We review the antigens that have been identified thus far to regulate members of the human Vδ1 population and discuss what players are involved in transducing phosphoantigen-mediated signals to human Vγ9Vδ2 T cells. We also briefly review distinguishing features of these cells in terms of TCR signaling, use of coreceptor and costimulatory molecules and their development. These cells have great potential to be harnessed in a clinical setting, but caution must be taken to understand their unique capabilities and how they differ from the populations to which they are commonly compared.

Diagnostic role of tests for T cell receptor (TCR) genes

Rapid advances in molecular biological techniques have made it possible to study disease pathogenesis at a genomic level. T cell receptor (TCR) gene rearrangement is an important event in T cell ontogeny that enables T cells to recognise antigens specifically, and any dysregulation in this complex yet highly regulated process may result in disease. Using techniques such as Southern blot hybridisation, polymerase chain reaction, and flow cytometry it has been possible to characterise T cell proliferations in malignancy and in diseases where T cells have been implicated in the pathogenesis. The main aim of this article is to discuss briefly the process of TCR gene rearrangement and highlight the disorders in which expansions or clonal proliferations of T cells have been recognised. It will also describe various methods that are currently used to study T cell populations in body fluids and tissue, their diagnostic role, and current limitations of the methodology.

Unusual T-cell receptor-delta gene rearrangement patterns revealed by screening of a large series of childhood acute lymphoblastic leukaemia by multiplex polymerase chain reaction

Rearrangements of the T-cell receptor (TCR) and immunoglobulin genes are considered as useful clonal markers in lymphoproliferative disorders of B- and T-cell lineage, and are frequently used for the detection of minimal residual disease (MRD). In this paper, we report on the unexpected results of an extensive analysis of TCR-delta chain gene rearrangement frequencies and patterns in leukaemic bone marrow DNA samples collected from 438 children with initial (n = 112) or relapsed (n = 326) acute lymphoblastic leukaemia (ALL). By applying a previously described multiplex polymerase chain reaction, the overall incidence of non-deleted TCR-delta gene rearrangements in ALL was 47% (206/438), 52% in initial ALL (58/112) and 45% in relapsed ALL (148/326). As expected, the majority of B-cell precursor (BCP) ALL had incomplete Vdelta2-Ddelta3 or Ddelta2-Ddelta3 TCR-delta gene rearrangements, whereas most T-ALL showed complete rearrangements of the TCR-delta gene locus (Vdelta1-Jdelta1, Vdelta2-Jdelta1, Vdelta3-Jdelta1). However, unexpectedly, 5/206 rearranged TCR-delta alleles in BCP-ALL showed a complete Vdelta-(Ddelta)-Jdelta gene rearrangement pattern, and 3/31 T-ALL had an incomplete recombination. Theoretically, complete TCR-delta gene rearrangements should not occur in cells other than T-lymphocytes and have only been reported once previously in BCP-ALL. The data contribute to the discussion about the reliable screening for clonal markers in ALL.

TCR gene polymorphisms and autoimmune disease

Autoimmunity may result from abnormal regulation within the immune system. As the T cell is the principal regulator of the immune system and its normal function depends on immune recognition or self/non-self discrimination, abnormalities of the idiotypic T-cell receptor (TCR) may be one cause of autoimmune disease. The TCR is a clonally distributed, cell-surface heterodimer which binds peptide antigen when complexed with HLA molecules. In order to recognize the variety of antigens it may possibly encounter, the TCR, by necessity, is a diverse structure. As with immunoglobulin, it is the variable domain of the TCR which interacts with antigen and exhibits the greatest amount of amino acid variability. The underlying genetic basis for this structural diversity is similar to that described for immunoglobulin, with TCR diversity relying on the somatic recombination, in a randomly imprecise manner, of smaller gene segments to form a functional gene. There are a large number of gene segments to choose from (particularly the TCRAV, TCRAJ and TCRBV gene segments) and some of these also exhibit allelic variation. Finally, polymorphisms in non-coding regions of TCR genes, leading to biased recombination or expression, are also beginning to be recognized. All these factors contribute to the polymorphic nature of the TCR, in terms of both structure and repertoire formation. It follows that inherited abnormalities in either coding or regulatory regions of TCR genes may predispose to aberrant T-cell function and autoimmune disease. This review will outline the genomic organization of the TCR genes, the genetic mechanisms responsible for the generation of diversity, and the results of investigations into the association between germline polymorphisms and autoimmune disease.

