Divergent telomerase and CD28 expression patterns in human CD4 and CD8 T cells following repeated encounters with the same antigenic stimulus

Induction of telomerase, the enzyme that extends telomeres, accompanies human T lymphocyte activation. Nevertheless, high proportions of memory T cells with shortened telomeres are present in vivo during HIV infection and aging. To elucidate the long-term telomerase dynamics in human T cells, longitudinal analyses were performed on T cells subjected to repeated encounters with an allogeneic cell line in long-term culture. Whereas CD4(+) and CD8(+) T cells showed similarly dramatic increases in telomerase activity following primary stimulation, by the fourth stimulation, telomerase activity was nearly undetectable in the CD8(+) subset, but remained high in the CD4(+) subset. In addition, we document the dependence of antigen-specific telomerase inducibility on CD28 and that the decline in telomerase activity parallels the loss of CD28 expression. These findings suggest stringent telomerase regulation in human T cells, a property that may ultimately contribute to telomere shortening, finite replicative potential, and loss of control over certain pathogens.     

CD20dim-positive T-cell large granular lymphocytic leukemia in a patient with concurrent hairy cell leukemia and plasma cell myeloma

We report a CD20dim- positive T-cell large granular lymphocytic (T-LGL) leukemia in a patient with concurrent hairy cell leukemia and plasma cell myeloma. This patient was first diagnosed with T-LGL leukemia with dim CD20 expression, which by itself was a rare entity. He received no treatment for T-LGL leukemia. The patient later developed a hairy cell leukemia, which went into complete clinical remission after one cycle of 2-CdA. Five years later, he was diagnosed with a third malignancy, plasma cell myeloma. Complex cytogenetic aberrancies were present at the time when plasma cell myeloma was diagnosed. This is the first report, to the best of our knowledge, in the English literature with the aforementioned three distinct hematopoietic malignancies in one patient.     

CD28 signals the differential control of regulatory T cells and effector T cells

One possible means of driving antigen‐specific immune suppression is to expand or induce antigen‐specific FoxP3‐expressing Treg cells. One way of activating and expanding these specialized cells, both in vitro and in vivo, is by strong costimulation via CD28 with an agonistic anti‐CD28 monoclonal antibody, called anti‐CD28 superagonist (CD28SA). However, CD28SA also strongly activates conventional T (Tconv) cells to secrete proinflammatory cytokines and, under certain conditions, causes serious cytokine release syndrome. In this issue of European Journal of Immunology, Tabares et al. [Eur. J. Immunol. 2014. 44: 1225–1236] address how CD28SA can be used for the differential control of human Treg and Tconv cells to suppress immune responses without serious adverse effects. They show that, depending on the dose of the antibody or by comedication of cortico‐steroid, the selective expansion of Treg cells can be achieved without significantly activating Tconv cells to produce inflammatory cytokines. This difference in CD28 signal sensitivity between the two populations can be exploited for better control of immune responses.     

CD28 days later: Resurrecting costimulation for CD8+ memory T cells

Rapid activation and proliferative expansion of specific CD8⁺ memory T (CD8⁺T_M) cells upon antigen re‐encounter is a critical component of the adaptive immune response that confers enhanced immune protection. In this context, however, the requirements for costimulation in general, and CD28 signaling in particular, remain incompletely defined. In the current issue of the European Journal of Immunology, Fröhlich et al. [Eur. J. Immunol. 2016. 46: 1644‐1655] provide definitive evidence that optimal elaboration of CD8⁺T_M‐cell recall responses is indeed contingent on CD28 expressed by these cells. Here, we discuss the “CD28 costimulation paradigm” in its historical context and highlight some of the unresolved complexities pertaining to CD28‐dependent interactions that shape CD8⁺ T‐cell phenotypes, functionalities, and recall reactivity.     

