Different effects of Nef-mediated HLA class I down-regulation on human immunodeficiency virus type 1-specific CD8(+) T-cell cytolytic activity and cytokine production

A previous study using a Nef-defective human immunodeficiency virus type 1 (HIV-1) mutant suggested that Nef-mediated down-regulation of HLA class I on the infected cell surface affects the cytolytic activity of HIV-1-specific cytotoxic T-lymphocyte (CTL) clones for HIV-1-infected primary CD4(+) T cells. We confirmed this effect by using a nef-mutant HIV-1 strain (NL-M20A) that expresses a Nef protein which does not induce down-regulation of HLA class I molecules but is otherwise functional. HIV-1-specific CTL clones were not able to kill primary CD4(+) T cells infected with a Nef-positive HIV-1 strain (NL-432) but efficiently lysed CD4(+) T cells infected with NL-M20A. Interestingly, CTL clones stimulated with NL-432-infected CD4(+) T cells were able to produce cytokines, albeit at a lower level than when stimulated with NL-M20A-infected CD4(+) T cells. This indicates that Nef-mediated HLA class I down-regulation affects CTL cytokine production to a lesser extent than cytolytic activity. Replication of NL-432 was partially suppressed in a coculture of HIV-1-infected CD4(+) T cells and HIV-1-specific CTL clones, while replication of NL-M20A was completely suppressed. These results suggest that HIV-1-specific CD8(+) T cells are able to partially suppress the replication of HIV-1 through production of soluble HIV-1-suppressive factors such as chemokines and gamma interferon. These findings may account for the mechanism whereby HIV-1-specific CD8(+) T cells are able to partially but not completely control HIV-1 replication in vivo.     

Selective depletion of high-avidity human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells after early HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells in early infection are associated with the dramatic decline of peak viremia, whereas their antiviral activity in chronic infection is less apparent. The functional properties accounting for the antiviral activity of HIV-1-specific CD8+ T cells during early infection are unclear. Using cytokine secretion and tetramer decay assays, we demonstrated in intraindividual comparisons that the functional avidity of HIV-1-specific CD8+ T cells was consistently higher in early infection than in chronic infection in the presence of high-level viral replication. This change of HIV-1-specific CD8+ T-cell avidity between early and chronic infections was linked to a substantial switch in the clonotypic composition of epitope-specific CD8+ T cells, resulting from the preferential loss of high-avidity CD8+ T-cell clones. In contrast, the maintenance of the initially recruited clonotypic pattern of HIV-1-specific CD8+ T cells was associated with low-level set point HIV-1 viremia. These data suggest that high-avidity HIV-1-specific CD8+ T-cell clones are recruited during early infection but are subsequently lost in the presence of persistent high-level viral replication.     

The role of CD4+ T cell help and CD40 ligand in the in vitro expansion of HIV-1-specific memory cytotoxic CD8+ T cell responses

CD4(+) T cells have been shown to play a critical role in the maintenance of an effective anti-viral CD8(+) CTL response in murine models. Recent studies have demonstrated that CD4(+) T cells provide help to CTLs through ligation of the CD40 receptor on dendritic cells. The role of CD4(+) T cell help in the expansion of virus-specific CD8(+) memory T cell responses was examined in normal volunteers recently vaccinated to influenza and in HIV-1 infected individuals. In recently vaccinated normal volunteers, CD4(+) T cell help was required for optimal in vitro expansion of influenza-specific CTL responses. Also, CD40 ligand trimer (CD40LT) enhanced CTL responses and was able to completely substitute for CD4(+) T cell help in PBMCs from normal volunteers. In HIV-1 infection, CD4(+) T cell help was required for optimal expansion of HIV-1-specific memory CTL in vitro in 9 of 10 patients. CD40LT could enhance CTL in the absence of CD4(+) T cell help in the majority of patients; however, the degree of enhancement of CTL responses was variable such that, in some patients, CD40LT could not completely substitute for CD4(+) T cell help. In those HIV-1-infected patients who demonstrated poor responses to CD40LT, a dysfunction in circulating CD8(+) memory T cells was demonstrated, which was reversed by the addition of cytokines including IL-2. Finally, it was demonstrated that IL-15 produced by CD40LT-stimulated dendritic cells may be an additional mechanism by which CD40LT induces the expansion of memory CTL in CD4(+) T cell-depleted conditions, where IL-2 is lacking.     

