The TCR repertoire of an immunodominant CD8+ T lymphocyte population

The TCR repertoire of an epitope-specific CD8(+) T cell population remains poorly characterized. To determine the breadth of the TCR repertoire of a CD8(+) T cell population that recognizes a dominant epitope of the AIDS virus, the CD8(+) T cells recognizing the tetrameric Mamu-A*01/p11C(,CM) complex were isolated from simian immunodeficiency virus (SIV)-infected Mamu-A*01(+) rhesus monkeys. This CD8(+) T cell population exhibited selected usage of TCR V beta families and complementarity-determining region 3 (CDR3) segments. Although the epitope-specific CD8(+) T cell response was clearly polyclonal, a dominance of selected V beta(+) cell subpopulations and clones was seen in the TCR repertoire. Interestingly, some of the selected V beta(+) cell subpopulations and clones maintained their dominance in the TCR repertoire over time after infection with SIV of macaques. Other V beta(+) cell subpopulations declined over time in their relative representation and were replaced by newly evolving clones that became dominant. The present study provides molecular evidence indicating that the TCR repertoire shaped by a single viral epitope is dominated at any point in time by selected V beta(+) cell subpopulations and clones and suggests that dominant V beta(+) cell subpopulations and clones can either be stable or evolve during a chronic infection.     

Oligoclonality of CD8+ T cells in breast cancer patients.

Substantial evidence has suggested that T cells play an important role in antitumor immunity. T cells with cytotoxic activity against tumors have been isolated from in vitro culture of tumor-infiltrated lymphocytes of cancer patients. In addition, clonal expansions of T cells have been identified in lesions of tumors by using a PCR-based CDR3 analysis of T cell receptors (TCR). Since the CDR3 region of the T cell receptor directly interacts with the antigen-MHC complex and is thus highly polymorphic, a dominant CDR3 length in a particular TCR V beta population will indicate the clonal expansion of a specific T cell clone. Utilizing this technique, we have analyzed the T cell repertoire in lymph nodes (LNs) and peripheral blood of 20 breast cancer patients. Our results show that in most cases, peripheral blood mononuclear cells (PB-MCs) and LN express dominant CD8+ T cell clones in different V beta gene families, and the number of dominant clones is higher in PBMC than in the LN. Furthermore, in 7 out of 16 patients' lymph nodes, there is a dominant V beta 18 T cell clonal expansion in the CD8+ T cell subset. The frequency of an oligoclonal expansion of V beta 18 CD8+ T cells in non-breast cancer lymph nodes is 1 out of 9, but no obvious motif in the CDR3 region of V beta 18 TCR can be identified. The prevalence of the clonal dominance found in breast cancer is discussed in the context of a possible tumor-related antigen stimulation.     

Lack of CD28 expression on HIV-specific cytotoxic T lymphocytes is associated with disease progression

During HIV infection, CD8+ T cells lacking the costimulatory molecule CD28 increase in number and proportion. This accumulation is associated with disease activity and possibly with CD8+ T-cell dysfunction. In this study, CD8+CD28+ and CD8+CD28- T cells from 41 HIV-infected individuals at various stages of disease were compared in terms of HIV-specific cytotoxicity, TCR beta V repertoire diversity, and cytokine production. We found that the CD28 phenotype of anti-HIV CTL evolves in parallel with disease progression and disease activity. Absolute numbers of CD4+ T cells and CD4+/CD8+ T-cell ratios progressively decreased in 3 groups with an increasing prevalence of CD28- HIV-specific CTL. Conversely, HIV replication levels progressively increased in parallel with the prevalence of CD28- HIV-specific CTL. Repertoire diversity at the level of TCR beta V gene family expression was maintained at normal levels for both CD28+ and CD28- T cells at all stages of infection. Diversity at the level of junctional length polymorphism was more restricted in the CD8+CD28- T-cell population, but this difference remained relatively constant through different stages of infection. Both CD28+ and CD28- T cells produced IL-2 and IFN-gamma, regardless of disease stage and/or the predominant CD28 phenotype of anti-HIV CTL.     

