Analysis of the T-cell receptor repertoire of human T-cell leukemia virus type 1 (HTLV-1) Tax-specific CD8+ cytotoxic T lymphocytes from patients with HTLV-1-associated disease: evidence for oligoclonal expansion

Conserved CDR3 regions in T-cell receptor (TCR) CD8(+) T cells that recognize the Tax11-19/HLA-A*0201 complex in a subject infected with human T-cell leukemia virus type 1: relationship of T-cell fine specificity and major histocompatibility complex/peptide/TCR crystal structure

We investigated the T-cell receptor (TCR) repertoire of CD8(+) T cells that recognize the Tax11-19 immunodominant epitope of Tax protein expressed by human T-cell leukemia virus (HTLV-1) that is implicated in the disease HTLV-1-associated myelopathy (HAM/TSP). A panel of Tax11-19-reactive CD8(+) T-cell clones was generated by single-cell cloning of Tax11-19/HLA-A*0201 tetramer-positive peripheral blood lymphocytes from an HTLV-1-infected individual. The analyses of TCR usage revealed that the combination of diverse TCR alpha and beta chains could be used for the recognition of Tax11-19 but the major population of T-cell clones (15 of 24 clones) expressed the TCR V beta 13S1 and V alpha 17 chain. We found striking similarities in CDR3 regions of TCR alpha and beta chains between our major group of CD8(+) T-cell clones and those originating from different subjects as previously reported, including TCRs with resolved crystal structures. A 3-amino-acid sequence (PG-G) in the CDR3 region of the V beta chain was conserved among all the Tax11-19-reactive T-cell clones expressing V beta 13S1 and V alpha 17 chains. Conserved amino acids in the CDR3 region do not directly contact the Tax11-19 peptide, as corroborated by the crystal structure of B7-TCR, a TCR that is almost identical to VB13S1 clones isolated in this study. Analysis of fine peptide specificity using altered peptide ligands (APL) of Tax11-19 revealed a similar recognition pattern among this panel of T-cell clones. These data suggest that the PG-G amino acids in the CDR3 beta loop provide a structural framework necessary for the maintenance of the tertiary TCR structure.

Longitudinal analysis of T cells responding to tetanus toxoid in healthy subjects as well as in pediatric patients after bone marrow transplantation: the identification of identical TCR-CDR3 regions in time suggests long-term stability of at least part of the antigen-specific TCR repertoire

To understand the nature of long-term Th immune responses, we investigated in the present study the TCRBV gene repertoire of CD4(+) T cells specific for the recall antigen tetanus toxoid (TT) in recipients of an allogeneic bone marrow transplantation (allo-BMT) at several time points after transplantation and in their BM donors. We observed that the TCR repertoire of TT-specific CD4(+) Th cells was heterogeneous, and differed between allo-BMT recipients and their respective donors. Some individuals, however, used similar TCR-complementarity-determining region (CDR) 3 motifs that could reflect recognition of and selection by similar promiscuous epitopes of TT. Longitudinal analysis of this TT-specific T cell response revealed that T cells with completely identical TCR were present at several time points after the first analysis in allo-BMT recipients, most probably reflecting long-term stability of at least part of the antigen-specific TCR repertoire. Similar stability of the TT-specific TCR repertoire in time was also noted in the allo-BMT donors. These observations reveal that within a given individual the dominant antigen-specific T cell clones persist in time in an otherwise diverse TT-specific CD4(+) T cell immune response.

Identification of a crucial energetic footprint on the alpha1 helix of human histocompatibility leukocyte antigen (HLA)-A2 that provides functional interactions for recognition by tax peptide/HLA-A2-specific T cell receptors

Structural studies have shown that class I major histocompatibility complex (MHC)-restricted peptide-specific T cell receptor (TCR)-alpha/betas make multiple contacts with the alpha1 and alpha2 helices of the MHC, but it is unclear which or how many of these interactions contribute to functional binding. We have addressed this question by performing single amino acid mutagenesis of the 15 TCR contact sites on the human histocompatibility leukocyte antigen (HLA)-A2 molecule recognized by the A6 TCR specific for the Tax peptide presented by HLA-A2. The results demonstrate that mutagenesis of only three amino acids (R65, K66, and A69) that are clustered on the alpha1 helix affected T cell recognition of the Tax/HLA-A2 complex. At least one of these three mutants affected T cell recognition by every member of a large panel of Tax/HLA-A2-specific T cell lines. Biacore measurements showed that these three HLA-A2 mutations also altered A6 TCR binding kinetics, reducing binding affinity. These results show that for Tax/HLA-A2-specific TCRs, there is a location on the central portion of the alpha1 helix that provides interactions crucial to their function with the MHC molecule.

In vivo selection of T-cell receptor junctional region sequences by HLA-A2 human T-cell lymphotropic virus type 1 Tax11-19 peptide complexes

Using HLA-peptide tetrameric complexes, we isolated human T-cell lymphotrophic virus type 1 Tax peptide-specific CD8(+) T cells ex vivo. Antigen-specific amino acid motifs were identified in the T-cell receptor Vbeta CDR3 region of clonally expanded CD8(+) T cells. This result directly confirms the importance of the CDR3 region in determining the antigen specificity in vivo.

Rapid identification of local T cell expansion in inflammatory organ diseases by flow cytometric T cell receptor Vbeta analysis

Oligoclonal expansion of antigen-specific T cells occurs frequently during inflammatory diseases. These cells may persist for a long time at high frequency in the body and be enriched in the affected tissues. As a screening test for expanded cell T cell populations at sites of inflammation, we developed an optimized methodology for flow-cytometry-based quantification of T cell receptor Vbeta (TCRBV) expression. We first validated the specificity of a TCRBV-specific monoclonal antibody set by direct comparison with PCR-based analysis of mono- and polyclonal T cell samples. This monoclonal antibody (mAb) panel recognized approximately two thirds of the T cell receptor alpha/beta repertoire in a group of 64 healthy donors and allowed defining TCR usage in the CD4+ and CD8+ subsets. The reliable detection of expanded Vbeta gene families in T cell populations was confirmed in experiments on superantigen-stimulated T cells. Through differential TCR analysis on T cell subpopulations in cerebrospinal fluid and blood in patients with acute encephalitis, we were able to identify locally expanded CD8+ T cells. The power of this approach affords not only high-throughput comparative TCR analysis for immunological studies in vitro, but also rapid ex vivo identification of cell populations enriched in organ compartments during inflammatory diseases.

