Enhanced replication of human T-cell leukemia virus type 1 in T cells from transgenic rats expressing human CRM1 that is regulated in a natural manner

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). To develop a better animal model for the investigation of HTLV-1 infection, we established a transgenic (Tg) rat carrying the human CRM1 (hCRM1) gene, which encodes a viral RNA transporter that is a species-specific restriction factor. At first we found that CRM1 expression is elaborately regulated through a pathway involving protein kinase C during lymphocyte activation, initially by posttranscriptional and subsequently by transcriptional mechanisms. This fact led us to use an hCRM1-containing bacterial artificial chromosome clone, which would harbor the entire regulatory and coding regions of the CRM1 gene. The Tg rats expressed hCRM1 protein in a manner similar to expression of intrinsic rat CRM1 in various organs. HTLV-1-infected T-cell lines derived from these Tg rats produced 100- to 10,000-fold more HTLV-1 than did T cells from wild-type rats, and the absolute levels of HTLV-1 were similar to those produced by human T cells. We also observed enhancement of the dissemination of HTLV-1 to the thymus in the Tg rats after intraperitoneal inoculation, although the proviral loads were low in both wild-type and Tg rats. These results support the essential role of hCRM1 in proper HTLV-1 replication and suggest the importance of this Tg rat as an animal model for HTLV-1.

Glucocorticoid-induced tumor necrosis factor receptor family-related protein triggering enhances HIV-specific CD4+ T cell cytokine secretion and protects HIV-specific CD4+ T cells from apoptosis

Human immunodeficiency virus (HIV)-specific CD4(+) T cell cytokine secretion is characteristically weak during HIV infection, in part because HIV-specific CD4(+) T cells undergo massive apoptotic deletion. Glucocorticoid-induced tumor necrosis factor (TNF) receptor family-related (GITR) protein triggering enhances murine antigen-specific T cell cytokine secretion by protecting T cells from apoptosis. Therefore, we investigated the impact of GITR triggering on HIV-specific CD4(+) T cell cytokine secretion and on apoptosis of HIV-specific CD4(+) T cells. In HIV-infected subjects, CD4(+) T cell surface expression of GITR was greater than that in uninfected control subjects, and phytohemagglutinin induction of additional GITR expression was impaired. However, antibody triggering of GITR significantly increased HIV-specific CD4(+) T cell expression of TNF- alpha and interferon (IFN)- gamma . The percentage increase in HIV-specific CD4(+) T cell expression of TNF- alpha correlated directly with the absolute peripheral CD4(+) T cell count. Furthermore, GITR triggering reduced the expression of intracellular activated caspase-3 in HIV-specific CD4(+) T cells. Taken together, these data suggest that, despite abnormal GITR expression during HIV infection, GITR triggering enhances HIV-specific CD4(+) T cell cytokine expression and protects HIV-specific CD4(+) T cells from apoptosis.

Identification of a CCR5-expressing T cell subset that is resistant to R5-tropic HIV infection

Infection with HIV-1 perturbs homeostasis of human T cell subsets, leading to accelerated immunologic deterioration. While studying changes in CD4(+) memory and naïve T cells during HIV-1 infection, we found that a subset of CD4(+) effector memory T cells that are CCR7(-)CD45RO(-)CD45RA(+) (referred to as TEMRA cells), was significantly increased in some HIV-infected individuals. This T cell subset displayed a differentiated phenotype and skewed Th1-type cytokine production. Despite expressing high levels of CCR5, TEMRA cells were strikingly resistant to infection with CCR5 (R5)-tropic HIV-1, but remained highly susceptible to CXCR4 (X4)-tropic HIV-1. The resistance of TEMRA cells to R5-tropic viruses was determined to be post-entry of the virus and prior to early viral reverse transcription, suggesting a block at the uncoating stage. Remarkably, in a subset of the HIV-infected individuals, the relatively high proportion of TEMRA cells within effector T cells strongly correlated with higher CD4(+) T cell numbers. These data provide compelling evidence for selection of an HIV-1-resistant CD4(+) T cell population during the course of HIV-1 infection. Determining the host factors within TEMRA cells that restrict R5-tropic viruses and endow HIV-1-specific CD4(+) T cells with this ability may result in novel therapeutic strategies against HIV-1 infection.