HIV-1-specific memory CD4+ T cells are phenotypically less mature than cytomegalovirus-specific memory CD4+ T cells

HIV-1-specific CD4(+) T cells are qualitatively dysfunctional in the majority of HIV-1-infected individuals and are thus unable to effectively control viral replication. The current study extensively details the maturational phenotype of memory CD4(+) T cells directed against HIV-1 and CMV. We find that HIV-1-specific CD4(+) T cells are skewed to an early central memory phenotype, whereas CMV-specific CD4(+) T cells generally display a late effector memory phenotype. These differences hold true for both IFN-gamma- and IL-2-producing virus-specific CD4(+) T cells, are present during all disease stages, and persist even after highly active antiretroviral therapy (HAART). In addition, after HAART, HIV-1-specific CD4(+) T cells are enriched for CD27(+)CD28(-)-expressing cells, a rare phenotype, reflecting an early intermediate stage of differentiation. We found no correlation between differentiation phenotype of HIV-1-specific CD4(+) T cells and HIV-1 plasma viral load or HIV-1 disease progression. Surprisingly, HIV-1 viral load affected the maturational phenotype of CMV-specific CD4(+) T cells toward an earlier, less-differentiated state. In summary, our data indicate that the maturational state of HIV-1-specific CD4(+) T cells cannot be a sole explanation for loss of containment of HIV-1. However, HIV-1 replication can affect the phenotype of CD4(+) T cells of other specificities, which might adversely affect their ability to control those pathogens. The role for HIV-1-specific CD4(+) T cells expressing CD27(+)CD28(-) after HAART remains to be determined.     

Preferential apoptosis of HIV-1-specific CD4+ T cells

In contrast to other viral infections such as CMV, circulating frequencies of HIV-1-specific CD4+ T cells in peripheral blood are quantitatively diminished in the majority of HIV-1-infected individuals. One mechanism for this quantitative defect is preferential infection of HIV-1-specific CD4+ T cells, although <10% of HIV-1-specific CD4+ T cells are infected. Apoptosis has been proposed as an important contributor to the pathogenesis of CD4+ T cell depletion in HIV/AIDS. We show here that, within HIV-1-infected individuals, a greater proportion of ex vivo HIV-1-specific CD4+ T cells undergo apoptosis compared with CMV-specific CD4+ T cells (45 vs 7.4%, respectively, p < 0.05, in chronic progressors). The degree of apoptosis within HIV-1-specific CD4+ T cells correlates with viral load and disease progression, and highly active antiretroviral therapy abrogates these differences. The data support a mechanism for apoptosis in these cells similar to that found in activation-induced apoptosis through the TCR, resulting in oxygen-free radical production, mitochondrial damage, and caspase-9 activation. That HIV-1 proteins can also directly enhance activation-induced apoptosis supports a mechanism for a preferential induction of apoptosis of HIV-1-specific CD4+ T cells, which contributes to a loss of immunological control of HIV-1 replication.     

Maintenance of HIV-specific CD4+ T cell help distinguishes HIV-2 from HIV-1 infection

Unlike HIV-1-infected people, most HIV-2-infected subjects maintain a healthy CD4+ T cell count and a strong HIV-specific CD4+ T cell response. To define the cellular immunological correlates of good prognosis in HIV-2 infection, we conducted a cross-sectional study of HIV Gag-specific T cell function in HIV-1- and HIV-2-infected Gambians. Using cytokine flow cytometry and lymphoproliferation assays, we show that HIV-specific CD4+ T cells from HIV-2-infected individuals maintained proliferative capacity, were not terminally differentiated (CD57-), and more frequently produced IFN-gamma or IL-2 than CD4+ T cells from HIV-1-infected donors. Polyfunctional (IFN-gamma+/IL-2+) HIV-specific CD4+ T cells were found exclusively in HIV-2+ donors. The disparity in CD4+ T cell responses between asymptomatic HIV-1- and HIV-2-infected subjects was not associated with differences in the proliferative capacity of HIV-specific CD8+ T cells. This study demonstrates that HIV-2-infected donors have a well-preserved and functionally heterogeneous HIV-specific memory CD4+ T cell response that is associated with delayed disease progression in the majority of infected people.     