Examination of CD8+ T cell function in humans using MHC class I tetramers: similar cytotoxicity but variable proliferation and cytokine production among different clonal CD8+ T cells specific to a single viral epitope

Following infection by human T cell lymphotrophic virus-I (HTLV-I), high frequencies of polyclonal Tax11-19-reactive CD8(+) T cells can be detected in the peripheral blood. To investigate whether there are differences in the effector functions of these cells, we generated a panel of Tax11-19-reactive T cell clones by single cell sorting of HLA-A2/Tax11-19 tetramer binding CD8(+) T cells followed by repeated stimulation with PHA and IL-2. Examination of the TCRs revealed 17 different T cell clones with unique clonal origins. Nine representative CD8(+) T cell clones showed a similar cytotoxic dose-response activity against Ag-pulsed target cells, even though they express different TCRs. This cytotoxic effector function was not influenced by the engagement of either CD28 or CD2 costimulatory molecules. In contrast to the cytotoxic activity, qualitatively different degrees of proliferative response and cytokine secretion were observed among T cell clones of different clonal origin. The induction of proliferation and cytokine secretion required the engagement of costimulatory molecules, particularly CD2-LFA-3 interaction. These results indicate that functionally diverse, polyclonal CTL populations can be activated specific to a single immunodominant viral epitope; they can manifest virtually identical cytotoxic effector function but have marked differences in proliferation and cytokine secretion.

Conversion of a T cell antagonist into an agonist by repairing a defect in the TCR/peptide/MHC interface: implications for TCR signaling

The structure of the A6 alphabetaTCR/HTLV-1 Tax-peptide/MHC I complex with proline 6 of Tax substituted with alanine (P6A), an antagonist, is nearly identical to the structure with wild-type Tax agonist. Neither the proline in the agonist nor the alanine in the antagonist is contacted by the alphabetaTCR. Here, we demonstrate that antagonist activity of P6A is associated with low affinity of the A6 alphabetaTCR for Tax-P6A/HLA-A2. We show that stepwise repair of a packing defect in the TCR/MHC interface using N-alkylated amino acids results in stepwise increases in TCR affinity and activity. Kinetic and thermodynamic measurements suggest that for some ligands the range of T cell outcomes does not correlate with either their alphabetaTCR affinity or the half-life of the alphabetaTCR/peptide/MHC complex.

Decreased GATA3 mRNA expression in human T-cell lymphotropic virus type 1 (HTLV-1) infection

GATA3 is a specific T-cell transcription factor involved in the expression of T-cell receptor (TCR). In order to characterize the relationship between HTLV-1 infection, which has been reported to be associated with down-regulation of genes belonging to the TCR/CD3 complex, and the transcription factor GATA3, we evaluated, by semi-quantitative RT-PCR, the expression of GATA3 gene in HTLV-1 carriers and individuals with related diseases. The study included 4 asymptomatic carriers, 2 patients with adult T-cell leukaemia/lymphoma (ATLL), 1 patient with HTLV-1 associated myelopathy (HAM)/tropical spastic paraparesis (TSP) and 7 healthy blood donors. A considerable decrease in the expression of the GATA3 mRNA was observed in all subjects infected by HTLV-1 and no expression of GATA3 mRNA was observed in 1 subject with ATLL and in 1 with HAM/TSP.

Tissue inhibitor of metalloproteinase 3, matrix metalloproteinase 9, and neopterin in the cerebrospinal fluid: preferential presence in HTLV type I-infected neurologic patients versus healthy virus carriers

The human retrovirus HTLV-I is responsible for the chronic progressive myelopathy, TSP/HAM, characterized by the presence of infiltrated T lymphocytes, cytokines, and matrix metalloproteinases (MMPs) within spinal cord lesions. MMPs have been associated with several neurological diseases, and we previously reported the specific presence of the extracellular matrix-degrading protease, MMP-9, in the cerebrospinal fluid of TSP/HAM patients. Nevertheless, previous studies have not yet shown whether the expression of MMP-9 is associated with HTLV-I infection per se, or with neurological symptoms following infection. In the present work, the presence of tissue inhibitors of metalloproteinases 1 and 3 (TIMP-1 and TIMP-3) and of MMP-9 in the CSF of HTLV-I-infected individuals was compared in TSP/HAM patients versus HTLV-I carriers without neurological symptoms. TIMP-3, a regulator of MMP activity and cell survival, was detected with a significantly higher frequency in the TSP/HAM group and paralleled the increased levels of MMP-9 and neopterin, a sensitive indicator of cellular immune activation. These data may reflect the intense cell remodeling that occurs intrathecally in inflamed tissue. Changes in MMP, TIMP, and neopterin expression were not related to age at onset of disease, grade of motor disability, progressor status, or duration of disease, presumably indicating that TSP/HAM patients are continuously subjected to viral and immunological pressure. All these observations suggest that TIMPs and MMPs may contribute to the pathogenesis of TSP/HAM, and hence a new therapeutic strategy targeting the MMP/TIMP balance is needed. These observations also suggest that MMP-9 and TIMP-3 in CSF may be useful markers in the follow-up of the efficacy of therapeutic trials in TSP/HAM patients.

The structure and stability of an HLA-A*0201/octameric tax peptide complex with an empty conserved peptide-N-terminal binding site

The crystal structure of the human class I MHC molecule HLA-A2 complexed with of an octameric peptide, Tax8 (LFGYPVYV), from human T cell lymphotrophic virus-1 (HTLV-1) has been determined. This structure is compared with a newly refined, higher resolution (1.8 A) structure of HLA-A2 complexed with the nonameric Tax9 peptide (LLFGYPVYV) with one more N-terminal residue. Despite the absence of a peptide residue (P1) bound in the conserved N-terminal peptide-binding pocket of the Tax8/HLA-A2 complex, the structures of the two complexes are essentially identical. Water molecules in the Tax8 complex replace the terminal amino group of the Tax9 peptide and mediate a network of hydrogen bonds among the secondary structural elements at that end of the peptide-binding groove. Thermal denaturation measurements indicate that the Tax8 complex is much less stable, DeltaTm = 16 degrees C, than the Tax9 complex, but both can sensitize target cells for lysis by some Tax-specific CTL from HTLV-1 infected individuals. The absence of a P1 peptide residue is thus not enough to prevent formation of a "closed conformation" of the peptide-binding site. TCR affinity measurements and cytotoxic T cell assays indicate that the Tax8/HLA-A2 complex does not functionally cross-react with the A6-TCR-bearing T cell clone specific for Tax9/HLA-A2 complexes.

