Synergy of IL-21 and IL-15 in regulating CD8+ T cell expansion and function

Interleukin (IL)-21 is the most recently recognized of the cytokines that share the common cytokine receptor gamma chain (gamma(c)), which is mutated in humans with X-linked severe combined immunodeficiency. We now report that IL-21 synergistically acts with IL-15 to potently promote the proliferation of both memory (CD44high) and naive (CD44low) phenotype CD8+ T cells and augment interferon-gamma production in vitro. IL-21 also cooperated, albeit more weakly, with IL-7, but not with IL-2. Correspondingly, the expansion and cytotoxicity of CD8+ T cells were impaired in IL-21R-/- mice. Moreover, in vivo administration of IL-21 in combination with IL-15 boosted antigen-specific CD8+ T cell numbers and resulted in a cooperative effect on tumor regression, with apparent cures of large, established B16 melanomas. Thus, our studies reveal that IL-21 potently regulates CD8+ T cell expansion and effector function, primarily in a synergistic context with IL-15.     

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.     

IL-15 trans-presentation by pulmonary dendritic cells promotes effector CD8 T cell survival during influenza virus infection

We have recently demonstrated that peripheral CD8 T cells require two separate activation hits to accumulate to high numbers in the lungs after influenza virus infection: a primary interaction with mature, antigen-bearing dendritic cells (DCs) in the lymph node, and a second, previously unrecognized interaction with MHC I–viral antigen–bearing pulmonary DCs in the lungs. We demonstrate that in the absence of lung-resident DC subsets, virus-specific CD8 T cells undergo significantly increased levels of apoptosis in the lungs; however, reconstitution with pulmonary plasmacytoid DCs and CD8α⁺ DCs promotes increased T cell survival and accumulation in the lungs. Further, our results show that the absence of DCs after influenza virus infection results in significantly reduced levels of IL-15 in the lungs and that pulmonary DC–mediated rescue of virus-specific CD8 T cell responses in the lungs requires trans-presentation of IL-15 via DC-expressed IL-15Rα. This study demonstrates a key, novel requirement for DC trans-presented IL-15 in promoting effector CD8 T cell survival in the respiratory tract after virus infection, and suggests that this trans-presentation could be an important target for the development of unique antiviral therapies and more effective vaccine strategies.Clearance of a primary influenza A virus (IAV) infection is known to require killing of virus-infected host cells by activated, antigen-specific CD8 T cells in the lungs (Topham et al., 1997). Until recently, antigen-specific CD8 T cells were thought to undergo programmed activation, whereby a single, brief interaction with a mature, antigen-bearing DC in the LN was sufficient to induce a full program of activation, division, and differentiation from naive to mature, cytotoxic CD8 T cells (Kaech and Ahmed, 2001; Wong and Pamer, 2001). Increasing evidence has suggested, however, that activation of antigen-specific CD8 T cells is not as simple as previously thought, and multiple factors, including cytokine signals such as IL-2 (Wong and Pamer, 2004), IFN-α (Marrack et al., 1999; Price et al., 2000; Kolumam et al., 2005), and IL-12 (Curtsinger et al., 2003a,b; Trinchieri, 2003), and late co-stimulatory signals such as CD70 (Dolfi and Katsikis, 2007) and 4-1BBL (Bertram et al., 2002; Lin et al., 2009), can regulate and fine tune the magnitude and duration of the effector response, as well as the nature of the ensuing memory T cell population.We have recently demonstrated in a model of IAV infection that the absence of specific pulmonary DC subsets, including plasmacytoid DC (pDCs) and CD8α⁺ DCs, from the lungs leads to a significant decrease in the number of virus-specific CD8 T cells (McGill et al., 2008). Reconstitution of the lungs with physiological numbers of pDCs or CD8α⁺ DCs is able to restore the pulmonary IAV-specific CD8 T cell response to near normal levels via a mechanism that is dependent on direct DC–T cell interactions, DC-expressed MHC I, and the presence of viral antigen. Interestingly, however, this rescue is DC subset specific, as reconstitution with purified alveolar and airway DCs (aDCs) or alveolar macrophages (aMϕs) was unable to rescue the virus-specific CD8 T cell response (McGill et al., 2008). After IAV infection there is an abundance of IAV antigen– and MHC I–expressing cells present in the lungs, including infected epithelial