Contribution of T-cell receptor repertoire breadth to the dominance of epitope-specific CD8+ T-lymphocyte responses

Dominant epitope-specific CD8(+) T-lymphocyte responses play a central role in controlling viral spread. We explored the basis for the development of this focused immune response in simian immunodeficiency virus (SIV)- and simian-human immunodeficiency virus (SHIV)-infected rhesus monkeys through the use of two dominant (p11C and p199RY) and two subdominant (p68A and p56A) epitopes. Using real-time PCR to quantitate T-cell receptor (TCR) variable region beta (Vbeta) family usage, we show that CD8(+) T-lymphocyte populations specific for dominant epitopes are characterized by a diverse Vbeta repertoire, whereas those specific for subdominant epitopes employ a dramatically more focused Vbeta repertoire. We also demonstrate that dominant epitope-specific CD8(+) T lymphocytes employ TCRs with multiple CDR3 lengths, whereas subdominant epitope-specific cells employ TCRs with a more restricted CDR3 length. Thus, the relative dominance of an epitope-specific CD8(+) T-lymphocyte response reflects the clonal diversity of that response. These findings suggest that the limited clonal repertoire of subdominant epitope-specific CD8(+) T-lymphocyte populations may limit the ability of these epitope-specific T-lymphocyte populations to expand and therefore limit the ability of these cell populations to contribute to the control of viral replication.     

Clonal expansion of CD8+ effector T cells in childhood tuberculosis

The role of CD8(+) T cells in human tuberculosis (TB) remains elusive. We analyzed the T cell repertoire and phenotype in 1) children with active TB (< or =4 years), 2) healthy latently Mycobacterium tuberculosis-infected children, and 3) noninfected age-matched (tuberculin skin test-negative) controls. Ex vivo phenotyping of T cell subpopulations by flow cytometry revealed a significant increase in the proportion of CD8(+)CD45RO(-)CD62L(-)CD28(-)CD27(-) effector T cells (T(EF)) in the peripheral blood of children with active TB (22.1 vs 9.5% in latently M. tuberculosis-infected children, vs 8.5% in tuberculin skin test-negative controls). Analyses of TCR variable beta-chains revealed markedly skewed repertoires in CD8(+) T(EF) and effector memory T cells. Expansions were restricted to single TCR variable beta-chains in individual donors indicating clonal growth. CDR3 spectratyping and DNA sequencing verified clonal expansion as the cause for CD8(+) effector T cell enrichment in individual TB patients. The most prominent enrichment of highly similar T(EF) clones (>70% of CD8(+) T(EF)) was found in two children with active severe TB. Therefore, clonal expansion of CD8(+) T(EF) occurs in childhood TB with potential impact on course and severity of disease.     

Liver CD4-CD8- NK1.1+ TCR alpha beta intermediate cells increase during experimental malaria infection and are able to exhibit inhibitory activity against the parasite liver stage in vitro

Experimental infection of C57BL/6 mice by Plasmodium yoelii sporozoites induced an increase of CD4-CD8- NK1.1+ TCR alpha beta int cells and a down-regulation of CD4+ NK1.1+ TCR alpha beta int cells in the liver during the acute phase of the infection. These cells showed an activated CD69+, CD122+, CD44high, and CD62Lhigh surface phenotype. Analysis of the expressed TCRV beta segment repertoire revealed that most of the expanded CD4-CD8- (double-negative) T cells presented a skewed TCRV beta repertoire and preferentially used V beta 2 and V beta 7 rather than V beta 8. To get an insight into the function of expanded NK1.1+ T cells, experiments were designed in vitro to study their activity against P. yoelii liver stage development. P. yoelii-primed CD3+ NK1.1+ intrahepatic lymphocytes inhibited parasite growth within the hepatocyte. The antiplasmodial effector function of the parasite-induced NK1.1+ liver T cells was almost totally reversed with an anti-CD3 Ab. Moreover, IFN-gamma was in part involved in this antiparasite activity. These results suggest that up-regulation of CD4-CD8- NK1.1+ alpha beta T cells and down-regulation of CD4+ NK1.1+ TCR alpha beta int cells may contribute to the early immune response induced by the Plasmodium during the prime infection.     