DNA甲基化在急性冠脉综合征患者CD4+CD28-T细胞CD28表达缺失中的作用

目的 通过研究急性冠脉综合征(acute coronary syndrome,ACS)患者外周血CD4+T细胞CD28 mRNA水平和CD28基因启动子调节序列的甲基化状态,旨在探讨DNA甲基化在ACS患者CD4+CD28-T细胞CD28表达缺失中的作用.方法 免疫磁珠分离CD4+T细胞经逆转录后,实时定量PCR(real time-PCR)技术检测CD4+T细胞CD28mRNA的表达水平,亚硫酸氢钠测序检测CD28基因启动子调节序列的甲基化状态.结果 与正常对照组相比,ACS患者CD4+T细胞CD28mRNA表达水平显著减低,差异具有统计学意义[正常对照组比ACS组:(1.066±0.162)比(0.401±0.069),P<0.05].CD28基因启动子区域的甲基化水平显著增高,差异有统计学意义[正常对照组比ACS组:(24.47±3.17)%比(43.33±1.52)%,P<0.05].CD28基因启动子区域DNA甲基化水平与CD28mRNA表达水平呈显著负相关(P=0.01,r=-0.579).结论 ACS患者CD4+T细胞CD28基因启动子区域高甲基化调控了CD28基因转录抑制.DNA甲基化参与了CD4+CD28-T细胞的形成.     

Low T cell reactivity to combined CD3 plus CD28 stimulation is predictive for progression to AIDS: correlation with decreased CD28 expression

In 219 HIV-1-infected men of the Amsterdam cohort we measured CD4⁺ T cell numbers and in vitro T cell responses to CD3 MoAbs with or without CD28 costimulation and phytohaemagglutinin (PHA). The value of these markers was estimated for disease progression within 4 years. CD28 expression on T cells has been related to T cell responses. CD28 costimulation considerably enhanced T cell reactivity (≈8–10-fold) with lower coefficients of variation compared with reactivity to CD3 MoAb alone (median 5 versus 20). T cell reactivity to CD3 plus CD28 MoAb was decreased during HIV-1 infection and was besides CD4⁺ T cell numbers the only independent predictor for progression to AIDS. Compared with the group with high CD4⁺ T cell numbers the relative risk (RR) for the group with intermediate levels was 2.28, with low levels 5.20. In the groups with intermediate and low CD3 plus CD28 responses the RR was 2.04 and 4.16, respectively. The combined RR for both was 4.65 and 21.63. The independence of this marker was confirmed when the group with low CD4⁺ T cell numbers was subdivided into groups with high, intermediate and low T cell responses. The expansion of CD8⁺CD28⁻ T cells was already apparent in HIV⁻ homosexual men, but CD8⁺CD28⁺ T cells specifically decreased in patients with AIDS. CD28 expression on T cells correlated moderately with T cell responses to CD3 plus CD28 MoAb. T cell reactivity to CD3 MoAb in the presence of CD28 MoAb is a stronger prognostic marker than T cell reactivity to CD3 MoAb alone.     

抗人CD28激发性单抗对T细胞淋巴瘤的抑制作用研究

目的:研究鼠抗人CD28单克隆抗体(克隆号:2F5)对T淋巴细胞瘤的抗肿瘤效应,为抗体介导肿瘤靶向治疗提供新的方法和思路。方法:流式细胞术检测鼠抗人CD28单克隆抗体2F5对人T淋巴瘤细胞株Jurkat细胞表面膜型CD28分子的识别;MTT法检测2F5对Jurkat细胞体外增殖的影响;将Jurkat细胞株接种于裸鼠腋下,建立Jurkat细胞荷瘤裸鼠模型;经瘤内多点注射2F5(注射剂量1μg/mm3),逐日观察肿瘤的大小和裸鼠的生存状态。结果:2F5能够识别Jurkat细胞表面CD28分子,阳性结合率可达93.37%;2F5与Jurkat细胞共培养后,显微镜下观察可见胞质中出现黑色颗粒,胞膜破裂,细胞的折光性和立体感减弱;MTT法分析结果显示,抗CD28单抗对Jurkat细胞的体外增殖具有明显的抑制作用;将Jurkat细胞接种35只裸鼠(成瘤率达70%);经瘤内多点注射2F5,35天后荷瘤小鼠体内肿瘤的生长速率明显降低;而生理盐水对照组肿瘤生长无明显改变。结论:鼠抗人CD28单克隆抗体2F5通过与Jurkat细胞表面膜型CD28分子结合对其增殖具有明显的抑制作用,提示CD28分子可作为治疗T淋巴瘤的一个潜在靶点,抗体对治疗CD28分子阳性的肿瘤具有潜在临床应用价值。     