Functional and phenotypic characterization of CD57+CD4+ T cells and their association with HIV-1-induced T cell dysfunction

HIV-1 replication is associated with reduced or absent HIV-1-specific CD4+ T cell proliferation and skewing of HIV-1-specific CD4+ T cells toward an IFN-gamma-producing, CCR7- phenotype. The CCR7- T cell population is heterogeneous and can be subdivided based on the expression of CD57. Although CD57 expression on CD8+ T cells is associated with proliferation incompetence and replicative senescence, less is known about the function of CD57-expressing CD4+ T cells. In this study, the frequency, phenotype, and function of CD57+CD4+ T cells were evaluated in 25 HIV-1-infected subjects and 10 seronegative controls. CD57+CD4+ T cells were found to be proliferation incompetent, even after strong mitogen stimulation. Percentages of CD4+ T cells that expressed CD57 were significantly higher in untreated HIV-1-infected subjects than in HIV-1-seronegative donors, and CD57 expression did not normalize in subjects receiving at least 6 mo of effective antiretroviral therapy. CD57 was predominately expressed on the CCR7- fraction of the CD4+ T cell compartment and accounted for the majority of cells in the CCR7-CD45RA+ population from untreated HIV-1-infected subjects. HIV-1-specific CD4+ T cells producing only IFN-gamma had the highest expression of CD57, whereas few cells producing IL-2 alone expressed CD57. These findings further define a novel population of proliferation-incompetent CD4+ T cells that are generated in the presence of chronic Ag exposure. A better understanding of the generation and persistence of CD57+ T cells in HIV-1 infection could provide important insights into the immunopathogenesis of this disease.     

Effects of sustained HIV-1 plasma viremia on HIV-1 Gag-specific CD4+ T cell maturation and function

An in vitro proliferative defect has been observed in HIV-1-specific CD4(+) T cells from infected subjects with high-level plasma HIV-1 viremia. To determine the mechanism of this defect, HIV-1 Gag-specific CD4(+) T cells from treated and untreated HIV-1-infected subjects were analyzed for cytokine profile, proliferative capacity, and maturation state. Unexpectedly high frequencies of HIV-1-specific, IL-2-producing CD4(+) T cells were measured in subjects with low or undetectable plasma HIV-1 loads, regardless of treatment status, and IL-2 frequencies correlated inversely with viral loads. IL-2-producing CD4(+) T cells also primarily displayed a central memory (T(Cm); CCR7(+)CD45RA(-)) maturation phenotype, whereas IFN-gamma-producing cells were mostly effector memory (T(Em), CCR7(-)CD45RA(-)). Among Gag-specific, IFN-gamma-producing CD4(+) T cells, higher T(Em) frequencies and lower T(Cm) frequencies were observed in untreated, high viral load subjects than in subjects with low viral loads. The percentage of HIV-1 Gag-specific CD4(+) T(Cm) correlated inversely with HIV-1 viral load and directly with Gag-specific CD4(+) T cell proliferation, whereas the opposite relationships were observed for HIV-1-specific CD4(+) T(Em). These results suggest that HIV-1 viremia skews Gag-specific CD4(+) T cells away from an IL-2-producing T(Cm) phenotype and toward a poorly proliferating T(Em) phenotype, which may limit the effectiveness of the HIV-1-specific immune response.     

OX40 ligation of CD4+ T cells enhances virus-specific CD8+ T cell memory responses independently of IL-2 and CD4+ T regulatory cell inhibition

We have previously shown that CD4(+) T cells are required to optimally expand viral-specific memory CD8(+) CTL responses using a human dendritic cell-T cell-based coculture system. OX40 (CD134), a 50-kDa transmembrane protein of the TNFR family, is expressed primarily on activated CD4(+) T cells. In murine models, the OX40/OX40L pathway has been shown to play a critical costimulatory role in dendritic cell/T cell interactions that may be important in promoting long-lived CD4(+) T cells, which subsequently can help CD8(+) T cell responses. The current study examined whether OX40 ligation on ex vivo CD4(+) T cells can enhance their ability to "help" virus-specific CTL responses in HIV-1-infected and -uninfected individuals. OX40 ligation of CD4(+) T cells by human OX40L-IgG1 enhanced the ex vivo expansion of HIV-1-specific and EBV-specific CTL from HIV-1-infected and -uninfected individuals, respectively. The mechanism whereby OX40 ligation enhanced help of CTL was independent of the induction of cytokines such as IL-2 or any inhibitory effect on CD4(+) T regulatory cells, but was associated with a direct effect on proliferation of CD4(+) T cells. Thus, OX40 ligation on CD4(+) T cells represents a potentially novel immunotherapeutic strategy that should be investigated to treat and prevent persistent virus infections, such as HIV-1 infection.     