cells. Given this fact and the inability of all DC subsets to rescue the virus-specific CD8 T cell response, it suggested that there were additional, undefined requirements for pDC- and CD8α⁺ DC–mediated rescue of the T cell response in the lungs. Further, it remained unclear what mechanism was contributing to decreased numbers of IAV-specific CD8 T cells in the lungs of aDC-depleted mice: impaired DC migration from the lungs to the LN, impaired CD8 T cell proliferation within the lungs, or impaired CD8 T cell survival within the lungs. It was also unclear what mechanism pulmonary DC subsets were using to rescue this defect.The cytokine IL-15 has been demonstrated to play a key role in promoting lymphoid homeostasis, particularly with respect to CD8 T cells (Budagian et al., 2006; Kim et al., 2008). IL-15 was initially thought to signal similar to IL-2, whereby IL-15Rα formed a heterotrimeric complex with IL-2/IL15Rβ and common γ for high affinity signaling. Although this model appears to hold true in certain situations, recent reports have demonstrated a unique, alternative signaling mechanism, termed trans-presentation. In this model, IL-15Rα is required for the processing and presentation of active IL-15 in trans to cells expressing the IL-2/IL15Rβ–common γ chain complex (Sandau et al., 2004; Schluns et al., 2004; Kobayashi et al., 2005). At this time, it is unclear which cell types serve as the primary trans-presenting cells during an immune response; however, several lines of evidence have indicated that DCs may play an important role (Burkett et al., 2003, 2004). It is known that DCs express protein for both IL-15 and IL-15Rα, and that stimulation by IFN-αβ (Mattei et al., 2001) or IFN-γ (Doherty et al., 1996; Musso et al., 1999), or exposure to viral infection leads to further up-regulation of these molecules (Liu et al., 2000; Dubois et al., 2005; Budagian et al., 2006; Mattei et al., 2009). Interestingly, DCs matured in the presence of IL-15 have been demonstrated to promote enhanced antigen-specific CD8 T cell proliferation (Jinushi et al., 2003; Mattei et al., 2009) and a robust Th1 skewing in vivo (Pulendran et al., 2004).IL-15 has been best characterized for its role in maintaining memory CD8 T cell homeostasis, primarily through promoting enhanced basal proliferation (Becker et al., 2002; Goldrath et al., 2002; Schluns et al., 2002). More recently, however, there is accumulating evidence that IL-15 is also important for promoting primary effector CD8 T cell responses (Akbar et al., 1996; Bulfone-Paus et al., 1997; Vella et al., 1998; Schluns et al., 2002; Rausch et al., 2006; Yajima et al., 2006). Surface expression of both IL-15Rα and IL-2/IL15-Rβ is up-regulated after TCR activation (Vella et al., 1998), and IL-15 has been proposed to enhance activated CD8 T cell survival after challenge with staphylococcal enterotoxin A (Vella et al., 1998), Mycobacterium tuberculosis (Rausch et al., 2006), and vesicular stomatitis virus infection (Sandau et al., 2004). Collectively, these studies suggest a particularly important role for IL-15 in the generation and maintenance of an appropriate immune response; however, it remains unclear what role IL-15 plays during the effector phase of the immune response or in what context IL-15 contributes to activated CD8 T cell survival in vivo.In this study, we demonstrate a previously unrecognized role for pulmonary DC–mediated IL-15 trans-presentation in regulating virus-specific CD8 T cell responses in the lungs after IAV infection. The reduction in T cell numbers observed in the lungs of aDC-depleted mice after IAV challenge results not from impaired proliferation within the lungs but is caused by significantly increased levels of apoptosis of virus-specific CD8 T cells compared with nondepleted controls. Further, reconstitution with purified pDCs or CD8α⁺ DCs rescues the IAV-specific CD8 T cell response by promoting increased CD8 T cell survival in the lungs of aDC-depleted mice. Additionally, our results show that IAV infection induces up-regulation of both IL-15 mRNA and protein in the lungs and that depletion of aDCs at 48 h post infection (p.i.) results in a significant reduction in pulmonary IL-15 expression. Finally, this study demonstrates that pulmonary DCs prevent virus-specific CD8 T cell apoptosis through trans-presentation of IL-15, as blockade of IL-15 or IL-15Rα on the surface of pulmonary DCs before adoptive transfer, or transfer of IL-15^−/− pulmonary DC subsets ablates the rescue of the virus-specific CD8 T cell response in the lungs of aDC-depleted mice.     