Role of Stat4-mediated signal transduction events in the generation of aggressor CD4+ T cells in herpetic stromal keratitis pathogenesis

Ocular infection with herpes simplex virus (HSV) causes a vision-impairing inflammatory reaction called herpetic stromal keratitis. In murine models, herpetic stromal keratitis lesions appear to be immunopathologic, mediated by CD4(+) T cells of Th1 phenotype. To provide insight about cytokine networks and signaling events involved in the development of aggressor CD4(+) T cells, ocular HSV infection was followed in mice deficient in Stat4 (Stat4(-/-) mice), the signal transducer for the cytokine interleukin-12 (IL-12). After ocular HSV infection of Stat4(-/-) and control BALB/c mice, clinical, histologic, and immunologic analyses were carried out. Further, to evaluate the involvement of Stat4 in the development of this aggressor population, naive CD4(+) T cells from Stat4(-/-) and BALB/c mice were adoptively transferred to C.B-17 SCID mice 1 day after corneal infection. Although Stat4(-/-) mice demonstrated increased susceptibility to lethal encephalitis and facial lesions, interestingly, these mice had less severe stromal keratitis in comparison to control animals. Adoptive transfer of naive CD4(+) T cells from Stat4(-/-) mice failed to produce disease in infected SCID recipients. The data imply a significant role of Stat4-mediated signaling events in the generation of an aggressor CD4(+) T cell population in stromal keratitis pathogenesis.

Correlates of preserved CD4(+) T cell homeostasis during natural, nonpathogenic simian immunodeficiency virus infection of sooty mangabeys: implications for AIDS pathogenesis

In contrast to HIV-infected humans, naturally SIV-infected sooty mangabeys (SMs) very rarely progress to AIDS. Although the mechanisms underlying this disease resistance are unknown, a consistent feature of natural SIV infection is the absence of the generalized immune activation associated with HIV infection. To define the correlates of preserved CD4(+) T cell counts in SMs, we conducted a cross-sectional immunological study of 110 naturally SIV-infected SMs. The nonpathogenic nature of the infection was confirmed by an average CD4(+) T cell count of 1,076 +/- 589/mm(3) despite chronic infection with a highly replicating virus. No correlation was found between CD4(+) T cell counts and either age (used as a surrogate marker for length of infection) or viremia. The strongest correlates of preserved CD4(+) T cell counts were a low percentage of circulating effector T cells (CD28(-)CD95(+) and/or IL-7R/CD127(-)) and a high percentage of CD4(+)CD25(+) T cells. These findings support the hypothesis that the level of immune activation is a key determinant of CD4(+) T cell counts in SIV-infected SMs. Interestingly, we identified 14 animals with CD4(+) T cell counts of <500/mm(3), of which two show severe and persistent CD4(+) T cell depletion (<50/mm(3)). Thus, significant CD4(+) T cell depletion does occasionally follow SIV infection of SMs even in the context of generally low levels of immune activation, lending support to the hypothesis of multifactorial control of CD4(+) T cell homeostasis in this model of infection. The absence of AIDS in these "CD4(low)" naturally SIV-infected SMs defines a protective role of the reduced immune activation even in the context of a significant CD4(+) T cell depletion.

Human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T(EMRA) cells in early infection are linked to control of HIV-1 viremia and predict the subsequent viral load set point

CD8(+) T cells are believed to play an important role in the control of human immunodeficiency virus type 1 (HIV-1) infection. However, despite intensive efforts, it has not been possible to consistently link the overall magnitude of the CD8(+) T-cell response with control of HIV-1. Here, we have investigated the association of different CD8(+) memory T-cell subsets responding to HIV-1 in early infection with future control of HIV-1 viremia. Our results demonstrate that both a larger proportion and an absolute number of HIV-1-specific CD8(+) CCR7(-) CD45RA(+) effector memory T cells (T(EMRA) cells) were associated with a lower future viral load set point. In contrast, a larger absolute number of HIV-1-specific CD8(+) CCR7(-) CD45RA(-) effector memory T cells (T(EM)) was not related to the viral load set point. Overall, the findings suggest that CD8(+) T(EMRA) cells have superior antiviral activity and indicate that both qualitative and quantitative aspects of the CD8(+) T-cell response need to be considered when defining the characteristics of protective immunity to HIV-1.

