Diversity and structure of human T cell receptor delta chain genes in peripheral blood gamma/delta-bearing T lymphocytes

Deep characterization of human γδ T cell subsets defines shared and lineage-specific traits

Under non-pathological conditions, human γδ T cells represent a small fraction of CD3+ T cells in peripheral blood (1-10%). They constitute a unique subset of T lymphocytes that recognize stress ligands or non-peptide antigens through MHC-independent presentation. Major human γδ T cell subsets, Vδ1 and Vδ2, expand in response to microbial infection or malignancy, but possess distinct tissue localization, antigen recognition, and effector responses. We hypothesized that differences at the gene, phenotypic, and functional level would provide evidence that γδ T cell subpopulations belong to distinct lineages. Comparisons between each subset and the identification of the molecular determinants that underpin their differences has been hampered by experimental challenges in obtaining sufficient numbers of purified cells. By utilizing a stringent FACS-based isolation method, we compared highly purified human Vδ1 and Vδ2 cells in terms of phenotype, gene expression profile, and functional responses. We found distinct genetic and phenotypic signatures that define functional differences in γδ T cell populations. Differences in TCR components, repertoire, and responses to calcium-dependent pathways suggest that Vδ1 and Vδ2 T cells are different lineages. These findings will facilitate further investigation into the ligand specificity and unique role of Vδ1 and Vδ2 cells in early immune responses.

Human Vδ2 T Cells and Their Versatility for Immunotherapeutic Approaches

Gamma/delta (γδ) T cells are innate-like immune effectors that are a critical component linking innate and adaptive immune responses. They are recognized for their contribution to tumor surveillance and fight against infectious diseases. γδ T cells are excellent candidates for cellular immunotherapy due to their unique properties to recognize and destroy tumors or infected cells. They do not depend on the recognition of a single antigen but rather a broad-spectrum of diverse ligands through expression of various cytotoxic receptors. In this manuscript, we review major characteristics of the most abundant circulating γδ subpopulation, Vδ2 T cells, their immunotherapeutic potential, recent advances in expansion protocols, their preclinical and clinical applications for several infectious diseases and malignancies, and how additional modulation could enhance their therapeutic potential.

Defying convention in the time of COVID-19: Insights into the role of γδ T cells

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is a complex disease which immune response can be more or less potent. In severe cases, patients might experience a cytokine storm that compromises their vital functions and impedes clearance of the infection. Gamma delta (γδ) T lymphocytes have a critical role initiating innate immunity and shaping adaptive immune responses, and they are recognized for their contribution to tumor surveillance, fighting infectious diseases, and autoimmunity. γδ T cells exist as both circulating T lymphocytes and as resident cells in different mucosal tissues, including the lungs and their critical role in other respiratory viral infections has been demonstrated. In the context of SARS-CoV-2 infection, γδ T cell responses are understudied. This review summarizes the findings on the antiviral role of γδ T cells in COVID-19, providing insight into how they may contribute to the control of infection in the mild/moderate clinical outcome.

Phenotypic and functional analysis of γδ T cells in the pathogenesis of human T-cell lymphotropic virus type 1 infection

The human T-cell leukemia virus type 1 (HTLV-1) is the cause of serious malignant and inflammatory diseases, including adult T-cell leukemia and lymphoma and tropical spastic paraparesis. The potential protective role of γδ T cells in HTLV-1 infection remains unclear. Here, demonstrate that there is a decrease in the amount of Vγ9Vδ2 T cells in patients with HTLV-1, especially in those with HTLV-1 associated pathologies. This suggests that γδ T cells could be involved in controlling the virus. Indeed, we found that Vγ9Vδ2 T cells, expanded from non-infected individuals, can kill cells expressing the viral proteins HBZ and Tax and this phenotype is reversed in the presence of mevastatin. Cytotoxicity by Vγ9Vδ2 T cells was not associated with an increase of INF-γ production. In sharp contrast, killing by NK cells was reduced by Tax expression. Thus, our study provides initial evidence for a potential protective role of Vγ9Vδ2 T cells against HTLV-1 infection. Therapeutic exploitation of these insights is feasible with current technologies of T-cell therapies and could provide novel tools to prevent and treat HTLV-1-associated malignancies and neurologic complications.

Double Negative T Regulatory Cells: An Emerging Paradigm Shift in Reproductive Immune Tolerance?

Immune regulation of female reproductive function plays a crucial role in fertility, as alterations in the relationship between immune and reproductive processes result in autoimmune subfertility or infertility. The breakdown of immune tolerance leads to ovulation dysfunction, implantation failure, and pregnancy loss. In this regard, immune cells with regulatory activities are essential to restore self-tolerance. Apart from regulatory T cells, double negative T regulatory cells (DNTregs) characterized by TCRαβ+/γδ+CD3+CD4–CD8– (and negative for natural killer cell markers) are emerging as effector cells capable of mediating immune tolerance in the female reproductive system. DNTregs are present in the female reproductive tract of humans and murine models. However, their full potential as immune regulators is evolving, and studies so far indicate that DNTregs exhibit features that can also maintain tolerance in the female reproductive microenvironment. This review describes recent progress on the presence, role and mechanisms of DNTregs in the female reproductive system immune regulation and tolerance. In addition, we address how DNTregs can potentially provide a paradigm shift from the known roles of conventional regulatory T cells and immune tolerance by maintaining and restoring balance in the reproductive microenvironment of female fertility.

Boosting the Immune System for HIV Cure: A γδ T Cell Perspective

The major barrier to HIV cure is a population of long-lived cells that harbor latent but replication-competent virus, are not eliminated by antiretroviral therapy (ART), and remain indistinguishable from uninfected cells. However, ART does not cure HIV infection, side effects to treatment still occur, and the steady global rate of new infections makes finding a sustained ART-free HIV remission or cure for HIV-seropositive individuals urgently needed. Approaches aimed to cure HIV are mostly based on the "shock and kill" method that entails the use of a drug compound to reactivate latent virus paired together with strategies to boost or supplement the existing immune system to clear reactivated latently infected cells. Traditionally, these strategies have utilized CD8+ cytotoxic lymphocytes (CTL) but have been met with a number of challenges. Enhancing innate immune cell populations, such as γδ T cells, may provide an alternative route to HIV cure. γδ T cells possess anti-viral and cytotoxic capabilities that have been shown to directly inhibit HIV infection and specifically eliminate reactivated, latently infected cells in vitro. Most notably, their access to immune privileged anatomical sites and MHC-independent antigen recognition may circumvent many of the challenges facing CTL-based strategies. In this review, we discuss the role of γδ T cells in normal immunity and HIV infection as well as their current use in strategies to treat cancer. We present this information as means to speculate about the utilization of γδ T cells for HIV cure strategies and highlight some of the fundamental gaps in knowledge that require investigation.