Therapeutic role of CD8+ T cells in HIV-1 infection: targets and suppressors of viral replication

CD8+ T cells are pivotal in controlling viral replication in HIV-1-infected subjects. However, in chronic infection, HIV-1-specific CD8+ T cells fail to adequately control infection, presenting incomplete maturation and more severe functional impairment with advanced disease. Accumulating evidence has shown that CD8+ T cells can also be productively infected by HIV-1. Whether HIV-1 infection of CD8+ T lymphocytes impacts on their antiviral activity remains to be determined. This review explores the potential mechanisms of HIV-1 infection of CD8+ T cells, its likely contribution to the immunopathogenesis of HIV-1 infection and potential therapeutic interventions.     

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.     

Antiviral CD4+ memory T cells are IL-15 dependent

Survival and intermittent proliferation of memory CD4(+) and CD8(+) T cells appear to be controlled by different homeostatic mechanisms. In particular, contact with interleukin (IL)-15 has a decisive influence on memory CD8(+) cells, but not memory CD4(+) cells. Past studies of memory CD4(+) cells have relied heavily on the use of naturally occurring memory phenotype (MP) cells as a surrogate for antigen (Ag)-specific memory cells. However, we show here that MP CD4(+) cells contain a prominent subset of rapidly proliferating major histocompatibility complex (MHC) II-dependent cells. In contrast, Ag-specific memory CD4 cells have a slow turnover rate and are MHC II independent. In irradiated hosts, these latter cells ignore IL-15 and expand in response to the elevated levels of IL-7 in the lymphopenic hosts. In contrast, in normal nonlymphopenic hosts where IL-7 levels are low, memory CD4 cells are heavily dependent on IL-15. Significantly, memory CD4(+) responsiveness to endogenous IL-15 reflects marked competition from other cells, especially CD8(+) and natural killer cells, and increases considerably after removal of these cells. Therefore, under normal physiological conditions, homeostasis of CD8(+) and CD4(+) memory cells is quite similar and involves IL-15 and IL-7.     

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.     

