Analysis of the Conservation of T Cell Receptor Alpha and Beta Chain Variable Regions Gene in pp65 Peptide-Specific HLA-A＊0201-Restricted CD8^＋ T Cells

Many viral epitope specific T cell receptors （TCRs） in MHC-matched individuals have been demonstrated to involve conserved amino acid motifs in β chain complementarity-determining region 3 （CDR3）. However, it is not sure whether the conserved motifs can also be found in TCR β chain. In previous studies, we developed a modified method to enlarge the percentage of cytomegalovirus （CMV） pp65 peptide-specific CD8^＋ T cells in PBMC by continuous peptide stimulation in vitro, which provides sufficient number of specific T cells for detection. In this study, we further analyzed the restrictive usage of TCR Vα and Vβ gene families and investigated the CDR3 gene sequence of pp65 peptide-specific CD8β T cells. Analysis of CDR3 spectratypes suggested a restricted usage of TCR α chain AV8, AV12, AV21, AV31 families and TCR βchain BV3, BV14, BV21, BV23, BVll families in donor CD8^＋ T cells stimulated by pp65 peptide. The sequences of these T cells involved similar sequence （TX） G （X） A in CDR3 region of TCR α chain and L （XT） G （X） A in TCR β chain.     

Anti-Idiotypic Regulatory Responses Induced by Vaccination with DNA Encoding Murine TCR Vα5 and Vβ2

There is evidence suggesting that anti-idiotypic regulation against T cells plays a role in maintaining homeostasis in the immune system, although its mechanism is not fully understood. By using DNA constructs encoding the TCR Vα5.2 and Vβ2.1 chains derived from ：in ovalbumin （OVA）-specific T cdl clone （OVA-T）, we herein demonstrated that vaccination with TCR-DNA effectively induced anti-idiotypic cellular as well as humoral responses. Serum samples from the TCR-DNA-vaccinated BALB/c mice were able to stain T cells in an idiotype-specific manner. CD4^＋ T cells from the TCR-DNA-vaccinated mice proliferated in response to stimulation with irradiated syngeneic OVA-T calls and secreted interferon-y but very little IL-4. Splenocytes from the TCR-DNA-vaccinated mice showed strong idiotype-specific CTL activity against the OVA-T cdls. Furthermore, adoptive transfer of the CD4^＋ or CD8^＋ T cells from the TCR-DNA-vaccinated mice resulted in hyporesponsiveness of syngeneic recipients. These results demonstrated that vaccination with DNA encoding TCR can effectively activate anti-idiotypic regulatory responses in vivo and thus providing a useful way for immunological intervention.     

Naturally Occurring Self-Reactive CD4^＋CD25^＋ Regulatory T Cells： Universal Immune Code

Naturally occurring thymus-arisen CD4^＋CD25^＋ regulatory T （Treg） cells are considered to play a central role in self-tolerance. Precise signals that promote the development of Treg cells remain elusive, but considerable evidence suggests that costimulatory molecules, cytokines, the nature of the TCR and the niche or the context in which the T cell encounters antigen in the thymus play important roles. Analysis of TCR from Treg cells has demonstrated that a large proportion of this population has a higher avidity to self-antigen in comparison with TCR from CD4^＋CD25^＋ cells and that peripheral antigen is required for their development, maintenance, or expansion. Treg cells have been shown to undergo expansion in the periphery, likely regulated by the presence of self-antigen. Many studies have shown that the involvement of Treg cells in the tolerance induction is antigen-specific, even with MHC-mismatched, in transplantation/graft versus host disease （GVHD）, autoimmunity, cancer, and pregnancy. Theses studies concluded a vital role for self-reactive Treg cells in maintenance of the body integrity. Based on those studies, we hypothesize that self-reactive Treg cells are shared among all healthy individuals and recognize same self-antigens and their TCR encodes for few dominant antigens of each organ which defines the healthy self. These dominant self antigens can be regarded as ＂universal immune code＂. Cellular ＆ Molecular Immunology.     