Differential impairment of lytic and cytokine functions in senescent human immunodeficiency virus type 1-specific cytotoxic T lymphocytes

Telomere length is abnormally short in the CD8(+) T-cell compartment of human immunodeficiency virus type 1 (HIV-1)-infected persons, likely because of chronic cell turnover. Although clonal exhaustion of CD8(+) cytotoxic T lymphocytes (CTL) has been proposed as a mechanism for loss of antigen-specific responses, the functional consequences of exhaustion are poorly understood. Here we used telomerase transduction to evaluate the impact of senescence on CTL effector functions. Constitutive expression of telomerase in an HIV-1-specific CTL clone results in enhanced proliferative capacity, in agreement with prior studies of other human cell types. Whereas the CTL remain phenotypically normal in terms of antigenic specificity and requirements for proliferation, their cytolytic and antiviral capabilities are superior to those of control CTL. In contrast, their ability to produce gamma interferon and RANTES is essentially unchanged. The selective enhancement of cytolytic function in memory CTL by ectopic telomerase expression implies that loss of this function (but not cytokine production) is a specific consequence of replicative senescence. These data suggest a unifying mechanism for the in vivo observations that telomere lengths are shortened in the CD8(+) cells of HIV-1-infected persons and that HIV-1-specific CTL are deficient in perforin. Telomerase transduction could therefore be a tool with which to explore a potential therapeutic approach to an important pathophysiologic process of immune dysfunction in chronic viral infection.     

Production of transmembrane and secreted forms of tumor necrosis factor (TNF)-alpha by HIV-1-specific CD4+ cytolytic T lymphocyte clones. Evidence for a TNF-alpha-independent cytolytic mechanism.

Candidate AIDS vaccines consisting of recombinant forms of the HIV-1 envelope glycoprotein induce, in seronegative human volunteers, an env-specific T cell response that includes CD4+, MHC class II-restricted CTL capable of lysing HIV-1-infected target cells. In this study, we have analyzed the production of the cytokines TNF-alpha and lymphotoxin (LT) by a set of env-specific CD4+ human CTL clones. TNF-alpha and LT are of interest because of their potential role in target cell destruction by CD4+ CTL. Our studies focused on the possibility that a cell surface form of TNF-alpha expressed by CTL after physiologic activation with target APC might participate in the cytolytic reactions mediated by these clones. We found that, upon interaction with target cells expressing env epitopes in the context of the appropriate MHC class II molecules, CD4+ CTL released TNF-alpha with kinetics that were rapid, compared with other cytokines, and that were generally similar to the kinetics of target cell destruction. LT secretion was not detected during the time course of the cytolytic reactions. A novel flow cytometric assay was used to show that physiologic activation of CD4+ CTL with target APC induced expression by the CTL of cell surface forms of TNF-alpha. Immunoprecipitations from activated, surface-iodinated CTL clones revealed two forms of surface TNF-alpha, a 26-kDa form, representing the transmembrane precursor of secreted TNF-alpha, as well as the 17-kDa secreted form bound to the cell surface. For a subset of CD4+ CTL, we found that treatment of CTL with cyclosporin A inhibited Ag-induced production of both transmembrane and secreted forms of TNF-alpha but had no effect on cytolysis. Thus, although transmembrane and secreted TNF-alpha produced by HIV-1-specific CD4+ CTL may have important effects in vivo, the rapid destruction of target APC by the set of CD4+ CTL clones described here occurs through a TNF-alpha-independent mechanism.     