The production of alpha/beta and gamma/delta double negative (DN) T-cells and their role in the maintenance of pregnancy

The ability of the thymus gland to convert bone marrow-derived progenitor cells into single positive (SP) T-cells is well known. In this review we present evidence that the thymus, in addition to producing SP T-cells, also has a pathway for the production of double negative (DN) T-cells. The existence of this pathway was noted during our examination of relevant literature to determine the cause of sex steroid-induced thymocyte loss. In conducting this search our objective was to answer the question of whether thymocyte loss is the end product of a typical interaction between the reproductive and immune systems, or evidence that the two systems are incompatible. We can now report that "thymocyte loss" is a normal process that occurs during the production of DN T-cells. The DN T-cell pathway is unique in that it is mediated by thymic mast cells, and becomes functional following puberty. Sex steroids initiate the development of the pathway by binding to an estrogen receptor alpha located in the outer membrane of the mast cells, causing their activation. This results in their uptake of extracellular calcium, and the production and subsequent release of histamine and serotonin. Lymphatic vessels, located in the subcapsular region of the thymus, respond to the two vasodilators by undergoing a substantial and preferential uptake of gamma/delta and alpha/beta DN T- cells. These T- cells exit the thymus via efferent lymphatic vessels and enter the lymphatic system.The DN pathway is responsible for the production of three subsets of gamma/delta DN T-cells and one subset of alpha/beta DN T-cells. In postpubertal animals approximately 35 % of total thymocytes exit the thymus as DN T-cells, regardless of sex. In pregnant females, their levels undergo a dramatic increase. Gamma/delta DN T-cells produce cytokines that are essential for the maintenance of pregnancy.

Evolution and function of the TCR Vgamma9 chain repertoire: It's good to be public

Lymphocytes expressing a T cell receptor (TCR) composed of Vgamma9 and Vdelta2 chains represent a minor fraction of human thymocytes. Extrathymic selection throughout post-natal life causes the proportion of cells with a Vgamma9-JP rearrangement to increase and elevates the capacity for responding to non-peptidic phosphoantigens. Extrathymic selection is so powerful that phosphoantigen-reactive cells comprise about 1 in 40 circulating memory T cells in healthy adults and the subset expands rapidly upon infection or in response to malignancy. Skewing of the gamma delta TCR repertoire is accompanied by selection for public gamma chain sequences such that many unrelated individuals overlap extensive in their circulating repertoire. This type of selection implies the presence of a monomorphic antigen-presenting molecule that is an object of current research but remains incompletely defined. While selection on a monomorphic presenting molecule may seem unusual, similar mechanisms shape the alpha beta T cell repertoire including the extreme examples of NKT or mucosal-associated invariant T cells (MAIT) and the less dramatic amplification of public Vbeta chain rearrangements driven by individual MHC molecules and associated with resistance to viral pathogens. Selecting and amplifying public T cell receptors whether alpha beta or gamma delta, are important steps in developing an anticipatory TCR repertoire. Cell clones expressing public TCR can accelerate the kinetics of response to pathogens and impact host survival.

Identification of a new cluster of T-cell receptor delta recombining elements

Within the human T-cell receptor delta (TCRD) gene we have identified a new cluster of seven delta recombining elements (deltaRec2.1-2.7), located 2.6-5.2 kilobases downstream of the Vdelta2 gene segment. The deltaRec2 elements are isolated recombining signal sequences (RSS), which were shown to rearrange with the Ddelta3 and Jdelta1 segments of the TCRD gene as well as with the psiJalpha of the TCRA gene. Rearrangements involving the deltaRec2 elements were found in all peripheral blood (PB) samples from 10 healthy individuals, although their frequency was about 100-fold lower than that of classical deltaRec rearrangements. The total frequency of deltaRec2 rearrangements was lower in PB T lymphocytes, as compared with thymocytes, suggesting that they are deleted during T-cell development. The decrease of the frequency of the deltaRec2-Ddelta3 rearrangements was most prominent: 11 times lower in PB T lymphocytes than in thymocytes. Since the deltaRec2-Jdelta1 rearrangements contained the Ddelta3 segment in the junctional region, we assume that they are derived from the deltaRec2-Ddelta3 rearrangements. In contrast, the majority of deltaRec2-psiJalpha rearrangements did not contain the Ddelta3 segment, indicating that they are single step rearrangements. The deltaRec2-Jdelta1 and deltaRec2-psiJalpha rearrangements seem to be T-lineage specific, but the deltaRec2-Ddelta3 rearrangements were also found at very low frequencies in B lymphocytes and natural killer cells. Our results suggest that deltaRec2 rearrangements are transient steps in the recombinatorial process of the TCRAD locus and are probably deleted by subsequent Valpha-Jalpha rearrangements. We hypothesize, that in a similar manner to the classical deltaRec rearrangements, the deltaRec2 rearrangements might also contribute to T-cell differentiation towards the TCR-alphabeta lineage.

Novel T-cell receptor delta gene rearrangement involving a recombining element located 2.6 kb 3' from the Vdelta2 gene segment

In this study, we describe a novel T-cell receptor delta (TCRdelta) gene rearrangement observed in acute myeloid leukemia with coexpression of T-lymphoid antigens (Ly+AML) and in peripheral blood leukocytes (PBL) from one out of ten healthy donors. The rearrangement was identified by Southern blot analysis using a joining region (Jdelta1) specific probe and amplified by polymerase chain reaction (PCR) with a variable region (Vdelta2) and Jdelta1 specific primers. The nucleotide sequence analysis of an atypical 3000 bp PCR product allowed localization of the breakpoint within the TCRdelta gene locus, 2.6 kb 3' from the Vdelta2 gene segment. A regular Ddelta2-Ddelta3-Jdelta1 joining was found at the 3' end of the breakpoint, indicating that the rearrangement was mediated by the VDJ recombinase, but no TCRdelta gene segment was detected at the 5' end. Analysis of the germline sequence 3' from the breakpoint revealed an isolated recombination signal sequence (RSS) capable of initiating a rearrangement. The RSS motif described by us is the second TCRdelta recombining element (deltaRec2). The deltaRec2(Ddelta)Jdelta1 recombination is a rather rare event and can be found in acute leukemia and in PBL from healthy individuals. Most likely, the nonfunctional deltaRec2(Ddelta)Jdelta1 rearrangement is a transient step during the VDJ recombination. It may potentially lead to deletion of the deltaRec2(Ddelta)Jdelta1 complex and either to direct joining of a Vdelta region to one of the downstream Jdelta regions or to a rearrangement of the TCRalpha gene.

