Their T Cell Receptor Research Articles

Increased interleukin 4 and immunoglobulin E production in transgenic mice overexpressing NK1 T cells.

Natural Killer (NK)1.1+ (NK1) T cells are a specialized subset of alpha/beta T cells that coexpress surface receptors that are normally associated with the NK cell lineage of the innate immune system. On recognition of the conserved, major histocompatibility complex class I-like CD1 molecule, these cells are able to release explosive bursts of interleukin 4 (IL-4), a cytokine that promotes the T helper type 2 (Th2) effector class of an immune response. A unique feature of their T cell receptor (TCR) repertoire is the expression of an invariant TCR alpha chain, V alpha 14-J alpha 281, and of a restricted but polyclonal set of V beta gene families, V beta 8, V beta 7, and V beta 2. Here, we show that transgenic expression of this TCR alpha chain during thymic development is sufficient information to bias the differentiation of mainstream thymocytes towards the NK1 developmental pathway. It markedly increases the frequency of cells with the NK1 pattern of T cell differentiation and also has drastic consequences for the selection of the V beta repertoire. Transgenic CD4 cells exhibited a 10-100-fold increase in IL-4 production on mitogen stimulation in vitro and in vivo, and baseline levels of the Th2-controlled serum immunoglobulin isotypes, IgE and IgG1, were also selectively elevated in vivo.

Effects of Vaccination against Different T Cell Receptors on Maintenance of Immune Function during Murine Retrovirus Infection

Murine retrovirus infection causes an aberrant stimulation of several subsets of T helper 2 cells identified by their T cell receptors (TCR). C57BL/6 mice were treated with synthetic peptides based upon different human TCR Vβ CDR1 sequences following experimental infection with the murine retrovirus. Previous studies established that retrovirally infected mice produced autoantibodies to certain of these peptides, and their administration after infection diminished many of the cytokine abnormalities induced by the virus. This study determined whether the complete 16-mer synthetic peptides modeling the Vβ CDR1/FR3 were required, and whether admixture of autoantigenic peptides synergized immune preservation. Treatment with complete TCR pep β3 and pep Vβ5.2 peptide alone and combined largely prevented the retrovirus-induced reduction in B and T cell proliferation and Th1 cytokine secretion while suppressing excessive production of Th2 cytokines, which are stimulated by retrovirus infection. Treatment with overlapping short peptides corresponding to the N-terminal 11-mer and C-terminal 12-mer did not significantly prevent the immune dysfunction in retrovirus-infected mice. These data suggest that immune dysfunction and abnormal cytokine production, induced by murine retrovirus infection, were largely prevented by TCR Vβ CDR1 peptides, and the complete CDR1 in association with the five residues from FR2 was required.

Altered T cell development in mice with a targeted mutation of the CD3-epsilon gene.

To determine which CD3 components are required for early T cell development, we generated mice with a targeted mutation of the CD3-epsilon gene and characterized their T cell populations relative to those found in CD3-zeta/eta-and recombinase activating gene (RAG)-deficient mice. In the absence of intact CD3-epsilon subunit, thymocytes do not progress beyond the CD44-/lowCD25+ triple-negative stage and appear to be arrested at the very same developmental control point as RAG-deficient thymocytes. In contrast, the disruption of the CD3-epsilon/eta gene does not totally abrogate the progression through this control point. CD3-epsilon-deficient thymocytes do rearrange their T cell receptor (TCR) beta gene segments and produce low levels of full-length TCR beta transcripts. Taken together, these results establish an essential role for the CD3-epsilon gene products during T cell development and further suggest that the CD3-epsilon polypeptides start to exert their function as part of a pre-TCR through which CD44-/lowCD25+ triple-negative cells monitor the occurrence of productive TCR beta gene rearrangements. Finally, the absence of intact CD3-epsilon polypeptides had no discernible effect on the completion of TCR gamma and TCR delta gene rearrangements, emphasizing that they are probably not subjected to the same epigenetic controls as those operating on the expression of TCR alpha and beta genes.