An altered peptide ligand antagonizes antigen-specific T cells of patients with human T lymphotropic virus type I-associated neurological disease

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an inflammatory neurologic disease associated with HTLV-I infection, in which chronically activated, HTLV-I-specific CD8+ CTL have been suggested to be immunopathogenic. In HLA-A2 HAM/TSP patients, CD8+ HTLV-I-specific CTLs recognize an immunodominant peptide of the HTLV-I Tax protein, Tax11-19. We examined the functional outcome on activation of both cloned peripheral blood and cerebrospinal spinal fluid-derived CTL and bulk PBMC from HAM/TSP patients by altered peptide ligands (APL) derived from HTLV-I Tax11-19. In CTL clones generated from PBMC and CSF of HLA-A2 HAM/TSP patients, an APL substituted at position 5 significantly decreased CTL responses when compared with the native peptide. Moreover, these ligands were also shown to inhibit CTL responses to the native peptide in bulk PBMC of HLA-A2 HAM/TSP patients. These data suggest that a modification of an antigenic peptide at the central position can manipulate the T cell responses in bulk PBMC from different individuals with an inflammatory disease. Additionally, these results have implications for the potential use of APL-based immunotherapy in this T cell-mediated CNS disease.

Real-time polymerase chain reaction assay for cell-associated HTLV type I DNA viral load

We have developed a quantitative real-time PCR assay for HTLV-I DNA. This assay approach uses real-time monitoring of fluorescent signal generation as a consequence of Taq-mediated amplification of specific target sequences to allow real-time kinetic analysis of amplicon production. This kinetic approach yields excellent sensitivity and an extremely broad linear dynamic range, and ensures that quantitation is based on analysis during the exponential phase of amplification, regardless of the input template copy number. The HTLV-I DNA assay has a nominal threshold sensitivity of 10 copy Eq/reaction, although single-copy plasmid template can be detected at frequencies consistent with statistical prediction. The linear dynamic range is in excess of 5 logs. Interassay reproducibility averages 14% (coefficient of variation) for control templates over a range of 10(1) to 10(6) copy Eq/reaction and 25%, based on studies of extraction and analysis of replicate aliquots of PBMC specimens from HTLV-I-infected subjects. The primer/probe combination targets tax sequences conserved across described HTLV-I and HTLV-II isolates. Parallel quantitation in the same samples of an endogenous sequence present at a known copy number per cell allows normalization of results for potential variation in DNA recovery. Availability of this assay should facilitate studies of basic pathogenesis and clinical evaluation of HTLV-I and HTLV-II infection, as well as assessment of therapeutic approaches.

Accumulation of common T cell clonotypes in the salivary glands of patients with human T lymphotropic virus type I-associated and idiopathic Sjögren's syndrome

To clarify the pathogenesis of human T lymphotropic virus type I (HTLV-I)-associated Sjögren's syndrome (SS), the TCR Vbeta gene usage by the infiltrating lymphocytes in the target organ was examined. The Vbeta families predominantly used in the labial salivary gland (LSG) from the HTLV-I-seropositive (HTLV-I+) SS patients were more restricted than those from the HTLV-I-seronegative (idiopathic) SS patients, and were commonly Vbeta5.2, Vbeta6, and Vbeta7. The single-strand conformation polymorphism analysis revealed that T cell clonotypes with Vbeta5.2, Vbeta6, and Vbeta7 accumulate in the LSG from the HTLV-I+ and idiopathic SS patients. Among junctional sequences of the most dominant Vbeta7 transcripts, the conserved amino acid motif (QDXG: X is any amino acid) was found in six of the five HTLV-I+ SS patients and was also detected in two of the five idiopathic SS patients. Using the probes specific to the motif, the Vbeta7 transcripts with the motif were detected in the LSG from all of the seven HTLV-I+ and five of the six idiopathic SS patients, but not from eight healthy subjects. The Vbeta7 transcripts with this motif were also detected in the HTLV-I-infected T cell lines obtained from the LSG of an HTLV-I+ SS patient. The accumulation of HTLV-I-infected T cells expressing TCR with the conserved motif was thus indicated. These T cells were commonly present in patients with idiopathic SS and are strongly suggested to most likely be involved in the pathogenesis of both HTLV-I-associated and idiopathic SS.

Kinetics of T-cell receptor binding by bivalent HLA-DR. Peptide complexes that activate antigen-specific human T-cells

Monovalent major histocompatibility complex-peptide complexes dissociate within seconds from the T-cell receptor (TCR), indicating that dimerization/multimerization may be important during early stages of T-cell activation. Soluble bivalent HLA-DR2.myelin basic protein (MBP) peptide complexes were expressed by replacing the F(ab) arms of an IgG2a antibody with HLA-DR2.MBP peptide complexes. The binding of bivalent HLA-DR2.peptide complexes to recombinant TCR was examined by surface plasmon resonance. The bivalent nature greatly enhanced TCR binding and slowed dissociation from the TCR, with a t((1)/(2)) of 2.1 to 4.6 min. Soluble bivalent HLA-DR2.MBP peptide complexes activated antigen-specific T-cells in the absence of antigen presenting cells. In contrast, soluble antibodies to the TCR.CD3 complex were ineffective, indicating that they failed to induce an active TCR dimer. TCR/CD3 antibodies induced T-cell proliferation when bound by antigen presenting cells that expressed Fc receptors. In the presence of dendritic cells, bivalent HLA-DR2. MBP peptide complexes induced T-cell activation at >100-fold lower concentrations than TCR/CD3 antibodies and were also superior to peptide or antigen. These results demonstrate that bivalent HLA-DR. peptide complexes represent effective ligands for activation of the TCR. The data support a role for TCR dimerization in early TCR signaling and kinetic proofreading.