Restriction of the T-cell receptor V delta gene repertoire is due to preferential rearrangement and is independent of antigen selection

To determine whether the limited V gene usage by the T-cell receptor delta (TCRD) chain is dictated by preferential rearrangement or by antigen selection, we characterized and compared the TCRDV gene repertoire of the productive with that of the unproductive allele in 80 human TCRG/TCRD clones. Six different V genes were found on the expressed allele; two of them, provisionally named DV7 and DV8, have not been described before on the surface of TCRG/TCRD T cells. Overall, six V genes and six non-V elements were isolated from the unproductive allele. Interestingly, the same set of genes was rearranged both in the productive and in the unproductive chromosome. These findings seem to suggest that antigen-independent mechanisms play a major role in the restriction of the TCRDV gene repertoire.

Gene rearrangements and chromosomal translocations in T cell lymphoma--diagnostic applications and their limits

The diversity of the T cell receptor (TCR) repertoire is established for individual T lymphocytes by developmentally regulated gene rearrangements and shaped by predominantly intrathymic selection procedures. TCR gene probes in Southern blot experiments and TCR primers for the polymerase chain reaction (PCR) help to distinguish polyclonal from abnormal clonal T cell proliferations and to monitor clonal disease after treatment. Rearrangement studies can identify the lineage and developmental stage of a lymphocyte clone. Cross-lineage rearrangements, false positive or negative results are rarely misleading when morphology and immunophenotypical findings are considered. Rearrangement studies, however, have not contributed significantly to the comprehension of lymphomagenesis. Analyses of characteristic chromosomal translocations in T cell leukaemias and lymphomas may provide further insight into the mechanisms of malignant transformation. Transcription factors are often involved and sometimes abnormally transcribed, which may alter the physiological intracellular signalling in T cells. Interphase cytogenetic analysis by chromosomal fluorescence in situ hybridization (FISH) has become a new tool in the search for transformed T cells carrying specific translocations. Archival biopsy material is now accessible for PCR rearrangement studies and FISH cytogenetics. This adds another dimension to the diagnosis, disease monitoring and biological understanding of malignant T cell lymphomas and leukaemias.

Generation and reactivation of T-cell receptor A joining region pseudogenes in primates

Tandemly duplicated T-cell receptor (Tcr) AJ (J alpha) segments contribute significantly to TCRA chain junctional region diversity in mammals. Since only limited data exists on TCRA diversity in nonhuman primates, we examined the TCRAJ regions of 37 chimpanzee and 71 rhesus macaque TCRA cDNA clones derived from inverse polymerase chain reaction on peripheral blood mononuclear cell cDNA of healthy animals. Twenty-five different TCRAJ regions were characterized in the chimpanzee and 36 in the rhesus macaque. Each bears a close structural relationship to an equivalent human TCRAJ region. Conserved amino acid motifs are shared between all three species. There are indications that differences between nonhuman primates and humans exist in the generation of TCRAJ pseudogenes. The nucleotide and amino acid sequences of the various characterized TCRAJ of each species are reported and we compare our results to the available information on human genomic sequences. Although we provide evidence of dynamic processes modifying TCRAJ segments during primate evolution, their repertoire and primary structure appears to be relatively conserved.

TCR gene segments from at least one third of V alpha subfamilies rearrange at the delta locus

Using PCR and an experimentally validated V alpha subfamily-specific oligonucleotide panel (V alpha 1-w29), we have investigated whether the TCR delta chain may increase its combinatorial diversity by using V genes considered as alpha chain-specific. We show that at least 10 distinct human V alpha segments rearrange at the J delta locus, leading to scrambling of the two V gene repertoires. Fifty-five per cent of the V alpha/J delta transcripts characterized here were in frame. The 17 V alpha/C delta chains analysed included an extended CDR3 region with up to 18 aa encoded by the junctional region. In addition, a new J delta segment (J delta 4) has been characterized. Together, these findings demonstrate that combinatorial diversity in the human delta locus is larger than previously thought.

