Chromatin conformation governs T-cell receptor Jß gene segment usage.

T cells play fundamental roles in adaptive immunity, relying on a diverse repertoire of T-cell receptor (TCR) α and ß chains. Diversity of the TCR ß chain is generated in part by a random yet intrinsically biased combinatorial rearrangement of variable (Vß), diversity (Dß), and joining (Jß) gene segments. The mechanisms that determine biases in gene segment use remain unclear. Here we show, using a high-throughput TCR sequencing approach, that a physical model of chromatin conformation at the DJß genomic locus explains more than 80% of the biases in Jß use that we measured in murine T cells. This model also predicts correctly how differences in intersegment genomic distances between humans and mice translate into differences in Jß bias between TCR repertoires of these two species. As a consequence of these structural and other biases, TCR sequences are produced with different a priori frequencies, thus affecting their probability of becoming public TCRs that are shared among individuals. Surprisingly, we find that many more TCR sequences are shared among all five mice we studied than among only subgroups of three or four mice. We derive a necessary mathematical condition explaining this finding, which indicates that the TCR repertoire contains a core set of receptor sequences that are highly abundant among individuals, if their a priori probability of being produced by the recombination process is higher than a defined threshold. Our results provide evidence for an expanded role of chromatin conformation in VDJ rearrangement, from control of gene accessibility to precise determination of gene segment use.

Notch signaling is required for proliferation but not for differentiation at a well-defined beta-selection checkpoint during human T-cell development.

Notch signaling is absolutely required for beta-selection during mouse T-cell development, both for differentiation and proliferation. In this report, we investigated whether Notch has an equally important role during human T-cell development. We show that human CD34(+) thymocytes can differentiate into CD4(+)CD8beta(+) double positive (DP) thymocytes in the absence of Notch signaling. While these DP cells phenotypically resemble human beta-selected cells, they lack a T-cell receptor (TCR)-beta chain. Therefore, we characterized the beta-selection checkpoint in human T-cell development, using CD28 as a differential marker at the immature single positive CD4(+)CD3(-)CD8alpha(-) stage. Through intracellular TCR-beta staining and gene expression analysis, we show that CD4(+)CD3(-)CD8alpha(-)CD28(+) thymocytes have passed the beta-selection checkpoint, in contrast to CD4(+)CD3(-)CD8alpha(-)CD28(-) cells. These CD4(+)CD3(-)CD8alpha(-)CD28(+) thymocytes can efficiently differentiate into CD3(+)TCRalphabeta(+) human T cells in the absence of Notch signaling. Importantly, preselection CD4(+)CD3(-)CD8alpha(-)CD28(-) thymocytes can also differentiate into CD3(+)TCRalphabeta(+) human T cells without Notch activation when provided with a rearranged TCR-beta chain. Proliferation of human thymocytes, however, is clearly Notch-dependent. Thus, we have characterized the beta-selection checkpoint during human T-cell development and show that human thymocytes require Notch signaling for proliferation but not for differentiation at this stage of development.

Nonsense codons trigger an RNA partitioning shift.

T-cell receptor-beta (TCRbeta) genes naturally acquire premature termination codons (PTCs) as a result of programmed gene rearrangements. PTC-bearing TCRbeta transcripts are dramatically down-regulated to protect T-cells from the deleterious effects of the truncated proteins that would otherwise be produced. Here we provide evidence that two responses collaborate to elicit this dramatic down-regulation. One is rapid mRNA decay triggered by the nonsense-mediated decay (NMD) RNA surveillance pathway. We demonstrate that this occurs in highly purified nuclei lacking detectable levels of three different cytoplasmic markers, but containing an outer nuclear membrane marker, suggesting that decay occurs either in the nucleoplasm or at the outer nuclear membrane. The second response is a dramatic partitioning shift in the nuclear fraction-to-cytoplasmic fraction mRNA ratio that results in few TCRbeta transcripts escaping to the cytoplasmic fraction of cells. Analysis of TCRbeta mRNA kinetics after either transcriptional repression or induction suggested that this nonsense codon-induced partitioning shift (NIPS) response is not the result of cytoplasmic NMD but instead reflects retention of PTC(+) TCRbeta mRNA in the nuclear fraction of cells. We identified TCRbeta sequences crucial for NIPS but found that NIPS is not exclusively a property of TCRbeta transcripts, and we identified non-TCRbeta sequences that elicit NIPS. RNA interference experiments indicated that NIPS depends on the NMD factors UPF1 and eIF4AIII but not the NMD factor UPF3B. We propose that NIPS collaborates with NMD to retain and degrade a subset of PTC(+) transcripts at the outer nuclear membrane and/or within the nucleoplasm.