Molecular interactions between extracellular components of the T-cell receptor signaling complex

The structural and biochemical basis of antigen recognition by the T-cell receptor (TCR)-CD3 signaling complex has been illuminated greatly over the past few years. Structural biology has contributed enormously to this understanding through the determination of crystal structures of many of the individual components of this complex, and some of the complexes. A number of general principles can be derived for the structure of the alpha beta TCR and its interaction with peptide-major histocompatibility complex (pMHC) in class I systems, as well as interaction of the CD8 co-receptor with MHC. Large buried surface areas within the protein-protein interfaces, and varying degrees of shape complementarity appear critical for modulating the stability of the multicomponent, low-affinity macromolecular complexes consisting of TCR, pMHC, CD8 or CD4, and CD3 gamma, delta, epsilon and zeta. Significant structural alterations in TCR and pMHC, upon complex formation, hint at an as yet unclear role for conformational change in both recognition and activation. Subtle chemical alterations in key peptide residues which contact the TCR can have dramatic agonist or antagonist effects on receptor activation, which correlate only loosely with the TCR/pMHC complex affinity, implying an ability of the signaling complex to "sense" fine differences in the interface. The stoichiometry of an activated TCR signaling complex is still an unresolved issue, as is the structure and disposition of the CD3 components. However, functional experiments are bridging this gap and providing us with preliminary working models of the multimeric assemblies.

Four A6-TCR/peptide/HLA-A2 structures that generate very different T cell signals are nearly identical

The interactions of three singly substituted peptide variants of the HTLV-1 Tax peptide bound to HLA-A2 with the A6 T cell receptor have been studied using T cell assays, kinetic and thermodynamic measurements, and X-ray crystallography. The three peptide/MHC ligands include weak agonists and antagonists with different affinities for TCR. The three-dimensional structures of the three A6-TCR/peptide/HLA-A2 complexes are remarkably similar to each other and to the wild-type agonist complex, with minor adjustments at the interface to accommodate the peptide substitutions (P6A, V7R, and Y8A). The lack of correlation between structural changes and the type of T cell signals induced provides direct evidence that different signals are not generated by different ligand-induced conformational changes in the alphabeta TCR.

Human CD28−CD8+ T Cells Contain Greatly Expanded Functional Virus-Specific Memory CTL Clones

At birth, almost all human peripheral blood CD8+ T cells express the costimulatory molecule CD28. With increasing age, the proportion of CD8+ T cells that lack CD28 increases. Because the Ag specificity of CD28−CD8+ T cells has not previously been defined, we studied the contribution of CD28−CD8+ T cells to the memory CD8+ CTL response against two human persistent viruses, human CMV (HCMV) and HIV. From PBMC of healthy virus carriers we generated multiple independent CTL clones specific for defined viral peptides and sequenced their TCR β-chains. We designed clonotypic oligonucleotides complementary to each β-chain hypervariable sequence and quantified the size of individual immunodominant CTL clones in PBMC. Some individual CTL clones were very large, comprising up to 3.1% of all CD8+ T cells in PBMC, and were generally maintained at a stable level for months. Individual virus-specific CTL clones were consistently more abundant in purified CD28− cells than in the CD8+ population as a whole. Because CD28−CD8+ cells as a population have been reported to proliferate poorly in response to mitogen, we studied the function of these virus-specific CD28− CTL clones by quantifying the frequency of peptide-specific CTL precursors using limiting dilution analysis. CD28−CD8+ T cells contained high frequencies of functional memory CTL precursors specific for peptides of HCMV or HIV, generally higher than in the CD8+ T cell population as a whole. We conclude that in asymptomatic HCMV and HIV infection, human CD28−CD8+ T cells contain high frequencies of functional virus-specific memory CTL clones.

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) pathogenesis hypothesis. A shift of homologous peptides pairs, central nervous system (CNS)/HTLF-1, HTLV-1/thymus, thymus/CNS, in a thymus-like CNS environment, underlies the pathogenesis of HAM/TSP

Determinants shared by thymus, brain and HTLV-1 induce lymphocytic neurotropism and demyelinization in HAM/TSP, within the framework thymus-like brain environment. The disease evolves in two phases. The first phase of the disease would be dependent on CD4 T-lymphocytes specific for thymic autoantigens, reactivated by viral antigens homologous to thymus and CNS autoantigens. During this phase, demyelinization could be due initially to a stop in the synthesis of myelin following an altered expression of adhesion proteins at the surface of oligodendrocytes and neurons. The second phase, which covers the inflammatory and chronic character of the disease, would be dependent, on the one hand, on CD8 T-lymphocytes specific for viral peptides, and on the other hand, on CD8 T-lymphocytes specific for peptides arising from the cell-proteases induced progressive proteolysis of protein components from the myelin layers and other protein components of the CNS. Non-specific inflammatory and non-inflammatory cytokines keep the activation going of the different cellular types. The thoracic spinal cord cell-location specificity would be linked to a peptidic coherence between HTLV-1 (significant agent), thymus and thoracic spinal cord antigens, genetically peculiar to HAM/TSP patients.

Peptide Recognition by Two HLA-A2/Tax11–19-Specific T Cell Clones in Relationship to Their MHC/Peptide/TCR Crystal Structures

The crystal structures of two human TCRs specific for a HTLV-I Tax peptide bound to HLA-A2 were recently determined, for the first time allowing a functional comparison of TCRs for which the MHC/peptide/TCR structures are known. Extensive amino acid substitutions show that the native Tax residues are optimal at each peptide position. A prominent feature of the TCR contact surface is a deep pocket that accommodates a tyrosine at position 5 of the peptide. For one of these TCRs, this pocket is highly specific for aromatic residues. In the other TCR structure, this pocket is larger, allowing many different residues to be accommodated. The CTL clones also show major differences in the specificity for several other peptide residues, including side chains that are not directly contacted by the TCR. Despite the specificity of these clones, peptides that are distinct at five or six positions from Tax11–19 induce CTL activity, indicating that substantial changes of the peptide surface are tolerated. Human peptides with limited sequence homology to Tax11–19 represent partial TCR agonists for these CTL clones. The distinct functional properties of these CTL clones highlight structural features that determine TCR specificity and cross-reactivity for MHC-bound peptides.