Hepatosplenic and subcutaneous panniculitis-like gamma/delta T cell lymphomas are derived from different Vdelta subsets of gamma/delta T lymphocytes

Gamma/delta T cell lymphomas (gamma/delta TCL) represent rare, often aggressive types of T cell malignancy that are clinically and pathologically diverse. Most gamma/delta TCL occur as a hepatosplenic or subcutaneous type. To date, analysis of the T cell receptor delta (TCRS) gene repertoire of hepatosplenic gamma/delta TCL (gamma/delta HSTCL) and subcutaneous panniculitis-like gamma/delta TCL (gamma/delta SPTCL) has been reported only in a limited number of cases. In this study we analyzed 11 gamma/delta HSTCL and 4 gamma/delta SPTCL by polymerase chain reaction and immunostaining to determine their usage of the Vdelta subtypes (Vdelta1-6). It is noteworthy that 10 of 11 gamma/delta HSTCL expressed the Vdelta1 gene. The remaining case also expressed T cell receptor delta (TCRS) as determined by flow cytometry and TCRdelta rearrangement in Southern blot. However, the Vdelta gene expressed by this lymphoma could not be determined, which suggests usage of an as yet unidentified Vdelta gene. In striking contrast to the gamma/delta HSTCL, all 4 gamma/delta SPTCL expressed the Vdelta2 gene. Our data demonstrate that gamma/delta HSTCL are preferentially derived from the Vdelta1 subset of gamma/delta T lymphocytes, whereas gamma/delta SPTCL are preferentially derived from the Vdelta2 subset. The pattern of Vdelta gene expression in HSTCL and SPTCL corresponds to the respective, predominant gamma/delta T cell subsets normally found in the spleen and skin. This finding suggests that gamma/delta TCL are derived from normal gamma/delta T lymphocytes which reside in the affected tissues. Furthermore, the selective, lymphoma type-specific Vdelta gene segment usage may provide a molecular tool to distinguish better among various types of gamma/delta TCL lymphoma particularly in the clinically advanced, widely disseminated cases.

The evolution of vertebrate antigen receptors: a phylogenetic approach

Classical T cells, those with alpha beta T-cell receptors (TCRs), are an important component of the dominant paradigm for self-nonself immune recognition in vertebrates. alpha beta T cells recognize foreign peptide antigens when they are bound to MHC molecules on the surfaces of antigen-presenting cells. gamma delta T cells bear a similar receptor, and it is often assumed that these T cells also require specialized antigen-presenting molecules for immune recognition, which we term "indirect antigen recognition." B-cell receptors, or immunoglobulins, bind directly to antigens without the help of a specialized antigen-presenting molecule. Phylogenetically, it has been assumed that T-cell receptors and the genes that encode them are a monophyletic group, and that "indirect" antigen recognition evolved before the split into two types of TCR. Recently, however, it has been proposed that gamma delta-TCRs bind directly to antigens, as do immunoglobulins (Ig's). This calls into question the null hypothesis that indirect antigen recognition is a common characteristic of TCRs and, by extension, the hypothesis that all TCR gene sequences form a monophyletic group. To determine whether alternative explanations for antigen recognition and other historical relationships among TCR genes might be possible, we performed phylogenetic analyses on amino acid sequences of the constant and variable regions which encode the basic subunits of TCR and Ig molecules. We used both maximum-parsimony and genetic distance-based methods and could find no strong support for the hypothesis of TCR monophyly. Analyses of the constant region suggest that TCR gamma or delta sequences are the most ancient, implying that the ancestral immune cell was like a modern gamma delta T cell. From this gamma delta-like ancestor arose alpha beta T cells and B cells, implying that indirect antigen recognition is indeed a derived property of alpha beta-TCRs. Analyses of the variable regions are complicated by strong selection on antigen-binding sequences, but imply that direct antigen binding is the ancestral condition.

Clonal dissemination of T-lymphocytes in scid mice from familial hemophagocytic lymphohistiocytosis

BACKGROUND

Although familial hemophagocytic lymphohistiocytosis (FHL) has been considered a disorder of T-cell dysfunction, there is no evidence of the clonal origin of T-cells in this disease.

PROCEDURE

We engrafted mononuclear cells (MNCs) from five FHL patients into scid mice and examined the infiltration of human cells in mouse organs. The characterization of human cells that infiltrated in the mouse organs was then performed.

RESULTS

A diffuse infiltration of human lymphoid cells was detected in scid mice treated with 1 x 10(6) MNCs from one of the five patients. These cells were positive for HLA-DR and CD3, but negative for CD4, CD8, CD20, and CD68, suggesting the infiltration of double negative (DN) T-cells. The MNCs from the other four patients induced murine lymphoma-like disease; T-cell lymphoma in one and lymphoma of unknown origin in three. The characterization of these human DN T-cells was performed. The analysis of the Vbeta repertoire showed no preferential usage of the Vbeta family in MNCs, while the dominant expression of Vbeta13 was detected in T-cells infiltrating in the spleen and lung. A Jbeta analysis showed the restricted usage of Jbeta1.2 for Vbeta13 in these cells, and the clonality of Vbeta13-Jbeta1.2 fragment was confirmed by a single-strand confirmation polymorphism analysis. The analysis of the Valpha repertoire showed that Valpha24 was exclusively used in these DN T-cells, but no usage of JalphaQ for Valpha24 was observed.

CONCLUSIONS

A clonal expansion of T-cells was induced in scid mice by the engraftment of MNCs from an FHL patient. The infiltration of DN alphabeta T-cells bearing invariant Valpha24 T-cell receptor in mouse organs may provide a useful clue to the pathogenesis of FHL. In the patients whose MNCs induced murine lymphoma-like disease, some cytokines or unknown factors that stimulate the growth and the tumorigenicity of murine lymphocytes might be produced by the MNCs engrafted in scid mice. Further study is needed to confirm the validity of our experimental approach and the findings observed in scid mice by using more FHL samples.

The Generation of Human γδ T Cell Repertoires During Fetal Development

The nature of how human γδ T cells are normally generated is not clear. We have used an RT-PCR assay and DNA sequencing to identify and compare δ-encoded TCRs (TCRDs) that are generated de novo in the fetal gut, liver, and thymus and to determine when, where, and how the TCRD repertoire is established during normal embryonic development. Rearranged TCRDV genes are first expressed outside of the thymus in the liver and primitive gut between 6 and 9 wk gestation. Although DV1Rs and/or DV2Rs predominated, differences in the pattern of TCRDV gene rearrangement and transcription in each tissue during ontogeny were identified. Specific, DV2-encoded TCRs are highly conserved throughout ontogeny in the tissues from the same and between genetically distinct donors. Although the thymic and intestinal γδ T cell repertoires partially overlap early in development, they diverge and become nonoverlapping during the second trimester, and the generation of the intestinal γδ T cell repertoire is characterized by differences in the processing of DV1Rs and DV2Rs. Whereas the structural diversity of DV1Rs progressively increases during gut development up to birth, DV2Rs have limited structural diversity throughout ontogeny. Together, our findings provide evidence for the ability of different fetal tissues to support the development of γδ T cells.