Restricted usage of T-cell receptor V alpha sequence and variable-joining pairs after normal T-cell development and bone marrow transplantation

TCR V alpha 3 and V alpha 5 transcripts in PBLs from healthy individuals of multiple age groups and from BMT recipients were analyzed. PCR, cloning, and sequencing studies revealed significant V-J junctional diversity among TCR transcripts from all tested blood samples, as provided both by N/P-region addition and exonuclease activity. However, results illustrated restrictions in TCR alpha diversity at several additional levels. First, V alpha 5 and V alpha 3 gene families, which were expected to be composed of multiple members, were dominated in each case by a single sequence at the transcript level. Second, restrictions existed in V-J pairing in that J alpha genes, which were encoded toward the 5' region of the locus, were rearranged frequently with V alpha 3 and rarely with V alpha 5. Conversely, J alpha genes encoded toward the 3' region of the locus preferentially rearranged with V alpha 5. Healthy individuals showed few differences with regard to V-J pairing patterns, while one of three BMT recipients demonstrated a skewed usage of 3' J alpha genes. In total, results demonstrated qualitative restrictions that may limit the working TCR repertoire in human peripheral tissues, both among BMT recipients and their healthy donors.

Characterization of T cell receptor assembly and expression in a Ti gamma delta-positive cell line

T cell antigen receptor (TcR) heterodimers of both the Ti-alpha beta and Ti-gamma delta types are expressed at the surface of T cells noncovalently associated with the CD3 complex composed of the monomorphic chains gamma, delta, epsilon and zeta. The structural relationship and assembly of the various components of this multimeric protein complex is still not fully understood. In this report, the human leukemic T cell line Lyon which expresses a Ti-gamma delta/CD3 complex, was characterized and compared to another human leukemic T cell line Jurkat (Ti-alpha beta/CD3). Membrane TCR-/CD3- variants of the T cell Lyon were induced and found to produce all of the Ti/CD3 components, with the exception of Ti-delta. Biochemical analysis indicated that: (1) Ti-gamma/CD3 gamma, delta, epsilon complexes were formed in the endoplasmic reticulum in the absence of Ti-delta; (2) the CD3-zeta chain did not associate with the Ti-gamma/CD3 gamma delta epsilon complex and (3) the Ti-delta chain was required for cell surface expression of the Ti-gamma delta/CD3 complex. Introduction of Jurkat wild-type Ti-alpha cDNA into Lyon T cells resulted in Ti-alpha beta/CD3 expression and abrogated Ti-gamma delta/CD3 expression. In contrast, the expression of the Ti-gamma delta/CD3 complex was not affected by transfection of a mutated Ti-alpha cDNA into Lyon cells. The mutated Ti-alpha chain formed complexes with Ti-beta and CD3 gamma delta epsilon, but the CD3-zeta chain did not associate with these complexes. Taken together analysis of Lyon cells transfected with either wild-type or mutated Ti-alpha suggested that the CD3-zeta chain may have higher affinity for Ti-alpha beta/CD3 complexes than for Ti-gamma delta/CD3 complexes.

T cell receptor alpha chain polymorphisms in multiple sclerosis

Numerous studies have implicated the major histocompatibility complex (MHC) class II alleles, DR2 and DQw1, as multiple sclerosis (MS) susceptibility loci, however, the involvement of other loci is implied by twin studies and the relative lack of haplotype sharing for MHC. To evaluate the role that the TCR alpha chain genes may have in MS susceptibility, three variable (V) alpha polymorphisms were examined for associations in MS patients. Genotype and allele frequencies were compared to four different control groups: unaffected siblings and parents of the MS patients, patients with insulin-dependent diabetes mellitus (IDDM) and healthy unrelated Caucasians. No significant differences in allele and genotype frequencies at these three loci were observed in the MS population compared to the control groups. In addition, we analysed the distribution of haplotype sharing in affected sibling pairs. Among 30 informative families, there was no significant increase in haplotypes shared by affected siblings over that expected based on random segregation. Our results do not support suggestions that germline TCR alpha chain genes contribute to genetic susceptibility in MS.

Nucleotide sequence analysis of 95 kb near the 3' end of the murine T-cell receptor alpha/delta chain locus: strategy and methodology

The nucleotide sequence of a region at the 3' terminus of the murine T-cell receptor alpha/delta chain locus is presented. This region, which encodes the constant region genes for alpha and delta chain polypeptides and all 50 joining gene segments for the alpha chain polypeptide, spans 94,647 bp and includes more than 50 noncoding sequence elements important for T-cell receptor gene rearrangement and expression. DNA sequencing of this region included complete analysis of two cosmid clones and five additional restriction fragments using a random subcloning approach with various manual and automated sequencing strategies. The automated sequencing strategies hold considerable promise for future large-scale DNA sequencing efforts.