The memory cytotoxic T-lymphocyte (CTL) response to human cytomegalovirus infection contains individual peptide-specific CTL clones that have undergone extensive expansion in vivo

Human cytomegalovirus (HCMV)-specific CD8(+) cytotoxic T lymphocytes (CTL) appear to play an important role in the control of virus replication and in protection against HCMV-related disease. We have previously reported high frequencies of memory CTL precursors (CTLp) specific to the HCMV tegument protein pp65 in the peripheral blood of healthy virus carriers. In some individuals, the CTL response to this protein is focused on only a single epitope, whereas in other virus carriers CTL recognized multiple epitopes which we identified by using synthetic peptides. We have analyzed the clonal composition of the memory CTL response to four of these pp65 epitopes by sequencing the T-cell receptors (TCR) of multiple independently derived epitope-specific CTL clones, which were derived by formal single-cell cloning or from clonal CTL microcultures. In all cases, we have observed a high degree of clonal focusing: the majority of CTL clones specific to a defined pp65 peptide from any one virus carrier use only one or two different TCRs at the level of the nucleotide sequence. Among virus carriers who have the same major histocompatibility complex (MHC) class I allele, we observed that CTL from different donors that recognize the same peptide-MHC complex often used the same Vbeta segment, although other TCR gene segments and CDR3 length were not in general conserved. We have also examined the clonal composition of CTL specific to pp65 peptides in asymptomatic human immunodeficiency virus-infected individuals. We have observed a similarly focused peptide-specific CTL response. Thus, the large population of circulating HCMV peptide-specific memory CTLp in virus carriers in fact contains individual CTL clones that have undergone extensive clonal expansion in vivo.

Clonal Expansion Within CD4+ and CD8+ T Cell Subsets in Human T Lymphotropic Virus Type I-Infected Individuals

To investigate the diversity of the T cell repertoire involved in human T lymphotropic virus type I (HTLV-I) infections, peripheral blood T cell subsets were analyzed by using a PCR-based assay that permits determination of complementarity-determining region 3 (CDR3) length variation in TCR Vβ transcripts. In two of four asymptomatic HTLV-I carriers and in four of five patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), mono- or oligoclonal expansions were detected in the CD4+ T cell subset. In one patient with adult T cell leukemia, a specific clone bearing Vβ7 was detected in the CD4+ T cell subset. In contrast, clonal expansion was not observed in the CD4 T cell subsets of three individuals with asymptomatic HTLV-II infection or in our previous studies of a large number of uninfected individuals. Oligoclonal expansions in the CD8+ T cell subset were detected in all subjects, including the patient with adult T cell leukemia. No differences in the number of expanded clones were noted between asymptomatic carriers and in patients with HAM/TSP and there was no obvious restriction in the TCR V region usage. Direct sequencing revealed no significant bias in the CDR3 motifs utilized by the predominant clones. This report is the first direct demonstration of clonal expansions within fractionated T cell subsets (CD4+ and CD8+) in HTLV-I infections and suggests that 1) clonal expansion of CD4+ T lymphocytes likely occurs as a direct result of infection and 2) polyclonal CD8+ T cell expansion occurs frequently and independently of disease association.

Inhibitors of dipeptidyl peptidase IV/CD26 suppress activation of human MBP-specific CD4+ T cell clones

The ectoenzyme dipeptidyl peptidase IV (DP IV, EC 3.4.14.5, CD26) has been shown to play a crucial role in T cell activation. Specific inhibitors of DP IV suppress DNA synthesis as well as cytokine production (IL-2, IL-10, IL-12, IFN-gamma) of stimulated human and mouse T cells suggesting a potential application of these effectors in transplantations and autoimmune diseases. In the present study, we have examined the expression of DP IV/CD26 on six myelin basic protein (MBP)(87-99)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) as well as the biological effects of the two synthetic DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide on the function of these cells. All TCC expressed high levels of DP IV/CD26, as shown by flow cytometry and by enzymatic DP IV assay. Enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 h after PHA stimulation. The DP IV inhibitors suppress DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulation of activation of autoreactive TCC. Further in-vivo investigations, first in experimental models, will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS or other autoimmune diseases.

Direct visualization of antigen-specific T cells: HTLV-1 Tax11-19- specific CD8(+) T cells are activated in peripheral blood and accumulate in cerebrospinal fluid from HAM/TSP patients

Human T lymphotropic virus type 1 (HTLV-1) -associated myelopathy/tropic spastic paraparesis is a demyelinating inflammatory neurologic disease associated with HTLV-1 infection. HTLV-1 Tax11-19-specific cytotoxic T cells have been isolated from HLA-A2-positive patients. We have used a peptide-loaded soluble HLA-A2-Ig complex to directly visualize HTLV-1 Tax11-19-specific T cells from peripheral blood and cerebrospinal fluid without in vitro stimulation. Five of six HTLV-1-associated myelopathy/tropic spastic paraparesis patients carried a significant number (up to 13.87%) of CD8(+) lymphocytes specific for the HTLV-1 Tax11-19 peptide in their peripheral blood, which were not found in healthy controls. Simultaneous comparison of peripheral blood and cerebrospinal fluid from one patient revealed 2.5-fold more Tax11-19-specific T cells in the cerebrospinal fluid (23.7% vs. 9.4% in peripheral blood lymphocyte). Tax11-19-specific T cells were seen consistently over a 9-yr time course in one patient as far as 19 yrs after the onset of clinical symptoms. Further analysis of HTLV-1 Tax11-19-specific CD8(+) T lymphocytes in HAM/TSP patients showed different expression patterns of activation markers, intracellular TNF-alpha and gamma-interferon depending on the severity of the disease. Thus, visualization of antigen-specific T cells demonstrates that HTLV-1 Tax11-19-specific CD8(+) T cells are activated, persist during the chronic phase of the disease, and accumulate in cerebrospinal fluid, showing their pivotal role in the pathogenesis of this neurologic disease.

Lack of over-expression of T cell receptor Vbeta5.2 in myelin basic protein-specific T cell lines derived from HLA-DR2 positive multiple sclerosis patients and controls

Based on studies reporting an overexpression of certain V genes in myelin basic protein (MBP)-specific T cells from MS patients, immunotherapies targeting single TCR (Vbeta5.2, Vbeta6.1) are currently under way. In order to assess the basic assumption for one of these therapeutic strategies, i.e. the overexpression of Vbeta5.2 by MBP-specific T cells, we analyzed 100 MBP-specific T cell lines (TCL) for Vbeta5.2 expression. Only 4 out of 100 TCL expressed Vbeta5.2, and expression of this TCR gene is therefore not more frequent than expected from the normal peripheral blood distribution.

