Rearrangement Of T-cell Antigen Receptor Genes Research Articles

Significance of clonal TCR gene rearrangement in acquired pure red cell aplastic anemia

To evaluate the significance of T-cell antigen receptor (TCR) gene rearrangement among patients with acquired pure red cell aplastic anemia (A-PRCA). For 16 patients with A-PRCA, an immunosuppressive regimen based on cyclosporin A (CsA) was applied. Rearrangement of the TCR gene was detected by PCR, and T lymphocyte subsets in peripheral blood specimens was detected with flow cytometry. Five patients had presented with TCR clonal rearrangement and were positive for both TCR γ and TCR δ. The blood of 13 patients have returned to normal with the treatment, which included 3 cases with bone marrow returning to normal. In 7 cases, the red cell hyperplasia of bone marrow is still down, but has increased with the treatment. Three patients were close to cure, 7 showed remission, 3 were improved, but 3 were ineffective. The rate of effective treatment in those with TCR rearrangement (2/5) was significantly lower than that those without (11/11, chi-square=8.123, P < 0.05). Compared with those without the TCR gene rearrangement, the Th cells and proportion of Th/Ts were significantly lower, while the Ts cell (CD3+CD8+) were significantly higher in those with the rearrangement (P < 0.05). TCR gene rearrangement may play a role in the pathogenesis of A-PRCA. CsA is effective for the treatment of A-PRCA, but patients presenting clonal TCR gene rearrangement may response poorly to the treatment.

Canine inflamed nonepitheliotropic cutaneous T‐cell lymphoma: a diagnostic conundrum

Cutaneous T-cell lymphoma (CTCL) in dogs is a heterogeneous disease complex, which consists of nonepitheliotropic (NE) and epitheliotropic forms. These lymphomas are readily recognized by the presence of dominant populations of cytologically atypical lymphocytes. The objective of this study was to introduce the key features of inflamed NE-CTCL, which is easily confused with reactive, inflammatory histiocytic disease. Twenty-four dogs (mean age 7.5 years) presented with inflamed NE-CTCL. Lesions presented as nodules, plaques or masses. An initial diagnosis of cutaneous reactive histiocytosis (11 dogs) or histiocytic neoplasia (three dogs) was made by primary pathologists. Lesions were assessed by histology and immunohistochemistry to detect canine leukocyte antigens. Lesional genomic DNA was extracted and gene rearrangement analysis of the T-cell receptor γ locus was assessed. The cutaneous lesions consisted of pleocellular infiltration of the dermis with variable extension into the subcutis. The lesions often surrounded vessels and adnexae. Epitheliotropism was minimal or lacking. Small lymphocytes, plasma cells and intermediate to large, cytologically atypical lymphocytes were scattered between prominent histiocytic infiltrates. Atypical lymphocytes often had marked variation in the intensity of CD3 expression. Molecular clonality analysis of the T-cell receptor γ locus revealed clonal expansion of T cells in 22 of 23 dogs tested. The recognition of inflamed NE-CTCL and its differentiation from cutaneous reactive histiocytosis depends on careful assessment of lymphocyte morphology and immunostaining patterns. Confirmation of the diagnosis is best accomplished by T-cell antigen receptor gene rearrangement analysis.

T cell heterogeneity in patients with common variable immunodeficiency as assessed by abnormalities of T cell subpopulations and T cell receptor gene analysis.

