Johan K. Sandberg

Activation, exhaustion, and persistent decline of the antimicrobial MR1-restricted MAIT-cell population in chronic HIV-1 infection

Mucosal-associated invariant T (MAIT) cells are an evolutionarily conserved antimicrobial MR1-restricted T-cell subset. MAIT cells are CD161(+), express a V7.2 TCR, are primarily CD8(+) and numerous in blood and mucosal tissues. However, their role in HIV-1 infection is unknown. In this study, we found levels of MAIT cells to be severely reduced in circulation in patients with chronic HIV-1 infection. Residual MAIT cells were highly activated and functionally exhausted. Their decline was associated with time since diagnosis, activation levels, and the concomitant expansion of a subset of functionally impaired CD161(+) V7.2(+) T cells. Such cells were generated in vitro by exposure of MAIT cells to Escherichia coli. Notably, whereas the function of residual MAIT cells was at least partly restored by effective antiretroviral therapy, levels of MAIT cells in peripheral blood were not restored. Interestingly, MAIT cells in rectal mucosa were relatively preserved, although some of the changes seen in blood were recapitulated in the mucosa. These findings are consistent with a model in which the MAIT-cell compartment, possibly as a result of persistent exposure to microbial material, is engaged, activated, exhausted, and progressively and persistently depleted during chronic HIV-1 infection.

Functional Heterogeneity of Cytokines and Cytolytic Effector Molecules in Human CD8+ T Lymphocytes

CD8+ T cells use a number of effector mechanisms to protect the host against infection. We have studied human CD8+ T cells specific for CMV pp65495–503 epitope, or for staphylococcal enterotoxin B, for the expression patterns of five cytokines and cytolytic effector molecules before and after antigenic stimulation. Ex vivo, the cytolytic molecule granzyme B was detected in a majority of circulating CMV-specific CD8+ T cells, whereas perforin was rarely expressed. Both were highly expressed after Ag-specific activation accompanied by CD45RO up-regulation. TNF-α, IFN γ, and IL-2 were sequentially acquired on recognition of Ag, but surprisingly, only around half of the CMV-specific CD8+ T cells responded to antigenic stimuli with production of any cytokine measured. A dominant population coexpressed TNF-α and IFN-γ, and cells expressing TNF-α only, IFN-γ only, or all three cytokines together also occurred at lower but clearly detectable frequencies. Interestingly, perforin expression and production of IFN-γ and TNF-α in CD8+ T cells responding to staphylococcal enterotoxin B appeared to be largely segregated, and no IL-2 was detected in perforin-positive cells. Together, these data indicate that human CD8+ T cells can be functionally segregated in vivo and have implications for the understanding of human CD8+ T cell differentiation and specialization and regulation of effector mechanisms.

Selective Loss of Innate CD4+ Vα24 Natural Killer T Cells in Human Immunodeficiency Virus Infection

ABSTRACT Vα24 natural killer T (NKT) cells are innate immune cells involved in regulation of immune tolerance, autoimmunity, and tumor immunity. However, the effect of human immunodeficiency virus type 1 (HIV-1) infection on these cells is unknown. Here, we report that the Vα24 NKT cells can be subdivided into CD4+ or CD4− subsets that differ in their expression of the homing receptors CD62L and CD11a. Furthermore, both CD4+ and CD4− NKT cells frequently express both CXCR4 and CCR5 HIV coreceptors. We find that the numbers of NKT cells are reduced in HIV-infected subjects with uncontrolled viremia and marked CD4+ T-cell depletion. The number of CD4+ NKT cells is inversely correlated with HIV load, indicating depletion of this subset. In contrast, CD4− NKT-cell numbers are unaffected in subjects with high viral loads. HIV infection experiments in vitro show preferential depletion of CD4+ NKT cells relative to regular CD4+ T cells, in particular with virus that uses the CCR5 coreceptor. Thus, HIV infection causes a selective loss of CD4+ lymph node homing (CD62L+) NKT cells, with consequent skewing of the NKT-cell compartment to a predominantly CD4− CD62L− phenotype. These data indicate that the key immunoregulatory NKT-cell compartment is compromised in HIV-1-infected patients.