Two human T cell receptors bind in a similar diagonal mode to the HLA-A2/Tax peptide complex using different TCR amino acids

The three-dimensional structure of a human alphabeta T cell receptor (TCR), B7, bound to the HLA-A2 molecule/HTLV-1 Tax peptide complex was determined by x-ray crystallography. Although different from the A6 TCR, previously studied, in 16 of the 17 residues that contact HLA-A2/Tax, the B7 TCR binds in a similar diagonal manner, only slightly tipped and rotated, relative to the A6 TCR. The structure explains data from functional assays on the specificity differences between the B7 and A6 TCRs for agonist, partial agonist, and null peptides. The existence of a structurally similar diagonal binding mode for TCRs favors mechanisms based on the formation of geometrically defined supramolecular assemblies for initiating signaling.

Structural basis of plasticity in T cell receptor recognition of a self peptide-MHC antigen

The T cell receptor (TCR) inherently has dual specificity. T cells must recognize self-antigens in the thymus during maturation and then discriminate between foreign pathogens in the periphery. A molecular basis for this cross-reactivity is elucidated by the crystal structure of the alloreactive 2C TCR bound to self peptide-major histocompatibility complex (pMHC) antigen H-2Kb-dEV8 refined against anisotropic 3.0 angstrom resolution x-ray data. The interface between peptide and TCR exhibits extremely poor shape complementarity, and the TCR beta chain complementarity-determining region 3 (CDR3) has minimal interaction with the dEV8 peptide. Large conformational changes in three of the TCR CDR loops are induced upon binding, providing a mechanism of structural plasticity to accommodate a variety of different peptide antigens. Extensive TCR interaction with the pMHC alpha helices suggests a generalized orientation that is mediated by the Valpha domain of the TCR and rationalizes how TCRs can effectively "scan" different peptides bound within a large, low-affinity MHC structural framework for those that provide the slight additional kinetic stabilization required for signaling.

Counting antigen-specific CD8 T cells: a reevaluation of bystander activation during viral infection

Viral infections induce extensive T cell proliferation in vivo, but the specificity of the majority of the responding T cells has not been defined. To address this issue we used tetramers of MHC class I molecules containing viral peptides to directly visualize antigen-specific CD8 T cells during acute LCMV infection of mice. Based on tetramer binding and two sensitive assays measuring interferon-gamma production at the single-cell level, we found that 50%-70% of the activated CD8 T cells were LCMV specific [2 x 10(7) virus-specific cells/spleen]. Following viral clearance, antigen-specific CD8 T cell numbers dropped to 10(6) per spleen and were maintained at this level for the life of the mouse. Upon rechallenge with LCMV, there was rapid expansion of memory T cells, but after infection with the heterologous vaccinia virus there was no detectable change in the numbers of LCMV-specific memory CTL. Therefore, much of the CD8 T cell expansion seen during viral infection represents antigen-specific cells and warrants a revision of our current thinking on the size of the antiviral response.

Analysis of the expression of peptide-major histocompatibility complexes using high affinity soluble divalent T cell receptors

Understanding the regulation of cell surface expression of specific peptide-major histocompatibility complex (MHC) complexes is hindered by the lack of direct quantitative analyses of specific peptide-MHC complexes. We have developed a direct quantitative biochemical approach by engineering soluble divalent T cell receptor analogues (TCR-Ig) that have high affinity for their cognate peptide-MHC ligands. The generality of this approach was demonstrated by specific staining of peptide-pulsed cells with two different TCR-Ig complexes: one specific for the murine alloantigen 2C, and one specific for a viral peptide from human T lymphocyte virus-1 presented by human histocompatibility leukocyte antigens-A2. Further, using 2C TCR- Ig, a more detailed analysis of the interaction with cognate peptide-MHC complexes revealed several interesting findings. Soluble divalent 2C TCR-Ig detected significant changes in the level of specific antigenic-peptide MHC cell surface expression in cells treated with gamma-interferon (gamma-IFN). Interestingly, the effects of gamma-IFN on expression of specific peptide-MHC complexes recognized by 2C TCR-Ig were distinct from its effects on total H-2 Ld expression; thus, lower doses of gamma-IFN were required to increase expression of cell surface class I MHC complexes than were required for upregulation of expression of specific peptide-MHC complexes. Analysis of the binding of 2C TCR-Ig for specific peptide-MHC ligands unexpectedly revealed that the affinity of the 2C TCR-Ig for the naturally occurring alloreactive, putatively, negatively selecting, complex, dEV-8-H-2 Kbm3, is very low, weaker than 71 microM. The affinity of the 2C TCR for the other naturally occurring, negatively selecting, alloreactive complex, p2Ca-H-2 Ld, is approximately 1000-fold higher. Thus, negatively selecting peptide-MHC complexes do not necessarily have intrinsically high affinity for cognate TCR. These results, uniquely revealed by this analysis, indicate the importance of using high affinity biologically relevant cognates, such as soluble divalent TCR, in furthering our understanding of immune responses.

Expression of HLA class I-specific inhibitory natural killer cell receptors in HIV-specific cytolytic T lymphocytes: impairment of specific cytolytic functions

Human T lymphocytes have been shown to express inhibitory natural killer cell receptors (NKR), which can down-regulate T cell antigen receptor-mediated T cell function, including cytolytic activity. In the present study, we demonstrate that CD3+NKR+ cells can be identified in HIV-infected patients. HIV-specific cytolytic activity was analyzed in five patients in whom autologous lymphoblastoid B cell lines could be derived as a source of autologous target cells. Phytohemagglutinin-activated T cell populations that had been cultured in interleukin 2 displayed HIV-specific cytotoxic T lymphocyte (CTL) activity against HIV env, gag, pol, and nef in 3 of 5 patients. Addition of anti-NKR mAb of IgM isotype could increase the specific CTL activity. Moreover, in one additional patient, HIV-specific CTL activity was undetectable; however, after addition of anti-NKR mAb such CTL activity appeared de novo. Similar results were obtained by analysis of CD3+NKR+ clones derived from two patients. These data provide direct evidence that CD3+NKR+ cells may include antigen (HIV)-specific CTLs and that mAb-mediated masking of inhibitory NKR may revert the down-regulation of CTL function.

