Loss of HIV-1-specific CD8+ T cell proliferation after acute HIV-1 infection and restoration by vaccine-induced HIV-1-specific CD4+ T cells

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection, but do not correlate with control of viremia in chronic infection, suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here, we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection, but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies, and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection, but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions.     

From mice to humans - murine intelligence for human CD8+ T cell vaccine design

There has been considerable progress in the design of vaccines capable of safely and effectively inducing CD8(+) T cells for prophylaxis and treatment of chronic infectious diseases and cancer. Much of what is known about CD8(+) T cell-mediated immunity has come from pioneering work in mice; this broad overview discusses recent work in mouse systems where lessons may be drawn for human vaccine development. The areas highlighted include antivector immunity, immunodominance, dendritic cell biology and targeting, the role of Toll-like receptors and their exploitation by novel adjuvants, the role of CD4(+) T cell help, regulatory T cells and, finally, some comments on the different requirements of prophylactic versus therapeutic vaccines.     

Expansion of pre-existing, lymph node-localized CD8+ T cells during supervised treatment interruptions in chronic HIV-1 infection

To date, most studies have focused on the characterization of HIV-1-specific cellular immune responses in the peripheral blood (PB) of infected individuals. Much less is known about the comparative magnitude and breadth of responses in the lymphoid tissue. This study analyzed HIV-1-specific CD8+ T cell responses simultaneously in PB and lymph nodes (LNs) of persons with chronic HIV-1 infection and assessed the dynamics of these responses during antiretroviral treatment and supervised treatment interruption (STI). In untreated chronic infection, the magnitude of epitope-specific CD8+ T cell activity was significantly higher in LNs than in PB. Responses decreased in both compartments during highly active antiretroviral therapy, but this decline was more pronounced in PB. During STI, HIV-1-specific CD8+ T cell responses in PB increased significantly. Enhancement in breadth and magnitude was largely due to the expansion of pre-existing responses in the LNs, with new epitopes infrequently targeted. Taken together, these data demonstrate that HIV-1-specific CD8+ T cells are preferentially located in the LNs, with a subset of responses exclusively detectable in this compartment. Furthermore, the enhanced CD8+ T cell responses observed during STI in chronically infected individuals is largely due to expansion of pre-existing virus-specific CD8+ T cells, rather than the induction of novel responses.     

登革热患者外周血CD4+、CD8+T细胞及IL-10的检测分析

目的:观察登革热患者外周血CD4+、CD8+T细胞及白介素-10(IL-10)的变化,探讨其在登革热疾病的发生和发展中的作用.方法:12例健康人和18例登革热患者于治疗前后采静脉血,采用流式细胞仪检测CD4+、CD8+T细胞并计算CD4+/CD8+比值,ELISA法检测血清IL-10水平,同时作外周血白细胞、血小板计数.结果:与正常健康人和治疗后相比,登革热患者治疗前外周血CD4+细胞百分比、CD4+/CD8+比值明显降低(P＜0.01),CD8+细胞百分比和血清IL-10显著增高(P＜0.01),白细胞、血小板计数均明显下降(P＜0.01);治疗后患者以上指标均与健康人无明显差异.结论:CD4+、CD8+T细胞在登革热病毒感染后异常激活,CD4+/CD8+比值明显降低,IL-10分泌增高,可能在登革热的发病中起重要作用.     

p38 signaling inhibits mTORC1-independent autophagy in senescent human CD8+ T cells

T cell senescence is thought to contribute to immune function decline, but the pathways that mediate senescence in these cells are not clear. Here, we evaluated T cell populations from healthy volunteers and determined that human CD8⁺ effector memory T cells that reexpress the naive T cell marker CD45RA have many characteristics of cellular senescence, including decreased proliferation, defective mitochondrial function, and elevated levels of both ROS and p38 MAPK. Despite their apparent senescent state, we determined that these cells secreted high levels of both TNF-α and IFN-γ and showed potent cytotoxic activity. We found that the senescent CD45RA-expressing population engaged anaerobic glycolysis to generate energy for effector functions. Furthermore, inhibition of p38 MAPK signaling in senescent CD8⁺ T cells increased their proliferation, telomerase activity, mitochondrial biogenesis, and fitness; however, the extra energy required for these processes did not arise from increased glucose uptake or oxidative phosphorylation. Instead, p38 MAPK blockade in these senescent cells induced an increase in autophagy through enhanced interactions between p38 interacting protein (p38IP) and autophagy protein 9 (ATG9) in an mTOR-independent manner. Together, our findings describe fundamental metabolic requirements of senescent primary human CD8⁺ T cells and demonstrate that p38 MAPK blockade reverses senescence via an mTOR-independent pathway.     