T lymphocyte regulation of immunoglobulin production may be abnormal in some patients with common variable immunodeficiency (CVI). Phenotypic analysis of peripheral blood T lymphocytes from nine patients with CVI was conducted to examine whether an abnormal distribution could be detected in a functionally distinct T lymphocyte subpopulation. The percentage of CD8+ lymphocytes proved to be increased in some patients and decreased in others. In comparison with normal controls, many patients with CVI had reduced percentages of lymphocytes expressing both CD4 and CD45RA, a phenotype associate with naive CD4+ cells. There was no significant difference in CD4+ populations bearing CD29 or leucocyte adhesion molecule-1 (LAM-1) antigens. The pattern of gene rearrangement of the T cell antigen receptor (TCR) was studied using peripheral blood lymphocytes from these patients with CVI. Genomic DNA from freshly isolated lymphocytes as well as from selectively propagated CD4+ or CD8+ populations were examined using Southern blot analysis and a probe for the beta chain of the TCR. A polyclonal pattern of TCR gene rearrangement, without the appearance of dominant non-germline bands, was demonstrated in all patient samples. These data suggest that the T lymphocytes in patients with CVI have a polyclonal pattern of TCR rearrangement despite an abnormal distribution of T cell subpopulations in some patients.

Revision of the antigen receptor of T-lymphocytes

This review considers a crucially new mechanism of T-cell antigen-recognizing repertoire formation. It includes the revision of T-cell antigen receptor (TCR), which implies the secondary rearrangement of TCR genes in peripheral T-lymphocytes and surface expression of a new antigen receptor with altered specificity. Factors and mechanisms involved in the induction of this process have been analyzed. Certain attention is paid to a possible role of TCR revision in the formation of peripheral tolerance in the processes of "avidity maturation" of T-lymphocytes during immune response and also negative consequences related to appearance of potentially autoreactive clones in the periphery.

CD4 and CD8 expression and T cell antigen receptor gene rearrangement in early intrathymic precursor cells.

The earliest T precursor population in the adult mouse thymus, considered to have the surface phenotype CD4lo8-3-44+25-Thy-1lo c-kit+ (termed the low CD4 precursor), has been shown to have the capacity to produce B cells and dendritic cells, as well as T cells, and to have the T cell antigen receptor (TCR) C beta gene region in germ-line configuration. Because of evidence that this precursor population may have low levels of CD8 as well as CD4 on the cell surface, it was isolated, stained for surface CD4 and CD8 and assayed for the expression of messenger RNA (mRNA) for CD4 and CD8 by the reverse transcriptase polymerase chain reaction (RT-PCR). The low CD4 precursors gave definite, moderate levels of staining for both CD8 and CD4, in contrast to downstream precursors which showed only marginal staining and so could be considered as genuine CD4-8-3- triple negatives. The low CD4 precursor expressed a significant level of mRNA for CD4, indicating that the surface CD4 was produced by these cells. However, the low CD4 precursor did not express a detectable level of mRNA for CD8, suggesting that the surface CD8 was acquired from other cells. Since the low CD4 precursor population was found already to express mRNA for enzymes involved in TCR gene rearrangement, including in this study terminal deoxynucleotidyl transferase (TdT), a PCR procedure was used to assay early precursors for D-J rearrangements at the TCR beta gene locus. However, the low CD4 precursor had the TCR beta D-J genes in germ-line configuration, D-J gene rearrangements being first detected several stages downstream in the CD3-4-8-44-25-+ precursor population. We conclude that a transient synthesis of CD4, but not of CD8, characterize these early thymus precursors. Although they have initiated synthesis of some recombination-associated enzymes, full commitment to the T lineage and TCR gene rearrangement is a later event.