伴颈动脉粥样硬化脑梗患者CD4+CD28null T细胞CD158j表达和ERK磷酸化水平的关系

Objective To investigate the relationship between CD158j expression and phosphorylated ERK (p-ERK) in CD4+ CD28null T cells in cerebral infarction (CI) patients- with carotid atherosclerosis and its effects on carotid atherosclerotic plaque stability. Methods Percentage of peripheral CD4+ CD28null and the expression of CD158j and perform on CD4+ CD28null cells was analyzed with flow cytometry in 106 CI patients with carotid atherosclerosis, 33 CI patients with normal carotid arteries and in 50 normal controls, respectively; p-ERK expression was assayed with flow cytometry in 36 CI patients with unstable plaque, and serum IFN-γ was detected with ELISA. The intima-media thickness (IMT) of bilateral carotid arteries in all subjects was confirmed by the colour Doppler ultrasonograph imagingResults Percentage of the CD4+ CD28null T cells, expression of CD158j and perform on CD4+ CD28null T cells and the serum IFN-γ levels was dramatically higher in CI patients than that in normal controls, respectively (all P <0.01), which was decreased in an order of CI patients with patients with unstable plaque, stable plaque, carotid artery IMT and with normal carotid artery. A strong positive correlation was observed between the CD158j expression and degree of p-ERK in CI patients with unstable plaque (P < 0. 01). Conclusion CD4+ CD28null T cells were significantly increased in CI patients with carotid atherosclerosis. CD158j might up-regulate p-ERK expression and induce the proliferation of the CD4+ CD28nullT cells; consequently, higher cytokine production such as IFN-γ produced by CD4+ CD28null T cells may cause the formation of unstable plaque.     

伴颈动脉粥样硬化脑梗患者CD4+CD28null T细胞CD158j表达和ERK磷酸化水平的关系

Objective To investigate the relationship between CD158j expression and phosphorylated ERK (p-ERK) in CD4+ CD28null T cells in cerebral infarction (CI) patients- with carotid atherosclerosis and its effects on carotid atherosclerotic plaque stability. Methods Percentage of peripheral CD4+ CD28null and the expression of CD158j and perform on CD4+ CD28null cells was analyzed with flow cytometry in 106 CI patients with carotid atherosclerosis, 33 CI patients with normal carotid arteries and in 50 normal controls, respectively; p-ERK expression was assayed with flow cytometry in 36 CI patients with unstable plaque, and serum IFN-γ was detected with ELISA. The intima-media thickness (IMT) of bilateral carotid arteries in all subjects was confirmed by the colour Doppler ultrasonograph imagingResults Percentage of the CD4+ CD28null T cells, expression of CD158j and perform on CD4+ CD28null T cells and the serum IFN-γ levels was dramatically higher in CI patients than that in normal controls, respectively (all P <0.01), which was decreased in an order of CI patients with patients with unstable plaque, stable plaque, carotid artery IMT and with normal carotid artery. A strong positive correlation was observed between the CD158j expression and degree of p-ERK in CI patients with unstable plaque (P < 0. 01). Conclusion CD4+ CD28null T cells were significantly increased in CI patients with carotid atherosclerosis. CD158j might up-regulate p-ERK expression and induce the proliferation of the CD4+ CD28nullT cells; consequently, higher cytokine production such as IFN-γ produced by CD4+ CD28null T cells may cause the formation of unstable plaque.     

Homeostasis of T cell diversity

T cell homeostasis commonly refers to the maintenance of relatively stable T cell numbers in the peripherallymphoid organs.Among the large numbers of T cells in the periphery,T cells exhibit structural diversity,i.e.,theexpression of a diverse repertoire of T cell receptors(TCRs),and functional diversity,i.e.,the presence of T cells atnave,effector,and memory developmental stages.Although the homeostasis of T cell numbers has been extensivelystudied,investigation of the mechanisms underlying the maintenance of structural and functional diversity of Tceils is still at an early stage.The fundamental feature throughout T cell development is the interaction between theTCR and either self or foreign peptides in association with MHC molecules.In this review,we present evidenceshowing that homeostasis of T cell number and diversity is mediated through competition for limiting resources.The number of T cells is maintained through competition for limiting cytokines,whereas the diversity of T cells ismaintained by competition for self-peptide-MHC complexes.In other words,diversity of the self-peptide repertoirelimits the structural(TCR)diversity of a T cell population.We speculate that cognate low affinity self-peptides,acting as weak agonists and antagonists,regulate the homeostasis of T cell diversity whereas non-cognate or nullpeptides which are extremely abundant for any given TCR,may contribute to the homeostasis of T cell number byproviding survival signals.Moreover,self-peptides and cytokines may form specialized niches for the regulation ofT cell homeostasis.Cellular & Molecular Immunology.2005;2(1):1-10.     