CD25+ regulatory T cells isolated from HIV-infected individuals suppress the cytolytic and nonlytic antiviral activity of HIV-specific CD8+ T cells in vitro

HIV infection is characterized by CD4(+) T cell depletion and progressive immune dysfunction; particularly impacted are HIV-specific T cell responses. An important component of immune-mediated control of HIV replication, killing of infected cells, appears to be impaired, in part due to poor cytolytic activity of HIV-specific cytotoxic T cells (CTL). In vitro, several functions of HIV-specific T cells, such as cytokine production, can be enhanced by the depletion of the immunosuppressive CD25(+) FoxP3(+) CD4(+) regulatory (Treg) cell subset. However, the effect of CD25(+) Treg cells on virus-specific cytolytic activity in the context of HIV or any human viral infection has not been investigated. The present study demonstrates that CD25(+) Treg cells isolated from the peripheral blood of HIV-infected subjects significantly suppress HIV Gag-specific cytolytic activity in vitro. In addition, CD25(+) Treg cells suppress effector function (coexpression of TNF-alpha and IFN-gamma) of HIV-specific CD8(+) T cells that proliferate in response to HIV antigen. Finally, the secretion of HIV-inhibitory CC-chemokines by HIV-specific and nonspecific CD8(+) T cells is significantly reduced in the presence of CD25(+) Treg cells. These data suggest that CD25(+) Treg-mediated suppression of the antiviral activity of HIV-specific CD8(+) T cells could impact the ability of HIV-infected individuals to control HIV replication in vivo.

HIV-1 envelope T cell epitope "hotspots " among mice and humans and among CD4+ and CD8+ T cell subpopulations

HIV-1-specific T cell responses correlate with control of infection and disease, thus encouraging a full understanding of the peptides and antigen-processing mechanisms that govern T cell activation. We have previously demonstrated that CD4(+) T cell epitopes cluster nonrandomly within envelope protein "hotspot" regions. The current study was initiated to determine whether envelope-specific CD8(+) T cells might share epitope "hotspots" with the CD4(+) T cell population. Identification of CD8(+) T cell determinants by ELISPOT assays with peripheral blood mononuclear cells from four HIV-1-infected individuals, in conjunction with a survey of determinants in the Los Alamos database, revealed similarities among "hotspot" positions for CD4(+) and CD8T(+) cells within mice and humans. These results emphasized the important influence that envelope peptide position may have on antigen processing, and the consequent impact such processing may have on HIV-1-specific CD4(+) and CD8(+) T-cell activities.

Suppression of HIV-specific T cell activity by lymph node CD25+ regulatory T cells from HIV-infected individuals

CD25(+) CD4(+) FoxP3(+) regulatory T (Treg) cells isolated from the peripheral blood of asymptomatic HIV-infected individuals have been demonstrated to significantly suppress HIV-specific immune responses in vitro. CD25(+) Treg cell suppressor activity in the peripheral blood seems to diminish with progression of HIV disease, and it has been suggested that loss of Treg cells contributes to aberrant immune activation and disease progression. However, phenotypic studies suggest that Treg cells may migrate to, and be maintained or even expanded in, tissue sites of HIV replication. Currently, it is not known whether tissue-associated Treg cells maintain suppressive activity in the context of HIV infection, particularly in individuals with advanced disease. The present study demonstrates that CD25(+) Treg cells isolated from lymph nodes and peripheral blood of HIV(+) subjects, even those with high viral loads and/or low CD4(+) T cell counts, maintain potent suppressive activity against HIV-specific cytolytic T cell function. This activity was better in lymph node as compared with peripheral blood, particularly in patients with high levels of plasma viremia. In addition, the expression of certain CD25(+) Treg-associated markers on CD4(+) T cells isolated from lymph nodes differed significantly from those on CD4(+) T cell subsets isolated from the peripheral blood. These data suggest that CD25(+) Treg cell-mediated suppression of HIV-specific responses continues throughout the course of HIV disease and, because of their particularly potent suppression of HIV-specific CTL activity in lymphoid tissue, may considerably impact the ability to control HIV replication in vivo.