Organization, structure, and function of 95 kb of DNA spanning the murine T-cell receptor C alpha/C delta region

We have analyzed the organization, structure, and function of the murine T-cell receptor C alpha/C delta region. This region spans 94.6 kb of DNA and contains the C alpha and C delta genes, as well as the V delta 5, J delta 2, and 50 different J alpha gene segments. Within this sequence we have identified 15 new J alpha gene segments, 40 new 5' RNA splice signals, and 40 new DNA rearrangement signals for the J alpha gene segments. The murine C alpha/C delta sequence contains an exceptionally high level of coding sequence with over 5.7% of the total sequence found in the exons. This is much more than that found in the beta-globin locus and the HPRT locus. Using the sequence data obtained from the C alpha/C delta region, we have designed simple assays to test for J alpha gene segment transcription and to determine the level of polymorphism for simple repeat sequences among different inbred strains of mice using the polymerase chain reaction. Furthermore, comparisons of this 95 kb of sequence with the available sequence from homologous regions of other species have led to the identification of a highly conserved sequence that is present throughout vertebrates and in the mouse binds lymphocyte-specific nuclear proteins. Comparisons of a 10-kb region, which includes the C alpha gene in human and mouse, average 66% sequence similarity. These studies support the contention that large-scale DNA sequencing projects of homologous regions of mouse and human will provide powerful new tools for studying the biology and evolution of loci such as the T-cell receptor and for identifying and posing new questions about the functions of conserved sequences.

Somatic cell mapping of T-cell receptor CD3 complex and CD8 genes in cattle

Bovine genes encoding T-cell receptor, CD3, and CD8 molecules have been mapped to syntenic groups using bovine x rodent hybrid somatic cells. T-cell receptor alpha and delta chains were assigned to bovine syntenic group U5, and the beta and gamma genes were syntenic with each other and with markers on U13. CD3E and CD3D genes were syntenic with each other and located to bovine syntenic group U19. CD8 was most concordant with markers of syntenic group U16, although the concordancy was only 85% and the assignment must be regarded as tentative. The comparative gene maps of human chromosome 7, bovine syntenic group U13, and mouse chromosomes 6 and 13 suggest extensive evolutionary conservation.

Molecular analysis of an ataxia telangiectasia T-cell clone with a chromosomal translocation t(14;18)--evidence for a breakpoint in the T-cell receptor delta-chain gene

We established a clonal T-cell line with a reciprocal chromosomal translocation t(14;18)(q11;q23) from a patient with ataxia telangiectasia (AT) and T-cell chronic lymphocytic leukemia (T-CLL). The tumor cells and the derived T-cell line were compared with respect to phenotype, karyotype, and rearrangement pattern. Restriction fragment analyses of the T-cell receptor (TCR)-delta gene, which is located within the TCR-alpha gene on chromosome 14q11, indicated that the breakpoint is located within the TCR-delta locus, splitting the TCR-delta gene between the variable and joining segments. This specific chromosomal translocation was only detected in the derived T-cell line and may be involved in the genesis of T-cell malignancies in AT.

Studies on the human T cell receptor alpha/beta variable region genes. I. Identification of 7 additional V alpha subfamilies and 14 J alpha gene segments

The anchored-polymerase chain reaction has been used to study further the diversity of the human T cell receptor alpha chain. The analysis of 308 cDNA transcripts from human peripheral lymphocytes hybridizing with a C alpha probe led to the identification of a series of additional V alpha and J alpha gene segments. The sequences of seven V alpha gene segments which individually define a novel V alpha subfamily (termed V alpha w23 to V alpha w29) are reported. The sequences of some previously described V alpha 1, V alpha 2, V alpha 5, V alpha 7 and V alpha 22 gene segments are also extended. In addition, we report 14 novel J alpha gene segment sequences. Taken together, these data indicate that the contribution of the alpha chain combinatorial diversity to the human T cell receptor alpha/beta variability has not yet been fully appreciated.