Molecular Diagnosis of Lymphocytic Infiltrates of the Skin

Advances in our understanding of the molecular genetics of lymphocyte antigen receptors (B-cell immunoglobulin and T-cell antigen receptor), have led to the application of molecular biologic techniques to molecularly characterize lymphocytic infiltrates of the skin. Molecular diagnosis refers to the application of these techniques as a diagnostic aid in the clinicopathologic evaluation of cutaneous lymphocytic infiltrates. Molecular studies have clinical application in the determination of lineage and detection of retroviruses in cutaneous lymphoid neoplasms, distinguishing between lymphoproliferative and reactive infiltrates, and staging and monitoring response to therapy in cutaneous T-cell lymphoma. Southern blot analysis of immunoglobulin and T-cell antigen receptor gene rearrangements may fail to aid the clinician in establishing a diagnosis of a cutaneous malignancy due to the limits of detection sensitivity in minimally infiltrated lesions (eg, parapsoriasis and patch-stage mycosis fungoides) or the still uncertain prognostic significance of clonality in benign cutaneous diseases (eg, follicular mucinosis, pityriasis lichenoides et varioliformis acuta, lymphomatoid papulosis, and cutaneous lymphoid hyperplasia). Molecular studies have enormous research value, providing new means to explore the pathogenesis and clonal evolution of lymphoproliferative skin diseases. Presently, however, they have limited applications as an independent diagnostic tool. As our understanding of the clinical and biologic significance of the molecular detection of clonal lymphocyte populations in the skin expands and as the application of polymerase chain reaction amplification provides us with greater detection sensitivity and specificity, the clinical utility of molecular diagnosis of lymphocytic infiltrates of the skin will be enhanced.

Extrathymic development of V alpha 14-positive T cells.

It is known that rearrangement of the T cell antigen receptor (TCR) gene occurs in the thymus during T cell development and consequently results both in the deletion of DNA between the variable (V) and diversity/joining segments and in the formation of a circular DNA with recombination signal sequences. Here, we provide evidence that V alpha 14+ TCR gene rearrangements take place in extrathymic sites, such as bone marrow, liver, and intestine, but not in spleen, because we were able to detect frequent productive and nonproductive V alpha 14+ coding and signal sequences as a result of TCR rearrangements in extrathymic sites. Similar findings were also detected in athymic mice. Quantitative analysis shows that the relative amounts of V alpha 14 gene-mediated signal sequences in extrathymic tissues are higher than those in thymus. On the contrary, TCR rearrangements of V alpha 1.1 T cells, which are known to develop in the thymus, were mainly detected in the thymus, Peyer's patch, and spleen, but not in other extrathymic tissues, showing patterns distinct from V alpha 14 TCR rearrangements. These findings are evidence of extrathymic development of V alpha 14+ T cells. Differential characteristic TCR rearrangement patterns also indicate that distinct TCR repertoires are generated in different lymphoid tissues.

Prognostic Implications of Evaluation for Lymph Node Involvement by T-Cell Antigen Receptor Gene Rearrangement in Mycosis Fungoides

Abstract We investigated the correlation between the detection of clonal rearrangement of the T-cell antigen receptor gene (TCRR) in lymph node tissue with histopathologic lymph node classification in 33 patients with mycosis fungoides with and without the Sezary Syndrome. We analyzed DNA extracted from lymph nodes that were histologically uninvolved (LN1–2), dermatopathic nodes with clusters of atypical cells (LN3), and nodes effaced with lymphoma (LN4) and found TCRR in none of five LN1–2 nodes, 8 of 17 LN3 nodes, and 10 of 11 LN4 nodes. Further, the detection of TCRR correlated with presence of palpable adenopathy (P2 less than .0001) and was associated with a worse survival (P2 = .0024). Within the subgroup of patients with LN3 nodes, there was a trend (P2 = .14) toward inferior survival if nodes were involved by TCRR, irrespective of extent of skin disease. We conclude that detection of TCRR in nodes from mycosis fungoides patients is an objective and reliable means of assessing tumor infiltration of lymph node and is associated with an inferior survival.

Frequent detection of Epstein-Barr virus DNA by the polymerase chain reaction in lymph node biopsies from patients with Hodgkin's disease without genomic evidence of B- or T-cell clonality