动脉粥样硬化患者单个核细胞Siglec-1在促进CD4+和CD8+T淋巴细胞增殖和分泌细胞因子中的作用

目的 探讨动脉粥样硬化(AS)患者单个核细胞(PBMC)唾液酸黏附素(Siglec-1)在刺激白细胞分化抗原(CD)4+和CD8+T淋巴细胞活化增殖中的作用.方法 实验研究.用磁珠分离长征医院18例急性冠状动脉综合征(ACS)和41例稳定型心绞痛(SA)患者及32名健康对照者CD14阳性PBMC后,用不同浓度α-干扰素(IFN-α,0、2、5、10 ng/ml)刺激Siglec-1高表达,或用小干扰RNA或抗Siglec-1单抗靶向抑制Siglec-1表达,再与1名第三方健康献血者CD4 +/CD8+T淋巴细胞共培养5d.然后,将实验分为11组:健康人CD14(1组),健康人CD14+ IFN-α5 ng/ml(2组),健康人CD14+ IFN-Ω 5 ng/ml+ anti-Siglec-1 2 μg/ml(3组),ACS CD14(4组),ACS CD14+ siRNA干扰对照组(Mock,5组),ACS CD14+ siRNA 679 40 nmol/L(6组),ACS CD14+ anti-Siglec-1 2μg/ml(7组),SACD14(8组),SA CD14+ Mock(9组),SA CD14+ siRNA 679 40 nmol/L(10组),SA CD14+ anti-Siglec-12 μg/ml(11组);每组测定10份标本.用CCK-8活细胞计数试剂盒检测共培养T淋巴细胞增殖,用ELISA检测共培养T淋巴细胞分泌白细胞介素(IL)-2、IL-10、IL-12、γ干扰素(IFN-γ).测定各组PBMC刺激T淋巴细胞分泌细胞因子的计量数据用中位数(四分位数)表示,采用非参数秩和检验.结果 靶向阻断Siglec-1后(6组),PBMC刺激CD4+T淋巴细胞及CD8+T淋巴细胞的增殖能力减弱,PBMC刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为67.00(62.50～ 87.30)、0.86(0 ～1.63)、47.82(37.60 ～ 56.67) pg/ml,且分泌能力减弱;IL-10为56.00(46.25 ～67.40) pg/ml,且分泌能力增强;未处理组(4组)上述细胞因子分别为213.70(187.50 ～ 275.30)、6.87 (4.90 ～8.93)、114.90(89.50～167.40)、21.08(15.70～33.20) pg/ml,二者差异有统计学意义(U值分别为8.50、17.00、8.50、87.50,P均＜0.05).当健康对照组单核细胞经IFN-α刺激上调Siglec-1表达后(2组),刺激CD4+T淋巴细胞分泌IL-2、IL-12、IFN-γ分别为220.44(174.30 ～ 312.30)、7.90 (6.540 ～10.40)、143.75(78.20～210.00) pg/ml,且能力增强;IL-10为21.95(16.30 ～25.00) pg/ml,而能力减弱,与1组比较,差异有统计学意义(U值分别为89.50、98.00、100.00、0,P均＜0.05).抑制或增强Siglec-1对CD8+T淋巴细胞分泌的上述细胞因子无影响(P均＞0.05).结论 IFN-α可刺激Siglec-1表达增加,Siglec-1可通过促进CD4+/CD8+T淋巴细胞增殖或CD4+T淋巴细胞分泌Th1型细胞因子参与AS发病过程.     

PD1-based DNA vaccine amplifies HIV-1 GAG-specific CD8+ T cells in mice

Viral vector–based vaccines that induce protective CD8⁺ T cell immunity can prevent or control pathogenic SIV infections, but issues of preexisting immunity and safety have impeded their implementation in HIV-1. Here, we report the development of what we believe to be a novel antigen-targeting DNA vaccine strategy that exploits the binding of programmed death-1 (PD1) to its ligands expressed on dendritic cells (DCs) by fusing soluble PD1 with HIV-1 GAG p24 antigen. As compared with non–DC-targeting vaccines, intramuscular immunization via electroporation (EP) of the fusion DNA in mice elicited consistently high frequencies of GAG-specific, broadly reactive, polyfunctional, long-lived, and cytotoxic CD8⁺ T cells and robust anti-GAG antibody titers. Vaccination conferred remarkable protection against mucosal challenge with vaccinia GAG viruses. Soluble PD1–based vaccination potentiated CD8⁺ T cell responses by enhancing antigen binding and uptake in DCs and activation in the draining lymph node. It also increased IL-12–producing DCs and engaged antigen cross-presentation when compared with anti-DEC205 antibody-mediated DC targeting. The high frequency of durable and protective GAG-specific CD8⁺ T cell immunity induced by soluble PD1–based vaccination suggests that PD1-based DNA vaccines could potentially be used against HIV-1 and other pathogens.     

Direct activation of CD8+ cytotoxic T lymphocytes by dendritic cells

Recent experiments (11-13) have shown that antigen-specific, CD8+, CD4- T lymphocytes can be induced to proliferate and become killer cells in the absence of a second population of "helper" CD8-, CD4+ cells. We have studied early events in the activation of CD4+ and CD8+ T cell subsets in the primary mixed leukocyte reaction. Dendritic cells are a major if not essential accessory cell for the activation of both subpopulations. Antigen-bearing macrophages fail to stimulate unprimed CD8+ cells, but act as targets for the sensitized cytolytic lymphocytes that are induced by dendritic cells. The initial proliferative response is comparable for CD4+ and CD8+ lymphocyte subsets. For both subpopulations, dendritic cells efficiently cluster the responding lymphocytes on the first day and induce the release of IL-2. The data indicate that CD4+ and CD8+ lymphocytes can be activated by a similar mechanism, and illustrate the special role of dendritic cells in the sensitization stage of cell-mediated immunity.     