Phenotype, ontogeny, and repertoire of CD4-CD8- T cell receptor alpha beta + thymocytes. Variable influence of self-antigens on T cell receptor V beta usage

We have characterized CD4-CD8- double negative (DN) thymocytes that express TCR-alpha beta and represent a minor thymocyte subpopulation expressing a markedly skewed TCR repertoire. We found that DN TCR-alpha beta + thymocytes resemble mature T cells in that they (a) are phenotypically CD2hiCD5hiQa2+HSA-, (b) appear late in ontogeny, and (c) are susceptible to cyclosporin A-induced maturation arrest. In addition, we found that DNA sequences 5' to the CD8 alpha gene were demethylated relative to their germline state, suggesting that DN TCR-alpha beta + thymocytes are derived from cells that had at one time expressed their CD8 alpha gene locus. Because DN TCR-alpha beta + thymocytes are known to express an unusual TCR repertoire with significant overexpression of V beta 8, we were interested in examining the possible role played by self-Ag in shaping their TCR repertoire. It has been suggested that DN TCR-alpha beta + thymocytes are derived from potentially self-reactive thymocytes that have escaped clonal deletion by down-regulating their surface expression of CD4 and/or CD8 determinants. However, apparently inconsistent with such an hypothesis, we found that the frequency of DN thymocytes expressing various anti-self TCR (V beta 6, V beta 8.1, V beta 11, V beta 17a) were not increased in strains expressing their putative self-Ag, but instead were either unaffected or significantly reduced in those strains. With regard to V beta 8 expression among DN TCR-alpha beta + thymocytes, V beta 8 overexpression in DN TCR-alpha beta + thymocytes appeared to be independent of, and superimposed on, the developmental appearance of the basic DN thymocyte repertoire. Even though V beta 8 overexpression appeared to be generated by a mechanism distinct from that generating the rest of the DN TCR-alpha beta + thymocyte repertoire, we found that super-Ag against which V beta 8 TCR react introduced into the neonatal differentiation environment also significantly reduced, rather than increased, the frequency of DN TCR-alpha beta + V beta 8+ thymocytes. Thus, the present study is consistent with DN TCR-alpha beta + thymocytes being mature cells derived from CD8+ precursors, and documents that their TCR repertoire can be influenced, at least negatively, by either self-Ag or Ag introduced into the neonatal differentiation environment. However, we found no evidence to support the hypothesis that DN TCR-alpha beta + thymocytes are enriched in cells expressing TCR reactive against self-Ag.     

Chronic modulation of the TCR repertoire in the lymphoid periphery

Using TCR V beta 5 transgenic mice as a model system, we demonstrate that the induction of peripheral tolerance can mold the TCR repertoire throughout adult life. In these mice, three distinct populations of peripheral T cells are affected by chronic selective events in the lymphoid periphery. First, CD4+V beta 5+ T cells are deleted in the lymphoid periphery by superantigens encoded by mouse mammary tumor viruses-8 and -9 in an MHC class II-dependent manner. Second, mature CD8+V beta 5+ T cells transit through a CD8lowV beta 5low deletional intermediate during tolerance induction by a process that depends upon neither mouse mammary tumor virus-encoded superantigens nor MHC class II expression. Third, a population of CD4-CD8-V beta 5+ T cells arises in the lymphoid periphery in an age-dependent manner. We analyzed the TCR V alpha repertoire of each of these cellular compartments in both V beta 5 transgenic and nontransgenic C57BL/6 mice as a function of age. This analysis revealed age-related changes in the expression of V alpha families among different cellular compartments, highlighting the dynamic state of the peripheral immune repertoire. Our work indicates that the chronic processes maintaining peripheral T cell tolerance can dramatically shape the available TCR repertoire.     