CD40 interacts directly with RAG1 and RAG2 in autoaggressive T cells and Fas prevents CD40-induced RAG expression

CD4＋ T cells expressing CD40 （Th40 cells） constitute a pathogenic T-cell subset that is necessary and sufficient to transfer autoimmune disease. We have previously demonstrated that CD40 signals peripheral Th40 cells to induce RAG1 and RAG2 expression, proteins necessary for the expression of T-cell receptor （TCR）, leading to TCR revision. The dependency of TCR expression in the thymus on RAG proteins has long been known. However, despite numerous publications, there is controversy as to whether TCR expression can be altered in the periphery, post-thymic selective pressures. Therefore, a better understanding of TCR expression in primary peripheral cells is needed. We now show that the CD40 protein itself interacts with RAG1 and RAG2 as well as with Ku70 and translocates to the nucleus in Th40 cells. This indicates that the CD40 molecule is closely involved in the mechanism of TCR expression in the periphery. In addition, Fas signals act as a silencing mechanism for CD40-induced RAGs and prevent CD40 translocation to the nucleus. It will be important to further understand the involvement of CD40 in peripheral TCR expression and how TCR revision impacts auto-antigen recognition in order to effectively target and tolerize autoaggressive T cells in autoimmune disease.     

Critical role of butyrophilin 3A1 in presenting preny pyrophosphate antigens to human y~ T cells

Tlymphocytes recognize antigen via the heterodimeric T-cell receptor（TCR） which is closely associated with the signal-transducing CD3 complex. αβ TCR-expressing T cells recognize peptides presented by MHC class II （for CD4＋ T cells） or MHC class I molecules （for CD8＋ T cells）. In striking contrast, the majority of human y8 T cells expres- sing the Vy9V82-encoded TCR recog- nize small non-peptidic phosphorylated ligands which have been identified as pyrophosphate intermediates of micro- bial and eukaryotic isoprenoid synthesis.     

Altered allogeneic immune responses in middle-aged mice

It is well known that leukocyte composition,T cell phenotypes and immune function change in aged mice andhumans.However,limited and conflicting results on the age-related immune changes in middle-aged mice werereported.Identification of the characteristics of allogeneic immune responses in aging mice may offerimportant information for transplantation immunology.The major age-related changes in the immune cellphenotypes and function of 12 months old mice include:1)the significantly decreased CD4~+ cell population inthe peripheral blood,the major peripheral CD4~+ cells is CD45RB~(low)CD62L~(low)memory phenotype;2)the invitro responses to alloantigens and Con A of splenocytes markedly reduced;3)the in vivo secondary humoralimmune responses to alloantigens significantly declined;4)the age-related alteration in the thymus mainlyoccurred in CD4/CD8 double positive(DP)stage;and 5)increased CD80~+ and MHC class II~+ cell population inspleens.Thus,the major age-related immune changes in 12 months old mice occurred in CD4~+ T cells in theperiphery and DP stage in the thymus,which may subsequently lead to the decreased allogeneic immuneresponses and the different sensitivity to immunosuppressive drugs and treatments.Further studies on thecharacteristics of allogeneic immunity in aging individuals may help to determine the appropriated treatmentfor transplant aging individuals.Cellular & Molecular Immunology.2004;1(6):440-446.     

Evidence for the persistence of monoclonal expansions of CD8+ T cells following primary simian immunodeficiency virus infection

A longitudinal study of the CD8⁺ TCR variable (Vβ) chain repertoire was performed in rhesus macaques experimentally infected with simian immunodeficiency virus (SIV) using both TCR Vβ chain-specific monoclonal antibodies and TCR β chain CDR3 length analysis. Expansions of subpopulations of CD8⁺ T cells were detected during the acute phase of SIV infection. In all monkeys studied, monoclonal expansions persisted for at least 18 months and increasingly dominated the repertoire of CD8⁺ T cells expressing the relevant Vβ chain. This study shows that persistent CD8⁺ T cell expansions develop in response to a virus infection. This is important not only for our understanding of the T cell response to viruses but also for understanding the factors that determine the normal CD8⁺ TCR repertoire.     