Massive expansion of EBV+ monoclonal T cells with CD5 down regulation in EBV-associated haemophagocytic lymphohistiocytosis

Haemophagocytic lymphohistiocytosis (HLH) comprises primary and secondary forms; the secondary form is most commonly triggered by the Epstein-Barr virus (EBV; EBV-HLH). Patients with EBV-HLH usually exhibit oligoclonal or monoclonal T cell proliferation, which may mimic T cell lymphoproliferative disorder (T-LPD). This article reports on EBV-HLH in a 17-month-old girl with an extreme surge of reactive T lymphocytosis (absolute count 167x10(9)/l) with CD5 down regulation. Bone marrow aspirate and trephine contained florid haemophagocytosis and massive infiltration of CD3+ Epstein-Barr virus-encoded RNA+ lymphocytes, as seen by double labelling. These lymphocytes were monoclonal for EBV and T cell receptor gamma chain gene rearrangement. The patient responded dramatically to intravenous immunoglobulin, interferon alpha2b, ganciclovir and prednisolone, suggesting restoration of her immune system and eradication of the clonal T cells through these immunoregulatory agents. Thus, careful clinicopathological correlation is warranted in the interpretation of immunophenotyping and clonality data in T cell proliferation in association with EBV-HLH to avoid erroneous diagnosis of T-LPD.

In vitro characterization of primary SIVsmm isolates belonging to different lineages. In vitro growth on rhesus macaque cells is not predictive for in vivo replication in rhesus macaques

We report in vitro characterization of 11 SIVsmm strains of six lineages co-circulating in naturally infected sooty mangabeys (SMs) from US Primate Centers and showed no major differences in the in vitro replication pattern between different SIVsmm lineages. Primary SIVsmm isolates utilized CCR5 and Bonzo co-receptors in vitro. SIVsmm growth in human T cell lines was isolate-, not lineage-specific, with poor replication on Molt4-Clone8, CEMss and PM1 cells and better replication on MT2, SupT1 and CEMx174 cells. All primary SIVsmm isolates replicated on SM and human PBMCs. In vitro replication in macaques varied widely, with moderate to high replication in pig-tailed macaque PBMCs, enhanced by CD8+ T cell depletion, and highly variable replication on rhesus macaque (Rh) PBMCs. Primary SIVsmm isolates replicated in Rh monocyte-derived dendritic cells (MDDCs) and monocyte-derived macrophages (MDMs). In vivo, SIVsmm isolates replicated at high levels in all SIVsmm-infected Rh. The poor in vitro replication of primary SIVsmm isolates in Rh cells did not correlate with in vivo replication, emphasizing the value of in vivo studies.

HIV infection of primary CD4+ Th2 cells, defined by expression of the chemoattractant receptor-homologous (CRTH2), induces a Th0 phenotype

The association between HIV, cytokine profile, and disease progression is controversial. In this study, we evaluated whether HIV infection of a primary T helper-like type 2 cytokine (Th2) cell subset augments their cytokine profile. We utilized the CRTH2 (chemoattractant receptor-homologous) marker to identify CD4+ Th2 cells. Approximately 2-4% of CD4+ T cells are CRTH2+. CRTH2+ expression is confirmed to delineate a Th2 subset as indicated by robust inducible IL-4 response. CD4+ CRTH2+ T cells were also more inherently activated than their CRTH2-negative counterpart as indicated by a higher percent expression of CD69, CD45RO, CD95, CD25, and HLA-DR. CD4+CRTH2+ T cells were not terminally differentiated as indicated by expression of CD27 and CD28. In vitro HIV infection of primary human CD4 CRTH2T cells, independent of chemokine coreceptor usage, potently upregulated IFN-gamma production while still maintaining robust IL-4 expression. This Th0 (IFNgamma+ IL-4+) phenotype was upregulated in CD4+CRTH2+ T cells post-HIV infection by 18-fold, demonstrating a shift to a Th0 phenotype. Ex vivo studies also demonstrated that HIV+ patients exhibited a decline in CD4+CRTH2+ cells and a shift of this population toward cells that express both IFN-gamma and IL-4. Collectively, these data indicate that HIV replication in Th2 cells induces a Th0 phenotype. This phenomenon may be a deliberate viral escape mechanism to prevent the skewing of the immune response toward Th1 or Th2.