Detection of antigen receptor gene rearrangements in lymphoproliferative malignancies by fluorescent polymerase chain reaction

Monoclonal rearrangements of antigen receptor genes in lymphoproliferative diseases are characterized by the specific sequence and the length of their junctional region, which can be used as markers of the proliferating clone. PCR techniques have greatly simplified routine detection of monoclonal rearrangements. But on the one hand, identification of the sequences requires sequencing methods and on the other hand, sizing of rearrangements by conventional analysis of PCR products on agarose or nondenaturing polyacrylamide gels may be uncertain. We have developed an approach based on amplification of rearranged IGH, TCRG and TCRD locus by fluorescent PCR associated to a computerized analysis of generated PCR products allowing their objective sizing. We tested this method on DNA samples from patients with acute lymphoblastic leukemia and chronic lymphocytic leukemia, whose pattern of IGH and TCRG rearrangements had been previously identified by Southern blot techniques. TCRG-PCR assay allowed detection of 100% of rearranged samples. No false-negative results were found but a high rate (60%) of Southern-negative and PCR-positive samples were identified. TCRD PCR-assay detected VD1-JD1 or VD2-D2/3 rearrangements in both acute lymphoblastic leukemia and chronic lymphocytic leukemia samples. IGH PCR assay permitted detection of all known rearranged samples. The sensitivity of these three different PCR assays (1% leukemic cells) was equivalent to that of other published PCR protocols. These results show the validity and reliability of the fluorescent PCR method for routine detection of IGH, TCRG and TCRD rearrangements. Sizing of PCR products by computerized analysis was also validated. It provides additional information on rearrangement patterns in lymphoproliferative diseases, as clonal rearrangements can be recognized by their size. This can be of great interest in various circumstances, particularly for detection and follow-up of oligoclonality.

Gamma delta T-cells in human cutaneous immunology

Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells.

T-stem cell leukemia/lymphoma with both myeloid lineage conversion and T-specific delta recombination

We evaluated retrospectively the clinical and biological characteristics of six patients with CD7+ early T-acute lymphoblastic leukemia and lymphoma (T-ALL/LBL) originating from prothymocyte stage I (pro-T I) or II cells. Patients exhibited mediastinal mass (five of six) and lymphoadenopathy (five of six) but without leukocytosis and circulating blast cells (six of six). All patients achieved a complete remission. All but one had a relapse with a transformation to the mixed type (triphenotype--three cases, biphenotype-two cases) including myeloid features in three patients. The altered phenotypes were myeloperoxidase (MPO)+ (three of five), CD13+ (four of five), CD33+ (three of five) and CD19+ (three of five). The difference for MPO-positivity were observed between the bone marrow (BM)- and lymph node (LN)-blast cells (three of three). On cytogenetic analysis, there is no common abnormality in these patients. Immunomolecular analysis revealed T-cell lineage specific delta gene rearrangements [D delta 2-J delta 1 (five of six) and V delta 1-J delta 1 (one of six)] in all cases. Furthermore, D delta 2-J delta 1 occurred even in the cases with the pro-T I phenotype. Rearrangements of TCR beta, gamma or immunoglobulin heavy chain genes occurred in three patients. The same rearranged band(s) appeared at both diagnosis and relapse, indicating the same originality of the pro-T leukemic cell clone (three of three). We suggest that this type of CD7+ early T-ALL/LBL was transformed from a pro-T I or II cell, such as T-stem cell leukemia/lymphoma, which is a subtype of CD7+ stem cell leukemia as defined by Kurtzberg et al. This study reveals that pro-T I and II cells might be capable of myeloid, T- and B-lymphoid differentiation, and T-cell lineage specific TCR delta recombination occurs.

High incidence of a T nucleotide at the second position of codon 97 in Vdelta2-(D)-Jdelta1 junctional sequences of human normal skin gamma delta T-cells

In this investigation, we have demonstrated that in-frame polyclonal Vdelta2-(D)-Jdelta1 junctional sequences from human skin gammadelta T-cells contain a high incidence of T nucleotides at the second position of codon 97. Analysis of the deduced amino acid sequences based on in-frame Vdelta2-(D)-Jdelta1 junctional nucleotide sequences from normal skin gammadelta T-cells revealed a high incidence of the amino acids valine and leucine at position 97. These results are consistent with the studies in peripheral blood gammadelta T-cells, but not with previous findings in skin gammadelta T-cells, where random nucleotides were observed in the second position of codon 97 of Vdelta2-(D)-Jdelta1 junctional sequences and only a small minority of the deduced Vdelta2-(D)-Jdelta 1 amino acid sequences showed the amino acids valine and leucine at codon 97. Therefore, our findings indicate that the human skin gamma delta T-cells with a T-cell receptor consisting of a Vdelta2-(D)-Jdelta1-C delta1 chain are not a subset distinct from the subpopulation of human peripheral blood gammadelta T-cells expressing the same chain.

Detection of T-cell receptor delta gene rearrangement in T-cell malignancies by clonal specific polymerase chain reaction and its application to detect minimal residual disease

A clonal-specific polymerase chain reaction technique to detect T-cell receptor delta gene rearrangement in acute lymphoblastic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL) was evaluated. It was applied to detect minimal residual disease. A sensitive and specific technique to detect minimal residual disease for T-cell malignancies was explored. Southern analysis and polymerase chain reaction (PCR) were used to detect the rearranged V-D-J segment of T-cell receptor delta (TCR delta) gene from malignant cell specimens of patients with leukemia and lymphoma of T-cell lineage. The PCR product was sequenced and from the DNA sequences of the V-D-J region, a 3' anti-sense primer was designed and synthesized for clonal specific PCR (CS-PCR). T-cell receptor delta (TCR-delta) gene rearrangement was studied in 40 cases of acute leukaemia and lymphoma of T-cell lineage at diagnosis. Using Southern analysis, the positive rates were 28 and 32% for the 18 T-lymphoma and 22 T-ALL, respectively. A one stage Polymerase Chain Reaction (PCR) technique was used to detect the rearrangement in Southern positive cases and the PCR positive rates were 80 and 86%, respectively. The PCR technique had a sensitivity of 0.1%. Serial follow-up marrow specimens were available from 4 T-ALL patients following chemotherapy for monitoring of minimal residual disease. Their PCR products were DNA sequenced. A 3' primer was designed for each case for a clonal specific (CS) PCR. The technique had a sensitivity of 0.003%. It was applied to detect minimal residual disease in serial follow-up marrow samples. The first patient had persistent negative CS-PCR results and enjoyed continuous remission for more than 3 years. The second patient with negative one stage PCR but positive CS-PCR results had eventual relapse of leukaemia. The other two patients never achieved a morphological remission. These preliminary results appeared to support the usefulness of these PCR techniques in detecting minimal residual disease and predicting relapses for ALL. However, further clinical correlation in larger populations of patients is necessary.

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.