This study of 52 Swiss patients with Hodgkin's disease (HD), including 17 cases with a high content of Sternberg-Reed (SR) and Hodgkin (H) cells, was performed to determine the percentage of cases harboring Epstein-Barr virus (EBV) DNA and/or clonal rearrangements of Ig and T- cell antigen receptor (TcR) genes in diagnostic lymph node biopsies. Special attention was drawn to the heavily infiltrated cases to detect a possible relationship between clonality and EBV DNA identification. EBV DNA was detected by the polymerase chain reaction (PCR) using three different sets of specific primers. The viral origin of the amplification products was confirmed by hybridization with a radiolabeled internal probe or demonstration of a specific Sma I restriction site. Genomic rearrangement of Ig and TcR genes was studied by Southern blot analysis. EBV DNA was identified by PCR in 38 of 48 cases (79%). Clonal rearrangements were identified in only 4 of 52 cases (Ig genes) and were independent of the degree of infiltration by SR cells and the presence of EBV DNA. The absence of EBV DNA in three cases with numerous SR cells (only one of them showed clonal rearrangement) and the presence of only a few viral copies in four further cases with numerous SR cells (semiquantitative analysis of viral DNA by PCR was performed in 26 EBV-positive cases) suggests that this virus is modulating rather than an etiologic agent in a considerable proportion of HD cases.

Frequent Detection of Epstein-Barr Virus DNA by the Polymerase Chain Reaction in Lymph Node Biopsies From Patients With Hodgkin's Disease Without Genomic Evidence of B- or T-Cell Clonality

This study of 52 Swiss patients with Hodgkin's disease (HD), including 17 cases with a high content of Sternberg-Reed (SR) and Hodgkin (H) cells, was performed to determine the percentage of cases harboring Epstein-Barr virus (EBV) DNA and/or clonal rearrangements of Ig and T-cell antigen receptor (TcR) genes in diagnostic lymph node biopsies. Special attention was drawn to the heavily infiltrated cases to detect a possible relationship between clonality and EBV DNA identification. EBV DNA was detected by the polymerase chain reaction (PCR) using three different sets of specific primers. The viral origin of the amplification products was confirmed by hybridization with a radiolabeled internal probe or demonstration of a specific Sma I restriction site. Genomic rearrangement of Ig and TcR genes was studied by Southern blot analysis. EBV DNA was identified by PCR in 38 of 48 cases (79%). Clonal rearrangements were identified in only 4 of 52 cases (Ig genes) and were independent of the degree of infiltration by SR cells and the presence of EBV DNA. The absence of EBV DNA in three cases with numerous SR cells (only one of them showed clonal rearrangement) and the presence of only a few viral copies in four further cases with numerous SR cells (semiquantitative analysis of viral DNA by PCR was performed in 26 EBV-positive cases) suggests that this virus is modulating rather than an etiologic agent in a considerable proportion of HD cases.

Heterogeneity of immunoglobulin gene rearrangements in B‐cell lymphomas

We have examined 69 B-cell non-Hodgkin's lymphomas (NHL) for rearrangements of the immunoglobulin (Ig) or T-cell antigen receptor (TCR) genes. The lymphomas were assigned to the categories of the Kiel classification and their B-cell nature was confirmed by immunostaining. Only 2 cases (with CLL) displayed clonal T beta-chain TCR gene rearrangements together with rearranged heavy- and light-chain Ig genes. The remaining 67 lymphomas had a germline beta-chain TCR-gene configuration. Three different patterns of Ig gene rearrangements were identified; (A) presence of both heavy- and light-chain rearrangements (H+L+); (B) rearrangement of heavy-chain gene only (H+L-); (C) heavy- and light-chain genes in germline configuration (H-L-). All the 45 low-grade NHLs and the 4 immunoblastic lymphomas exhibited pattern A and all had their kappa gene rearranged or deleted. Of 24 low-grade lymphomas tested, 13 (54%) had an addition rearrangement of the lambda light-chain gene. In contrast, the 19 high-grade centroblastic (cb) B-NHLs had distinct patterns of Ig-gene rearrangement: 12 with pattern A, 4 with B and 2 with C. In this group only 2 of 17 (12%) cases analyzed had evidence of lambda light-chain rearrangement whereas 12 of 18 (67%) had a kappa gene rearrangement or deletion. In one case expressing sIgM/lambda and with heavy chain Ig-rearrangement, no DNA was available for Ig light-chain analysis.