HIV-1-specific CD4+ T cells are detectable in most individuals with active HIV-1 infection, but decline with prolonged viral suppression

The role of HIV-1-specific CD4+ T-cell responses in controlling HIV-1 infection remains unclear. Previous work has suggested that such cells are eliminated in the early stages of infection in most subjects, and thus cannot substantially contribute to host defense against HIV-1. Here, using flow cytometric detection of antigen-induced intracellular cytokines, we show that significant frequencies of gag specific, T-helper-1 CD4+ memory T cells are detectable in most subjects with active/progressive HIV-1 infection (median frequency, 0.12% of memory subset; range, 0-0.66%). Median frequencies of these cells were considerably higher in nonprogressive HIV-1 disease (0.40%), but there was substantial overlap between the two groups (range of nonprogressors, 0.10-1.7%). Continuous HIV-1 suppression with anti-retroviral therapy was associated with a time-dependent reduction in median frequencies of gag-specific CD4+ memory T cells: 0.08% in subjects treated for 4-24 weeks, and 0.03% in subjects treated for 47-112 weeks. Thus, functional HIV-1-specific CD4+ T cells are commonly available for support of anti-HIV-1 effector responses in active disease, but their decline with anti-retroviral therapy indicates that immunologic participation in long-term HIV-1 control will probably require effective vaccination strategies.     

Visualization of polyoma virus-specific CD8+ T cells in vivo during infection and tumor rejection.

T cells are critical for clearing infection and preventing tumors induced by polyoma virus, a natural murine papovavirus. We previously identified the immunodominant epitope for polyoma virus-specific CTL in tumor-resistant H-2k mice as the Dk-restricted peptide, MT389-397, derived from the polyoma middle T oncoprotein. In this study, we developed tetrameric Dk complexes containing the MT389-397 peptide to directly visualize and enumerate MT389-397-specific CTL during polyoma virus infection. We found that Dk/MT389 tetramer+CD8+ T cells undergo a massive expansion during primary infection such that by day 7 postinfection these Ag-specific CD8+ T cells constitute approximately 20% of the total and approximately 40% of the activated CD8+ T cells in the spleen. This expansion of Dk/MT389 tetramer+CD8+ T cells parallels the emergence of MT389-397-specific ex vivo cytolytic activity and clearance of polyoma virus. Notably, Dk/MT389 tetramer+CD8+ T cells are maintained in memory at very high levels. The frequencies of Dk/MT389 tetramer+CD8+ effector and memory T cells in vivo match those of CD8+ T cells producing intracellular IFN-gamma after 6-h in vitro stimulation by MT389-397 peptide. Consistent with preferential Vbeta6 expression by MT389-397-specific CD8+CTL lines and clones, Dk/MT389 tetramer+CD8+ T cells exhibit biased expression of this Vbeta gene segment. Finally, we show that Dk/MT389 tetramer+CD8+ T cells efficiently infiltrate a polyoma tumor challenge to virus-immune mice. Taken together, these findings strongly implicate virus-induced MT389-397-specific CD8+ T cells as essential effectors in eliminating polyoma-infected and polyoma-transformed cells in vivo.     

Interleukin-21-producing HIV-1-specific CD8 T cells are preferentially seen in elite controllers

A hallmark of human immunodeficiency virus type 1 (HIV-1) pathogenesis is the rapid loss of CD4 T cells leading to generalized immune dysfunction, including an exhausted CD8 T cell phenotype. Understanding the necessary factors that govern the functional quality and protective potential of antiviral T cell responses would facilitate rational vaccine design and improve therapeutic strategies to combat persistent infections. Mouse models of chronic viral infection demonstrate that interleukin-21 (IL-21), produced primarily by CD4 T cells, is required for the generation and maintenance of functionally competent CD8 T cells and viral containment. We reasoned that preserved IL-21 production during HIV-1 infection would be associated with enhanced CD8 T cell function, allowing improved viral control. Here we analyzed the ability of CD4 and CD8 T cells to produce several cytokines in addition to IL-21 ex vivo following stimulation with overlapping HIV-1 peptides. Both CD4 and CD8 T cells were able to produce IL-21 in response to HIV-1 infection, with the latter cell type more closely associated with viral control. Furthermore, IL-21-producing HIV-1-specific CD4 T cells (compared to those producing other cytokines) were the best indicator of functional CD8 T cells. Our results demonstrate that HIV-1-specific IL-21-producing CD8 T cells are induced following primary infection and enriched in elite controllers, suggesting a critical role for these cells in the maintenance of viremia control.     