Essential role of Rap signal in pre-TCR-mediated beta-selection checkpoint in alphabeta T-cell development.

We demonstrate that lck promoter-driven conditional expression of transgenic SPA-1, a Rap GTPase-activation protein, causes a profound defect of alphabeta T-cell development at the CD4/CD8 double-negative (DN) stage due to enhanced cell death without affecting gammadelta T-cell development. The effect was specific to the DN stage, because CD4 promoter-driven SPA-1 expression hardly affected T-cell development. Rap1A17, a dominant-negative Rap mutant, interfered with the generation of double-positive (DP) cells from Rag2(-/-) fetal thymocytes in vitro in the presence of anti-CD3epsilon antibody and Notch ligand. Rap GTPases were activated in a DN cell line by the expression of self-oligomerizing CD3 (CD8:CD3epsilon chimera), which substituted autonomous pre-T-cell receptor (TCR) signal, inducing CD69 expression and CD25 down-regulation. Reciprocally, expression of C3G, a Rap guanine nucleotide exchange factor, in both normal and Rag2(-/-) DN cells markedly enhanced Notch-dependent generation and expansion of DP cells without additional anti-CD3epsilon antibody, thus bypassing pre-TCR. Defective alphabeta T-cell development in the conditional SPA-1-transgenic mice was restored completely by introducing a p53(-/-) mutation. These results suggest that endogenous Rap GTPases downstream of pre-TCR play an essential role in rescuing pre-T cells from the p53-mediated checkpoint response, thus allowing Notch-mediated expansion and differentiation.

Rearrangement of T-cell receptor beta and gamma genes in thymoma.

To investigate the differentiation stage of tumor-infiltrating lymphocytes in thymoma tissue, we performed Southern blot analysis of T-cell receptor beta and gamma genes in thymomas resected from 19 patients. At the same time, we conducted flow cytometric analysis of T-cell surface markers and examined the clinicopathological features of the thymomas. We found that the incidence of T-cell receptor gamma gene rearrangement was significantly higher in Masaoka stage I thymomas (11 of 12 cases) than in stage II or III invasive thymomas (3 of 7 cases). Moreover, gamma gene rearrangement was observed in all 10 type AB and B1 thymoma specimens and in 4 of 6 type B2 thymoma specimens. The 2 specimens of type B3 thymomas, which were classified as stage III, showed neither gamma nor beta gene arrangement and were single-positive for CD4 or CD8. Six thymoma specimens that showed beta gene rearrangement expressed both CD4 and CD8. In conclusion, thymomas have the capability of T-lineage cell differentiation, except for a subset of invasive thymomas with malignant characteristics.

Regulation of immunoglobulin heavy-chain gene rearrangements.

Regulated assembly of antigen receptor gene segments to produce functional genes is a hallmark of B- and T-lymphocyte development. The immunoglobulin heavy-chain (IgH) and T-cell receptor beta-chain genes rearrange first in B and T lineages, respectively. Both loci require two recombination events to assemble functional genes; D-to-J recombination occurs first followed by V-to-DJ recombination. Despite similarities in overall rearrangement patterns, each locus has unique regulatory features. Here, we review the characteristics of IgH gene rearrangements such as developmental timing, deletion versus inversion, DH gene segment utilization, ordered recombination of VH gene segments, and feedback inhibition of rearrangement in pre-B cells. We summarize chromatin structural features of the locus before and during recombination and, wherever possible, incorporate these into working hypotheses for understanding regulation of IgH gene recombination. The picture emerges that the IgH locus is activated in discrete, independently regulated domains. A domain encompassing DH and JH gene segments is activated first, within which recombination is initiated. VH genes are activated subsequently and, in part, by interleukin-7. These observations lead to a model for feedback inhibition of IgH rearrangements.