Cross-Lineage Gene Rearrangements in Human Leukemic B-Precursor Celis Occur Frequently With V-DJ Rearrangements of IgH Genes

AbstractGene configurations of immunoglobulin (Ig), T-cell antigen receptor (TCR) β chain, and T-cell rearranging gene γ (TRGγ) were studied in human B-precursor lymphoblastic leukemic cells. These cells were phenotypically classified into three developmental stages (stages II through IV) according to Nadler's criteria. All of them showed the Ig heavy chain (IgH) gene rearrangement, and 67% of the cells in stage IV had the rearranged TRGγ, albeit seldom in other stages. We further analyzed IgH gene rearrangements in detail using upstream to DH (diversity region of IgH) region probe to distinguish DJ from V-DJ recombination. All dual genotyped cells in each stage except one case in stage II showed the V-DJ rearrangements. This suggests the cross-lineage involvement of the putative recombinase, particularly in the process of V-DJ rearrangements. We next examined the transcriptional status of Ig genes as an indirect reflection of the accessibility of these genes to the recombinase. Properly spliced IgH transcripts of normal size were observed in stage IV and surface Ig positive stage, but not in stage II nor III. However, IgH transcripts of aberrant sizes were seen in stage II, III, and also IV. Cross-lineage gene rearrangements were shown to occur frequently when normally spliced IgH gene begins to be transcribed or just before this. These findings may implicate that V-DJ or V-VDJ gene rearrangements forming functional IgH genes, induce frequently TCR or TRG gene rearrangements. We propose these dual genotypes are different in origin from those observed in stem cell leukemia.

Cross-lineage gene rearrangements in human leukemic B-precursor cells occur frequently with V-DJ rearrangements of IgH genes

Gene configurations of immunoglobulin (Ig), T-cell antigen receptor (TCR) beta chain, and T-cell rearranging gene gamma (TRG gamma) were studied in human B-precursor lymphoblastic leukemic cells. These cells were phenotypically classified into three developmental stages (stages II through IV) according to Nadler's criteria. All of them showed the Ig heavy chain (IgH) gene rearrangement, and 67% of the cells in stage IV had the rearranged TRG gamma, albeit seldom in other stages. We further analyzed IgH gene rearrangements in detail using upstream to DH (diversity region of IgH) region probe to distinguish DJ from V-DJ recombination. All dual genotyped cells in each stage except one case in stage II showed the V-DJ rearrangements. This suggests the cross- lineage involvement of the putative recombinase, particularly in the process of V-DJ rearrangements. We next examined the transcriptional status of Ig genes as an indirect reflection of the accessibility of these genes to the recombinase. Properly spliced IgH transcripts of normal size were observed in stage IV and surface Ig positive stage, but not in stage II nor III. However, IgH transcripts of aberrant sizes were seen in stage II, III, and also IV. Cross-lineage gene rearrangements were shown to occur frequently when normally spliced IgH gene begins to be transcribed or just before this. These findings may implicate that V-DJ or V-VDJ gene rearrangements forming functional IgH genes, induce frequently TCR or TRG gene rearrangements. We propose these dual genotypes are different in origin from those observed in stem cell leukemia.

Pseudoleukemia in Down’s Syndrome: Analysis of Immunophenotype and Gene Rearrangement