Noncytolytic inhibition of X4 virus by bulk CD8(+) cells from human immunodeficiency virus type 1 (HIV-1)-infected persons and HIV-1-specific cytotoxic T lymphocytes is not mediated by beta-chemokines

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) mediate immunologic selection pressure by both cytolytic and noncytolytic mechanisms. Non cytolytic mechanisms include the release of beta-chemokines blocking entry of R5 HIV-1 strains. In addition, CD8(+) cells inhibit X4 virus isolates via release of as yet poorly characterized soluble factors. To further characterize these factors, we performed detailed analysis of CTL as well as bulk CD8(+) T lymphocytes from six HIV-1-infected individuals and from six HIV-1-seronegative individuals. Kinetic studies revealed that secreted suppressive activities of HIV-1-specific CTL and bulk CD8(+) T lymphocytes from all HIV-1-infected persons are significantly higher than that of supernatants from seronegative controls. The suppressive activity could be blocked by monensin and brefeldin A, was heat labile, and appeared in a pattern different from that of secretion of chemokines (MDC, I-309, MIP-1alpha, MIP-1beta, and RANTES), cytokines (gamma interferon, tumor necrosis factor alpha, and granulocyte-macrophage colony-stimulating factor), and interleukins (interleukin-13 and interleukin-16). This suppression activity was characterized by molecular size exclusion centrifugation and involves a suppressive activity of >50 kDa which could be bound to heparin and a nonbinding inhibitory activity of <50 kDa. Our data provide a functional link between CD8(+) cells and CTL in the noncytolytic inhibition of HIV-1 and suggest that suppression of X4 virus is mediated through proteins. The sizes of the proteins, their affinity for heparin, and the pattern of release indicate that these molecules are not chemokines.     

Evaluation of human immunodeficiency virus type 1 (HIV-1)-specific cytotoxic T-lymphocyte responses utilizing B-lymphoblastoid cell lines transduced with the CD4 gene and infected with HIV-1.

Analysis of major histocompatibility complex-restricted cytotoxic T lymphocytes (CTL) capable of killing human immunodeficiency virus type 1 (HIV-1)-infected targets is essential for elucidating the basis for HIV-1 disease progression and the potential efficacy of candidate vaccines. The use of primary CD4+ T cells with variable infectivity as targets for such studies has significant limitations, and immortal autologous cells with high levels of CD4 expression that can be consistently infected with HIV-1 would be of much greater utility. Therefore, we transduced Epstein-Barr-virus-transformed B-lymphoblastoid cell lines (LCL) with a retroviral vector, LT4SN, containing the human CD4 gene. Stable LCL in which more than 95% of cells expressed membrane CD4 were obtained. Aliquots were infected with HIV-1, and, after 4 to 7 days, nearly all of the cells contained cytoplasmic gag and produced high levels of p24 antigen. The ability of major histocompatibility complex-restricted CD8+ CTL to lyse such HIV-1-infected CD4-transduced LCL (LCL-CD4HIV-1) was evaluated. These autologous targets were lysed by CTL generated from an HIV-1-uninfected vaccinee over a broad range of effector-to-target ratios. Similarly, the LCL-CD4HIV-1 were efficiently lysed by fresh circulating CTL from HIV-1-infected individuals, as well as by CTL activated by in vitro stimulation. Both HIV-1 env- and gag-specific CTL effectors lysed LCL-CD4HIV-1, consistent with the cellular expression of both HIV-1 genes. The LCL-CD4HIV also functioned as stimulator cells, and thus are capable of amplifying CTL against multiple HIV-1 gene products in HIV-1-infected individuals. The ability to produce HIV-1-susceptible autologous immortalized cell lines that can be employed as target cells should enable a more detailed evaluation of vaccine-induced CTL against both homologous and disparate HIV-1 strains. Furthermore, the use of LCL-CD4HIV-1 should facilitate the analysis of the range of HIV-1 gene products recognized by CTL in seropositive persons.     