Lack of intrinsic CTLA-4 expression has minimal effect on regulation of antiviral T-cell immunity

CTLA-4 is considered one of the most potent negative regulators of T-cell activation. To circumvent experimental limitations due to fatal lymphoproliferative disease associated with genetic ablation of CTLA-4, we have used radiation chimeras reconstituted with a mixture of CTLA-4+/+ and CTLA-4-/- bone marrow that retain a normal phenotype and allow the evaluation of long-term T-cell immunity under conditions of intrinsic CTLA-4 deficiency. Following virus infection, we profiled primary, memory, and secondary CD8+ and CD4+ T-cell responses directed against eight different viral epitopes. Our data demonstrate unaltered antigen-driven proliferation, acquisition of effector functions, distribution of epitope hierarchies, T-cell receptor repertoire selection, functional avidities, and long-term memory maintenance in the absence of CTLA-4. Moreover, regulation of memory T-cell survival and homeostatic proliferation, as well as secondary responses, was equivalent in virus-specific CTLA4+/+ and CTL-A-4-/- T-cell populations. Thus, lack of CTLA-4 expression by antigen-specific T cells can be compensated for by extrinsic factors in the presence of CTLA-4 expression by other cells. These findings have implications for the physiologic, pathological, and therapeutic regulation of costimulation.

Vaccinia virus inhibits T cell receptor-dependent responses by human gammadelta T cells

Vaccinia virus (VV) is an effective vaccine and vector but has evolved multiple mechanisms for evading host immunity. We characterized the interactions of VV (TianTan and New York City Board of Health strains) with human gammadelta T cells because of the role they play in immune control of this virus. Exposure to VV failed to trigger proliferative responses in gammadelta T cells from unprimed individuals, but it was an unexpected finding that VV blocked responses to model antigens by the Vgamma2Vdelta2 T cell subset. Infectious or ultraviolet light-inactivated VV inhibited proliferative Vgamma2Vdelta2 T cell responses to phosphoantigens and tumor cells, prevented cytolysis of Daudi B cells, and reduced cytokine production. Inhibiting Vgamma2Vdelta2 T cells may be a mechanism for evading host immunity and increasing VV virulence. Increased VV replication or expression in the absence of gammadelta T cell responses might contribute to its potency as a vaccine against poxvirus and recombinant antigens.

Naive T-cell depletion related to infection by X4 human immunodeficiency virus type 1 in poor immunological responders to highly active antiretroviral therapy

The reasons for poor CD4+ T-cell recovery in some human immunodeficiency virus (HIV)-infected subjects despite effective highly active antiretroviral therapy (HAART) remain unclear. We recently reported that CXCR4-using (X4) HIV-1 could be gradually selected in cellular reservoirs during sustained HAART. Because of the differential expression of HIV-1 coreceptors CCR5 and CXCR4 on distinct T-cell subsets, the residual replication of R5 and X4 viruses could have different impacts on T-cell homeostasis during immune reconstitution on HAART. We examined this hypothesis and the mechanisms of CD4+ T-cell restoration by comparing the virological and immunological features of 15 poor and 15 good immunological responders to HAART. We found a high frequency of X4 viruses in the poor immunological responders. But the levels of intrathymic proliferation of the two groups were similar regardless of whether they were infected by R5 or X4 virus. The frequency of recent thymic emigrants in the poor immunological responders was also similar to that found in the good immunological responders, despite their reduced numbers of naïve CD4+ T cells. Our data, rather, suggest that the naïve T-cell compartment is drained by a high rate of mature naïve cell loss in the periphery due to bystander apoptosis or activation-induced differentiation. X4 viruses could play a role in the depletion of naïve T cells in poor immunological responders to HAART by triggering persistent T-cell activation and bystander apoptosis via gp120-CXCR4 interactions.