Qa-1 restriction of CD8+ suppressor T cells

There is increasing evidence that the immune response can be inhibited by several T cell subsets, including NK T cells, CD25+CD4+ T cells, and a subpopulation of CD8+ T cells. Animal model studies of multiple sclerosis have suggested an important role for suppressor CD8+ T cells in protection against disease recurrence and exacerbation. The molecular lynchpin of CD8+ suppressive activity is the murine MHC molecule Qa-1, termed HLA-E in humans. Here we summarize findings from work on Qa-1 that have begun to delineate suppressor CD8+ T cells and their mechanisms of action in the context of self tolerance and autoimmune disease.     

Large ex vivo expansion of human umbilical cord blood CD4+ and CD8+ T cells.

The use of human umbilical cord (UC) blood as a source of transplantable hematopoietic stem cells and progenitor cells may present some advantages over the use of BM. For example, it has been suggested that the degree of HLA matching may be less stringent, and the risk of GvHD may be lower. We have been studying the ex vivo expansion of UC blood T lymphocytes with a view to their use in the adoptive immunotherapy of cancer, autoimmunity, and infectious disease. We have developed a new method involving the use of a conditioned medium (XLCM) that consistently results in levels of UC blood T cell expansion not hitherto possible. Primary cultures of unfractionated low-density MNC (LDMNC) derived from UC blood treated with 5% XLCM routinely show expansions greater than 10,000-fold within 4 weeks. By contrast, similar FBS-free cultures treated with IL-2 expand less than 10-fold and not after 1 week, and cultures treated with IL-2 and concanavalin A (ConA) expand to a maximum of only 300-500-fold over 2 weeks and fail to continue to proliferate thereafter. The MAb, OKT3, which, when combined with IL-2 and FBS, is known to stimulate proliferation of adult peripheral blood lymphocytes, permitted only a 17-fold expansion of UC blood lymphocytes under the same conditions. Thus, XLCM, which can also stimulate adult peripheral blood lymphocyte expansion to levels exceeding 100,000-fold in 3-4 weeks, is uniquely able to stimulate proliferation of UC blood lymphocytes to high levels. From initiation of the UC blood or adult peripheral blood LDMNC/XLCM cultures up to approximately 2 weeks, the cultures are dominated by CD4+ T lymphocytes. By 4 weeks, >80% of the cultured cells bear the CD8+ phenotype, whereas UC blood T lymphocytes cultured in the presence of IL-2 are predominantly CD8+. Thus, XLCM not only allows high levels of expansion of UC blood T lymphocytes not heretofore possible but also permits the selective expansion of different T lymphocyte subsets from a single source.     

IL-7 administration to humans leads to expansion of CD8+ and CD4+ cells but a relative decrease of CD4+ T-regulatory cells

Lymphopenia is a serious consequence of HIV infection and the administration of cancer chemotherapeutic agents. Although growth factors can be administered to patients to increase circulating neutrophils, there is no effective method to stimulate CD8+ lymphocyte production in humans, in vivo. This report is the first to describe the administration of recombinant interleukin-7 to humans and demonstrates the ability of this cytokine to mediate selective increases in CD4+ and CD8+ lymphocytes along with a decrease in the percentage of CD4+ T-regulatory cells. These studies suggest an important role for interleukin-7 in the treatment of patients with lymphopenia.     