Greater CD8+ TCR heterogeneity and functional flexibility in HIV-2 compared to HIV-1 infection

Virus-specific CD8(+) T cells are known to play an important role in the control of HIV infection. In this study we investigated whether there may be qualitative differences in the CD8(+) T cell response in HIV-1- and HIV-2-infected individuals that contribute to the relatively efficient control of the latter infection. A molecular comparison of global TCR heterogeneity showed a more oligoclonal pattern of CD8 cells in HIV-1- than HIV-2-infected patients. This was reflected in restricted and conserved TCR usage by CD8(+) T cells recognizing individual HLA-A2- and HLA-B57-restricted viral epitopes in HIV-1, with limited plasticity in their response to amino acid substitutions within these epitopes. The more diverse TCR usage observed for HIV-2-specific CD8(+) T cells was associated with an enhanced potential for CD8 expansion and IFN-gamma production on cross-recognition of variant epitopes. Our data suggest a mechanism that could account for any possible cross-protection that may be mediated by HIV-2-specific CD8(+) T cells against HIV-1 infection. Furthermore, they have implications for HIV vaccine development, demonstrating an association between a polyclonal, virus-specific CD8(+) T cell response and an enhanced capacity to tolerate substitutions within T cell epitopes.     

Virus-specific cytotoxic T lymphocytes in human immunodeficiency virus type 1-infected chimpanzees.

Chimpanzees have been important in studies of human immunodeficiency virus type 1 (HIV-1) pathogenesis and in evaluation of HIV-1 candidate vaccines. However, little information is available about HIV-1-specific cytotoxic T lymphocytes (CTL) in these animals. In the present study, in vitro stimulation of peripheral blood mononuclear cells (PBMC) from infected chimpanzees with HIV-1 Gag peptides was shown to be a sensitive, reproducible method of expanding HIV-1-specific CD8(+) effector CTL. Of interest, PBMC from two chimpanzees had CTL activity against Gag epitopes also recognized by major histocompatibility complex class I-restricted CTL from HIV-1-infected humans. The use of peptide stimulation will help to clarify the role of CTL in vaccine-mediated protection and HIV-1 disease progression in this important animal model.     

CD4+ CD25+ regulatory T cells impair HIV-1-specific CD4 T cell responses by upregulating interleukin-10 production in monocytes

T cell dysfunction in the presence of ongoing antigen exposure is a cardinal feature of chronic viral infections with persistent high viremia, including HIV-1. Although interleukin-10 (IL-10) has been implicated as an important mediator of this T cell dysfunction, the regulation of IL-10 production in chronic HIV-1 infection remains poorly understood. We demonstrated that IL-10 is elevated in the plasma of individuals with chronic HIV-1 infection and that blockade of IL-10 signaling results in a restoration of HIV-1-specific CD4 T cell proliferation, gamma interferon (IFN-γ) secretion, and, to a lesser extent, IL-2 production. Whereas IL-10 blockade leads to restoration of IFN-γ secretion by HIV-1-specific CD4 T cells in all categories of subjects investigated, significant enhancement of IL-2 production and improved proliferation of CD4 T helper cells are restricted to viremic individuals. In peripheral blood mononuclear cells (PBMCs), this IL-10 is produced primarily by CD14(+) monocytes, but its production is tightly controlled by regulatory T cells (Tregs), which produce little IL-10 directly. When Tregs are depleted from PBMCs of viremic individuals, the effect of the IL-10 signaling blockade is abolished and IL-10 production by monocytes decreases, while the production of proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), increases. The regulation of IL-10 by Tregs appears to be mediated primarily by contact or paracrine-dependent mechanisms which involve IL-27. This work describes a novel mechanism by which regulatory T cells control IL-10 production and contribute to dysfunctional HIV-1-specific CD4 T cell help in chronic HIV-1 infection and provides a unique mechanistic insight into the role of regulatory T cells in immune exhaustion.     

Expression of CD161 (NKR-P1A) defines subsets of human CD4 and CD8 T cells with different functional activities

A subset of T cells in human peripheral blood expresses CD161 (NKR-P1A) receptors that are primarily associated with NK cells. In the current study we isolated blood T cell subsets according to the expression of CD161 and examined their contents of naive, central memory, and effector memory cells and their capacities for proliferation, cytokine secretion, and natural cytolysis. We found that CD4+CD161- and CD8+CD161- subsets contained predominantly naive T cells that secreted high levels of IL-2 after in vitro stimulation, and CD4+CD161int and CD8+CD161int subsets contained predominantly effector and central memory T cells that secreted high levels of IFN-gamma and TNF-alpha. All of these subsets showed vigorous proliferation after stimulation in vitro, but none had NK lytic activity. Unexpectedly, the CD8+CD161+ cells contained an anergic CD8alpha+CD8betalow/-CD161high T cell subset that failed to proliferate, secrete cytokines, or mediate NK lytic activity.