T‐Cell Receptor Gene Structures of HLA‐A26‐restricted Cytotoxic T Lymphocyte Lines against Human Autologous Pancreatic Adenocarcinoma

We isolated two cytotoxic T lymphocyte (CTL) lines, which were independently obtained by mixed lymphocyte‐tumor cell culture from tumor‐infiltrating lymphocytes of a patient with pancreatic adenocarcinoma. Both lines behaved identically in all the functional aspects tested and appeared to be HLA‐A26‐restricted. We analyzed their T cell receptor (TCR) gene structures, including V‐(D)‐J junctional sequences, which are unique to each T‐cell clonotype and contribute to TCR diversity. Each line consisted of a clonal T‐cell expressing Vα18 and Vβ7. The α chain gene was composed of Vα18/ JαF/Cα and the, β‐chain gene, of Vβ7.1/Dβ/Jβ1.4/Cβ2. The sequences were all in‐frame and therefore should yield functional transcripts. The junctional sequences were identical between the two lines. These data suggested that the two CTL clones having the same CDR3 had descended from a common precursor lymphocyte. The clonal expansion of CTL lines with the identical CDR3 implies that they are directed against the same tumor antigen, which seemed to be immunologically dominant in the specific interaction between the CTL and the autologous pancreatic adenocarcinoma.

Superantigen-staphylococcal-enterotoxin-A-dependent and antibody-targeted lysis of GD2-positive neuroblastoma cells.

Superantigens such as the staphylococcal enterotoxin A (SEA) are among the most potent T cell activators known. They bind to major histocompatibility complex (MHC) class II molecules and interact with T cells depending on their T cell receptor (TCR) V beta expression. Superantigens also induce a variety of cytokines and trigger a direct cytotoxic effect against MHC-class-II-positive target cells. In order to extend superantigen-dependent cell-mediated cytotoxicity (SDCC) to MHC-class-II-negative neuroblastoma cells, SEA was linked to the anti-ganglioside GD2 human/mouse chimeric monoclonal antibody (mAb) ch14.18. Ganglioside GD2 is expressed on most tumours of neuroectodermal origin but is expressed to a lesser extent on normal tissues. The linkage of ch14.18 to SEA was achieved either with a protein-A-SEA fusion protein or by chemical coupling. Both constructs induced T-cell-mediated cytotoxicity towards GD2-positive neuroblastoma cells in an effector-to-target(E:T)-ratio- and dose-dependent manner in vitro. To reduce the MHC class II affinity of SEA, a point mutation was introduced in the SEA gene (SEAm9) that resulted in 1000-fold less T cell killing of MHC-class-II-expressing cells as compared to native SEA. However, a protein-A-SEAm9 fusion protein mediated cytotoxicity similar to that of protein-A-SEA on ch14.18-coated, MHC-class-II-negative neuroblastoma cells. Taken together, these findings suggest that superantigen-dependent and monoclonal-antibody-targeted lysis may be a potent novel approach for neuroblastoma therapy.

Control of memory CD4 T cell activation: MHC class II molecules on APCs and CD4 ligation inhibit memory but not naive CD4 T cells

Memory or antigen-experienced CD4 T cells differ from naive CD4 T cells both phenotypically by cell surface marker expression, and functionally by their dissimilar pattern of cytokine secretion and activation requirements through their T cell receptor (TCR). We show here that activation of memory CD4 T cells (CD45RB lo subset), but not naive CD4 T cells (CD45RB hi subset), is inhibited by MHC class II molecules on antigen-presenting cells and by CD4 ligation. We propose that the selective negative signal in memory cells is a direct result of the differences in signaling via CD4 and CD3, exemplified in the disparate pattern of tyrosine-phosphorylated proteins visible after activation of the two subsets. In vivo, this inhibitory signal may serve to prevent irrelevant interactions between memory CD4 T cells and bystander MHC class II + cells, and may also be responsible for the defective functioning of memory CD4 T cells in AIDS.