Intestinal CD8 alpha alpha and CD8 alpha beta intraepithelial lymphocytes are thymus derived and exhibit subtle differences in TCR beta repertoires

Intraepithelial lymphocytes (IEL) of the small intestine are anatomically positioned to be in the first line of cellular defense against enteric pathogens. Therefore, determining the origin of these cells has important implications for the mechanisms of T cell maturation and repertoire selection. Recent evidence suggests that murine CD8 alpha alpha intestinal IELs (iIELs) can mature and undergo selection in the absence of a thymus. We analyzed IEL origin by cell transfer, using two congenic chicken strains. Embryonic day 14 and adult thymocytes did not contain any detectable CD8 alpha alpha T cells. However, when TCR(+) thymocytes were injected into congenic animals, they migrated to the gut and developed into CD8alphaalpha iIELs, while TCR(-) T cell progenitors did not. The TCR V beta 1 repertoire of CD8 alpha alpha(+) TCR V beta 1(+) iIELs contained only part of the TCR V beta 1 repertoire of total iIELs, and it exhibited no new members compared with CD8(+) T cells in the thymus. This indicated that these T cells emigrated from the thymus at an early stage in their developmental process. In conclusion, we show that while CD8 alpha alpha iIELs originate in the thymus, T cells acquire the expression of CD8 alpha alpha homodimers in the gut microenvironment.     

Generation of CD4(+)CD25(+) regulatory T cells from autoreactive T cells simultaneously with their negative selection in the thymus and from nonautoreactive T cells by endogenous TCR expression

Normal T cell repertoire contains regulatory T cells that control autoimmune responses in the periphery. One recent study demonstrated that CD4(+)CD25(+) T cells were generated from autoreactive T cells without negative selection. However, it is unclear whether, in general, positive selection and negative selection of autoreactive T cells are mutually exclusive processes in the thymus. To investigate the ontogeny of CD4(+)CD25(+) regulatory T cells, neo-autoantigen-bearing transgenic mice expressing chicken egg OVA systemically in the nuclei (Ld-nOVA) were crossed with transgenic mice expressing an OVA-specific TCR (DO11.10). Ld-nOVA x DO11.10 mice had increased numbers of CD4(+)CD25(+) regulatory T cells in the thymus and the periphery despite clonal deletion. In Ld-nOVA x DO11.10 mice, T cells expressing endogenous TCR alpha beta chains were CD4(+)CD25(-) T cells, whereas T cells expressing autoreactive TCR were selected as CD4(+)CD25(+) T cells, which were exclusively dominant in recombination-activating gene 2-deficient Ld-nOVA x DO11.10 mice. In contrast, in DO11.10 mice, CD4(+)CD25(+) T cells expressed endogenous TCR alpha beta chains, which disappeared in recombination-activating gene 2-deficient DO11.10 mice. These results indicate that part of autoreactive T cells that have a high affinity TCR enough to cause clonal deletion could be positively selected as CD4(+)CD25(+) T cells in the thymus. Furthermore, it is suggested that endogenous TCR gene rearrangement might critically contribute to the generation of CD4(+)CD25(+) T cells from nonautoreactive T cell repertoire, at least under the limited conditions such as TCR-transgenic models, as well as the generation of CD4(+)CD25(-) T cells from autoreactive T cell repertoire.     

Virus-specific CD8+ T-cell responses in mice transgenic for a T-cell receptor beta chain selected at random.