Contribution of CD4+, CD8+CD28+, and CD8+CD28- T cells to CD3+ lymphocyte homeostasis during the natural course of HIV-1 infection.

The relationship between the number of circulating CD4+ T cells and the presence of particular CD8+ T cell subsets was analyzed by flow cytometry on PBL from asymptomatic HIV-1-infected patients whose specimens were collected every 2 mo for a total period of 32 mo. Only slight variations were detected in the absolute number of lymphocytes and percentage of CD3+ lymphocytes, whereas both CD4+ and CD8+ T cell subsets showed wide intrapatient variation. Variations in the number of CD8+CD28+ cells paralleled those of the CD4+ T cell subset in each patient tested, while the presence of CD8+CD28- T cells correlated inversely with CD4+ and CD8+CD28+ T cells. These data show that changes in the number of circulating CD4+-and CD8+CD28+ T cells are strongly related to the presence of CD8+CD28- T cells in these patients. Insight into the significance of CD8+CD28- T cell expansion will allow us to understand the mechanisms and significance of the HIV-1- driven change in CD4+CD8+ T cell homeostasis and the basic immunopathology of HIV disease.     

CD30 expression by CD8+ T cells producing type 2 helper cytokines. Evidence for large numbers of CD8+CD30+ T cell clones in human immunodeficiency virus infection

A large panel of CD8+ T cell clones generated from peripheral blood lymphocytes (PBL) of healthy donors or human immunodeficiency virus (HIV)-infected individuals were assessed for both cytokine secretion profile and CD30 expression and release. The great majority of CD8+ T cell clones generated from healthy individuals showed the ability to produce interferon gamma (IFN-gamma), but not interleukin 4 (IL-4), and none of them either expressed membrane CD30 or released substantial amounts of soluble CD30 (sCD30) in their supernatant. In contrast, high numbers of CD8+ T cell clones generated from HIV-infected individuals, which produced IL-4 (and IL-5) in addition to IFN-gamma or IL-4 (and IL- 5) alone, expressed membrane CD30 and released detectable amounts of sCD30 in their supernatants. Indeed, CD30 expression appeared to be positively correlated with the ability of CD8+ T cell clones to produce IL-4 and IL-5 and inversely correlated with their ability to produce IFN-gamma, whereas no correlation between CD30 expression and production of IL-10 was observed. These data suggest that CD30 is a marker for CD8+ T cells that have switched to the production of type 2 helper cytokines.     

PD-1 is a regulator of virus-specific CD8+ T cell survival in HIV infection

Here, we report on the expression of programmed death (PD)-1 on human virus-specific CD8(+) T cells and the effect of manipulating signaling through PD-1 on the survival, proliferation, and cytokine function of these cells. PD-1 expression was found to be low on naive CD8(+) T cells and increased on memory CD8(+) T cells according to antigen specificity. Memory CD8(+) T cells specific for poorly controlled chronic persistent virus (HIV) more frequently expressed PD-1 than memory CD8(+) T cells specific for well-controlled persistent virus (cytomegalovirus) or acute (vaccinia) viruses. PD-1 expression was independent of maturational markers on memory CD8(+) T cells and was not directly associated with an inability to produce cytokines. Importantly, the level of PD-1 surface expression was the primary determinant of apoptosis sensitivity of virus-specific CD8(+) T cells. Manipulation of PD-1 led to changes in the ability of the cells to survive and expand, which, over several days, affected the number of cells expressing cytokines. Therefore, PD-1 is a major regulator of apoptosis that can impact the frequency of antiviral T cells in chronic infections such as HIV, and could be manipulated to improve HIV-specific CD8(+) T cell numbers, but possibly not all functions in vivo.     

A gammaherpesvirus-secreted activator of Vbeta4+ CD8+ T cells regulates chronic infection and immunopathology

Little is known about herpesvirus modulation of T cell activation in latently infected individuals or the implications of such for chronic immune disorders. Murine gammaherpesvirus 68 (MHV68) elicits persistent activation of CD8(+) T cells bearing a Vbeta4(+) T cell receptor (TCR) by a completely unknown mechanism. We show that a novel MHV68 protein encoded by the M1 gene is responsible for Vbeta4(+) CD8(+) T cell stimulation in a manner reminiscent of a viral superantigen. During infection, M1 expression induces a Vbeta4(+) effector T cell response that resists functional exhaustion and appears to suppress virus reactivation from peritoneal cells by means of long-term interferon-gamma (IFNgamma) production. Mice lacking an IFNgamma receptor (IFNgammaR(-/-)) fail to control MHV68 replication, and Vbeta4(+) and CD8(+) T cell activation by M1 instead contributes to severe inflammation and multiorgan fibrotic disease. Thus, M1 manipulates the host CD8(+) T cell response in a manner that facilitates latent infection in an immunocompetent setting, but promotes disease during a dysregulated immune response. Identification of a viral pathogenecity determinant with superantigen-like activity for CD8(+) T cells broadens the known repertoire of viral immunomodulatory molecules, and its function illustrates the delicate balance achieved between persistent viruses and the host immune response.     