Long-Term Culture and T Cell Receptor Analysis of T Cell Clones Isolated from a Patient with Adenosine Deaminase Deficiency and Type I Diabetes

We performed limiting dilution culture of T cells from a patient affected by primary immunodeficiency as a result of complete lack of adenosine deaminase (ADA) activity and also affected by insulin-dependent diabetes mellitus (type I diabetes). Despite the occurrence of immunodeficiency, we were able to raise and grow T cell clones derived from this patient in long-term culture. These T cells displayed ADA enzymatic activity and produced interleukin-2 after engagement of their T cell receptor (TCR)/CD3 complex. We analyzed the TCR repertoire of such clones by nucleotide sequencing of TCR β chains. The results show that the T cell clones express different Vβ but similar J regions. However, the CDR3 regions which are implicated in antigen recognition were found to be heterogeneous.

Anti-SCID mouse reactivity shapes the human CD4+ T cell repertoire in hu-PBL-SCID chimeras.

Injecting human peripheral blood mononuclear cells into severe combined immunodeficient (SCID) mice results in long-term engraftment of human lymphocytes, of which > 98% are phenotypically mature, activated T cells. Here we have characterized the human T cells that populate such hu-PBL-SCID chimeras. We report that these human T cells do not mobilize Ca2+ after CD3 stimulation, i.e., their T cell receptor (TCR)-mediated signal transduction is deficient. Chimera-derived human T cells do not secrete lymphokines or undergo blastogenesis after CD3 stimulation, but proliferate in response to interleukin 2 (IL-2), defining the chimera derived human T cells as anergic. Anergy was seen in both the CD4+ and the CD8+ subpopulations. We established human T cell lines from chimeras. These T cells retained their anergic state for 1-2 mo in culture, after which they simultaneously regained the ability to mobilize Ca2+, secrete lymphokines, and to undergo blastogenesis following stimulation via the TCR. Once regaining proliferative responsiveness to CD3 stimulation, these CD4+ T cell lines displayed anti-SCID mouse reactivity and showed no specificity for recall antigens. All CD3-responsive CD4+ T cell clones obtained from such lines were SCID mouse specific, recognizing native major histocompatibility complex class II products on the murine cells. In contrast, chimera-derived human CD8+ cell lines and clones did not display detectable anti-mouse reactivity. The data show that the human T cell system in long term hu-PBL-SCID chimeras is nonfunctional due to both anergy and the limitation of the CD4+ repertoire to xenoreactive clones. The data suggest that long-term hu-PBL-SCID chimerism represents an atypical graft-versus-host reaction in which the human effector T cells become anergic in the murine environment.

A quantitative analysis of antigen-presenting cell function: activated B cells stimulate naive CD4 T cells but are inferior to dendritic cells in providing costimulation.

Ligation of CD28 on CD4 Th1 clones and freshly isolated mixtures of naive and memory CD4 T cells triggered their T cell receptors (TCR) is sufficient to induce the costimulatory signals necessary for interleukin 2 (IL-2) production by these cells. CTLA-4-reactive ligands expressed on antigen-presenting cells (APC) are critical in providing costimulatory signals to these T cell populations. We demonstrate that these activation characteristics apply equally to purified naive CD4 T cells. Because B cell blasts express CTLA-4-reactive ligands and high levels of adhesion and major histocompatibility complex class II molecules, they would be expected to engage both the TCR and CD28 and consequently stimulate IL-2 production by naive CD4 T cells. Using purified populations of cells in limiting dilution cultures, we have carried out a quantitative analysis of the interaction between naive CD4 T cells and either activated B or dendritic cells. We demonstrate that B cell blasts stimulate a high frequency of naive CD4 T cells. Slight differences in TCR signaling efficiency between the two APC types were observed. Even at optimal peptide concentrations, however, the amount of IL-2 made by individual T cells was fourfold lower in response to B cell blasts than to dendritic cells. This relative deficiency of activated B cells was due to their inability to optimally costimulate naive CD4 T cells.