肺癌患者外周血T淋巴细胞及亚群CD28表达和活化的改变

目的检测共刺激分子CD28在肺癌患者外周血T淋巴细胞及亚群中的表达密度和细胞活化程度的变化,并探讨该变化与肺癌临床分期的关系.方法用三色荧光直标流式细胞法分别检测38例正常人与42例肺癌患者中血T淋巴细胞亚群中CD28的阳性率以及CD28+T淋巴细胞亚群活化率.结果与正常人相比,肺癌患者外周血中的CD3+CD28+,CD4+CD28+,CD8+CD28+淋巴细胞百分比均有下降(P＜0.05).淋巴细胞及其T亚群中的CD25+CD28+,CD38+CD28+淋巴细胞百分比亦有所下降(P＜0.05),但在不同临床分期的患者之间无显著性差异(P＞0.05).结论肺癌患者外周血T淋巴细胞的CD28表达密度及CD28+T细胞的活性均有降低,但下降幅度与临床分期无关.     

Human mast cells costimulate T cells through a CD28‐independent interaction

Mast cells are innate immune cells usually residing in peripheral tissues, where they are likely to activate T‐cell responses. Similar to other myeloid immune cells, mast cells can function as antigen‐presenting cells. However, little is known about the capacity of human mast cells to costimulate CD4⁺ T cells. Here, we studied the T‐cell stimulatory potential of human mast cells. Peripheral blood derived mast cells were generated and cocultured with isolated CD4⁺ T cells. In the presence of T‐cell receptor triggering using anti‐CD3, mast cells promoted strong proliferation of T cells, which was two‐ to fivefold stronger than the “T‐cell promoting capacity” of monocytes. The interplay between mast cells and T cells was dependent on cell–cell contact, suggesting that costimulatory molecules on the mast cell surface are responsible for the effect. However, in contrast to monocytes, the T‐cell costimulation by mast cells was independent of the classical costimulatory molecule CD28, or that of OX40L, ICOSL, or LIGHT. Our data show that mast cells can costimulate human CD4⁺ T cells to induce strong T‐cell proliferation, but that therapies aiming at disrupting the interaction of CD28 and B7 molecules do not inhibit mast cell mediated T‐cell activation.     

CD28-mediated costimulation impacts on the differentiation of DC vaccination-induced T cell responses

Costimulatory signals such as the ones elicited by CD28/B7 receptor ligation are essential for efficient T cell activation but their role in anti-tumour immune responses remains controversial. In the present study we compared the efficacy of DC vaccination-induced melanoma specific T cell responses to control the development of subcutaneous tumours and pulmonary metastases in CD28-deficient mice. Lack of CD28-mediated costimulatory signals accelerated tumour development in both model systems and also the load of pulmonary metastases was strongly increased by the end of the observation period. To scrutinize whether lack of CD28 signalling influences priming, homing or effector function of Trp-2(180-188)/K(b)-reactive T cells we investigated the characteristics of circulating and tumour infiltrating T cells. No difference in the frequency of Trp-2(180-188)/K(b)-reactive CD8+ T cells could be demonstrated among the cellular infiltrate of subcutaneous tumours after DC vaccination between both genotypes. However, the number of IFN-gamma-producing Trp-2-reactive cells was substantially lower in CD28-deficient mice and also their cytotoxicity was reduced. This suggests that CD28-mediated costimulatory signals are essential for differentiation of functional tumour-specific CD8+ T-effector cells despite having no impact on the homing of primed CD8+ T cells.     