Complementary dendritic cell-activating function of CD8+ and CD4+ T cells: helper role of CD8+ T cells in the development of T helper type 1 responses

Dendritic cells (DCs) activated by CD40L-expressing CD4+ T cells act as mediators of "T helper (Th)" signals for CD8+ T lymphocytes, inducing their cytotoxic function and supporting their long-term activity. Here, we show that the optimal activation of DCs, their ability to produce high levels of bioactive interleukin (IL)-12p70 and to induce Th1-type CD4+ T cells, is supported by the complementary DC-activating signals from both CD4+ and CD8+ T cells. Cord blood- or peripheral blood-isolated naive CD8+ T cells do not express CD40L, but, in contrast to naive CD4+ T cells, they are efficient producers of IFN-gamma at the earliest stages of the interaction with DCs. Naive CD8+ T cells cooperate with CD40L-expressing naive CD4+ T cells in the induction of IL-12p70 in DCs, promoting the development of primary Th1-type CD4+ T cell responses. Moreover, the recognition of major histocompatibility complex class I-presented epitopes by antigen-specific CD8+ T cells results in the TNF-alpha- and IFN-gamma-dependent increase in the activation level of DCs and in the induction of type-1 polarized mature DCs capable of producing high levels of IL-12p70 upon a subsequent CD40 ligation. The ability of class I-restricted CD8+ T cells to coactivate and polarize DCs may support the induction of Th1-type responses against class I-presented epitopes of intracellular pathogens and contact allergens, and may have therapeutical implications in cancer and chronic infections.     

Robust expansion of viral antigen-specific CD4+ and CD8+ T cells for adoptive T cell therapy using gene-modified activated T cells as antigen presenting cells

Cytomegalovirus (CMV) reactivation after stem cell transplantation can be treated with CMV-specific T cells, but current in vitro techniques using dendritic cells as antigen-presenting cells are time-consuming and expensive. To simplify the production of clinical grade CMV-specific T cells, we evaluated gene-modified activated T cells [antigen presenting T cells (T-APCs)] as a reliable and easily produced source of APCs to boost CD4+ and CD8+ T-cell responses against the immunodominant CMV antigen pp65. T-APCs expressing the full-length immunodominant CMV pp65 gene were used to stimulate the expansion of autologous T cells. After 10 to 14 days, the T cell lines were tested for antigen specificity by using the flow cytometric intracellular detection of interferon-gamma after stimulation for 6 hours with a pp65 peptide library of 15-mers, overlapping by 11 amino acids. Under optimal conditions, this technique induced a median 766-fold and a 652-fold expansion of pp65-specific CD4+ and CD8+ responder cells, respectively, in 15 T cell lines. In 13 of 15 T cell lines, over 10 antigen-specific CD4+ plus CD8+ T cells were generated starting with only 5x10 peripheral blood mononuclear cells, representing an over 3-log increase. These data indicate that T-APCs efficiently boost pp65-specific CD4+ and CD8+ T cell numbers to clinically useful levels. The approach has the advantage of using a single leukocyte collection from the donor to generate large numbers of CMV-specific T cells within a total 3-week culture period using only one stimulation of antigen.     

IL-15 regulates memory CD8+ T cell O-glycan synthesis and affects trafficking

Memory and naive CD8⁺ T cells exhibit distinct trafficking patterns. Specifically, memory but not naive CD8⁺ T cells are recruited to inflamed tissues in an antigen-independent manner. However, the molecular mechanisms that regulate memory CD8⁺ T cell trafficking are largely unknown. Here, using murine models of infection and T cell transfer, we found that memory but not naive CD8⁺ T cells dynamically regulate expression of core 2 O-glycans, which interact with P- and E-selectins to modulate trafficking to inflamed tissues. Following infection, antigen-specific effector CD8⁺ T cells strongly expressed core 2 O-glycans, but this glycosylation pattern was lost by most memory CD8⁺ T cells. After unrelated infection or inflammatory challenge, memory CD8⁺ T cells synthesized core 2 O-glycans independently of antigen restimulation. The presence of core 2 O-glycans subsequently directed these cells to inflamed tissue. Memory and naive CD8⁺ T cells exhibited the opposite pattern of epigenetic modifications at the Gcnt1 locus, which encodes the enzyme that initiates core 2 O-glycan synthesis. The open chromatin configuration in memory CD8⁺ T cells permitted de novo generation of core 2 O-glycans in a TCR-independent, but IL-15–dependent, manner. Thus, IL-15 stimulation promotes antigen-experienced memory CD8⁺ T cells to generate core 2 O-glycans, which subsequently localize them to inflamed tissues. These findings suggest that CD8⁺ memory T cell trafficking potentially can be manipulated to improve host defense and immunotherapy.     