Characteristics of CD4+ T Cells Which Transfer Murine AIDS (MAIDS)

The murine acquired immunodeficiency syndrome (MAIDS) is caused in susceptible C57BL/6 (B6) mice by a defective murine leukemia virus (MuLV) and resembles human AIDS in several respects. The disease is characterized by hypergammaglobulinemia, polyclonal B cell activation, lymphadenopathy, and generalized immunosuppression within 5-8 weeks postinfection. The virus has been shown to infect B cells and macrophages and both T and B cells are required for MAIDS development. The manner in which T cells contribute to the disease process is got known. We report here that this retroviral infection leads to induction of a Thy-CD4+ T cell subpopulation capable of transferring all the symptoms of MAIDS disease to normal B6 and B6 nu/nu. Essentially 100% or T cells recovered from B6 nu/nu mice, injected with CD4+ T cells from B6 MAIDS animal, is of the Thy CD4+ phenotype. The proliferation of these T cells in culture and their ability to cause MAIDS in SCID mice is totally dependent on the presence of B cells. These T cells do not exhibit significant Vβ restriction of their T cell receptors (TCR) and, by PCR analysis, have defective virus-specific sequences in the cellular genome. By several criteria, however, these cells do not produce the infectious virus. These results suggest that a B-cell-dependent population of CD4+ T cells from MAIDS animals, in the absence of detectable infectious virus production, has the ability to transfer MAIDS-like disease.

T-Cell Receptor Diversity in Dendritic Epidermal T Cells in the Rat

The rat epidermis contains a population of dendritic CD3+ cells. For a better characterization of these cells and to investigate their relationship to epidermal lymphocytes of other species, we stained rat epidermal sheets using a variety of monoclonal antibodies against rat leukocyte differentiation antigens in an indirect immunofluorescence procedure. Additionally, we attempted to define their T-cell receptor (TCR) isotype at both the nucleic acid and protein level. Results obtained showed that the majority of the CD3+ dendritic epidermal cells are CD45+, CD2+, TCR alpha beta-, major histocompatibility complex class II-, Thy-1-, asialo GM1-, CD4-, CD5-, and CD8- lymphocytes. We further observed that, in contrast to the mouse system, the rat epidermis additionally harbors a small but distinctive portion of dendritic CD3+ cells that exhibit reactivity with an anti-pan TCR alpha beta monoclonal antibody. Our further finding that rat epidermal cells enriched for CD3+ lymphocytes express full-length C delta mRNA suggests that the vast majority of rat epidermal T cells carry surface-bound TCR gamma delta moieties. On the basis of these findings, one may speculate that the indigenous T-cell population of the epidermis is not necessarily programmed to uniformly express monomorphic TCR gamma delta molecules but, to effectively fulfill its role in host defense, is capable of adaptation to the specific challenges encountered by a given species.

Human T-cell responses to Mycoplasma arthritidis-derived superantigen.

When injected into mice, Mycoplasma arthritidis causes a chronic arthritis that resembles rheumatoid arthritis, histologically. The organism produces a superantigen termed Mycoplasma arthritidis mitogen or MAM, that in humans preferentially expands T cells whose antigen receptors express V beta 17. T cells with this phenotype appear to be increased in rheumatoid synovial effusions. We describe a novel approach to isolating and characterizing human MAM-reactive T-cell lines and determining their T-cell receptor (TCR) V beta usage. Lines were prepared from T cells that clustered with dendritic cells during a 2-day exposure to MAM. Cluster and noncluster fractions of T cells were then expanded by using feeder cells and a polyclonal mitogen. Most of the MAM reactivity was found in dendritic T-cell clusters, as were most of the T cells expressing TCR V beta 17. After expansion, 76% of the cluster-derived T-cell lines were MAM reactive, while no reactivity was seen in cell lines derived from the noncluster fraction. Of the MAM-reactive lines, 49% expressed V beta 17 on some or all of the cells. Cell lines from both cluster and noncluster fractions were analyzed for TCR V beta mRNA expression by PCR amplification. Other V beta genes (5.1, 7, 8, 12, and 20) were found to be expressed by lines that were MAM reactive, although these were not a major component of the cluster-derived T cells. Some non-cluster-derived lines expressed V beta s 17, 12, and 7, but these proved to be nonreactive to MAM. Therefore, dendritic cells can be used to immunoselect and characterize T cells that express superantigen-reactive TCRs.