Peripheral human CD8(+)CD28(+)T lymphocytes give rise to CD28(-)progeny, but IL-4 prevents loss of CD28 expression.

At birth, virtually all peripheral CD8(+) T cells express the CD28 co-stimulatory molecule, but healthy human adults accumulate CD28(-)CD8(+) T cells that often express the CD57 marker. While these CD28(-) subpopulations are known to exert effector-type functions, the generation, maintenance and regulation of CD28(-) (CD57(+) or CD57(-)) subpopulations remain unresolved. Here, we compared the differentiation of CD8(+)CD28(bright)CD57(-) T cells purified from healthy adults or neonates and propagated in IL-2, alone or with IL-4. With IL-2 alone, CD8(+)CD28(bright)CD57(-) T cell cultures yielded a prevailing CD28(-) subpopulation. The few persisting CD28(dim) and the major CD28(-) cells were characterized by similar telomere shortening at the plateau phase of cell growth. Cultures from adults donors generated four final CD8(+) phenotypes: a major CD28(-)CD57(+), and three minor CD28(-)CD57(-), CD28(dim)CD57(-) and CD28(dim)CD57(dim). These four end-stage CD8(+) subpopulations displayed a fairly similar representation of TCR V(beta) genes. In cultures initiated with umbilical cord blood, virtually all the original CD8(+)CD28(bright) T cells lost expression of CD28, but none acquired CD57 with IL-2 alone. IL-4 impacted on the differentiation pathways of the CD8(+)CD28(bright)CD57(-) T cells: the addition of IL-4 led both the neonatal and the adult lymphocytes to keep their expression of CD28. Thus, CD8(+)CD28(bright)CD57(-) T cells can give rise to four end-stage subpopulations, the balance of which is controlled by both the cytokine environment, IL-4 in particular, and the proportions of naive and memory CD8(+)CD28(+) T cells.     

Impaired interleukin-2 synthesis and T cell proliferation following antibody-mediated CD3 and CD2 or CD28 cross-linking in trans: evidence that T cell activation requires the engagement of costimulatory molecules within the immunological synapse

Although the T cell costimulatory molecules CD2 and CD28 are enriched within the immunological synapse (IS), it has been suggested that costimulatory molecules need not be localized to the contact site between a T cell and an antigen-presenting cell (APC) in order to costimulate T cell activation. To determine whether CD2 or CD28 engagement outside of the IS is sufficient to costimulate T cell activation, we compared mouse T cell responses to anti-CD3 and anti-CD2 monoclonal antibodies (mAbs) or anti-CD3 and anti-CD28 mAbs immobilized on the same, i.e., in cis, or on different, i.e., in trans, 10 micron polystyrene microspheres. In comparison to T cells that were stimulated with co-immobilized anti-CD3 and anti-CD2 or anti-CD28 mAbs, DNA synthesis, interleukin (IL)-2 production, and cellular proliferation were all severely impaired following T cell stimulation with anti-CD3 and anti-CD2 mAbs or anti-CD3 and anti-CD28 mAbs on different microspheres. Deficient cellular proliferation and IL-2 synthesis by T cells that experienced CD3 and CD2 or CD28 cross-linking in trans provides evidence that costimulatory molecules must function in the context of the IS for optimal T cell activation.     

Impaired T cell signal transduction through CD28 in a patient with idiopathic thrombocytopenia.