Both CD8+ and CD16+ human T cell clones can provide B cell help for immunoglobulin production

Summary The functional properties of two CD4⁺CD8⁻CD16⁻, five CD4⁻CD8⁺CD16⁻ and three CD4⁻CD8⁻CD16⁺ human T cell clones were compared. All CD4⁻ T cell clones displayed strong cytolytic activity in the lectin-dependent lytic assay against the P815 murine mastocytoma cell line, but only the CD4⁻CD8⁻CD16⁺ T cell clones exhibited lytic activity against the natural killer-sensitive K562 cell line. Upon activation with anti-CD3 monoclonal antibody, all T cell clones were able to support IgM and IgA synthesis in autologous B cells. Both CD4⁺ and CD4⁻ T cell clones required cell-to-cell interaction with the B cells in order to exert their helper activity for immunoglobulin production. However, unlike CD4⁺, CD4⁻CD8⁺CD16⁻ and CD4⁻CD8⁻CD16⁺ T cell clones provided helper function for immunoglobulin synthesis only when low T/B cell ratios were used in culture. At higher T/B cell ratios, there was a decline in the B cell helper activity of CD4⁻ T cell clones that was probably related to the expression of cytolytic capacity against the antigen-presenting B cell. These data support the notion that under certain experimental conditions even cytotoxic T lymphocytes and natural killer cells may provide B cell helper function.     

Viral antigen and extensive division maintain virus-specific CD8 T cells during chronic infection

Efficient maintenance of memory CD8 T cells is central to long-term protective immunity. IL-7- and IL-15-driven homeostatic proliferation is essential for long-term memory CD8 T cell persistence after acute infections. During chronic infections, however, virus-specific CD8 T cells respond poorly to these cytokines. Yet, virus-specific CD8 T cells often persist for long periods of time during chronic infections. We have addressed this apparent paradox by examining the mechanism for maintaining virus-specific CD8 T cells during chronic infection. We find that homeostatic cytokines (e.g., IL-7/15), inflammatory signals, and priming of recent thymic emigrants are not sufficient to maintain virus-specific CD8 T cells over time during chronic infection. Rather, our results demonstrate that viral peptide is required for virus-specific CD8 T cell persistence during chronic infection. Moreover, this viral antigen-dependent maintenance results in a dramatically different type of T cell division than is normally observed during memory T cell homeostasis. Rather than undergoing slow, steady homeostatic turnover during chronic viral infection, CD8 T cells undergo extensive peptide-dependent division, yet cell numbers remain relatively stable. These results indicate that antigen-specific CD8 T cell responses during persisting infection are maintained by a mechanism distinct from that after acute infection.     

CD4+CD25+ T cells regulate virus-specific primary and memory CD8+ T cell responses

Naturally occurring CD4+CD25+ regulatory T cells appear important to prevent activation of autoreactive T cells. This article demonstrates that the magnitude of a CD8+ T cell-mediated immune response to an acute viral infection is also subject to control by CD4+CD25+ T regulatory cells (Treg). Accordingly, if natural Treg were depleted with specific anti-CD25 antibody before infection with HSV, the resultant CD8+ T cell response to the immunodominant peptide SSIEFARL was significantly enhanced. This was shown by several in vitro measures of CD8+ T cell reactivity and by assays that directly determine CD8+ T cell function, such as proliferation and cytotoxicity in vivo. The enhanced responsiveness in CD25-depleted animals was between three- and fourfold with the effect evident both in the acute and memory phases of the immune response. Surprisingly, HSV infection resulted in enhanced Treg function with such cells able to suppress CD8+ T cell responses to both viral and unrelated antigens. Our results are discussed both in term of how viral infection might temporarily diminish immunity to other infectious agents and their application to vaccines. Thus, controlling suppressor effects at the time of vaccination could result in more effective immunity.     