Longitudinal study of myelin basic protein-specific T-cell receptors during the course of multiple sclerosis

This study analyzed the stability of the myelin basic protein (MBP)-specific T-cell receptor (TCR) repertoire during the course of multiple sclerosis (MS) in three patients who were monitored for three years by gadolinium-enhanced magnetic resonance imaging. Bulk-culture T-cell lines (TCLs) were generated from 3-4 time points for each patient, including times of active and quiescent disease. TCR analysis of these TCLs indicated that both the V alpha and V beta usage was similar over time for each patient. Sequencing of TCRs demonstrated conserved complementarity-determining region 3 (CDR3) sequences within TCLs that expressed the same V alpha segment over time, although the J alpha usage was different for each TCR. This indicates that the population of MBP-reactive T-cells is changing during the course of MS, but that host and/or environmental factors may be selecting T-cells with particular MHC/peptide binding domains.

Immunodominance of a low-affinity major histocompatibility complex-binding myelin basic protein epitope (residues 111-129) in HLA-DR4 (B1*0401) subjects is associated with a restricted T cell receptor repertoire

The pathogenesis of multiple sclerosis (MS) is currently ascribed in part to a T cell-mediated process targeting myelin components. The T cell response to one candidate autoantigen, myelin basic protein (MBP), in the context of HLA-DR15Dw2, has been previously studied in detail. However, the characteristics of cellular immunity in the context of other MS-associated HLA-DR haplotypes are scarcely known. MBP-specific T cell lines (TCL) were generated from HLA-DR4 (B1*0401)-positive MS subjects. Out of 275 MBP-specific TCL, 178 (64. 7%) specifically recognized region MBP(111-129), predominantly in the context of DRB1*0401. The major T cell epitope for MBP recognition corresponded to residues MBP(116-123). These TCL expressed disparate profiles of cytokine secretion and cytotoxicity. T cell receptor analysis, on the other hand, revealed a strikingly limited heterogeneity of rearrangements. In contrast to MBP(81-99), which binds with high affinity to HLA-DR15 and is recognized by a diverse T cell repertoire, MBP(111-129) binds weakly to DRB1*0401, suggesting that only high affinity T cell receptors might be able to efficiently engage such unstable MHC/peptide complexes, thus accounting for the T cell receptor restriction we observed. This study provides new insight about MBP recognition and proposes an alternative mechanism for immunodominance of self-antigen T cell epitopes in humans.

In vitro modulation of human, autoreactive MBP-specific CD4 + T-cell clones by cyclosporin A

Cyclosporin A (CsA) is a potent immunosuppressant affecting many components of cellular and humoral immunity. Its main action probably results from inhibition of T-lymphocyte activation and interference with secretion of cytokines like IL-2, IL-4, IFN-gamma and TNF-alpha. Correspondingly, CsA has beneficial effects on the course of several autoimmune diseases thought to be mediated by T-lymphocytes, including a mild effect on multiple sclerosis. We exposed CD4 + cytotoxic T-lymphocytes specific for myelin basic protein, a putative target autoantigen in MS, to CsA in vitro, and determined the drug's effects on proliferation, expression of high affinity IL-2R, secretion of the proinflammatory cytokines IFN-gamma and TNF-alpha as well as on the secretion of the chemokines MIP-1 alpha and MIP-1 beta. In all instances, we observed a partial to complete inhibition. In contrast, the response of activated cells to IL-2 was resistant to CsA. Our observations are in line with results obtained in different experimental systems. The discrepancy between the profound inhibition of T-cells and the modest therapeutic effects on MS is discussed.

Major histocompatibility complex class I-specific receptors on human natural killer and T lymphocytes

Human NK cells express several specialized inhibitory receptors that recognize major histocompatibility complex (MHC) class I molecules expressed on normal cells. The lack of expression of one or more HLA class I alleles leads to NK-mediated target cell lysis. Receptors specific for groups of HLA-C (p58), HLA-B (p70) and HLA-A (p140) alleles belong to the Ig superfamily with two or three Ig-like domains in their extracellular portion, and a long cytoplasmic tail containing ITIM motifs and associated with a non-polar transmembrane portion. In contrast, the CD94/ NKG2-A receptor complex is composed of type II proteins with a C-type lectin domain which displays a more broad specificity for different class I alleles. Recently, activatory forms of the HLA-C-specific receptors have been identified in some donors. They are virtually identical to the inhibitory forms in their extracellular portions, but display a short cytoplasmic tail lacking ITIM motifs associated with a Lys-containing transmembrane portion (p50). A subset of activated T-lymphocytes, primarily CD8+ and oligoclonal or monoclonal in nature, express NK-type class I-specific receptors. These receptors exert an inhibitory activity on T-cell receptor-mediated functions and may provide an important mechanism of down-regulation of T-cell responses.

Pathogenesis of chronic progressive myelopathy associated with human T-cell lymphotropic virus type I

Human T-cell lymphotropic virus type I (HTLV-I) induces a chronic demyelinating disease known as HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). While only 0.25% of HTLV-I-infected individuals develop HAM/TSP, the mechanisms responsible for the progression of an HTLV-I carrier state to clinical disease are not clear. In particular, no specific sequence differences have been found between HTLV-I recovered from HAM patients and HTLV-I-infected carriers. Since CD4 T cells are the major reservoir of the virus, at least three hypotheses implicating CD4 T cells directly or indirectly have been proposed: 1) The cytotoxic hypothesis predicts that activated and HTLV-I-infected CD4 T cells migrate to the CNS and infect resident cells. Cytotoxic CD8 T cells may then recognize viral antigens on HTLV-I-infected CNS cells causing a cellularly mediated cytotoxic demyelination. 2) The autoimmune hypothesis predicts that either (a) virally reactive T cells crossreact with a CNS antigen, or (b) random infection of CD4 T cells eventually results in the infection of CNS-autoreactive CD4 T cells that, by virtue of the productive HTLV-I infection, become activated, expand and migrate to the CNS, where they encounter their antigen. This results in a specific immune response and demyelination, as is known to occur in experimental autoimmune encephalomyelitis. 3) The bystander damage hypothesis does not implicate a specific response against CNS cells. Instead this hypothesis suggests that the presence of IFN-gamma-secreting HTLV-I-infected CD4 T cells and their recognition by virally specific CD8 T cells in the CNS induce microglia to secrete cytokines, such as TNF-alpha, which may be toxic for the myelin.