Prevalent role of TCR alpha-chain in the selection of the preimmune repertoire specific for a human tumor-associated self-antigen.

The specificity of recognition of pMHC complexes by T lymphocytes is determined by the V regions of the TCR alpha- and beta-chains. Recent experimental evidence has suggested that Ag-specific TCR repertoires may exhibit a more V alpha- than V beta-restricted usage. Whether V alpha usage is narrowed during immune responses to Ag or if, on the contrary, restricted V alpha usage is already defined at the early stages of TCR repertoire selection, however, has remained unexplored. Here, we analyzed V and CDR3 TCR regions of single circulating naive T cells specifically detected ex vivo and isolated with HLA-A2/melan-A peptide multimers. Similarly to what was previously observed for melan-A-specific Ag-experienced T cells, we found a relatively wide V beta usage, but a preferential V alpha 2.1 usage. Restricted V alpha 2.1 usage was also found among single CD8(+) A2/melan-A multimer(+) thymocytes, indicating that V alpha-restricted selection takes place in the thymus. V alpha 2.1 usage, however, was independent from functional avidity of Ag recognition. Thus, interaction of the pMHC complex with selected V alpha-chains contributes to set the broad Ag specificity, as underlined by preferential binding of A2/melan-A multimers to V alpha 2.1-bearing TCRs, whereas functional outcomes result from the sum of these with other interactions between pMHC complex and TCR.

Inactivation of Notch1 impairs VDJbeta rearrangement and allows pre-TCR-independent survival of early alpha beta Lineage Thymocytes.

Notch proteins influence cell fate decisions in many developmental systems. During lymphoid development, Notch1 signaling is essential to direct a bipotent T/B precursor toward the T cell fate, but the role of Notch1 at later stages of T cell development remains controversial. We have recently reported that tissue-specific inactivation of Notch1 in immature (CD44(-) CD25(+)) thymocytes does not affect subsequent T cell development. Here, we demonstrate that loss of Notch1 signaling at an earlier (CD44(+)CD25(+)) developmental stage results in severe perturbation of alpha beta but not gamma delta lineage development. Immature Notch1(-/-) thymocytes show impaired VDJ beta rearrangement and aberrant pre-TCR-independent survival. Collectively, our data demonstrate that Notch1 controls several nonredundant functions necessary for alpha beta lineage development.

Failure of rearranged TCR transgenes to prevent age-associated thymic involution.

After puberty, the thymus undergoes a dramatic loss in volume, in weight and in the number of thymocytes, a phenomenon termed age-associated thymic involution. Recently, it was reported that age-associated thymic involution did not occur in mice expressing a rearranged transgenic (Tg) TCRalphabeta receptor. This finding implied that an age-associated defect in TCR rearrangement was the major, if not the only, cause for thymic involution. Here, we examined thymic involution in three other widely used MHC class I-restricted TCRalphabeta Tg mouse strains and compared it with that in non-Tg mice. In all three TCRalphabeta Tg strains, as in control mice, thymocyte numbers were reduced by approximately 90% between 2 and 24 mo of age. The presence or absence of the selecting MHC molecules did not alter this age-associated cell loss. Our results indicate that the expression of a rearranged TCR alone cannot, by itself, prevent thymic involution. Consequently, other presently unknown factors must also contribute to this phenomenon.

Analysis of antigen receptor genes in Hodgkin's disease.

AIM: To analyse the configuration of the antigen receptor genes in Hodgkin's disease. METHODS: DNA extracted from 45 samples of Hodgkin's disease was analysed using Southern blotting and DNA hybridisation, using probes to the joining region of the immunoglobulin heavy chain gene, the constant region of kappa immunoglobulin light chain gene, and the constant region of the beta chain of the T cell receptor gene. RESULTS: A single case of nodular sclerosing disease showed clonal rearrangement of the immunoglobulin heavy and light chain genes, all other samples having germline immunoglobulin genes. The nature of the clonal population in the diseased tissue is uncertain, because the intensity of the rearranged bands did not correlate with the percentage of Reed-Sternberg cells present. The T cell receptor genes were in germline configuration in all the samples. CONCLUSIONS: Antigen receptor gene rearrangement is a rare finding in unselected cases of Hodgkin's disease.