Limited heterogeneity of T cell receptor variable region gene usage in juvenile rheumatoid arthritis synovial T cells.

The aim of this study was to determine whether synovial fluid (SF) T cells in patients with juvenile rheumatoid arthritis (JRA) are restricted in their T cell receptor (TcR) gene repertoire. The quantitative polymerase chain reaction (QPCR) was used to compare the transcription of V beta and V alpha gene families in freshly isolated SF T cells, in interleukin-2 receptor-positive (IL-2R+) T cells and in peripheral blood (PB) T cells from 18 patients. Significantly less V beta families are detected in SF when compared with PB (p greater than 0.0003). The TcR V beta gene usage by IL-2R+ T cells was even less heterogeneous when compared with freshly isolated SF T cells (p greater than 0.0002). Freshly isolated SF T cells from the left and the right knees of four patients transcribed the same V beta families. Furthermore, we demonstrate that in SF the distribution of certain TcR V beta gene segments in CD4+ and CD8+ T cells differed from that in PB of the same patient. The TcR V alpha usage was studied in IL-2R+ T cells from six patients who had shown restriction in their SF TcR V beta gene usage. Only two to five TcR alpha transcripts were detected in three of these patients while a broad TcR V alpha usage was seen in the other three patients. Sequence analysis of the SF V beta 20 cDNA clones generated from the IL-2R+ T cells of two patients demonstrated an oligoclonal expansion. Taken together, our data could indicate an antigen- and/or superantigen-driven expansion of selected T cells in the synovial compartment.

Presentation of superantigen by human T cell clones: a model of T-T cell interaction.

Superantigens (SAg) interact with T lymphocytes bearing particular V beta sequences as part of their T cell receptor (TcR). The interaction, however, requires the presence of major histocompatibility complex (MHC) class II molecules on antigen-presenting cell (APC). In peculiar circumstances, MHC class II+ T cell clones (TCC) have been shown to present peptides and selected antigens interacting with antigen-specific TCC in the absence of APC. In this report we studied the capacity of SAg to mediate a T-T cell interaction, investigating the TCC ability to present a panel of staphylococcal enteroxins (SE) independently of the presence of added APC. Upon exposure to a broad range of SE concentrations, MHC class II+ TCC showed an intense proliferative response even in the absence of professional APC. Diverse SE optimally stimulated responder TCC at different concentrations. The proliferation was inhibited by anti-DR monoclonal antibodies, both in the presence and in the absence of APC. The SE activation of TCC in the absence of APC induced the same series of phenotypic variations as that observed following the TCC stimulation with APC. Irradiated TCC efficiently presented membrane-bound SE to responder TCC as well as professional APC. These results show that a single cell of a given clone effectively presents the SE to other cells of the same clone, and provide evidence that SAg can efficiently mediate T-T cell interaction. In addition, the possibility also exists that one cell of the clone can actually undergo an auto-stimulation via SAg-mediated interactions between its own TcR and MHC class II molecule. It has recently been suggested that the V beta-selective depletion of T cells observed in acquired immunodeficiency syndrome (AIDS) patients might be a consequence of the interaction between a human immunodeficiency virus (HIV)-encoded SAg and T cells expressing a SAg complementary V beta. We suggest that the hypothesized HIV-encoded SAg might mediate T-T cell interactions that could play a relevant role in the V beta-selective depletion of T lymphocytes observed in HIV-infected patients.