Infection of CD127+ (interleukin-7 receptor+) CD4+ cells and overexpression of CTLA-4 are linked to loss of antigen-specific CD4 T cells during primary human immunodeficiency virus type 1 infection

We recently found that human immunodeficiency virus (HIV)-specific CD4+ T cells express coreceptor CCR5 and activation antigen CD38 during early primary HIV-1 infection (PHI) but then rapidly disappear from the circulation. This cell loss may be due to susceptibility to infection with HIV-1 but could also be due to inappropriate apoptosis, an expansion of T regulatory cells, trafficking out of the circulation, or dysfunction. We purified CD38+++CD4+ T cells from peripheral blood mononuclear cells, measured their level of HIV-1 DNA by PCR, and found that about 10% of this population was infected. However, a small subset of HIV-specific CD4+) T cells also expressed CD127, a marker of long-term memory cells. Purified CD127+CD4+ lymphocytes contained fivefold more copies of HIV-1 DNA per cell than did CD127-negative CD4+ cells, suggesting preferential infection of long-term memory cells. We observed no apoptosis of antigen-specific CD4+ T cells in vitro and only a small increase in CD45RO+CD25+CD127dimCD4+ T regulatory cells during PHI. However, 40% of CCR5+CD38+++ CD4+ T cells expressed gut-homing integrins, suggesting trafficking through gut-associated lymphoid tissue (GALT). Furthermore, 80% of HIV-specific CD4+ T cells expressed high levels of the negative regulator CTLA-4 in response to antigen stimulation in vitro, which was probably contributing to their inability to produce interleukin-2 and proliferate. Taken together, the loss of HIV-specific CD4+ T cells is associated with a combination of an infection of CCR5+ CD127+ memory CD4+ T cells, possibly in GALT, and a high expression of the inhibitory receptor CTLA-4.

Gamma delta T cells facilitate adaptive immunity against West Nile virus infection in mice

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, and gammadelta T cells are involved in the protective immune response against viral challenge. We have now examined whether gammadelta T cells contribute to the development of adaptive immune responses that help control WN virus infection. Approximately 15% of TCRdelta(-/-) mice survived primary infection with WN virus compared with 80-85% of the wild-type mice. These mice were more susceptible to secondary challenge with WN virus than the wild-type mice that survived primary challenge with the virus. Depletion of gammadelta T cells in wild-type mice that survived the primary infection, however, does not affect host susceptibility during secondary challenge with WN virus. Furthermore, gammadelta T cells do not influence the development of Ab responses during primary and at the early stages of secondary infection with WN virus. Adoptive transfer of CD8(+) T cells from wild-type mice that survived primary infection with WN virus to naive mice afforded partial protection from lethal infection. In contrast, transfer of CD8(+) T cells from TCRdelta(-/-) mice that survived primary challenge with WN virus failed to alter infection in naive mice. This difference in survival correlated with the numeric and functional reduction of CD8 memory T cells in these mice. These data demonstrate that gammadelta T cells directly link innate and adaptive immunity during WN virus infection.

Cutting edge: central memory T cells do not show accelerated proliferation or tissue infiltration in response to localized herpes simplex virus-1 infection

Memory T cells mount an enhanced response to secondary infections. Such an enhancement has been attributed in part to the ability of memory cells to more rapidly respond to cognate stimulation. In this study we have examined the rapidity with which murine CD8(+) memory T cells respond to a localized infection with HSV. Although central memory T cells (TcM), but not the effector memory T cells, mounted a strong recall response to secondary infection, the kinetics of TcM proliferation, the magnitude of their expansion, and their infiltration into infected nonlymphoid tissues were not advanced compared with that observed for naive T cells. These findings imply that it is the lack of accelerated proliferation kinetics and the subsequent delayed dissemination into the periphery that limits the ability of TcM to rapidly control localized virus replication.

Complex T cell memory repertoires participate in recall responses at extremes of antigenic load

The CD8 T cell memory response to the HLA-A2-restricted influenza epitope M1(58-66) can be an instructive model of immune memory to a nonevolving epitope of a frequently encountered pathogen that undergoes clearance. This memory repertoire can be complex, composed of a large number of clonotypes represented at low copy numbers, while maintaining a focus on the use of VB17 T cell receptors with identified Ag recognition motifs. Such a repertoire structure might provide a panoply of clonotypes whose differential avidity for the epitope would allow responses under varying antigenic loads. This possibility was tested experimentally by characterizing the responding repertoire in vitro while varying influenza Ag concentration over five orders of magnitude. At higher and lower Ag concentrations there was increased cell death, yet a focused but diverse response could still be observed. Thus, one of the characteristics of complex memory repertoires is to provide effector function at extremes of Ag load, a characteristic that is not generally considered in vaccination development but may be important in measuring its efficacy.