CD8+ T cell tolerance and cancer immunotherapy

To provide protection against all foreign pathogens one can possibly encounter during their lifetime, the T cell repertoire has to be as diverse as possible. At the same time, it is desirable that the T cell repertoire remains unresponsive towards healthy tissues. To realize this self/nonself discriminatory property, T cells undergo tightly controlled selection processes during maturation in the thymus. The key parameter determining the outcome of these selection processes is the avidity of the T cells for self-MHC/self-peptide complexes expressed in the thymus; low avidity interactions result in positive selection, whereas high avidity interactions lead to negative selection. Despite the selection processes, self-tolerance is far from absolute. In many cases, this is due to the presence of self-antigen in the thymus at a level that is too low to induce thymic deletion. In addition, T cells with a low avidity for ubiquitously expressed self-antigens can escape clonal deletion and enter the periphery. A thorough understanding of the self-specific T cell repertoire is important because many potential targets for cancer immunotherapy are self-proteins. In this review, the authors discuss the impact of self-antigen expression on the CD8+ T cell repertoire. An overview of the fate and functional capacities of self-specific T cells with specificity for tissue-restricted self-antigens and for ubiquitously expressed self-antigens is provided. Furthermore, the authors discuss the influence of negative selection on the antitumor reactivity of the mature T cell repertoire.     

mTORC1 and mTORC2 selectively regulate CD8+ T cell differentiation

Activation of mTOR-dependent pathways regulates the specification and differentiation of CD4⁺ T effector cell subsets. Herein, we show that mTOR complex 1 (mTORC1) and mTORC2 have distinct roles in the generation of CD8⁺ T cell effector and memory populations. Evaluation of mice with a T cell–specific deletion of the gene encoding the negative regulator of mTORC1, tuberous sclerosis complex 2 (TSC2), resulted in the generation of highly glycolytic and potent effector CD8⁺ T cells; however, due to constitutive mTORC1 activation, these cells retained a terminally differentiated effector phenotype and were incapable of transitioning into a memory state. In contrast, CD8⁺ T cells deficient in mTORC1 activity due to loss of RAS homolog enriched in brain (RHEB) failed to differentiate into effector cells but retained memory characteristics, such as surface marker expression, a lower metabolic rate, and increased longevity. However, these RHEB-deficient memory-like T cells failed to generate recall responses as the result of metabolic defects. While mTORC1 influenced CD8⁺ T cell effector responses, mTORC2 activity regulated CD8⁺ T cell memory. mTORC2 inhibition resulted in metabolic reprogramming, which enhanced the generation of CD8⁺ memory cells. Overall, these results define specific roles for mTORC1 and mTORC2 that link metabolism and CD8⁺ T cell effector and memory generation and suggest that these functions have the potential to be targeted for enhancing vaccine efficacy and antitumor immunity.     

Both CD8+ and CD16+ human T cell clones can provide B cell help for immunoglobulin production.

The functional properties of two CD4+CD8-CD16-, five CD4-CD8+CD16- and three CD4-CD8-CD16+ human T cell clones were compared. All CD4- T cell clones displayed strong cytolytic activity in the lectin-dependent lytic assay against the P815 murine mastocytoma cell line, but only the CD4-CD8-CD16+ T cell clones exhibited lytic activity against the natural killer-sensitive K562 cell line. Upon activation with anti-CD3 monoclonal antibody, all T cell clones were able to support IgM and IgA synthesis in autologous B cells. Both CD4+ and CD4- T cell clones required cell-to-cell interaction with the B cells in order to exert their helper activity for immunoglobulin production. However, unlike CD4+, CD4-CD8+CD16- and CD4-CD8-CD16+ T cell clones provided helper function for immunoglobulin synthesis only when low T/B cell ratios were used in culture. At higher T/B cell ratios, there was a decline in the B cell helper activity of CD4- T cell clones that was probably related to the expression of cytolytic capacity against the antigen-presenting B cell. These data support the notion that under certain experimental conditions even cytotoxic T lymphocytes and natural killer cells may provide B cell helper function.     

慢性乙型肝炎患者病程中CD5^＋B细胞及CD4／CD8的变化研究

目的研究CD5^＋B细胞和CIM／CD8在慢性乙型肝炎发病中的作用，以及他们之间的相关性。方法采用免疫荧光双标记技术和流式细胞仪对48例慢性乙型肝炎患者发病前后周围血中CIM／CD8比例和CD5^＋B细胞的百分率和37例健康对照者进行比较。结果在慢性乙型肝炎患者发病高峰期周围血CIM／CD8比例显著低于病情恢复期，且和健康对照组比较差异有显著性；而CD5^＋B细胞在慢性乙型肝炎患者发病高峰期，显著高于健康对照组和慢性乙型肝炎患者恢复期，差异有显著性。结论慢性乙型肝炎的发病和T细胞免疫功能的紊乱相关，而CD5^＋B可能在乙型肝炎的慢性化机制中发挥作用。