Recombinative events of the T cell antigen receptor delta gene in peripheral T cell lymphomas

Recombinative events of the T cell antigen receptor (TCR) delta-chain gene were studied in 37 cases of peripheral T cell lymphoma (PTCL) and related to their clinical presentation and the expression of the alpha beta or gamma delta heterodimers as determined by immunostaining of frozen tissue samples. There were 22 cases of alpha beta, 5 cases of gamma delta, and 10 cases of silent TCR expressing neither the alpha beta nor gamma delta TCR. 5 different probes were used to examine the delta locus. The 22 cases of alpha beta PTCL displayed biallelic and monoallelic deletions; a monoallelic V delta 1 J delta 1 rearrangement was observed in 1 case and a monoallelic germ line configuration in 7 cases. The 5 cases of gamma delta PTCL displayed biallelic rearrangements: the productive rearrangements could be ascribed to V delta 1J delta 1 joining in 3 cases and VJ delta 1 joining in 2 cases according to the combined pattern of DNA hybridization with the appropriate probes and of cell reactivity with the TCR delta-1, delta TCS-1, and anti-V delta 2 monoclonal antibodies. In the VJ delta 1 joining, the rearranged V segments were located between V delta 1 and V delta 2. Interestingly, in the third group of 10 cases of silent PTCL, 5 cases were found to have a TCR gene configuration identical to that in the TCR alpha beta PTCL, as demonstrated by biallelic delta gene deletion. These 5 cases were CD3 positive. The 5 remaining cases showed a monoallelic delta gene rearrangement with a monoallelic germ line configuration in 4 and a monoallelic deletion in 1. Four of these cases were CD3 negative, which was consistent with an immature genotype the TCR commitent of which could not be ascertained. Finally, TCR gamma delta PTCL consisted of a distinct clinical morphological and molecular entity whereas TCR alpha beta and silent PTCL had a similar presentation.

Molecular biology and leukaemia diagnosis

The diagnosis and classification of leukaemia started with simple morphological examination and now embraces use of special stains, cytochemistry and immunophenotyping. Genetic studies have progressed from karyotyping to detection of genetic changes within genes. The methods described in this chapter are still at an early stage of development and, so far, have provided relatively little in the way of an extension of available diagnostic information. Sometimes the methods provide extensions to existing techniques, for example by the detection of bcr rearrangements in patients who have CML or ALL but do not have a detectable Philadelphia chromosome. Another example is retrospective diagnosis of gene rearrangements using DNA from slide preparations. However, it should be noted that it has only very recently been shown that there is likely to be a causal relationship between the Ph chromosome and leukaemia. Daley et al (1990) induced CML in mice by bone marrow transplantation of cells infected with a retrovirus encoding P210bcr/abl and Heisterkamp et al (1990) produced mice transgenic for a BCR/ABL P190 DNA construct and showed that the progeny died of acute leukaemia (mostly ALL). We have not summarized studies of the incidence of activated oncogenes such as RAS in leukaemia and myelodysplasia. Such oncogenes appear to be involved in many tumours and may well indicate either a predisposition to cancer or a particular stage of malignancy, but their analysis does not at present help in making a diagnosis. It is likely that, as we understand more about the nature of the malignant process, we shall be able to use genetic techniques to enhance considerably both diagnostic and prognostic precision.

Human heavy chain variable region gene diversity, organization, and expression

Elucidation of the cellular and molecular mechanisms which determine the expressed antibody repertoire remains a major challenge in immunology. Knowledge of V gene diversity, organization, and expression is important to an understanding of the formation of the antibody repertoire in normal as well as diseased states. In the last few years, great advances have been made in our understanding of the human heavy chain variable region (VH) gene locus. In this review we present the current knowledge of VH gene diversity, organization, and utilization in normal individuals followed by a discussion of the possible relevance of these findings to autoimmunity.

T-cell receptor gene rearrangements and the diagnosis of human T-cell neoplasms

The rearranging antigen receptor genes of lymphoid cells serve as unique clonal markers of lymphoid neoplasms. Gene rearrangement analysis is a highly sensitive and reproducible tool which is useful in the diagnosis and classification of malignant lymphoma/leukemia. Although clonality can often be determined among B cell neoplasms by virtue of immunoglobulin isotype analysis, no such phenotypic marker of clonality exists for T cells. Therefore, clonality of T lymphoproliferative processes is most readily determined by rearrangement analysis of the T cell antigen receptor genes. The alpha, beta, gamma, and delta genes of the T cell receptor gene family encode heterodimeric surface antigen receptors and undergo rearrangement early in T cell differentiation. Identification of rearrangement of T cell antigen receptor genes provides valuable diagnostic information concerning cellular lineage, clonality and classification of T cell neoplasms. This molecular approach is applicable to the diagnosis of occult disease, relapse, and resolution of diagnostic dilemmas in any type of tissue sample including fluids and needle aspirations.