This report demonstrates a case of transient abnormal myelopoiesis (TAM) evolving in a patient with Down's syndrome. A diagnosis was established after the patient's blast cell count decreased considerably three weeks after the initial leukemic phase. The blast population in the authors' case expressed Leu-9 (CD7), 6D1, and TdT+. Cytochemistries showed some of the blast population to be peroxidase positive and Sudan black positive. Platelet peroxidase by electron microscopic examination showed some positive blasts. Therefore, surface markers and cytochemical studies in this case suggested an abnormal proliferation involving a pluripotential stem cell capable of expressing myeloid and lymphoid characteristics. Cytogenetics was performed at birth and showed 47,XY,+21/48,XY,+21,+mar, confirming the diagnosis of Down's syndrome. The origin of the chromosomal fragment was uncertain. It was of interest that during the remission phase of his pseudoleukemia there was a concomitant decrease in the extra chromosomal fragment. Immunoglobulin and T-cell antigen receptor gene rearrangement studies showed only germline patterns, indicating that the lymphoid cells in the blast population were not clonally expanded. Therefore, immunoglobulin and T-cell antigen receptor rearrangement analysis and immunophenotyping are extremely valuable techniques in distinguishing between TAM and acute lymphoblastic leukemia in patients with Down's syndrome.

Phenotype and differentiation stage of scid mouse thymocytes.

Scid mice are severely deficient in T and B cell function whereas other hematopoietic cells develop normally (Bosma et al. 1983; Custer et al. 1985). The effects which the scid mutation manipulates seem to occur after the commitment of lymphoid cells to the T and B cell lineages because early transcription of unrearranged genes for T cell antigen receptor (TCR) and immunoglobulin (Ig) is detected in scid thymus and fetal liver, respectively (Schuler et al. 1988), although these genes are not rearranged in the scid mice (Schuler et al. 1986; Habu et al. 1987a). In addition, experiments involving transfer of bone marrow cells into the scid mice indicate that the thymus and bone marrow microenvironments function normally for T and B cell differentiation (Custer et al. 1985). Thus, identification of the differentiation stage of scid mouse lymphoid cells will provide valuable information for understanding how TCR and Ig gene rearrangements and/or gene products function in early lymphoid differentiation. Here, we will demonstrate the expression of the scid phenotype in thymocytes and discuss the stage in the normal differentiation pathway of T cell lineages at which it occurs.KeywordsScid MouseSevere Combine ImmunodeficiencySingle Positive CellHanging Drop MethodAntigen Receptor GeneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Spontaneous regression of a monoclonal proliferation of large granular lymphocytes associated with reversal of anemia and neutropenia

A 43-year-old male with a phenotypically homogeneous, expanded subset of T cells presented in 1981 with anemia and neutropenia. The surface antigen phenotype of 99% of the peripheral blood lymphocytes was T3+, T8+, T4-, and they were morphologically large granular lymphocytes (LGL). The same cells comprised 37% of the marrow nucleated cells. Eight months after he presented, the peripheral blood T8+, LGL diminished spontaneously, and the anemia and neutropenia completely resolved. The patient remains hematologically normal as of October 1984. To determine if the T8+, LGL represented a clonal expansion, DNA from peripheral blood lymphocytes collected and cryopreserved when the patient was neutropenic and anemic, and when he was hematologically normal, was analyzed for clonal T-cell antigen receptor gene rearrangements. Using Southern blot analysis, a clonal DNA rearrangement was demonstrated, and this clone diminished but was still demonstrable in peripheral blood lymphocytes collected in 1984. The above observations implicate the expanded T8+, LGL in the pathogenesis of the neutropenia and anemia, yet the exact mechanism remains to be elucidated.

Spontaneous Regression of a Monoclonal Proliferation of Large Granular Lymphocytes Associated With Reversal of Anemia and Neutropenia

A 43-year-old male with a phenotypically homogeneous, expanded subset of T cells presented in 1981 with anemia and neutropenia. The surface antigen phenotype of 99% of the peripheral blood lymphocytes was T3+, T8+, T4-, and they were morphologically large granular lymphocytes (LGL). The same cells comprised 37% of the marrow nucleated cells. Eight months after he presented, the peripheral blood T8+, LGL diminished spontaneously, and the anemia and neutropenia completely resolved. The patient remains hematologically normal as of October 1984. To determine if the T8+, LGL represented a clonal expansion, DNA from peripheral blood lymphocytes collected and cryopreserved when the patient was neutropenic and anemic, and when he was hematologically normal, was analyzed for clonal T-cell antigen receptor gene rearrangements. Using Southern blot analysis, a clonal DNA rearrangement was demonstrated, and this clone diminished but was still demonstrable in peripheral blood lymphocytes collected in 1984. The above observations implicate the expanded T8+, LGL in the pathogenesis of the neutropenia and anemia, yet the exact mechanism remains to be elucidated.