Peripheral T-cell lymphoma involving the placenta.

BACKGROUND: Placental involvement by maternal malignant lymphoma is a rare complication of pregnancy. METHODS: The case of a 29-year-old woman found to have placental involvement by peripheral T-cell lymphoma (PTCL) diagnosed by morphologic study, immunoperoxidase stains, and molecular genetic studies is reported. RESULTS: The lymphoma was pathologic Stage IVB and although there were no adverse consequences for the child, but the neoplasm progressed rapidly during the postpartum period. CONCLUSIONS: The clinical course suggested that the immunologic changes of the pregnancy exerted a lymphoma-suppressive effect on the lymphoma. The authors know of no other report of a patient with placental involvement by PTCL.

CD3- T cells with cis- or trans-acting mutations affecting expression of T cell receptor beta-chain mRNA.

Mutants of an untransformed T cell clone that no longer respond to TCR/CD3 stimulation have been derived using a selection procedure based on the loss of functional response to Ag. This functional selection gives rise to clones of several different phenotypes. We have previously described mutants with a TCR/CD3+ cell surface phenotype whose TCR are uncoupled from cellular responses. We describe six additional mutants that do not express TCR/CD3 at the cell surface. One of the CD3- clones contains a deletion in the successfully rearranged TCR-alpha gene, whereas another carries a deletion in the successfully rearranged TCR-beta gene. TCR/CD3 expression in these deletion mutants can be restored by transfection of TCR-alpha or TCR-beta DNA. Four other clones do not express TCR-beta mRNA, yet contain no obvious deletions or rearrangements in the TCR-beta genes. One of these clones does not transcribe TCR-beta chain mRNA. The mutation in this clone does not reside in the TCR-beta gene itself, but may instead reside in a trans-acting regulatory element affecting TCR-beta gene expression, because the TCR-beta mRNA-phenotype is complemented by fusion with a TCR-alpha-beta- cell line. TCR-beta chain regulatory mutants will be valuable in contributing to our understanding of how TCR expression is regulated.

Mutations in T-cell antigen receptor genes alpha and beta block thymocyte development at different stages.

Analysis of mice carrying mutant T-cell antigen receptor (TCR) genes indicates that TCR-beta gene rearrangement or expression is critical for the differentiation of CD4-CD8- thymocytes to CD4+CD8+ thymocytes, as well as for the expansion of the pool of CD4+CD8+ cells. TCR-alpha is irrelevant in these developmental processes. The development of gamma delta T cells does not depend on either TCR-alpha or TCR-beta.

Unique genotypic features of infant acute lymphoblastic leukaemia at presentation and at relapse.

Acute lymphoblastic leukaemia (ALL) of infants aged less than 1 year represents a group of patients with peculiar biological features, poor response to therapy and unfavourable prognosis. In order better to characterize this type of leukaemia, we have investigated the immunoglobulin (Ig) and T-cell receptor (TCR) genes configuration of 21 infants with ALL, and compared the genotypic features with the phenotypic and karyotypic data, as well as with the clinical outcome. All cases had a pre-B phenotype; 12 (57%) of them were pre-pre-B ALL (CD10-, CD19+). Six of the 16 cases evaluated (38%) displayed chromosomal abnormalities; five had the typical translocation t(4;11)(q21;23). Eleven cases presented with a white blood cell count greater than 100 x 10(9)/l. The clinical course was unfavourable in 14 patients. The genotype of this group of ALL revealed several peculiarities. (1) Of the 21 cases, six (29%) displayed a multiple rearrangement pattern at the IgH locus. (2) In three cases (15%), the light chain genes were rearranged. (3) The TCR beta and gamma genes were rearranged in only one case (one case at the TCR beta and one at the TCR gamma locus). (4) The TCR delta chain was rearranged in eight cases (40%) and rarely deleted; the rearrangements observed were those most frequently observed in B cell-precursor ALL. Two cases were evaluated both at presentation and at relapse. While the immunophenotype had remained unmodified, comparison of Ig heavy chain gene rearrangements revealed clonal variations in both cases. Taken together, these findings further underline the biological peculiarities of infant ALL compared to ALL which occurs in older children and in adults, and stress the need of differentiated and aggressive therapeutic approach for these patients.