Alpha beta lineage-specific expression of the alpha T cell receptor gene by nearby silencers

T cells expressing either the alpha beta or gamma delta antigen receptor (TCR) are distinct cell lineages. The single locus encoding the TCR alpha and delta genes requires special regulation to avoid alpha gene expression in gamma delta T cells. We show here that the minimal alpha enhancer is active in the gamma delta T cell lineage but gains alpha beta lineage specificity through negative cis-acting elements 3' of the C alpha gene that silence the enhancer in gamma delta T cells. The negative elements at the C alpha locus consist of several silencers that work in an orientation- and distance-independent fashion. These silencers also act on a retroviral enhancer that is normally ubiquitously expressed, restricting its activity to alpha beta cells. The alpha silencers are active in non-T cell lines, suggesting that the decision of a cell to differentiate into the alpha beta T cell lineage may involve specific relief from these silencers. Silencers are likely to be as important as enhancers in establishing lineage-specific gene expression in many systems.

The promoter regions of the T-cell receptor V9 gamma (TRGV9) and V2 delta (TRDV2) genes display short direct repeats but no TATA box

T lymphocytes expressing the T-cell gamma delta receptor have been shown to express preferentially the T-cell receptor V9 gamma (TRGV9) gene, in association with the T-cell receptor V2 delta (TRDV2) gene. In this paper, we report that the promoter regions of the TRDV2 and TRGV9 genes, which are preferentially expressed early in T-cell differentiation, display short direct repeats but no TATA box, in contrast to the V gamma genes belonging to subgroup I. The TCCTCAGT octanucleotide found 100 pb upstream of the ATG of the HD-Mar V alpha transcript, a TCR V alpha gene without a TATA box, is observed upstream of TRDV2 but not TRGV9. Of interest is the presence of a characteristic decanucleotide AGGTGGT(T)GAG in the promoter regions of both the TRDV2 and TRGV9 genes.

Non-random expression of T cell receptor gamma and delta variable gene segments in functional T lymphocyte clones from human peripheral blood

Human T cell receptor (TcR) gamma delta displays a variety of protein forms. Disulfide-linked (type 1) or non disulfide-linked (type 2) receptors occur, with gamma chains encoded by the C gamma 1 or the C gamma 2 gene segment, respectively. Exon 2 of C gamma 2 may either be duplicated or triplicated (type 2a or 2b receptors). TcR gamma chains differ in molecular mass and charge between type 1 and type 2 receptors. The delta chains as well as the gamma chains have different structural properties between receptor types. This cannot be due to the use of different C delta gene segments, since the genome encodes only one. To understand the genetic basis of this dichotomy in gamma/delta combinations, rearrangement and expression of V gamma, J gamma, C gamma and V delta gene segments were determined in TcR gamma/delta+ clones derived randomly from peripheral blood of normal donors. Most clones used C gamma 1, a minority C gamma 2. The different protein properties of receptor types could be explained by the non-random expression of V gamma (J gamma) and V delta gene segments. Type 1 receptors preferentially used gamma chains encoded by the V gamma 9 and J gamma 1.2 gene segments together with delta chains encoded by V delta 2. In type 2a receptors, V gamma 9 was not predominant; often other V gamma gene segments were employed, but then in high frequency in coordination with V delta 1. Reactivity of the clones with monoclonal antibodies anti-Ti gamma A, BB3 and delta-TCS-1 correlated with the expression of the V gamma 9, V delta 2 and V delta 1 gene segments, respectively. Therefore, V gamma and V delta use in TcR gamma/delta+ cells from peripheral blood of eight healthy individuals, including the two donors of the clones, could be determined tentatively by double immunofluorescence. Indeed, the V gamma 9-V delta 2 combination was predominant, while the V gamma 9-V delta 1 and particularly the V gamma 9-"V delta other" combination was rare. These data indicate that the TcR gamma delta repertoire in peripheral blood of normal individuals is largely dependent on junctional diversity and suggest that selection of receptors occurs.