Immuno-monitoring in blood dyscrasias

Modern topics on immunophenotypic and immunogenotypic analysis of lymphoproliferative disorders are summarized.Recently developed various monoclonal antibodies against lymphocyte cell surface molecules have made it possible to classify B and T cells into functionally distinct detailed subsets.In these days, in addition to histopathological study, analysis of cell surface markers (immunophenotypic analysis) of lymphocytic leukemias and lymphomas comes to be necessary information to diagnose, detect the prognosis, and select the treatment protocols.Moreover, it has been revealed that many of the surface markers themselves serve as functional molecules to generate the subset specific functions. For example, T3 molecule, pan T cell marker, is a T cell antigen receptor (TCR)-related structure, and considered to be closely associated to T cell recognition and activation. Precise phenotypic analysis revealed that both T3 and interleukin 2 receptor (IL2R) are abnormally expressed on adult T cell leukemia (ATL) cells. ATL cells might be a useful tool to investigate the role of T3 molecule in T cell activation. Phenotypic analysis may not only classify the diseases, but also offer reseach materials of the special conditions of lymphocytes.On the otherhands, it is now available to follow the process of gene rearrangements of immunoglobulin (Ig) and TCR in lymphoid cells, using appropriate probes of each gene segments and Southern transfer technique. Such DNA analysis (immunogenotypic analysis) is now extensively carried out in many institutions. By these means, it comes to be possible to determine clonality and cell lineage of the lymphocyte population.Because the first step of Ig and TCR gene rearrangement occurs before lineage specific surface molecules appear, it is possible to determine the cell lineage of phenotypically nonT nonB lymphoid tumors. Not a small population of nonT nonB type were found to have Ig and TCR genes both in rearranged states.Here, two important knowledges brought from the clinical studies are introduced.One is that the study of each chain of Ig gene rearrangement in lymphoid tumors has determined the hierarchy of each chain rearrangement within a cell. Rearrangement occurs in the order of Heavy, s and finally λ chain.Another is to bring to light the relation of chromosomal abnormalities frequently seen in lymphoid neoplasmas and the locus of Ig, TCR gene and oncogenes. In many cases, at chromosomal break point, Ig or TCR gene and an oncogene, such as c-myc, sit side by side, and the expression of the oncogene is increased.Finally, one example of phenotypic and genotypic analysis of T cell lymphocytosis is indicated.

Expression of genes of the T-cell antigen receptor complex in precursor thymocytes.

The antigen receptor on T lymphocytes has recently been characterized as a heterodimeric, transmembrane glycoprotein consisting of disulphide-linked alpha (acidic) and beta (basic) subunits of relative molecular mass (Mr) 40,000-45,000 each. The genes encoding these proteins have been cloned and shown to resemble immunoglobulin genes in both overall structure and the requirement for DNA rearrangement before expression. In humans, three additional proteins, termed the T3 complex, are found associated with the clonotypic receptor, and a role for T3 in receptor expression has been proposed. Despite these recent advances in characterizing the antigen receptor complex, there is as yet little understanding of T-cell maturation, particularly the stage of T-cell ontogeny at which the genes encoding the antigen receptor and its associated structures are expressed and assembled. In the adult, stem cells destined to differentiate into T cells arise in the bone marrow and migrate to the thymus, where T-cell precursors proliferate, develop a preference for recognizing antigens in the context of self MHC molecules and are released to the periphery. Recently, cells that have the properties of immature murine thymocytes have been isolated and described. We have now analysed these cells with a series of molecular probes and we describe three distinct patterns of T-cell antigen receptor gene rearrangements in developing thymocytes.