The consequences of severely limiting the T-cell receptor (TCR) repertoire available for the response to intranasal infection with an influenza A virus or with Sendai virus have been analyzed by using H-2k mice (TG8.1) transgenic for a TCR beta-chain gene (V beta 8.1D beta 2J beta 2.3C beta 2). Analyzing the prevalence of V beta 8.1+ CD8+ T cells in lymph node cultures from nontransgenic (non-TG) H-2k controls primed with either virus and then stimulated in vitro with the homologous virus or with anti-CD3 epsilon showed that this TCR is not normally selected from the CD8+ T-cell repertoire during these infections. However, the TG8.1 mice cleared both viruses and generated virus-specific effector cytotoxic T lymphocytes (CTL) and memory CTL precursors, though the responses were delayed compared with the non-TG controls. Depletion of the CD4+ T-cell subset had little effect on the course of influenza virus infection but substantially slowed the development of the Sendai virus-specific CTL response and virus elimination in both the TG8.1 and non-TG mice, indicating that CD4+ helpers are promoting the CD8+ T-cell response in the Sendai virus model. Even so, restricting the available T-cell repertoire to lymphocytes expressing a single TCR beta chain still allows sufficient TCR diversity for CD8+ T cells (acting in the presence or absence of the CD4+ subset) to limit infection with an influenza A virus and a parainfluenza type 1 virus.     

Limited T cell receptor diversity of transplacentally acquired maternal T cells in severe combined immunodeficiency.

Circulating maternal T lymphocytes were noted in the peripheral blood of six patients with severe combined immunodeficiency. Phenotypical analyses revealed the presence of both CD4 and CD8 subsets in some but not all cases. The maternal T cells could be stimulated by anti-TCR/CD3 mAb +/- rIL-2, but were virtually silent in the MLR and against the recall Ag purified protein derivative of tuberculin and tetanus toxoid, even in immunized patients engrafted with T cells from a responding mother. Using a panel of mAb against TCR V region gene encoded epitopes including V beta 5, V beta 6, V beta 8, V beta 12, and V alpha 2, we show that maternal T cells displayed a profoundly reduced TCR diversity, characterized by a lack of one or even several TCR V subsets in all six cases and a dramatic (5- to 25-fold) expansion of other TCR V subsets in three cases. In one patient analyzed, limited TCR diversity was also seen in T cells cultured from bone marrow and skin; restimulation experiments of these cells against cells expressing host MHC Ag were unsuccessful, as were attempts to exclusively allocate anti-host proliferative responses of maternal control T cells to the TCR V subsets that had undergone expansion in vivo. We conclude that a severely reduced TCR diversity is a common feature of maternal T cells engrafted in severe combined immunodeficiency patients. These novel findings provide a structural basis to understand the failure of these cells to protect the host from infections and may also help to understand their relative inefficiency to induce lethal, multi-organ, graft vs host disease. Moreover, as an experiment of nature, the reported phenomenon clearly illustrates the functional consequences in vivo of an insufficient TCR diversity.     

Clonal CD8+ T Cell Persistence and Variable Gene Usage Bias in a Human Transplanted Hand

Immune prophylaxis and treatment of transplanted tissue rejection act indiscriminately, risking serious infections and malignancies. Although animal data suggest that cellular immune responses causing rejection may be rather narrow and predictable based on genetic background, there are only limited data regarding the clonal breadth of anti-donor responses in humans after allogeneic organ transplantation. We evaluated the graft-infiltrating CD8⁺ T lymphocytes in skin punch biopsies of a transplanted hand over 178 days. Profiling of T cell receptor (TCR) variable gene usage and size distribution of the infiltrating cells revealed marked skewing of the TCR repertoire indicating oligoclonality, but relatively normal distributions in the blood. Although sampling limitation prevented complete assessment of the TCR repertoire, sequencing further identified 11 TCR clonal expansions that persisted through varying degrees of clinical rejection and immunosuppressive therapy. These 11 clones were limited to three TCR beta chain variable (BV) gene families. Overall, these data indicate significant oligoclonality and likely restricted BV gene usage of alloreactive CD8⁺ T lymphocytes, and suggest that changes in rejection status are more due to varying regulation of their activity or number rather than shifts in the clonal populations in the transplanted organ. Given that controlled animal models produce predictable BV usage in T lymphocytes mediating rejection, understanding the determinants of TCR gene usage associated with rejection in humans may have application in specifically targeted immunotherapy.     

A T cell receptor V alpha region selectively expressed in CD4+ cells.