Human T-cell receptor variable gene segment families

Multiple DNA and protein sequence alignments have been constructed for the human T-cell receptor alpha/delta, beta, and gamma (TCRA/D, B, and G) variable (V) gene segments. The traditional classification into subfamilies was confirmed using a much larger pool of sequences. For each sequence, a name was derived which complies with the standard nomenclature. The traditional numbering of V gene segments in the order of their discovery was continued and changed when in conflict with names of other segments. By discriminating between alleles at the same locus versus genes from different loci, we were able to reduce the number of more than 150 different TCRBV sequences in the database to a repertoire of only 47 functional TCRBV gene segments. An extension of this analysis to the over 100 TCRAV sequences results in a predicted repertoire of 42 functional TCRAV gene segments. Our alignment revealed two residues that distinguish between the highly homologous V delta and V alpha, one at a site that in VH contacts the constant region, the other at the interface between immunoglobulin VH and VL. This site may be responsible for restricted pairing between certain V delta and V gamma chains. On the other hand, V beta and V gamma appear to be related by the fact that their CDR2 length is increased by four residues as compared with that of V alpha/delta peptides.

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.

The delta T cell receptor repertoire in human colon and peripheral blood is oligoclonal irrespective of V region usage

The majority of gamma/delta T cell receptors (TCR) in the human intestinal mucosa are thought to use the TCRDV1 (V delta 1) variable region gene segment, whereas gamma/delta T cells in the circulation predominantly express the TCRDV2 (V delta 2) gene segment. delta T cell receptors that use the TCRDV2 variable region gene segment generally have been regarded as highly diverse, whereas those that use the TCRDV1 gene segment are oligoclonal, whether present in the intestinal tract or in peripheral blood. We report herein that oligoclonality is a general feature of the peripheral delta T cell receptor repertoire in healthy human adults, irrespective of the variable region used and regardless of whether gamma/delta T cells reside in the intestinal mucosa or in peripheral blood. In addition, the delta T cell receptor repertoire is shown to be highly compartmentalized between such sites as the colon and peripheral blood, relatively stable over at least a 10-16-mo period, and unique in each individual. Further, the spectrum of variable region genes used by delta T cell receptor transcripts in the human colon is greater than previously recognized. Thus, in addition to the TCRDV1 and TCRDV2 variable region gene segments, delta T cell receptors in normal intestinal mucosa can use TCRDV3 (V delta 3) and TCRAV (V alpha) gene segments which, in some individuals, comprise a significant component of the mucosal delta T cell receptor repertoire. Our studies indicate that the potential of delta T cell receptors for extensive diversity is not reflected in the mature human repertoire. Moreover, these findings suggest a model wherein the delta T cell receptor repertoire in the colon and peripheral blood is shaped by selection and clonal expansion of gamma/delta T cells that ultimately seed throughout the length of the colon mucosa and populate the circulation.

Further evidence for the relationship of HIV-1 gp120 V3 loops with Ig superfamily members: similarity with the putative CDR3 region of T-cell receptor delta-chains

Twenty-five V3 loops of envelope gp 120 extracted from 30 HIV-1 isolates were compared with T-cell receptor (TCR) subunits variable (V) portions using pairwise alignments of 11-residue peptides. The results indicate that, in comparison with random sequences, the analyzed V3 loops, unlike control (unrelated) sequences, display highly significant local similarity with TCR V delta (p approximately 10(-20)). However, pattern-matching searches were performed on a much larger number of V3 loops (484). In particular, selective pattern TR * * * NT * K * I is shared by V delta from human T-cell line KT19E and 230 HIV-1 V3 loops (N-terminal portion). Pattern RA * YT * * * I * G is common for V delta chain isolated from T-cell line DS6 of an immunodeficient patient and 69 V3 loops (C-terminal portion). The presented delta-chain portions of sequence similarity with the V3 loops overlap the putative complementarity-determining region (CDR3), thus possibly indicating functional similarity too.

Gamma delta T cell receptor gene expression by muscle-infiltrating lymphocytes in the idiopathic inflammatory myopathies

Autoreactive alpha beta T cells have been implicated as playing a primary pathogenic role in a group of diseases characterized by chronic muscle inflammation known as the idiopathic inflammatory myopathies (IIM). gamma delta T cells, a distinct and enigmatic class of T cells, play a less certain role in a variety of human autoimmune diseases including the IIM. In an attempt to understand the significance of gamma delta T cells in the IIM, we utilized a sensitive polymerase chain reaction (PCR) technique to evaluate gamma delta T cell receptor (TCR) gene expression in 45 muscle biopsies obtained from 42 IIM patients (17 polymyositis, 12 dermatomyositis, and 13 inclusion body myositis). gamma delta TCR gene expression was not detected in 36 specimens, the majority of muscle biopsies surveyed. gamma delta TCR gene expression by muscle-infiltrating lymphocytes was detected among nine clinically heterogeneous patients. We further analysed the junctional sequence composition of the V gamma 3 and V delta 1 transcripts, whose expression was prominent among gamma delta positive patients. DNA sequence analysis of V gamma 3 amplification products from two patients revealed the presence of several productively rearranged transcripts with amino acid sequence similarities within the V gamma 3-N-J gamma junctional domain. No amino acid sequence similarities were evident within the V delta-N-D delta-N-J delta region of V delta 1 transcripts amplified from four patients, although a distinct and dominant clonotype was detected from each patient. Our cumulative data suggest that unlike alpha beta T cells, gamma delta T cells do not play a prominent pathologic role in the IIM. In fact, the sporadic nature of gamma delta TCR gene expression detected among these patients implies that gamma delta T cell infiltration, when it occurs, is a secondary event perhaps resulting from non-specific inflammatory processes.

Horse (Equus caballus) T-cell receptor alpha, gamma, and delta chain genes: nucleotide sequences and tissue-specific gene expression

Horse (Equus caballus) T-cell receptor alpha (TCRA), gamma (TCRG), and delta (TCRD) chain genes were isolated from a cDNA library and characterized. Five unique TCRAV families, including four full-length sequences, five distinct TCRAJ genes, and a single TCRAC gene were identified. TCRAV genes had closest homology with human sequences and least similarity to rat genes. Among eight horse TCRG genes, two distinct constant region genes with considerable variation in the connecting region were identified, but no variable or joining genes were present. Southern blot hybridization confirmed the presence of at least two TCRGC genes and indicated that the vast majority of horse alpha beta T cells rearrange either one or both TCRG alleles. Analysis of horse TCRD genes revealed the presence of eight unique TCRDV genes representing seven families, each having closest nucleotide homology with sheep sequences. Six unique TCRDJ genes were isolated; however, four of these sequences differed by only one base pair and thus likely represented alleles of a single gene. One horse TCRDC gene was present among fifteen clones analyzed and, based on Southern blot hybridizations, was deleted in polyclonal alpha beta T-cell populations, indicating that the TCRD locus is probably located within the TCRA locus as in other species. Polymerase chain reaction using horse-specific primers for the detection of TCRAC and TCRDC gene expression indicated that gamma delta T cells are located at numerous sites throughout the body, and with the exception of bone marrow where only TCRAC transcripts were detected, are closely associated with alpha beta T cells. This finding indicates that these two T-cell populations may be functionally interactive.