TCRBV CDR3 diversity of CD4+ and CD8+ T-lymphocytes in HIV-infected individuals

TCRBV CDR3 repertoire diversity was analyzed in a cross-sectional study of HIV-infected individuals by CDR3 fingerprinting/spectratyping and single strand conformation polymorphism (SSCP). Most TCRBV families were detected in CD4+ cells of HIV-infected patients with CD4 counts ranging from 35 to 1103. In patients with CD4 counts >500, CD4+ TCRBV CDR3 fingerprinting profiles contained subtle variations with generally gaussian-distributed sizes. Lower CD4 counts coincided with more fragmented TCRBV CDR3 repertoires, containing dominant bands and bands missing from the CDR3 profiles. The CD8+ population of the same patients exhibited skewed CDR3 profiles of the majority of TCR BV families at CD4 counts >500. Irregularity of CD8+ CDR3 size distribution was most profound at low CD4 counts and suggested domination of the CD8+ TCRBV repertoire by a limited number of clones. Skewed patterns of CDR3 diversity probably reflect (oligo)clonal expansion of particular CD4+ and CD8+ cell populations during chronic infection with HIV. In addition, irregular CDR3 profiles of CD4+ and CD8+ at low CD4 counts suggest diminished TCR repertoire diversity, which may contribute to immunodeficiency.     

肿瘤患者胸/腹水和外周血中TCR Vβ亚家族表达及调节性T细胞亚群的研究

目的:探讨肿瘤患者胸/腹水中肿瘤浸润性淋巴细胞(TIL)和外周血T细胞中T细胞受体(TCR)Vβ亚家族的表达变化情况、CD4/CD8细胞比例变化和Treg细胞的分布情况,分析肿瘤患者的免疫状态。方法:分离11例肿瘤患者胸/腹水和外周血以及4例健康人外周血的T细胞,采用流式方法检测Vβ24个亚家族及CD3、CD4、CD8、CD25、CD127的表达情况,统计分析T细胞中Vβ24个亚家族、Treg细胞的特点。结果:TCR Vβ亚家族的表达在肿瘤患者胸/腹水TIL中与血液淋巴细胞中存在着显著差异,其中肺癌患者(4/5)TIL中TCR Vβ8,结肠癌患者(3/4)TIL中TCR Vβ2等亚家族显著高表达;11例肿瘤患者胸/腹水样本中Treg的比例均比外周血高(P<0.05),其中5例肺癌患者胸腹水中CD8+T细胞比例降低。结论:肿瘤患者胸/腹水中的淋巴细胞TCR Vβ亚家族表达与外周血存在差异,表明肿瘤患者体内淋巴细胞发生了明显的优势取用和定向趋化。此外肿瘤微环境可能影响了TIL中CD4+细胞的分化导致胸腹水中Treg细胞的比例升高,同时伴随着CD8+T比例的下降,并可能因此影响到TIL中TCR Vβ亚家族的优势取用情况,且导致免疫耐受。     

Analysis of T cell receptor Vβ diversity in peripheral CD4+ and CD8+ T lymphocytes in patients with autoimmune thyroid diseases

Autoimmune thyroid diseases are characterized by intrathyroidal infiltration of CD4⁺ and CD8⁺ T lymphocytes reactive to self‐thyroid antigens. Early studies analysing T cell receptor (TCR) Vα gene usage have shown oligoclonal expansion of intrathyroidal T lymphocytes but not peripheral blood T cells. However, TCR Vβ diversity of the isolated CD4⁺ and CD8⁺ T cell compartments in the peripheral blood has not been characterized fully in these patients. We performed complementarity‐determining region 3 (CDR3) spectratyping as well as flow cytometric analysis for the TCR Vβ repertoire in peripheral CD4⁺ and CD8⁺ T cells from 13 patients with Graves' disease and 17 patients with Hashimoto's thyroiditis. Polyclonal TCR Vβ repertoire was demonstrated by flow cytometry in both diseases. In contrast, CDR3 spectratyping showed significantly higher skewing of TCR Vβ in peripheral CD8⁺ T cells but not CD4⁺ T cells among patients with Hashimoto's thyroiditis compared with healthy adults. We found trends towards a more skewed CDR3 size distribution in those patients having disease longer than 5 years and requiring thyroid hormone replacement. Patients with Graves' disease exhibited no skewing both in CD4⁺ and CD8⁺ T cells. These findings indicate that clonal expansion of CD8⁺ T cells in Hashimoto's thyroiditis can be detected in peripheral blood and may support the role of CD8⁺ T cells in cell‐mediated autoimmune attacks on the thyroid gland in Hashimoto's thyroiditis.     