The peripheral TCR V beta repertoire is strongly influenced by the processes of negative selection (deletion) and positive selection in the thymus. In order to investigate whether such selection events influence the V alpha repertoire, we have produced an anti-V alpha 11 mAb. This antibody was made by immunization with a chimeric TCR:Ig protein containing V alpha 11 in place of the VH of an IgG2a, lambda Ig. This scheme optimizes the specificity of immunization and facilitates the screening procedure. The antibody recognizes a panel of V alpha 11-expressing T cell clones. Analysis of mouse strains indicates that the antibody recognizes V alpha 11 only in mice of the C57 background. The expression of the epitope on peripheral T cells is strongly biased to the CD4+ subset, suggesting positive selection of V alpha 11 on class II MHC molecules. In some strain comparisons, the percentage of V alpha 11-expressing T cells in the CD4+ subset was elevated in I-E+ relative to I-E- strains. These data suggest that V alpha 11 can differentially influence the selection of T cells into the CD4+/CD8+ subsets.     

Thymic selection defines multiple T cell receptor V beta 'repertoire phenotypes' at the CD4/CD8 subset level

We describe here the use of a sensitive and accurate multiprobe V beta RNase protection assay in characterizing the expression levels of 17 V beta genes in separated CD4+ and CD8+ subsets of selected mouse strains. The IE-reactive V beta genes (V beta s 11, 12, 5.1 and 16) showed various patterns of skewed subset expression in different strains, suggesting additional influences of IA, class I, and non-MHC genes in the selection process. Clonal deletion of V beta 11- and V beta 12-bearing T cells, among others, was skewed strongly towards the CD4+ subset in many IE+ mouse strains, supporting the notion that negative selection can cause incomplete, subset biased, V beta clonal deletions. Broad analysis in separated CD4+ and CD8+ subsets gave improved resolution of V beta repertoire selection, and revealed significant strain and/or subset specific skewing for additional V beta genes; with consistent bias towards higher expression of V beta 7 and V beta 13 in the CD8+ subset, and V beta 15 in the CD4+ subset of most mouse strains. The influence of diverse non-MHC ligands in V beta repertoire selection was further illustrated by the identification of unique V beta repertoires for six different MHC-identical (H2k) strains. Such polymorphisms in TCR repertoire expression may help to define better disease susceptibility phenotypes.     

HIV replication leads to skewed maturation of CD8-positive T-cell responses in infected children

HIV-1 infection causes a severe T-cell impairment with alteration of immune response. However, in children the natural decline of lymphocytes and CD4 cells in early life makes it more difficult to monitor immunocompetence and progression of HIV-infection. Aim of this study was to characterize the CD8 response in non-vertically HIV-infected children exposed persistently to viremia and in HIV-infected children controlling efficiently viremia by ART, by analysing the effect of persistent viremia on CD4 and CD8 T-cells count, HIV-specific immune-response and naive/memory pattern of CD8 T-cell. Whereas, no differences of CD4 count between viremic patients and viral controllers were observed (1046.9 +/- 472.1 cells/microl vs 1101.3 +/- 415.4 cells/microl; p > 0.05), CD8 count was higher in the viremic patients (1080.6 +/- 652.1 cells/microl vs 747.5 +/- 389.9 cells/microl, p < 0.05). In viremic patients, HIV-specific CD8 T-cells correlated with viral load. However, in this group a loss of HIV-specific CD8 response was associated with a 7 fold decrease of na?ve and increase of pre-effector CD8 T-cells (62.8% +/- 10.21% vs 10.37% +/- 7.91%, p < 0.03). Persistent exposure to viremia alters HIV-specific CD8 response possibly through a persistent immune activation process leading to exhaustion of naive CD8 T-cells and skewed maturation of memory subset. Therefore, memory CD8 T-cells might lose the ability to respond correctly and efficiently to HIV-antigen exposure.     

The repertoire of CD4+ CD28- T cells in rheumatoid arthritis.