We describe an infant whose peripheral blood mononuclear cells were unable to proliferate or synthesize IL-2 in response to a mitogenic combination of antibodies directed against CD2 and CD28. This peculiar defect, which has been stable to date, was attributed to an impairment in CD28-mediated T cell activation, because further comitogenic combinations containing anti-CD28 monoclonals also failed to induce normal proliferation of the patient's T cells. In contrast, proliferation after membrane stimulation (with anti-CD2, recombinant IL-2, or certain lectins) or transmembrane activation (with phorbol ester and calcium ionophore) was normal, suggesting that his lymphocytes did not have a general membrane or intracellular signalling impairment. A T cell line derived from the patient confirmed the existence of a severe defect in CD28-mediated T cell proliferation, but also showed a profound impairment in CD3-induced T cell proliferation. Other cell surface molecules like CD2 and CD25 were, in contrast, capable of transducing normal proliferation signals. As all relevant molecules were detectable by cytofluorography and immunoprecipitation, we conclude that the patient's lymphocytes had an intrinsic defect in the delivery of CD28-mediated signals which, in the absence of monocytes, also affected CD3-mediated proliferation. The study of this novel kind of immunodeficiency may help to unravel the complex interactions that take place among CD2, CD3 and CD28 during T cell activation. The presence of an idiopathic thrombocytopenia in the patient suggests the intriguing possibility of a role for CD28 in the maintenance of peripheral blood platelets levels, although alternative interpretations are not ruled out.     

肝移植自发免疫耐受大鼠CD8+CD28-T抑制细胞的生物学特性

目的　研究近交系大鼠原位肝移植自发免疫耐受模型中CD8 CD2 8- T抑制细胞的生物学特点。方法　建立大鼠原位肝移植模型 ,流式细胞技术检测自发免疫耐受模型中CD8 CD2 8- T抑制细胞含量变化 ;通过体外混合淋巴细胞反应和体内输注验证CD8 CD2 8- T细胞的抑制功能 ,并检测其增殖、细胞因子mRNA的表达和诱导靶细胞发生凋亡的情况 ,并与急性排异组相比较。结果　自发免疫耐受模型大鼠脾脏CD8 CD2 8- T细胞含量 (31.5 %± 2 .6 % )显著高于正常大鼠 (5 .4 %±1.5 % )和急性排异组大鼠 (6 .0 %± 1.3% )。自发免疫耐受组CD8 CD2 8- T细胞明显抑制体外混合淋巴细胞反应的增殖 ,体内输注显著延长皮肤移植物的存活时间 (MST :10± 0 .8dvs 15± 1.8d ,P <0 .0 5 ) ,但急性排异组大鼠脾脏CD8 CD2 8- T细胞无抑制功能。外源性IL 2 4 0U ml可逆转CD8 CD2 8- T细胞的抑制功能。CD8 CD2 8- T细胞不会增加靶细胞凋亡的发生 ,其IFN γmRNA为高表达 ,而急性排异组无表达。PHA 5 0 μg ml和IL 2 4 0U ml、PMA ion 5 0 2 5 0ng ml和IL 2 4 0U ml联合应用可有效刺激CD8 CD2 8- T细胞增殖。结论　自发耐受组大鼠脾脏CD8 CD2 8- T细胞是一种T抑制细胞 ,在自发免疫耐受的形成过程中具有重要作用 ,其抑制作用可能与IFN     

Differential proliferative responses in subsets of human CD28+cells delineated by BB27 mAb

We report the Identification of a novel 140 kDa disulflde-llnkeddimer expressed by a subset of peripheral blood T lymphocytes.This molecule, which Is recognized by mAb BB27, is also detectedon cells of the myelomonocytlc lineage. In the T cell lineage,Its expression Is positively modulated after lymphocyte activation.A series of double-labeling experiments revealed that BB27 mAbIdentifies new CD4 and CDS cell subsets different from thosedefined by CD45RA, CD45RO, CD26, CD29, CD31, and CD38. Finally,BB27 mAb also subdivides the CD28 subset. Of the utmost interestIs the finding that a proliferative response to CD28 mAb andphorbol myrlstate acetate stimulation is exclusively obtainedin the CD28⁺BB27⁺ cell subset, whereas the CD28⁺BB27^–subset falls to proliferate.     