T-Cell receptor Vbeta repertoire CDR3 length diversity differs within CD45RA and CD45RO T-cell subsets in healthy and human immunodeficiency virus-infected children

The T-cell receptor (TCR) CDR3 length heterogeneity is formed during recombination of individual Vbeta gene families. We hypothesized that CDR3 length diversity could be used to assess the fundamental differences within the TCR repertoire of CD45RA and CD45RO T-cell subpopulations. By using PCR-based spectratyping, nested primers for all 24 human Vbeta families were developed to amplify CDR3 lengths in immunomagnetically selected CD45RA and CD45RO subsets within both CD4(+) and CD8(+) T-cell populations. Umbilical cord blood mononuclear cells or peripheral blood mononuclear cells obtained from healthy newborns, infants, and children, as well as human immunodeficiency virus (HIV)-infected children, were analyzed. All T-cell subsets from newborn and healthy children demonstrated a Gaussian distribution of CDR3 lengths in separated T-cell subsets. In contrast, HIV-infected children had a high proportion of predominant CDR3 lengths within both CD45RA and CD45RO T-cell subpopulations, most commonly in CD8(+) CD45RO T cells. Sharp differences in clonal dominance and size distributions were observed when cells were separated into CD45RA or CD45RO subpopulations. These differences were not apparent in unfractionated CD4(+) or CD8(+) T cells from HIV-infected subjects. Sequence analysis of predominant CDR3 lengths revealed oligoclonal expansion within individual Vbeta families. Analysis of the CDR3 length diversity within CD45RA and CD45RO T cells provides a more accurate measure of disturbances in the TCR repertoire than analysis of unfractionated CD4 and CD8 T cells.     

Shortening of complementarity determining region 3 of the T cell receptor α chain during thymocyte development

TCR diversity depends mainly on the hypervariable complementarity determining region 3 (CDR3) α and β loops generated by non-germline-encoded nucleotide insertions and/or deletions. It is known that the length of the CDR3β sequence shortens during the process of thymocyte development and that the extent of this shortening is strongly affected by germline-encoded Vβ segments or MHC haplotypes. To examine whether CDR3α shortens to the same extent as CDR3β and how it is affected by Vα segments or MHC haplotypes, we analyzed CDR3α length distributions in thymic CD4+CD8+ (DP), CD4+CD8− (CD4SP) and CD4−CD8+ (CD8SP) T cells of different strains of mice (C57BL/6, C.B10 and Balb/c). As expected, CDR3α shortening occurred in both the CD4SP and CD8SP cells of all strains tested and the extent of shortening varied considerably depending on Vα segment use. However, there was no correlation in the extent of CDR3α shortening in individual Vα segments between CD4SP and CD8SP cells. Interestingly, there was a significant correlation in the extent of CDR3α shortening among different strains of mice only in CD4SP but not CD8SP cells, independent of MHC haplotype. These results suggest that the extent of CDR3α shortening is primarily determined by germline-encoded Vα segments and affected by allelic variation of MHC class I but not of MHC class II. The present study showed that T cells with shorter CDR3α sequences are preferably selected for the functional TCR repertoire during thymocyte development, and this provides an intriguing insight into the interactions of the TCR and p-MHC ligand.     

识别猪SLA的特异性人T细胞系TCR BV基因取用格局和CDR3结构多样性分析

不同T细胞克隆TCR分子的序列不同 ,所识别的抗原特异性也不同。其中第三互补决定区 (CDR3)变异最大 ,是TCR主要的抗原结合部位。本文采用荧光标记半定量PCR技术 ,用DNA测序仪作程序分析 ,了解猪细胞抗原致敏前后的人T细胞群和 5个T细胞系 2 4个TCRBV基因家族取用格局 ,并以TCRα链C区的基因片断作为内参对取用情况作定量估计。发现首次抗原致敏后培养 2周的T细胞除了BV2 4、BV8和BV10未能检测出 ,其它BV基因都有不同程度的取用。然而 ,5个细胞系的TCRBV基因呈现十分有限的取用格局 ,其中两个CD4+ T细胞系都取用BV12和BV14;3个CD8+ T细胞系中都优势取用BV1,有两个还取用BV19。CD4+ T细胞系和CD8+ T细胞系之间TCRBV无交叉取用 ,提示两类细胞识别的抗原表位存在差异。进一步用变性凝胶扫描分析上述T细胞系取用TCRBV中的CDR3的多样性 ,发现未经抗原致敏的T细胞BV的CDR3结构为多峰型且呈正态分布 ,表明涉及多种结构不同的细胞克隆 ;而抗原特异性T细胞系CDR3除了一个CD8+ T细胞系BV1有两个主峰外其它无例外地都显示单峰或者仅一个主峰 ,这从另一个角度证明建系T细胞的单克隆性。     