BACKGROUND: While oligoclonality of circulating CD4- CD8 and of CD8+ T cells is not uncommon, clonal dominance within the CD4 compartment is not frequently found in healthy individuals. In contrast, the majority of patients with rheumatoid arthritis (RA) have clonally expanded CD4+ T cell populations. Previous studies have demonstrated that these clonogenic CD4+ T cells do not express the CD28 molecule. To examine the correlation between CD28 expression and clonal proliferation, we have analyzed the T cell receptor (TCR) diversity of CD4+ CD28- T cells in normal individuals and in RA patients. MATERIAL AND METHODS: The size of the peripheral blood CD4+ CD28- compartment was determined in 30 healthy individuals and 30 RA patients by two-color FACS analysis. In 10 RA patients and five controls with more than 2.5% CD4+ CD28- T cells, TCR BV gene segment usage was analyzed with 19 BV-specific antibodies. Oligoclonality was assessed in sorted CD4+ CD28+ and CD28- T cells using TCR BV-BC-specific polymerase chain reaction and size fractionation. Clonal dominance was confirmed by direct sequencing. RESULTS: The CD4+ CD28- T cell compartment was expanded to more than 2.5% in 70% of the RA patients and 30% of the normal individuals. Compared with the CD4+ CD28+ T cells, the TCR BV gene segment usage among CD4+ CD28- cells was grossly skewed with the dominance of single BV elements. Molecular TCR analysis provided evidence for oligoclonality in 17 of 21 expanded BV elements. In two unrelated RA patients who shared both HLA-DRB1 alleles, the TCR beta-chain sequences of dominant clonotypes were highly conserved. CONCLUSIONS: Oligoclonality is a characteristic feature of CD4+ CD28- T cells which are expanded in some healthy individuals and in the majority of RA patients. The lack of CD28 expression is a common denominator of CD4+, CD8+, and CD4- CD8- T cells prone to develop clonal dominance. The limited TCR diversity of clonal CD4+ CD28- populations in RA patients suggests that these T cells recognize a limited spectrum of antigens. The fact that the majority of individuals with marked expansions and oligoclonality of CD4+ CD28- T cells are RA patients suggests a role for these unusual lymphocytes in the pathogenetic events leading to RA.     

Impaired clonal expansion in athymic nude CD8+CD4- T cells

A comparative study of the phenotype and immune functions of highly purified CD8+CD4- T cells obtained from the spleen and thymus of normal mice and from the spleen of athymic nude mice was conducted. Of seven individual normal and nude mice examined, the range of V beta 8+ cells among CD8+ T cells was a heterogeneous 4.3 to 30.5% for athymic nude mice and a much more uniform spread from 14.7 to 18.5% for normal mice. In six of the seven nude mice examined, the fraction of V beta 8+ cells was below the lower limit of the V beta 8 distribution in normal mice. However, one of the seven nude mice contained nearly twice the percentage of normal V beta 8+ cells. A reduction in the density of V beta 8 as well as CD3 Ag expression was also observed in athymic CD8+CD4- cells although an Ly-6-linked Ag, B4B2 displayed a highly increased expression. Considering the battery of Ag analyzed in entirety, athymic CD8+CD4- T cells were clearly distinct from their "counterpart" CD8+CD4- T cells isolated from either thymus or spleen of normal (euthymic) mice. Anti-CD3-mediated triggering of the TCR:CD3 complex caused extensive clonal proliferation in cultures to which single responding CD8+ T cells had been deposited. Under identical conditions, however, anti-CD3 caused little, if any clonal expansion in CD8+ cells from athymic nude mice. Highly purified athymic CD8+CD4- cells produced readily detectable IL-2R expression and IL-2 synthesis and secretion upon stimulation by anti-CD3 and by Con A. Production of IL-2 by purified athymic CD8+CD4- cells was due to CD8+CD4- cells and not due to a minor population of contaminating CD8- cells as anti-CD8 + C treatment completely abrogated the ability of athymic CD8+CD4- cells to produce IL-2. Despite IL-2 production and IL-2R expression by athymic nude CD8+CD4- T cells in response to anti-CD3 and to Con A, an impaired proliferative response followed.