Alterations of natural killer cell and T-lymphocyte counts in adults infected with human immunodeficiency virus through blood and plasma sold in the past in China and in whom infection has progressed slowly over a long period

Natural killer (NK) cells, natural killer T (NKT) cells, and T lymphocytes were analyzed by using a flow cytometer in 225 human immunodeficiency virus (HIV)-positive individuals infected through the past sale of blood and plasma without receiving antiretroviral therapy in the People's Republic of China. According to CD4 T-cell counts these HIV-infected adults were stratified into three groups: long-term slow progressors, HIV-infected subjects, and AIDS patients. NK cell counts in long-term slow progressors were higher compared to HIV infection and AIDS patients (P < 0.05) and lower compared to normal controls (P < 0.05), whereas NKT cell counts in slow progressors and the HIV infection group were not different from those of normal controls. NK cell counts in HIV-seropositive subjects were positively correlated with CD4 T-cell counts (P < 0.05), and NKT cell counts were positively correlated with CD4 T-cell and CD8 T-cell counts (P < 0.05). The CD8 T-cell counts were higher in slow progressors compared to those with HIV infection, AIDS patients, and normal controls. These results indicated that HIV infection causes alterations of NK cells and T cells in slow progressors, HIV-infected subjects, and AIDS patient groups, but no difference was found in NKT cell counts and percentages in slow progressors and the HIV-infected group compared to normal controls.

Evaluation of immunological paradigms in a virus model: are dendritic cells critical for antiviral immunity and viral clearance?

We have examined the role of dendritic cells (DCs) in the antiviral immune response and viral clearance using a transgenic mouse model (CD11c-diphtheria toxin (DT) receptor GFP) that allows for their conditional ablation in vivo. DT administration systemically ablated conventional and IFN-producing plasmacytoid DCs (pDCs) in transgenic, but not nontransgenic littermates, without elimination of splenic macrophages. Unexpectedly, early (12 and 48 h postinfection) viral clearance of vesicular stomatitis virus was normal in DC-depleted mice despite markedly reduced serum titers of type I IFN. DC-depleted mice remained virus-free with the exception of a subset (approximately 30%) that developed overwhelming and fatal brain infections 6 days postinfection. However, DT treatment profoundly inhibited clonal expansion of naive CD8+ vesicular stomatitis virus-specific T cells without altering the primary Th1 and Th2 cytokine response. Optimal clonal expansion required pDCs because selective elimination of these cells in vivo with a depleting Ab also suppressed expansion of tetramer+ cells, although Th1/Th2 cytokine production remained unaltered. Collectively, these data indicate that conventional DCs and to a lesser extent pDCs are critical for proliferation of naive antiviral T cells. However, other components of the primary adaptive immune response (Th1/Th2 cytokines) are essentially normal in the absence of DCs, which may account for the efficient viral clearance seen in DC-depleted mice. Thus, sufficient redundancy exists in the immune system to sustain efficient viral clearance despite loss of an APC considered essential for induction of a primary antiviral immune response.

Circulating and liver resident CD4+CD25+ regulatory T cells actively influence the antiviral immune response and disease progression in patients with hepatitis B

CD4+CD25+ regulatory T cells (Treg) have been shown to maintain immune tolerance against self and foreign Ags, but their role in persistent viral infection has not been well-defined. In this study, we investigated whether and where CD4+CD25+ Treg contribute to the development of chronic hepatitis B (CHB). One hundred twenty-one patients were enrolled, including 16 patients with acute hepatitis B, 76 with CHB, and 29 with chronic severe hepatitis B. We demonstrated that in chronic severe hepatitis B patients, the frequencies of CD4+CD25+ Treg in both PBMC and liver-infiltrating lymphocytes were significantly increased and there was a dramatic increase of FoxP3(+)-cell and inflammatory cell infiltration in the liver compared with healthy controls. In CHB patients, circulating CD4+CD25+ Treg frequency significantly correlates with serum viral load. In acute hepatitis B patients, circulating CD4+CD25+ Treg frequency was initially low and with time, the profile reversed to exhibit an increased number of circulating Treg in the convalescent phase and restored to normal levels upon resolution. In PBMC taken from infected patients, depletion of CD4+CD25+ Treg led to an increase of IFN-gamma production by HBV-Ag-stimulated PBMC. In addition, CD4+CD25+ Treg were capable of suppressing proliferation of autologous PBMC mediated by HBV Ags, which probably reflects the generation of HBV-Ag-specific Treg in circulation and in the liver of HBV-infected patients. Together, our findings suggest that CD4+CD25+ Treg play an active role not only in modulating effectors of immune response to HBV infection, but also in influencing the disease prognosis in patients with hepatitis B.