CD8+ T cells rapidly acquire NK1.1 and NK cell-associated molecules upon stimulation in vitro and in vivo.

NKT cells express both NK cell-associated markers and TCR. Classically, these NK1.1+TCRαβ+ cells have been described as being either CD4+CD8− or CD4−CD8−. Most NKT cells interact with the nonclassical MHC class I molecule CD1 through a largely invariant Vα14-Jα281 TCR chain in conjunction with either a Vβ2, -7, or -8 TCR chain. In the present study, we describe the presence of significant numbers of NK1.1+TCRαβ+ cells within lymphokine-activated killer cell cultures from wild-type C57BL/6, CD1d1−/−, and Jα281−/− mice that lack classical NKT cells. Unlike classical NKT cells, 50–60% of these NK1.1+TCRαβ+ cells express CD8 and have a diverse TCR Vβ repertoire. Purified NK1.1−CD8α+ T cells from the spleens of B6 mice, upon stimulation with IL-2, IL-4, or IL-15 in vitro, rapidly acquire surface expression of NK1.1. Many NK1.1+CD8+ T cells had also acquired expression of Ly-49 receptors and other NK cell-associated molecules. The acquisition of NK1.1 expression on CD8+ T cells was a particular property of the IL-2Rβ+ subpopulation of the CD8+ T cells. Efficient NK1.1 expression on CD8+ T cells required Lck but not Fyn. The induction of NK1.1 on CD8+ T cells was not just an in vitro phenomenon as we observed a 5-fold increase of NK1.1+CD8+ T cells in the lungs of influenza virus-infected mice. These data suggest that CD8+ T cells can acquire NK1.1 and other NK cell-associated molecules upon appropriate stimulation in vitro and in vivo.

Enhancement of Human Immunodeficiency Virus Type 1—Specific CD4 and CD8 T Cell Responses in Chronically Infected Persons after Temporary Treatment Interruption

Immunologic and virologic outcomes of treatment interruption were compared for 5 chronically human immunodeficiency virus (HIV)-infected persons who have maintained antiretroviral therapy-mediated virus suppression, as compared with 5 untreated controls. After a median interruption of 55 days of therapy accompanied by rebound of virus, reinitiated therapy in 4 of 5 subjects resulted in suppression of 98.86% of plasma virus load by 21-33 days and no significant decrease in CD4 T cell percentage from baseline. Increased T helper responses against HIV-1 p24 antigen (P=. 014) and interferon-gamma-secreting CD8 T cell responses against HIV-1 Env (P=.004) were present during interruption of therapy and after reinitiation of treatment. The remaining subject whose treatment was interrupted did not resume treatment and continued to have a low virus load (<1080 HIV-1 RNA copies/mL) and persistent antiviral cell-mediated responses. In summary, cellular immunity against autologous HIV-1 has the potential to be acutely augmented in association with temporary treatment interruption in chronically infected persons.

CD56 negative NK cells: origin, function, and role in chronic viral disease

Natural killer (NK) cells serve as a first line of defense against acute viral infections. Immunogenetic association data suggest that NK cells also influence the course of chronic viral infections, such as infections with HIV-1 and hepatitis C virus (HCV). Chronic stages of these infections have a negative impact on NK cell function and promote the appearance of phenotypically and functionally abnormal NK cells. In this paper, we summarize available data on CD56(neg) NK cells, an aberrant NK cell subset found in small numbers in healthy individuals and at elevated levels in individuals chronically infected with HIV-1 and HCV. We discuss current knowledge of CD56(neg) NK cells, with a particular emphasis on their accumulation during chronic infection and the possible consequences of this for the host.