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.

Analysis of gamma delta V region usage in normal and diseased human intestinal biopsies and peripheral blood by polymerase chain reaction (PCR) and flow cytometry

The intestinal population of gamma delta T cell receptor (TCR)-bearing cells was characterized with regard to V delta and V gamma subtype expression. For this purpose, we utilized V gene-specific PCR of mRNA prepared from intestinal biopsies. Predominant expression of the V delta 1 subtype was demonstrated in the small intestine of patients with coeliac disease and in the inflamed colon of patients with inflammatory bowel diseases (IBD: ulcerative colitis and Crohn's disease) as well as in colon biopsies taken from macroscopically normal areas of colon. Although intestinal gamma delta T cells preferentially expressed V delta 1, other V delta transcripts could be detected, of which V delta 2 and V delta 5 were commonly expressed. Analysis of biopsies from mesenteric lymph nodes demonstrated a V delta repertoire similar to the mucosa. In peripheral blood on the other hand, high expression of both V delta 2 and V delta 1 was found. The predominant expression of V delta 1 transcripts in the intestinal mucosa of IBD patients correlated well with protein cell surface expression as analysed by flow cytometry using V delta 1- and V delta 2-specific antibodies. Selective expansion of gamma delta T cells could not be demonstrated within the inflamed mucosa as shown by mRNA analysis and flow cytometry. Instead, IBD patients demonstrated a decreased proportion of TCR gamma delta-carrying T cells in the inflamed mucosa compared with macroscopically normal area of colon. On the other hand, a significantly increased percentage of T cells bearing the gamma delta TCR was found in peripheral blood of patients with Crohn's disease compared with healthy individuals, indicating that local mucosal inflammation may influence the circulating gamma delta T cell population.

Heterogeneity of V delta 2 TCR delta gene rearrangements in acute myeloid leukemia

In a previous study, we described the occurrence of T-cell receptor (TCR)delta gene rearrangements in 9/100 acute myeloid leukemia (AML) cases. In this study, we further characterized these rearrangements by Southern Blot hybridization using a V delta 2 specific probe and polymerase chain reaction (PCR). Southern Blot analysis revealed that rearrangements involved the V delta 2 gene segment in four patients. Interestingly the restriction fragments detected by the V delta 2 probe differed markedly in size. PCR analysis revealed a complete V delta 2(Dn)J delta 1 gene rearrangement, an incomplete V delta 2D delta 3 rearrangement and a large amplification product, which cannot be explained with normal VDJ recombinatorial processes, in one case each. Furthermore although V delta 2 and J delta were rearranged, no comigration of rearranged fragments was observed and no PCR product was obtained in one case. Obtained results in AML differ from findings in acute lymphoblastic leukemia (ALL) of B-cell lineage, where a more homogeneous pattern of rearrangements has been described. This heterogeneity might be related to the illegitimate occurrence of TCR delta gene rearrangements in AML.

Different pattern of T cell receptor delta gene rearrangement in tumour-infiltrating lymphocytes and peripheral blood in patients with solid tumours

Tumour-infiltrating lymphocytes (TIL) and peripheral blood lymphocytes (PBL) from four patients with renal-cell carcinoma (three paired with blood), two colon carcinomas (both paired with blood) and two melanomas (blood was not available) were analysed for the T cell receptor (TCR) delta gene repertoire. Polymerase chain reaction analysis, employing a panel of specific primers for TCR delta gene segments, showed different gene rearrangement patterns in TIL and PBL in all patients. Simultaneous analysis of TIL and PBL revealed the presence of lymphoid cells in the tumour tissue that were not present in the periphery. These results demonstrate that, although tumour-infiltrating lymphocytes contain gamma/delta T cells within the range observed in peripheral blood, these cells differ from those in peripheral blood in their gene repertoire and this may account for selective accumulation or/and in situ amplification of gamma/delta lymphocytes at the tumour site, indicating a unique type of host reaction against tumour.

Restricted junctional diversity of T cell receptor delta gene rearrangements expressed in systemic lupus erythematosus (SLE) patients

SLE is an autoimmune connective tissue disorder affecting multiple organs, in which T cells may play a central role. This study investigated T cell receptor (TCR) gamma/delta repertoire expression in peripheral blood mononuclear cells (PBMC) of SLE patients and healthy individuals using variable (V) gene family-specific polymerase chain reaction (PCR) amplification of TCR cDNA. The expressed V gamma repertoires were diverse in SLE and control PBMC, although V gamma IV gene rearrangements were barely detectable or not expressed in some patients. In contrast, delta chain expression was limited in all SLE patients, with delta transcripts rearranged primarily to the V delta 1 and V delta 2 genes, as opposed to control PBMC, in which all six V delta genes were detected. To assess the clonality of TCR populations, cDNA clones containing rearranged V delta 1, V delta 2 and V gamma 9 transcripts were sequenced from PBMC of both patients and controls. For controls, delta chain junctional region sequences showed extensive molecular heterogeneity, since virtually all 34 V delta 1 and 32 V delta 2 cDNA clones analysed were unique. A few V gamma 9 cDNA clones (3/21) had the same junctional region sequence motif (EVQEL) encoded largely by the V gamma 9 and joining (J) gamma P gene segments. Identical V gamma 9 junctional sequences were found in SLE patients that did not contain the EVQEL motif present in normal peripheral blood gamma/delta lymphocytes. Moreover, the predominant V delta 1-J delta -constant (C) delta and V delta 2-J delta-C delta gene rearrangements expressed in SLE PBMC showed restricted junctional diversity, but the oligoclonal delta transcripts were different in each patient. These findings suggest in vivo oligoclonal expansion of gamma/delta T cells in the periphery of SLE patients in response to a limited number of nominal ligands. Whether gamma/delta T cells contribute to the development of systemic autoimmunity remains to be investigated.

The treatment of thrombotic thrombocytopenic purpura: plasma infusion or exchange?

Classic thrombotic thrombocytopenic purpura has substantial mortality and, because the pathogenesis is uncertain, multiple therapies are often used. These include corticosteroids and antiplatelet drugs, with plasma infusion or exchange most dramatically influencing outcome. To compare the relative efficacy of these latter two options, the records of 20 patients were retrospectively analysed. The groups were well matched for size and disease severity and received equivalent volumes of plasma. No significant difference in response rate or survival was demonstrated, although plasmapheresis may be preferable in the presence of impaired renal function with fluid overload.

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.