Preferential infection and depletion of Mycobacterium tuberculosis-specific CD4 T cells after HIV-1 infection

HIV-1 infection results in the progressive loss of CD4 T cells. In this study, we address how different pathogen-specific CD4 T cells are affected by HIV infection and the cellular parameters involved. We found striking differences in the depletion rates between CD4 T cells to two common opportunistic pathogens, cytomegalovirus (CMV) and Mycobacterium tuberculosis (MTB). CMV-specific CD4 T cells persisted after HIV infection, whereas MTB-specific CD4 T cells were depleted rapidly. CMV-specific CD4 T cells expressed a mature phenotype and produced very little IL-2, but large amounts of MIP-1β. In contrast, MTB-specific CD4 T cells were less mature, and most produced IL-2 but not MIP-1β. Staphylococcal enterotoxin B-stimulated IL-2-producing cells were more susceptible to HIV infection in vitro than MIP-1β-producing cells. Moreover, IL-2 production was associated with expression of CD25, and neutralization of IL-2 completely abrogated productive HIV infection in vitro. HIV DNA was found to be most abundant in IL-2-producing cells, and least abundant in MIP-1β-producing MTB-specific CD4 T cells from HIV-infected subjects with active tuberculosis. These data support the hypothesis that differences in function affect the susceptibility of pathogen-specific CD4 T cells to HIV infection and depletion in vivo, providing a potential mechanism to explain the rapid loss of MTB-specific CD4 T cells after HIV infection.     

HLA-E–restricted HIV-1–specific CD8+ T cell responses in natural infection

CD8⁺ T cell responses restricted by MHC-E, a nonclassical MHC molecule, have been associated with protection in an SIV/rhesus macaque model. The biological relevance of HLA-E–restricted CD8⁺ T cell responses in HIV infection, however, remains unknown. In this study, CD8⁺ T cells responding to HIV-1 Gag peptides presented by HLA-E were analyzed. Using in vitro assays, we observed HLA-E–restricted T cell responses to what we believe to be a newly identified subdominant Gag-KL9 as well as a well-described immunodominant Gag-KF11 epitope in T cell lines derived from chronically HIV-infected patients and also primed from healthy donors. Blocking of the HLA-E/KF11 binding by the B7 signal peptide resulted in decreased CD8⁺ T cell responses. KF11 presented via HLA-E in HIV-infected cells was recognized by antigen-specific CD8⁺ T cells. Importantly, bulk CD8⁺ T cells obtained from HIV-infected individuals recognized infected cells via HLA-E presentation. Ex vivo analyses at the epitope level showed a higher responder frequency of HLA-E–restricted responses to KF11 compared with KL9. Taken together, our findings of HLA-E–restricted HIV-specific immune responses offer intriguing and possibly paradigm-shifting insights into factors that contribute to the immunodominance of CD8⁺ T cell responses in HIV infection.     

Effects of cryopreservation on CD4+ CD25+ T cells of HIV-1 infected individuals

The role of T regulatory cells (Tregs) in human immunodeficiency virus (HIV)-1 infection, although not entirely clear, has recently been highlighted. Despite their lack of specificity, fluorochrome-labeled CD4 and CD25 antibodies are common flow cytometric reagents used to identify these cells with immunosuppressive potential. Cryopreservation has previously been shown to alter the proportions of lymphocytes with certain phenotypes expressed in peripheral blood mononuclear cells (PBMCs). The aim of this study was to assess the effect of cryopreservation on CD4+ CD25+ T cells in PBMCs from HIV-1+ individuals to guide the design of future studies on Tregs. We recruited 30 HIV-1+ individuals and nine healthy controls. CD25 expression in CD4+ T cells was compared between fresh and frozen/thawed PBMC samples from the same time point. In this study, cryopreservation significantly decreased the proportion of CD4+ CD25+ T cells in PBMC samples from HIV-1 infected subjects. This finding suggests that studies of CD4+ CD25+ T cells should be carried out on fresh samples to avoid bias introduced by cryopreservation.