CD8+ T cells and not CD4+ T cells are hyporesponsive to CD28- and CD40L-mediated activation in HIV-infected subjects

T cell dysfunction in HIV-infected subjects could be the consequence of altered sensitivity of CD4⁺ or CD8⁺ T cells to various costimulatory signals. Therefore, we studied proliferation and cytokine production in highly purified CD8⁺ and CD4⁺ T cells from HIV-infected and HIV⁻ subjects, induced by co-activation via cell-bound CD80, CD86 and CD40 or by allo-activation. Regardless of the nature of the first and the costimulatory signal, CD8⁺ T cells from patients proliferated consistently less than controls, while responses from CD4⁺ T cells were similar in patients and controls. This phenomenon was observed after ligation of CD28 combined with anti-CD3 or phorbol myristate acetate (PMA), but also after allogeneic stimulation and after activation by CD40 and anti-CD3. Anti-CD3 combined with CD80 or CD86 induced a mixed Th1/Th2-type cytokine profile in both CD4⁺ and CD8⁺ T cells from controls, whereas anti-CD3 plus CD40 induced only low levels of Th2-type cytokines and no interferon-gamma (IFN-γ) in CD4⁺ T cells. Compared with controls, CD4⁺ T cells from patients produced slightly lower levels of IL-10 but equal amounts of IFN-γ, IL-4 and IL-5, while CD8⁺ T cells from patients produced less of all cytokines tested. In conclusion, responses of purified CD4⁺ T cells from HIV⁺ subjects to various costimulatory pathways are relatively intact, whereas CD8⁺ T cells are hyporesponsive at the level of proliferation and cytokine production. A generalized intrinsic CD8⁺ T cell failure might contribute to viral and neoplastic complications of HIV infection.     

CD28 of T lymphocytes associates with phosphatidylinositol 3-kinase

T lymphocyte activation requires recognition of antigen by theantigen specific TCR as well as second co-stlmulatory signals.This recognition event results in the activation of non-TCRlinked protein tyroslne klnases (PTKs). The mechanism of co-stlmulatlonof T cells is unknown except for the involvement of PTKs. TheT cell surface molecule CD28 Is effective in delivering co-stlmulatorysignals and prevents T cell anergy by inducing T cell proliferationin TCR stimulated T cells, primarily due to an increase in IL-2production. The mechanism by which CD28 mediates this effectis currently unknown. Some conventional receptor molecules possessintrinsic tyroslne kinase and as a consequence of cross-linkingor llgand binding, phosphorylate numerous tyroslnes within theircytoplasmlc tall, leading these tyroslnes to become ‘activated’and bind cytoplasmlc effector molecules possessing Src homology2 domains which specifically recognize phosphorylated tyroslnes.One such cytoplasmlc effector molecule is the phosphattdyllnosltol-3-phosphatekinase (PI3 kinase) which recognizes the motif phosphotyroslne- methlone/vallne - X - methlonlne (X being any amlno acid)within the cytoplasmlc tails of numerous receptor tyroslne klnases.As CD28 contains a copy of the PI3 kinase binding motif withinits cytoplasmlc tail, we investigated CD28 signaling and PI3kinase activation. Here we demonstrate using the Jurkat cellline that CD28 becomes tyroslne phosphorylated following CD28cross-linking and associates with PI3 kinase. Furthermore, asynthetic peptlde representing the YM/VXM motif within the cytoplasmlctall of CD28 also interacts with PI3 kinase only when the tyroslneis phosphorylated. CD28 co-stimulation, therefore, similar tothat of CD19 and ‘co-stlmulatlon’ of B cells travelin part via the activation of the PI3 kinase pathway.     