Common sequence on distinct Vβ genes defines a protective idiotope in experimental encephalomyelitis

Synthetic TCR peptides expressed by encephalitogenic T cells can induce both cellular and humoral responses that protect against experimental encephalomyelitis. In the Lewis rat, encephalitogenic T cells predominantly express V beta 8.2, and a peptide in the CDR2 region representing residues 39-59 could both protect against and treat experimental autoimmune encephalitis (EAE). Similarly, the homologous and cross reactive 39-59 peptide from V beta 8.6 expressed by an EAE-protective clone also had protective and therapeutic activity against EAE. The consensus sequence between the V beta 8.2 and V beta 8.6 peptides, which included residues 44-54, was postulated to contain the protective idiotope. In this report, we demonstrate that this peptide, designated V beta 8-44-54, has comparable activity to the longer peptides for treating both active and passive EAE. Similar to the longer V beta 8.2-39-59 peptide, the V beta 8-44-54 peptide stimulates protective TCR peptide-specific CD4+, CD8dim T cells restricted by MHC I. We also report for the first time the recovery of V beta 8-44-54 reactive T cells that express a variety of V beta genes in their T-cell receptor (TCR), including V beta 4, 8, 10, 12, 15, 17, 19, and 20. Taken together, these data establish that the V beta 8-44-54 sequence constitutes an important autoregulatory idiotope in EAE.(ABSTRACT TRUNCATED AT 250 WORDS)

PREVENTION OF COLLAGEN INDUCED ARTHRITIS IN MICE BY TREATMENT WITH AN ANTIBODY DIRECTED AGAINST THE T CELL RECEPTOR αβ FRAMEWORK

Collagen induced arthritis (CIA) is an animal model of inflammatory polyarthritis. Type II collagen is the major matrix protein of hyaline cartilage. Susceptibility to CIA is linked to the Major Histocompatibility Complex Class II genes but the presence of T cells expressing specific variable beta (V beta) chain of their T cell receptor (TCR) is also required. Pretreatment with the monoclonal antibody H57-597 directed against the TCR alpha beta framework prevented the onset of arthritis in the majority of animals. The depletion of the T cell population did not lead to any apparent health problems. These experiments demonstrate the important role of the alpha/beta T cell and its receptors in the CIA model. Further, anti-TCR alpha beta antibodies may be of value in the therapy of autoreactive disorders.

Evidence for clonal selection of gamma/delta T cells in response to a human pathogen.

T cells bearing gamma/delta antigen receptors comprise a resident population of intraepithelial lymphocytes in organs such as skin, gut, and lungs, where they are strategically located to contribute to the initial defense against infection. An important unsolved question about antigen-driven gamma/delta T cell responses regards the breadth of their T cell receptor (TCR) repertoire, since many specific epithelial compartments in mice display limited diversity. We have examined the diversity of TCR delta gene expression among human gamma/delta T cells from skin lesions induced by intradermal challenge with Mycobacterium leprae. We show that the vast majority of gamma/delta cells from M. leprae lesions use either V delta 1-J delta 1 or V delta 2-J delta 1 gene rearrangements and, within a given region of the lesion, display limited junctional diversity. This contrasts markedly with the extensive diversity of gamma/delta T cells from peripheral blood of these same individuals, as well as skin from normal donors. These results indicate that the gamma/delta response to M. leprae involves the selection of a limited number of clones from among a diverse repertoire, probably in response to specific mycobacterial and/or host antigens.