A common V delta 2-D delta 2-D delta 3 T cell receptor gene rearrangement in precursor B acute lymphoblastic leukaemia.

Despite their apparent commitment to the B lymphocytic lineage, human precursor B cell acute lymphoblastic leukaemias (ALL) frequently rearrange their T cell antigen receptor (TCR) alpha, beta and gamma chain genes. Since these three genes are active sites of rearrangement in precursor B cell neoplasms, it seemed that the recently discovered fourth TCR gene, delta, might be similarly rearranged. To investigate this possibility, a series of precursor B cell leukaemias was analysed for rearrangements at the delta chain gene locus, using probes of the variable, joining, and constant regions of the delta chain gene. The majority of precursor B cell ALLs in this series (25/32, 78%) showed rearrangement or deletion of one or more TCR delta genes. This contrasts sharply with a series of 16 mature B cell neoplasms (chronic lymphocytic leukaemia) in which no TCR delta gene rearrangements were detected. An unusual TCR delta rearrangement, rarely observed in normal or neoplastic T cells, was seen in the majority (14/18) of precursor B cell ALLs with TCR delta rearrangements. In contrast to the utilization ov V delta 1 in T cell ALL, detailed restriction mapping of precursor B ALL revealed an incomplete rearrangement without involvement of J delta segments. Direct genomic sequencing was performed on one example and demonstrated a nonproductive V delta 2-D delta 2-D delta 3 recombination in this precursor B ALL. We conclude that the TCR delta chain gene is an active locus in precursor B cell neoplasia, involves an unusual type of rearrangement and provides a clonal tumour marker for diagnosis of precursor B ALL.

Lymphomatoid papulosis followed by large-cell lymphoma: immunophenotypical and genotypical analysis.

The immunophenotype and genotype of atypical cells in skin and lymph node infiltrates were investigated in a patient with lymphomatoid papulosis (LyP) complicated by anaplastic large-cell lymphoma of the lymph nodes. The large atypical cells in both skin and lymph nodes displayed an almost identical immunophenotype, i.e. CD30+ and CD25+. Southern blot analysis for T-cell receptor beta-chain gene rearrangement revealed an identical gene configuration in DNA extracted from skin and lymph node. Our results strongly support the hypothesis that clonal populations of T cells arising in cutaneous LyP lesions may undergo malignant transformation, spread into regional lymph nodes, and give rise to secondary malignant lymphomas, such as anaplastic large-cell lymphoma.

In vitro and in vivo antitumor properties of a T-cell clone generated from murine tumor-infiltrating lymphocytes.

We have shown that a T-cell clone derived from murine tumor-infiltrating lymphocytes (TILs) can be established that mediates in vitro and in vivo antitumor effects. Utilizing this clone as a model, we examined the effect of cytokines on T-cell antitumor effector mechanisms in vitro and in vivo. This clone, termed BF-1, was generated by limiting dilution culture of a freshly excised MC-38 tumor, growing it in low levels of interleukin-2 (IL-2), and has been maintained for over 600 days. This clone became specifically cytotoxic for the MC-38 tumor during its first 100 days of culture. Pretreatment of the parental MC-38 tumor cell line with tumor necrosis factor (TNF) and interferon-gamma (IFN-gamma) increased its susceptibility to lysis by the BF-1 TIL line, but not to lysis by lymphokine-activated killer cells, in in vitro cytotoxicity assays. This increased susceptibility of the cytokine-pretreated targets was restricted to the parental tumor (MC-38), since similar pretreatment of MCA-102, MCA-105, or MCA-106 tumors did not render them susceptible to lysis by BF-1 TILs. This increased sensitivity to lysis in vitro was not the result of a change in the expression of major histocompatibility complex class I molecules. In experiments testing the ability of TILs to treat established lung metastases, the combination of TNF, IFN-gamma, IL-2, and TILs was shown to increase significantly the antitumor properties of this therapy when compared to TILs and IL-2. This result demonstrates that combinations of lymphokines, which when administered alone do not affect micrometastatic tumor burdens (TNF, IFN-gamma), can synergize with cellular immunotherapy in the treatment of established tumor burdens and may have applicabilities to the treatment of cancer in humans.