Inhibition of lipid antigen presentation in dendritic cells by HIV-1 Vpu interference with CD1d recycling from endosomal compartments

Dendritic cells (DCs) play an important role in viral infections both as initiators of immunity and as viral targets. Interaction between DCs and the innate-like CD1d-restricted natural killer T (NKT) cells results in the mutual activation of both cells and the subsequent initiation of cellular immune responses. Here, we show that HIV-1 inhibits the surface expression of CD1d in productively infected DCs and identify this as a novel activity of the HIV-1 vpu gene product. Interestingly, the viral protein U (Vpu) does not enhance constitutive CD1d endocytosis or induce rapid CD1d degradation. Instead, the Vpu protein interacts with CD1d and suppresses its recycling from endosomal compartments to the cell surface by retaining CD1d in early endosomes. This interference with the CD1d antigen presentation pathway strongly inhibits the ability of infected DCs to activate CD1d-restricted NKT cells. Given that the interaction with CD1d-expressing DCs is central to the ability of NKT cells to regulate immunity, these data suggest that interference with the CD1d antigen presentation pathway represents an HIV-1 strategy to evade innate cellular immune responses and imply a role for the innate-like CD1d-restricted NKT cells in the host defense against HIV-1.

High Levels of Chronic Immune Activation in the T-Cell Compartments of Patients Coinfected with Hepatitis C Virus and Human Immunodeficiency Virus Type 1 and on Highly Active Antiretroviral Therapy Are Reverted by Alpha Interferon and Ribavirin Treatment

ABSTRACT Chronic immune activation is a driver of human immunodeficiency virus type 1 (HIV-1) disease progression. Here, we describe that subjects with chronic hepatitis C virus (HCV)/HIV-1 coinfection display sharply elevated immune activation as determined by CD38 expression in T cells. This occurs, despite effective antiretroviral therapy, in both CD8 and CD4 T cells and is more pronounced than in the appropriate monoinfected control groups. Interestingly, the suppression of HCV by pegylated alpha interferon and ribavirin treatment reduces activation. High HCV loads and elevated levels of chronic immune activation may contribute to the high rates of viral disease progression observed in HCV/HIV-1-coinfected patients.

Acquisition of innate-like microbial reactivity in mucosal tissues during human fetal MAIT-cell development

Innate-like, evolutionarily conserved MR1-restricted mucosa-associated invariant T (MAIT) cells represent a large antimicrobial T-cell subset in humans. Here, we investigate the development of these cells in second trimester human fetal tissues. MAIT cells are rare and immature in the fetal thymus, spleen and mesenteric lymph nodes. In contrast, mature IL-18Rα+ CD8αα MAIT cells are enriched in the fetal small intestine, liver and lung. Independently of localization, MAIT cells express CD127 and Ki67 in vivo and readily proliferate in response to Escherichia coli in vitro. Maturation is accompanied by the gradual post-thymic acquisition of the PLZF transcription factor and the ability to produce IFNγ and IL-22 in response to bacteria in mucosa. Thus, MAIT cells acquire innate-like antimicrobial responsiveness in mucosa before exposure to environmental microbes and the commensal microflora. Establishment of this arm of immunity before birth may help protect the newborn from a range of pathogenic microbes.

Dominant effector memory characteristics, capacity for dynamic adaptive expansion, and sex bias in the innate Vα24 NKT cell compartment

Vα24 natural killer T (NKT) cells are innate immune cells that recognize self and nonself glycolipids presented by CD1d molecules, and play immunoregulatory roles in autoimmunity and tumorimmunity. We have investigated the circulating Vα24 NKT cells in a large cohort of human subjects. CCR7– CD45RO+ effector memory cells dominated both CD4+ and CD4 NKT subsets, while a minority displayed a central memory phenotype. CD4– central memory NKT cells, however, were atypical in that they largely lacked CD62L expression. Overall, CD4– NKT cells displayed a functional phenotype with effector characteristics, while the CD4+ subset appeared immunoregulatory. Interestingly, NKT cell numbers in blood varied widely between subjects, and elevated numbers of these cells were much more common in women than in men. The CD4+ subset dominated the NKT cell compartment in both sexes, while circulating NKT cell numbers above 0.1% were associated with an expanded CD4– subset. Although NKT cell numbers were generally stable over time, we describe a dynamic fivefold expansion that was associated with a skewing of the NKT CD4+:CD4– ratio that persisted after numbers returned to base line. Thus, the two NKT cell subsets display different properties and dynamics that will influence theirfunction as innate immunoregulatory and effector cells.