Inhibitory receptors for HLA class I molecules on cytolytic T lymphocytes. Functional relevance and implications for anti-tumor immune responses

In recent years, the molecular mechanism by which natural killer cells lyze, or fail to lyze, different target cells has been elucidated. Natural killer cells express receptors which recognize MHC class I molecules on target cells. This interaction leads to inhibition of cytolytic activity, thus preventing lysis of target cells. The receptors belong to two distinct molecular types: (1) the lg superfamily which includes receptors (p58.1, p58.2, p70, and p140) which recognize specific HLA allotypes; (2) CD94 molecules which display a broad specificity for HLA class I molecules. Recently, a subset of cytolytic T lymphocytes has been shown to express the various natural killer cell receptors. Such T cells are detectable in peripheral blood, spleen, tonsils, and lymph nodes, but not in the thymus and cord blood. In some instances, two or more natural killer receptors can be coexpressed at the single cell level. Surface marker analysis has revealed that natural killer cell receptor-positive T cells always express a memory phenotype. Moreover, they are characterized by a skewed T cell receptor V beta repertoire. Further analysis of the T cell receptor VDI sequences revealed that natural killer cell receptor-positive, CD3-positive cells isolated from a given individual are oligoclonal or monoclonal in nature. Crosslinking of natural killer receptors leads to inhibition of different T cell functions, including non-specific lysis of appropriate HLA class I-negative target cells, T cell receptor mediated cytotoxicity, and cytokine production. The inhibitory effect on T cell receptor-mediated function has important implications. Thus, the expression of natural killer cell receptors as a consequence of chronic antigen stimulation may result in functional impairment of specific cytolytic T lymphocytes. Preliminary data indicate that this phenomenon may occur in tumor or virally infected patients. Remarkably, various patients with large granular lymphocyte expansions characterized by a CD3/ natural killer receptor-positive phenotype had chronic viral infections. The fact that antigen-specific cytolytic T lymphocytes may simultaneously express T cell and natural killer cell receptors, both recognizing HLA class I molecules but mediating opposite signals, offers new perspectives in our appreciation of the regulation of T cell responses and offers new clues for understanding the immunopathological events involved in certain diseases.

Structure of the complex between human T-cell receptor, viral peptide and HLA-A2

Recognition by a T-cell antigen receptor (TCR) of peptide complexed with a major histocompatibility complex (MHC) molecule occurs through variable loops in the TCR structure which bury almost all the available peptide and a much larger area of the MHC molecule. The TCR fits diagonally across the MHC peptide-binding site in a surface feature common to all class I and class II MHC molecules, providing evidence that the nature of binding is general. A broadly applicable binding mode has implications for the mechanism of repertoire selection and the magnitude of alloreactions.

Development of Epstein-Barr virus-specific memory T cell receptor clonotypes in acute infectious mononucleosis

The importance of cytotoxic T lymphocytes (CTLs) in the immunosurveillance of Epstein-Barr virus (EBV)-infected B cells is firmly established, and the viral antigens of CTL recognition in latent infection are well defined. The epitopes targeted by CTLs during primary infection have not been identified, however, and there is only limited information about T cell receptor (TCR) selection. In the present report, we have monitored the development of memory TCR-beta clonotypes selected in response to natural EBV infection in a longitudinal study of an HLA-B8+ individual with acute infectious mononucleosis (IM). By stimulating peripheral blood lymphocytes with HLA-B8+ EBV-transformed B lymphoblastoid cells, the primary virus-specific CTL response was shown to include specificities for two HLA-B8-restricted antigenic determinants, FLRGRAYGL and QAKWRLQTL, which are encoded within the latent EBV nuclear antigen EBNA-3. TCR-beta sequence analysis of CTL clones specific for each epitope showed polyclonal TCR-beta repertoire selection, with structural restrictions on recognition that indicated antigen-driven selection. Furthermore, longitudinal repertoire analysis revealed long-term preservation of a multiclonal effector response throughout convalescence, with the reemergence of distinct memory T cell clonotypes sharing similar structural restrictions. Tracking the progression of specific TCR-beta clonotypes and antigen-specific TCR-V beta family gene expression in the peripheral repertoire ex vivo using semiquantitative PCR strongly suggested that selective TCR-beta expansions were present at the clonotype level, but not at the TCR-V beta family level. Overall, in this first analysis of antigen-specific TCR development in IM, a picture of polyclonal TCR stimulation is apparent. This diversity may be especially important in the establishment of an effective CTL control during acute EBV infection and in recovery from disease.

Differential activation of human autoreactive T cell clones by altered peptide ligands derived from myelin basic protein peptide (87-99)

We have examined the functional consequences induced by interaction of DR2a-restricted myelin basic protein (MBP) (87-99)-specific T cell clones (TCC) with altered peptide ligands (APL) derived from MBP peptide (87-99). The immunodominant MBP peptide (87-99) has been implicated as a candidate antigen in multiple sclerosis (MS) by several lines of evidence. In the present study, we have defined the T cell receptor (TCR) contact residues for DR2a-restricted, (87-99)-specific T helper type 1 T cells to design APL suitable to modify the functions of such T cells potentially relevant for the pathogenesis of MS. We show that neutral (L-alanine substitutions) or conservative exchanges of the primary and secondary TCR contact residues lead to various alterations of T cell function, ranging from differences in interleukin-2 receptor up-regulation to anergy induction and TCR antagonism. The potential usefulness of APL as an immunomodulating therapy for DR2+ MS patients is discussed.

Human CD8+ T lymphocyte subsets that express HLA class I-specific inhibitory receptors represent oligoclonally or monoclonally expanded cell populations

A small percentage of human T lymphocytes, predominantly CD8+ T cells, express receptors for HLA class 1 molecules of natural killer type (NK-R) that are inhibitory for T-cell antigen receptor (TCR)-mediated functions. In the present study, it is demonstrated that the various NK-R molecules typically expressed by NK cells are also expressed on periheral blood T lymphocytes. These CD3+ NK-R+ cells have a cell surface phenotype typical of memory cells as indicated by the expression of CD45RO and CD29 and by the lack of CD28 and CD45RA. Furthermore, by the combined use of anti-TCR V beta-specific antibodies and a semiquantitative polymerase chain reaction assay, the TCR repertoire in this CD3+ NK-R+ cell subset was found to be skewed; in fact, one or two V beta families were largely represented, and most of the other V beta s were barely detected. In addition, analysis of recombinant clones of the largely represented V beta families demonstrated that these V beta s were oligoclonally or monoclonally expanded.