Quantitative analysis of T cell receptor diversity in clinical samples of human peripheral blood

The analysis of T cell receptor diversity provides a clinically relevant and sensitive marker of repertoire loss, gain, or skewing. Spectratyping is a broadly utilized technique to measure global TCR diversity by the analysis of the lengths of CDR3 fragments in each Vβ family. However the common use of large numbers of T cells to obtain a global view of TCR Vβ CDR3 diversity has restricted spectratyping analyses when limited T-cell numbers are available in clinical setting, such as following transplant regimens. We here demonstrate that one hundred thousand T cells are sufficient to obtain a robust, highly reproducible measure of the global TCR Vβ repertoire diversity among twenty Vβ families in human peripheral blood. We also show that use of lower cell number results not in a dwindling of observed diversity but rather in non-reproducible patterns in replicate spectratypes. Finally, we report here a simple to use but sensitive method to quantify repertoire divergence in patient samples by comparison to a standard repertoire profile we generated from fifteen normal donors. We provide examples using this method to statistically evaluate the changes in the global TCR Vβ repertoire diversity that may take place during T subset immune reconstitution after hematopoietic stem cell transplantation or after immune modulating therapies.     

TCRalphabeta repertoire diversity of human naturally occurring CD4+CD25+ regulatory T cells

We examined the alphabeta T cell receptor (TCR) repertoire of naturally occurring CD4+CD25+ regulatory T (Treg) cells isolated from healthy human blood. Three-color FACS analysis demonstrated that the usage of variable region segments of TCRbeta chains by CD4+CD25+ cells did not differ from those of CD4+CD25- cells. Complementarity-determining region 3 (CDR3) size distribution analyses demonstrated that the repertoire diversity of CDR3beta was almost identical between CD4+CD25+ and CD4+CD25- T cell subsets, and that there was no skewing of the CDR3beta repertoire of CD4+CD25+ T cells. In contrast, in vitro activated CD4+CD25+ T cells by cytomegalovirus-derived antigens showed a skewed CDR3 size distribution pattern. These findings support the hypothesis that naturally occurring CD4+CD25+ T cell subset in humans is 1argely composed of a T cell lineage positively selected in the thymus as a consequence of the interaction between self-peptides and TCRs and not derived from recent activation by a limited array of antigens.     

T-Cell Receptor Vβ Repertoire CDR3 Length Diversity Differs within CD45RA and CD45RO T-Cell Subsets in Healthy and Human Immunodeficiency Virus-Infected Children

The T-cell receptor (TCR) CDR3 length heterogeneity is formed during recombination of individual Vβ gene families. We hypothesized that CDR3 length diversity could be used to assess the fundamental differences within the TCR repertoire of CD45RA and CD45RO T-cell subpopulations. By using PCR-based spectratyping, nested primers for all 24 human Vβ families were developed to amplify CDR3 lengths in immunomagnetically selected CD45RA and CD45RO subsets within both CD4⁺ and CD8⁺ T-cell populations. Umbilical cord blood mononuclear cells or peripheral blood mononuclear cells obtained from healthy newborns, infants, and children, as well as human immunodeficiency virus (HIV)-infected children, were analyzed. All T-cell subsets from newborn and healthy children demonstrated a Gaussian distribution of CDR3 lengths in separated T-cell subsets. In contrast, HIV-infected children had a high proportion of predominant CDR3 lengths within both CD45RA and CD45RO T-cell subpopulations, most commonly in CD8⁺ CD45RO T cells. Sharp differences in clonal dominance and size distributions were observed when cells were separated into CD45RA or CD45RO subpopulations. These differences were not apparent in unfractionated CD4⁺ or CD8⁺ T cells from HIV-infected subjects. Sequence analysis of predominant CDR3 lengths revealed oligoclonal expansion within individual Vβ families. Analysis of the CDR3 length diversity within CD45RA and CD45RO T cells provides a more accurate measure of disturbances in the TCR repertoire than analysis of unfractionated CD4 and CD8 T cells.