T Cell Receptor Peptide Therapy Triggers Autoregulation of Experimental Encephalomyelitis

Encephalitogenic T cells specific for myelin basic protein share common V beta 8 peptide sequences in their T cell receptor (TCR) that can induce autoregulatory T cells and antibodies that prevent clinical signs of experimental autoimmune encephalomyelitis (EAE). It is not known, however, if TCR peptides can treat established disease. To test its therapeutic value, TCR-V beta 8-39-59 peptide was injected into rats with clinical signs of EAE. This treatment reduced disease severity and speeded recovery, apparently by boosting anti-V beta 8 T cells and antibodies raised naturally in response to encephalitogenic V beta 8+ T cells. These results demonstrate that synthetic TCR peptides can be used therapeutically, and implicate the TCR-V beta 8-39-59 sequence as a natural idiotope involved in EAE recovery. Similarly, human TCR peptides may be effective in enhancing natural regulation of autoreactive T cells that share common V genes.

T‐Cell Clones that react against Autologous Human Tumors

T cells (derived from peripheral blood lymphocytes [PBL], lymph nodes or tumor tissues and restimulated with autologous tumor cells and expanded in interleukin-2 [IL-2]), when cloned, produce three functional classes of clone. Class I T-cell clones exhibit the phenotype of alpha/beta cytotoxic T lymphocytes (CD3+, CD8+, CD4-, WT31+), use their CD3-alpha/beta complexes for cognate function, and lyse the autologous tumor cells specifically in a major histocompatibility complex (MHC) Class I-restricted manner. The second class of T cell clone expresses identical phenotype but exhibits a rather broad cytotoxic profile against the autologous and allogeneic tumor cells derived from tumors with similar and/or dissimilar histologies. Although these CTL clones can, at times, show MHC Class I-restricted killing and use their T-cell receptors (TCR) complexes for function, activation via certain accessory molecules, particularly lymphocyte-function associated (LFA-1) antigens, might induce their broad cytotoxic behavior. The nature of the tumor antigen recognized by the Class I antigen-specific CTL clones remains unknown. It is evident, however, that more than one antigen can be associated with a given tumor and they are recognized by different CTL clones from individual patients. The third class of T-cell clone is usually of CD4+ alpha/beta T cells (CD3+, CD4+, CD8-, WT31) and these T-cell clones exhibit no cytotoxicity toward the autologous or allogeneic target cells. When tested for potential regulatory property, one type of CD4+ T-cell clone exhibits the characteristics of helper T cells. This type induces or amplifies cytotoxic response in fresh PBL by elaborating interleukin-2 (IL-2) and interferon-gamma). These helper T-cell clones can proliferate against the autologous tumor cells and demonstrate functional specificity for the autologous tumor cells. The other type of CD4+ T-cell clone exhibits the phenotype of the helper T-cell clone (CD3+, CD4+, CD8-, WT31+) but suppresses the cytotoxic response of the autologous PBL in co-culture in the presence of the autologous tumor cells and exogenous IL-2. In some situations, these CD4+ suppressor T-cell clones exhibit considerable specificity for the autologous tumor cells. They do not suppress the cytotoxic response against allogeneic targets or against EBV-infected autologous lymphoblastoid cells. Furthermore, they specifically up-regulate their IL-2 receptors (IL-2R) when stimulated by the autologous tumor cells or with autologous tumor cell-pulsed antigen-presenting cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural Mutations of the T Cell Receptor ζ Chain and Its Role in T Cell Activation

T cell hybridomas that express zeta zeta, but not zeta eta, dimers in their T cell receptors (TCRs) produce interleukin-2 (IL-2) and undergo an inhibition of spontaneous growth when activated by antigen, antibodies to the receptor, or antibodies to Thy-1. Hybridomas without zeta and eta were reconstituted with mutated zeta chains. Cytoplasmic truncations of up to 40% of the zeta molecule reconstituted normal surface assembly of TCRs, but antigen-induced IL-2 secretion and growth inhibition were lost. In contrast, cross-linking antibodies to the TCR activated these cells. A point mutation conferred the same signaling phenotype as did the truncations and caused defective antigen-induced tyrosine kinase activation. Thus zeta allows the binding of antigen/major histocompatibility complex (MHC) to alpha beta to effect TCR signaling.