CD28 mRNA rapidly decays when activated T cells are functionally anergized with specific peptide

The induction of non-responsiveness in specific clones of Tcells In vivo might be expected to reverse immunologlcally mediateddisease processes. With this goal in mind, experiments in vitrowith cloned T cells have investigated the mechanisms of inductionof anergy. Resting T cells can be functionally inactivated invitro by high doses of appropriate peptide in either the presenceor absence of antigen presenting cells. During the inductionof anergy, the modulation of the surface phenotype of T cellsis similar to that of cells proliferating in response to animmunogenic stimulus. The amount of T cell receptor at the cellsurface is down regulated, whereas the CD2 and CD25 receptorsare increased in density. in contrast, CD28 has been identifiedas a membrane protein that is differentially regulated duringactivation and the induction of non-responsiveness. Ligatlonof CD28 provides an efficient costlmulatory signal for activationof T cells. In this report, we show that not only resting cells,but also fully activated T cells can be rendered non-responsiveand that this process is accompanied by profound downregulationof CD28, both at the level of cytoplaamic mRNA and surface expressionof the mature protein. This observation anticipates clinicalintervention in immunologically mediated disease, where thetarget T cells are more likely to be activated than in a restingstate.     

毛细胞白血病细胞表面糖蛋白三聚体的免疫电镜检测

目的 为毛细胞白血病(hairy cell leukemia，HCL)的诊断提供新方法。方法 采用对毛细胞白血病有高度特异性的单抗B-ly-7(CD103)对5例患者毛细胞表面的糖蛋白三聚体(trimeric glycoprotein，TGP)进行免疫电镜研究。结果 4例HCL患者毛细胞表达TGP，镜下显示细胞胞质突起呈现出清晰的黑色边缘，与邻近染色阴性的细胞形成明显区别。而1例伴绒毛淋巴细胞的脾淋巴瘤(splenic lymphoma with villous lymphocytes，SLVL)和6例B淋巴细胞慢性白血病(B-chronic lymphocytic leukemia，B-CLL)均显示阴性。结论 免疫电镜检测毛细胞膜上的TGP有助于毛细胞白血病的鉴别诊断。     

CD8+ CD28- and CD8+ CD57+ T cells and their role in health and disease

Chronic antigenic stimulation leads to gradual accumulation of late-differentiated, antigen-specific, oligoclonal T cells, particularly within the CD8(+) T-cell compartment. They are characterized by critically shortened telomeres, loss of CD28 and/or gain of CD57 expression and are defined as either CD8(+) CD28(-) or CD8(+) CD57(+) T lymphocytes. There is growing evidence that the CD8(+) CD28(-) (CD8(+) CD57(+)) T-cell population plays a significant role in various diseases or conditions, associated with chronic immune activation such as cancer, chronic intracellular infections, chronic alcoholism, some chronic pulmonary diseases, autoimmune diseases, allogeneic transplantation, as well as has a great influence on age-related changes in the immune system status. CD8(+) CD28(-) (CD8(+) CD57(+)) T-cell population is heterogeneous and composed of various functionally competing (cytotoxic and immunosuppressive) subsets thus the overall effect of CD8(+) CD28(-) (CD8(+) CD57(+)) T-cell-mediated immunity depends on the predominance of a particular subset. Many articles claim that CD8(+) CD28(-) (CD8(+) CD57(+)) T cells have lost their proliferative capacity during process of replicative senescence triggered by repeated antigenic stimulation. However recent data indicate that CD8(+) CD28(-) (CD8(+) CD57(+)) T cells can transiently up-regulate telomerase activity and proliferate under certain stimulation conditions. Similarly, conflicting data is provided regarding CD8(+) CD28(-) (CD8(+) CD57(+)) T-cell sensitivity to apoptosis, finally leading to the conclusion that this T-cell population is also heterogeneous in terms of its apoptotic potential. This review provides a comprehensive approach to the CD8(+) CD28(-) (CD8(+) CD57(+)) T-cell population: we describe in detail its origins, molecular and functional characteristics, subsets, role in various diseases or conditions, associated with persistent antigenic stimulation.