Coordinated V gamma and V delta gene segment rearrangements in human T cell receptor gamma/delta+ lymphocytes

Monoclonal antibodies (mAb) were used to characterize a panel (n = 46) of T cell receptor (TcR) gamma/delta+ T cell clones. Three of these antibodies have been described to react with specific variable region-encoded protein products and can therefore be used to detect functional gene rearrangements. The majority of peripheral blood-derived clones (43 out of 45) expressed the epitopes recognized by mAb BB3, encoded by the V delta 2 gene segment and mAb Ti gamma A, encoded by the V gamma 9 gene segment. These clones lacked the antigenic determinant recognized by mAb delta-TCS-1, encoded by the V delta 1 gene segment. The other two peripheral blood-derived clones and an ascites-derived clone were Ti gamma A-, BB3- and delta-TCS-1+. Biochemical analysis revealed that all Ti gamma A+, BB3+ T cell clones expressed the disulfide-linked form of the receptor. The two peripheral blood-derived delta-TCS-1+ T cell clones expressed the nondisulfide-linked form whereas the ascites-derived delta-TCS-1+ clone, AK119 expressed the disulfide-linked form of the TcR gamma/delta heterodimer. This indicates that V delta 1-encoded delta chains can be associated either with a C gamma 1- or a C gamma 2-encoded gamma chain. The preferential use of certain V gamma and V delta gene segments suggests the existence of a limited combinatorial diversity in TcR gamma/delta heterodimers, i.e. Ti gamma A+ (V gamma 9), BB3+ (V delta 2) and delta-TCS-1- disulfide-linked heterodimers and Ti gamma A-, BB3- and delta-TCS-1+ (V delta 1) disulfide- or non disulfide-linked forms.

Diversity and organization of human T cell receptor delta variable gene segments

Previous studies of the human TCR-delta gene identified a single commonly used V delta segment, denoted V delta 1. To better understand the extent of the human TCR-delta V gene repertoire, TCR-delta transcripts and gene rearrangements were examined in a new panel of cloned human TCR-gamma/delta lymphocytes. Through this analysis we identified and determined the structures of two new V delta segments, denoted V delta 2 and V delta 3. These V delta segments are different from previously characterized V alpha segments, supporting the notion that the human V delta and V alpha repertoires are distinct. Examination of V gamma gene segment usage in these cells reveals that the V delta 2 gene segment is used in conjunction with the V gamma 2 gene segment. Blot hybridization indicates that the V delta 2 gene segment lies between V delta 1 and D delta-J delta-C delta, and within 100 kb of the latter. Analysis of genomic clones indicates that the V delta 3 gene segment lies in an inverted orientation, approximately 2 kb 3' of C delta. This implies that rearrangement of V delta 3 to D delta-J delta-C delta occurs by inversion. Together with previous mapping studies, these results indicate that human V delta segments are dispersed, rather than clustered, within the TCR-alpha/delta locus. The analysis of rearrangements in polyclonal thymocyte DNA suggests that there may be a limited number of additional V delta gene segments yet to be characterized.

Structural and serological heterogeneity of gamma/delta T cell antigen receptor expression in thymus and peripheral blood

Monoclonal antibodies (mAb) reactive against the gamma/delta T cell antigen receptor (TcR) have been used to characterize the distribution and structural properties of gamma/delta TcR-bearing lymphocytes in blood and thymus. Consistent with prior reports the TcR gamma/delta-1 and delta-1 mAb react with all gamma/delta TcR+ T lymphocytes in blood and thymus. By contrast the TCS-delta mAb was found only to react with a subset of the gamma/delta TcR-bearing T cell population. Several lines of evidence suggest that this reagent preferentially reacts with the V delta 1 gene product. Using these reagents, it was observed that gamma/delta TcR+ T lymphocytes comprise 4.6 +/- 3.5% (range 1.0-16.3%) of peripheral blood lymphocytes. However, analysis of peripheral blood from normal adult donors revealed that in 29 of 32 the TCS-delta (possibly V delta 1)-bearing cells comprised less than 30% of the total gamma/delta-TcR+ population. Biochemical analysis demonstrated that the predominant form of the gamma/delta TcR in adult peripheral blood is a disulfide-linked heterodimer, indicating preferential use of the C gamma 1 gene. The delta TcR chain from these TcR-gamma/delta-1+/TCS-delta- T cells was remarkably basic in charge, as analyzed by nonequilibrium pH gradient electrophoresis. By contrast with peripheral blood the majority of freshly isolated and interleukin 2-cultured gamma/delta TcR+ thymocytes were predominantly TcR-gamma/delta-1+/TCS-delta +, and preferentially expressed V delta 1. Moreover, both disulfide-bonded and nondisulfide-bonded gamma/delta TcR heterodimers were expressed in all thymuses examined and both forms were contained within the TCS-delta + thymic subset. Similar to recent findings in the mouse, these studies suggest a possible bias in the structural form of gamma/delta TcR based on tissue location.