T-cell receptor V delta gene usage by tumour reactive gamma delta T lymphocytes infiltrating human lung cancer

In seven human adenocarcinomas and a non-neoplastic granulomatous disease of the lung, gamma delta+ infiltrating lymphocytes (TIL) could be isolated and selectively expanded in vitro upon culture in interleukin-2 (IL-2), without any additional stimuli, indicating a prior activation in vivo. In most cases gamma delta TIL were predominantly V delta 1+, despite a normal V delta 2:V delta 1 ratio in paired peripheral blood lymphocytes, suggesting a possible expansion of this subset in response to localized antigens/superantigens. Moreover, in five patients it was possible to identify a V delta 1- V delta 2- TIL population which by polymerase chain reaction (PCR) analysis was shown to be heterogeneous as V delta gene usage, inclusive of V delta 3,4,5,6,7 and 8. Of note, these V delta regions have not been found in peripheral blood so far. Finally, in all cases, gamma delta TIL displayed killing activity of the autologous tumour, which appeared to be more restricted in the case of V delta 1+ cells. Altogether, these findings suggest a preferential expansion, at the tumour site, of V delta 1+ cells and of cells expressing V delta genes other than V delta 2.

Molecular heterogeneity of a Graves' thyroid-infiltrating T cell population rich in CD8+ and gamma delta+ T cells

We report here on the isolation and repertoire characterization of a Graves' thyroid T cell population which, unlike most Graves' thyroid T cell isolates reported before, was rich in CD4-CD8- T cells (16%, all TcR gamma delta+) and CD8+ T cells (75%) [TcR alpha beta+ (59%) and TcR gamma delta+ (16%)]. Only 7% of the isolated T cells were CD4+. By contrast, < 2% of peripheral blood mononuclear cells from the same patient were gamma delta+ and < 14% were CD8+. Sequence analysis of 18 TcR delta cDNAs prepared from these cells indicated the presence of at least 17 different gamma delta+ T cell clonotypes with molecularly heterogeneous antigen-binding site sequences. As opposed to most peripheral blood gamma delta+ T cells (express V delta 2 TcRs), 13 of the 17 different TcR delta clonotypes used a V delta 1 gene, although PCR amplification of TcR gamma- and TcR delta-specific cDNAs with V delta- and V gamma-gene family-specific oligonucleotides confirmed usage of all 4 V gamma and all 6 V delta families. Sequence analysis of 21 TcR alpha cDNAs from a TcR alpha-specific cDNA library indicated the presence of at least 12 different clonotypes, using 8 different V alpha gene families and heterogeneous antigen-binding site sequences. These results are in contrast with the selective V alpha gene usage reported for other intrathyroidal T cell subpopulations in autoimmune thyroid disease.

The gamma delta T cell repertoire in Graves' disease and multinodular goitre

gamma delta T cells are a subset of T cells with unknown function, and restriction of the gamma delta T cell receptor (TCR) repertoire has been described in rheumatoid arthritis and multiple sclerosis. Elevated numbers of gamma delta T cells have been reported in the peripheral blood and thyroids of patients with Graves' disease. We have carried out flow cytometric analysis on peripheral blood mononuclear cells (PBMC) and intrathyroidal lymphocytes (ITL) from 12 patients with Graves' disease and nine patients with multinodular goitre (MNG), a thyroid disease of unknown etiology. There was no significant difference between the proportion of gamma delta T cells in the PBMC of Graves' and MNG patients, nor between the PBMC and ITL populations in either patient group. We have also carried out polymerase chain reaction amplification on RNA prepared from matched PBMC, ITL and the activated (CD25+) subset of ITL using six TCR V delta-family specific primers. Although there were differences in the amounts of each V delta transcript amplified from PBMC and ITL, there was no difference between the two patient groups. No consistent differences were therefore found between the gamma delta T cell populations in Graves' and MNG patients, arguing against the direct involvement of this T cell subset in the pathogenesis of Graves' disease.

In vivo clonal dominance and limited T-cell receptor usage in human CD4+ T-cell recognition of house dust mite allergens

Sensitivity to house dust mite antigens in atopic individuals is a major cause of allergic diseases, ranging from asthma to rhinitis and dermatitis. We have studied the T-cell receptor (TCR) usage of house-dust-mite-specific CD4+ T-cell clones isolated from an atopic individual, by using the anchored polymerase chain reaction, and have analyzed the peripheral TCR repertoire of the same individual. Several T-cell clones had identified TCRs at the sequence level, despite the fact that they had been independently isolated, in some cases, in different years. These data suggest the presence in vivo of long-lived T-cell clones. We have also shown that junctional sequences identical to these clones are present in peripheral blood T cells taken 6 years after the isolation of the T-cell clones. The analysis of TCR genes used by the panel of clones reveals oligoclonality, with the variable (V) region gene segments V alpha 8 and V beta 3 being dominant, although there is minimal conservation of junctional sequences. The results have implications for understanding the TCR recognition of an environmental aeroallergen and the life span of T-cell clones in vivo during a chronic immune response.

Gamma delta T cell receptor repertoire in brain lesions of patients with multiple sclerosis

The identification of activated T cells in the brains of patients with multiple sclerosis (MS) suggests that these cells are critical in the pathogenesis of this disease. Recently we have used the PCR method to analyse rearrangements of V alpha and V beta genes of the T cell receptor (TCR) in samples of MS and control brains. The results of these studies showed that TCR V gene usage in MS brains may be restricted and in particular that V beta genes may be preferentially rearranged in certain HLA haplotypes associated with susceptibility to MS. In view of the recent evidence that T lymphocytes bearing the gamma delta chains may have autoreactive potential, we have assessed whether or not such TCR-bearing lymphocytes were also present in chronic MS lesions. TCR V gamma and V delta were analysed by the PCR method using a panel of V gamma and V delta primers paired with C gamma or C delta primers in 12 MS brains, as well as in brain samples of ten normal post-mortem cases and three neurological controls. TCR V gamma-C gamma and V delta-C delta rearrangements were confirmed using Southern blotting and hybridisation of the PCR products with specific C gamma and C delta probes. Only one to four rearranged TCR V gamma and V delta transcripts were detected in each of the 23 brain samples obtained from 12 MS patients, with the majority of gamma delta T cells expressing the V gamma 2 and V delta 2 chains. In marked contrast, V gamma and V delta transcripts could only be found in one of the ten non-neurological control brains analysed. To assess the clonality of V gamma 2 and V delta 2 T cell receptor chains in the brain samples of MS patients, we have sequenced the junctional regions of the TCR V gamma-N-J gamma-C gamma and V delta-N-D delta-N-J delta-C delta segments amplified from brain tissues, CSF and spleens of two MS patients and from the spleen of two control subjects. The sequence analysis obtained so far shows no compelling evidence of an MS specific expansion of one or more clones expressing particular types of gamma delta T cell receptors. In contrast, a clonal expansion of a different population of TCR gamma delta-bearing T cells was found in the spleen of both an MS patient and one of the control individuals.(ABSTRACT TRUNCATED AT 400 WORDS)

Surface expression of two distinct functional antigen receptors on human gamma delta T cells

Lymphocytes recognize antigens with highly variable heterodimeric surface receptors. Although four distinct antigen receptors could in principle be produced by any lymphocyte, only one functional combination of receptor chains has thus far been found expressed on their surface. Examination of human gamma delta T cells revealed a population that violated this rule by expressing on their surface two distinct functional gamma delta T cell receptors (TCRs) that used different TCR gamma gene alleles. Thus, current models for T cell clonal selection may need modification, and a possible escape mechanism for autoreactive TCRs is suggested.