Stimulation History Dictates Memory CD8 T Cell Phenotype: Implications for Prime-Boost Vaccination

Heterologous prime-boost vaccination results in increased frequencies of memory T cells. Although these quantitative effects of reexposure to Ag are well documented, little is known about the impact of boosting on the functional qualities of memory T cells. To address this critical issue, we have used three different types of immunization regimens and examined how boosting effects the function and anatomic location of memory CD8 T cells. We found that memory T cell phenotype differed substantially depending on the number of immunizations and that secondary and tertiary responses resulted in the generation of memory CD8 T cells that retained effector-like properties and showed preferential accumulation in nonlymphoid tissues. These results show that memory differentiation is coupled to the history of Ag experience and that prime-boost vaccination strategies have important consequences on memory CD8 T cell quality and surveillance within mucosal tissues.

Bim mediates apoptosis of CD127(lo) effector T cells and limits T cell memory

Following an acute T cell response, most activated effector cells die, while some survive and become memory cells. The pro-apoptotic Bcl-2 family member, Bcl-2 interacting mediator of death (Bim) is critical for eliminating most effector T cells, while expression of CD127 (IL-7Ralpha) has been proposed to mark effector cells destined to become memory cells. Here, we examined the effects of Bim on the death of effector T cells in relationship to CD127 expression and on development of T cell memory following lymphocytic choriomeningitis virus (LCMV) infection. We found that large numbers of CD127(lo) LCMV-specific CD4(+) and CD8(+) T cells were lost in wild-type mice, but were spared in Bim(-/-) mice. Further, while the numbers of CD127(hi) T cells declined only slightly during contraction of the response in wild-type mice, they increased significantly in Bim(-/-) mice due to re-expression of CD127 on CD127(lo) T cells that had avoided apoptosis. Functional memory T cells were significantly increased in Bim(-/-) mice; however, they underwent a slow attrition due to decreased proliferative renewal. Taken together, these data suggest that the absence of Bim-mediated death of LCMV-specific CD4(+) and CD8(+) T cells in vivo can increase T cell memory, but other homeostatic mechanisms control the long-term maintenance of memory cells.

Dynamics of T cells subsets and lymphoproliferative responses during structured treatment interruption cycles and after definitive interruption of HAART in early chronic HIV type-1-infected patients

Little is known about the consequences of short cycles of structured treatment interruption or definitive interruption of HAART for both T cell subset dynamics and T lymphoproliferative responses (LPR). Immunological follow-up was performed in 45 early chronical HIV-1-infected patients during short STI cycles during the first 12 weeks after the definitive interruption of HAART (DTI) and, thereafter, until VL reached a plateau. During STI cycles, CD8(+), CD8(+), CD28(+), activation markers and naive CD4(+) T cells increased significantly (p < 0.0001), while both naive CD8(+) and memory CD4(+) T cells decreased. During DTI, CD8(+) CD28(+) T cells fell and CD4(+) naive T cells stabilized and the rest of the T cell subsets presented changes similar to those during STI cycles. Despite a transient increase in LPR to recall antigens and HIV proteins during STI cycles, LPR to polyclonal stimuli and pathogens decreased over the study. Differences in T cell subset dynamics and LPR observed throughout the study suggest that multiple exposures to low levels of antigen could improve the immune system, mainly by driving T cell maturation. Conversely, higher and longer viral replication after cessation of HAART overwhelms the immune system. These data may help to guide future immune-based therapies.