A novel human V delta gene expressed predominantly in the Ti gamma A fraction of gamma/delta+ peripheral lymphocytes

We have characterized a functional T cell receptor (TcR) delta transcript in a Ti gamma A+ human cloned cell line derived from peripheral blood. This cDNA includes a novel V gene (V-AB12), whose expression was initially studied in a series of TcR gamma/delta+ clones. Nine Ti gamma A+ clones derived independently from distinct donors have been tested: each of them was found to possess a unique V-AB12/J-IDP2 5.5-kb Eco RI rearrangement, which was constantly transcribed. Surface expression of the protein encoded by this unique rearranged gene was demonstrated by immunoprecipitations performed on three Ti gamma A+ polyclonal cell lines using a specific rabbit heteroantiserum. Further analysis strongly suggested that a monoclonal antibody (mAb), designated anti-BB3, detects a V-AB12-encoded antigenic determinant on the cell surface. Double-color immunofluorescence analysis of peripheral blood lymphocytes from ten donors indicated that most BB3+ cells are recognized by anti-Ti gamma A mAb. In previous studies, we have shown that a majority of TcR gamma/delta+ peripheral T cells expresses a gamma chain including V9 (Ti gamma A) and most frequently JP-encoded peptides. Given the present results on the delta chain, it can be concluded that, in many individuals, a predominant fraction (V gamma 9+/V-AB12+) of circulating CD3+ TcR alpha/beta- T lymphocytes expresses a receptor with little, if any, combinatorial diversity.

Human T-cell-receptor delta chain: genomic organization, diversity, and expression in populations of cells

The locus of the delta chain of the human T-cell receptor has been isolated and examined. Three D (diversity) regions and two J (joining) regions are present on the 5' side of the C (constant) region. The closest V (variable) region to the constant region is V delta 2, which in the germ line is found on the 3' side of the constant region in an inverted direction. The genomic structure of the human locus closely parallels its mouse counterpart. Several cDNA sequences and a series of rearranged genomic sequences are compared which demonstrate an enormous potential diversity in the junctional region, between the variable region and the joining region. We find the predominant utilization of the PEER variable region in thymic polyclonal gamma delta cell lines and in some peripheral blood gamma delta cell lines. Thus, the delta chain may have relatively limited variable-region diversity but a large junctional-region diversity. The implications of this observation are discussed.

Sequence and organization of the diversity, joining, and constant region genes of the human T-cell delta-chain locus

In this paper we describe the genomic organization and sequence of the human T-cell receptor delta-chain diversity, joining, and constant genes. There is one delta-chain constant region gene (C delta) located approximately equal to 85 kilobases (kb) upstream of the alpha-chain constant region. The delta-chain constant region consists of four exons, whose organization is very similar to that of the C alpha exons, suggesting that C alpha and C delta may have arisen from a gene duplication event. The first exon encodes most of the extracellular constant domain, the second encodes a hinge-like region, and the third encodes the entire transmembrane segment and intracytoplasmic portion, whereas the last exon contains exclusively 3' untranslated sequences. Three joining segments, J delta 1, J delta 2, and J delta 3, are found approximately equal to 12, approximately equal to 5.7, and approximately equal to 3.4 kb upstream of the first exon of C delta. Two functional diversity gene segments, D delta 1 and D delta 2, which can be productively translated in all three reading frames, are found 1 and 9.6 kb upstream of J delta 1. The presence of two D delta with such potential for diversity may offset the limited repertoire of the J delta and V delta genes. The spacer distribution in the recombinational signals flanking D delta and J delta segments allows recombination with V alpha gene segments; however, examination of delta-chain messages does not indicate that this is the case, suggesting that the delta chain uses unique variable gene segments and raising the question as to the reasons for this phenomenon.