Molecular analysis of the gamma delta T-cell receptor repertoire in normal human skin and in Oriental cutaneous leishmaniasis

The extent of diversity of the gamma delta T-cell receptor (TCR) in normal human skin and Oriental Cutaneous Leishmaniasis (OCL) was examined by molecular analysis of the variable (V) delta gene segment, junctional (J) delta gene segment and junctional regions. To examine the expression of TCR delta genes, segments of gamma delta T lymphocytes, DNA isolated from normal human skin and from OCL were subjected to enzymatic gene amplification by the polymerase chain reaction (PCR) method using TCR V delta- and J delta-specific oligonucleotides as primers. PCR amplification using these primers indicated that the V delta 2 gene segment was predominantly used by gamma delta T lymphocytes in both normal human skin and OCL. To determine the extent of junctional diversity in the delta gene of gamma delta T cells in normal human skin and OCL, we sequenced the nucleic acid sequences corresponding to the V delta 2/J delta 1 junctional regions. Sequence analysis of junctional regions demonstrated broad junctional diversity in normal skin but only limited diversity in OCL. Our findings support the hypothesis that skin gamma delta T lymphocytes may derive from a fetal subset of gamma delta T lymphocytes that leaves the thymus early and colonizes the periphery. The limited junctional diversity demonstrated in OCL lesions indicates that gamma delta T cells can undergo oligoclonal expansion following recognition of a specific ligand and supports the idea that junctional regions are important in the recognition of antigenic determinant.

Characterization of the human T cell receptor alpha-chain repertoire and demonstration of a genetic influence on V alpha usage

Despite considerable knowledge of the determinants and profile of the T cell receptor (TCR) beta-chain repertoire, very little is known about the repertoire of the V alpha and J alpha segments of the TCR in man or mouse. We have used the anchored polymerase chain reaction (PCR) to analyze the human TCR alpha-chain repertoire at the mRNA level in peripheral blood lymphocytes. We find marked differences in the usage of individual V alpha segments. The V alpha repertoire is determined both by differences in the use of individual V alpha gene segments at the time of gene rearrangement and by genetic influences on the selection of the expressed V alpha repertoire, presumably during thymic maturation. Analysis of the J alpha repertoire shows non-random usage of individual J alpha segments but no obvious relationship to chromosomal position. We also report three new V alpha segments, three new J alpha segments and possible allelic variation in V alpha gene segments. Two unusual TCR alpha transcripts are described which add new information on the nature of TCR alpha transcript assembly.

Gamma delta T lymphocytes in oriental cutaneous leishmaniasis: occurrence and variable delta gene expression

It has been suggested that T lymphocytes expressing gamma delta T-cell receptors could play an important role in defence against some intracellular infectious pathogens. The present study was undertaken to characterize the occurrence and variable delta gene expression of T lymphocytes expressing the gamma delta T-cell receptor in oriental cutaneous leishmaniasis. Eleven cases of oriental cutaneous leishmaniasis were investigated by immunohistological analysis using an alkaline phosphatase-anti-alkaline phosphatase (APAAP) technique. In three cases, we observed an increased percentage of gamma delta T cells (about 20% of CD3+ cells). In these cases gamma delta T cells generally expressed the V delta 2 segment, and only rarely the V delta 1 gene product. V delta 2+ cells were predominantly localized in the dermis, and were virtually absent in the epidermal compartment. The rare gamma delta T cells observed in the epidermis were almost exclusively V delta 1+. This study demonstrates that an increase of gamma delta T cells may be found in oriental cutaneous leishmaniasis, although it is not a constant feature of the disease. The finding of a preferential expansion of the V delta 2 subset suggests that this subpopulation of gamma delta T cells might be selectively involved in the recognition of Leishmania antigens. The distinct compartmentalization of gamma delta T-cell subpopulations indicates that these subsets may recognize distinct sets of antigens.

Preferential V delta 1 expression among TcR gamma/delta-bearing T cells in human oral epithelium

The oral cavity is a septic area colonized by various bacterial species, and the oral mucosa is frequently submitted to microtraumas. Several mechanisms are implicated in the defence of the oral tissue, but little is known concerning the eventual presence and role of gamma/delta T cells at this site. Samples of healthy keratinized oral mucosa were examined with immunochemical techniques using anti-CD3, CD4, CD8, CD22, TcR delta 1, V delta 1 and V delta 2 monoclonal antibodies. Whatever the site examined, gamma/delta T cells represent at most 2% of the T-cell population, a value similar to that found in other tissues. In the connective tissue, under the basement membrane, V delta 2+ gamma/delta T cells are predominant whereas the epithelium mostly contains V delta 1+ gamma/delta T cells. The significance of this preferential V delta 1 intraepithelial presence is discussed.

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.

The T cell receptor alpha beta V-J shuffling shows lack of autonomy between the combining site and the constant domain of the receptor chains

In order to assess the structural independence of the T cell receptor (TCR) combining site from the rest of the molecule we have generated two recombinant chains consisting of a TCR V-J alpha region linked to the C beta and a TCR V-J beta linked to the C alpha. If the V and C domains of the TCR form independent domains, as has been shown for the Ig molecules, we would expect to obtain a functional chimeric TCR. Interestingly, it was found that the shuffled molecules are produced intracellularly in T cell hybridomas, but are not expressed on the cell surface. To explain this failure of the shuffled molecules we propose that the TCR has a more compact structure, compared to the Ig, and that it is indispensable to keep a longitudinal inter-domain contact between the V-J and C portion to have a functional molecule.

T cell receptor heterogeneity in gamma delta T cell clones from intestinal biopsies of patients with celiac disease

In celiac disease large numbers of gamma delta T lymphocytes infiltrate the intestinal epithelia. We have isolated intestinal gamma delta T cell clones from patients with celiac disease and have analyzed their T cell receptor repertoire. T cell lines and clones were obtained from jejunal biopsies of 14 celiac patients and 12 individuals without celiac disease. These were analyzed by staining with monoclonal antibodies against CD3, alpha beta and gamma delta T cell receptor, by Southern blot with gamma- and delta-specific probes and by polymerase chain reaction using V delta-specific oligonucleotides. Intestinal gamma delta cells from patients with celiac disease differed from those of controls with normal jejunal histology in that V delta 1+ cells and V delta 1-V delta 2- cells were significantly increased. There was no evidence of the expansion of one or more clones expressing particular types of gamma delta T cell receptor.