Alan Steel

Early and nonreversible decrease of CD161++/MAIT cells in HIV infection

HIV infection is associated with immune dysfunction, perturbation of immune-cell subsets and opportunistic infections. CD161++ CD8+ T cells are a tissue-infiltrating population that produce IL17A, IL22, IFN, and TNFα, cytokines important in mucosal immunity. In adults they dominantly express the semi-invariant TCR Vα7.2, the canonical feature of mucosal associated invariant T (MAIT) cells and have been recently implicated in host defense against pathogens. We analyzed the frequency and function of CD161++ /MAIT cells in peripheral blood and tissue from patients with early stage or chronic-stage HIV infection. We show that the CD161++ /MAIT cell population is significantly decreased in early HIV infection and fails to recover despite otherwise successful treatment. We provide evidence that CD161++ /MAIT cells are not preferentially infected but may be depleted through diverse mechanisms including accumulation in tissues and activation-induced cell death. This loss may impact mucosal defense and could be important in susceptibility to specific opportunistic infections in HIV.

Loss of Discrete Memory B Cell Subsets Is Associated with Impaired Immunization Responses in HIV-1 Infection and May Be a Risk Factor for Invasive Pneumococcal Disease

Invasive pneumococcal infection is an important cause of morbidity and mortality in HIV-1-infected individuals. B cells play an important role in maintaining serologic memory after infection. IgM memory B cells are significantly reduced in HIV-1-infected patients and their frequency is similar to that observed in other patient groups (splenectomized individuals and patients with primary Ab deficiency) who are also known to have an increased risk of invasive pneumococcal infection. Antiretroviral therapy does not restore marginal zone B cell percentages. Immunization with the 23-valent polysaccharide pneumococcal vaccine shows that HIV-1-infected patients have impaired total IgM and IgG pneumococcal vaccines compared with healthy controls. Loss of switched memory B cells was associated with impaired tetanus toxoid IgG vaccine responses. Results of this study demonstrate that defects in B cell memory subsets are associated with impaired humoral immune responses in HIV-1 patients who are receiving antiretroviral therapy and may be a contributory factor to the increased risk of invasive pneumococcal infection observed in HIV-1 infection.

Tuberculosis antigen-specific immune responses can be detected using enzyme-linked immunospot technology in human immunodeficiency virus (HIV)-1 patients with advanced disease

There are limited data on the efficacy of T cell‐based assays to detect tuberculosis (TB) antigen‐specific responses in immune‐deficient human immunodeficiency virus (HIV) patients. The aim of this study is to determine whether TB antigen‐specific immune responses can be detected in patients with HIV‐1 infection, especially in those with advanced disease (CD4 T cell count < 300 cells/µl). An enzyme‐linked immunospot (ELISPOT) assay, which detects interferon (IFN)‐γ secreted by T cells exposed to TB antigens, was used to assess specific immune responses in a prospective study of 201 HIV‐1‐infected patients with risk factors for TB infection, attending a single HIV unit. The performance of the ELISPOT assay to detect TB antigen‐specific immune responses is independent of CD4 T cell counts in HIV‐1 patients. The sensitivity and specificity of this assay for the diagnosis of active tuberculosis does not differ significantly from values obtained in immunocompetent subjects. The negative predictive value of the TB ELISPOT test is 98·2%. A positive predictive value of 86% for the diagnosis of active tuberculosis was found when the combined number of early secretory antigen target‐6 (ESAT‐6) and culture filtrate protein‐10 (CFP‐10) IFN‐γ spots to CD4 T cell count ratio was > 1·5. TB antigen‐specific immune responses can be detected in HIV patients with low CD4 T cell counts using ELISPOT technology in a routine diagnostic laboratory and is a useful test to exclude TB infection in immune‐deficient HIV‐1 patients. A combination of TB antigen‐specific IFN‐γ responses and CD4 T cell counts has the potential to distinguish active tuberculosis from latent infection.

Switch from inhibitory to activating NKG2 receptor expression in HIV-1 infection: lack of reversion with highly active antiretroviral therapy.

Background:HIV-1 infection is characterized by increase in inhibitory receptors and loss of activating receptors on natural killer (NK) cells, resulting in loss of cell activity. Exceptionally, for an inhibitory receptor, the proportion of NK cells bearing CD94-NKG2A decreases during HIV-1 infection. It is not understood whether HIV-1 itself or other concomitant infections drive these changes. Objectives:To investigate the relationship between HIV-1 viraemia and changes in C-type lectin-like receptor expression in NK cells and to investigate the effect of highly active antiretroviral therapy (HAART) on these changes. Methods:Three cohorts of patients were studied: (1) before, during and after treatment interruption in aviraemic and viraemic patients receiving HAART (n = 15); (2) HIV-1-positive treatment-naive individuals (n = 13); and (3) HIV-1-positive individuals receiving successful HAART for a minimum of 1 year without interruption (n = 11). Flow cytometry was used to study the expression of NKG2A before and after treatment interruption and to define expanded populations of NK cells in untreated and treated HIV-1-positive individuals. Assays were performed in vitro to assess the cytotoxicity of the expanded populations. Results:Increases in plasma HIV-1 RNA during treatment interruption in aviraemic HAART-treated individuals did not influence the proportion of NK cells carrying the complex CD94-NKG2A. Loss of NKG2A NK cells corresponded to the dramatic expansion of a distinct population of cells expressing a functional activating CD94-NKG2C receptor with skewed expression of killer cell immunoglobulin-like receptor family and natural cytotoxicity receptors. Conclusion:Changes in the NK cell repertoire during HIV-1 infection were not a result of HIV-1 viraemia alone but resembled those associated with concomitant infections.

Viral Inhibition Assay: A CD8 T Cell Neutralization Assay for Use in Clinical Trials of HIV-1 Vaccine Candidates

We have characterized an assay measuring CD8 T cell-mediated inhibition of human immunodeficiency virus (HIV) type 1 replication, demonstrating specificity and reproducibility and employing a panel of primary HIV-1 isolates. The assay uses relatively simple autologous cell culture and enzyme-linked immunosorbent assay, avoids generation of T cell clones, and can be performed with <2 million peripheral blood mononuclear cells. Efficient CD8 T cell-mediated cross-clade inhibition of HIV-1 replication in vitro was demonstrated in antiretroviral therapy-naive HIV-1-infected subjects with controlled viral replication in vivo but not in viremic subjects. An HIV-1 vaccine candidate, consisting of DNA and recombinant adenovirus 5 vectors tested in a phase I clinical trial, induced CD8 T cells that efficiently inhibited HIV-1 in a HLA-I-dependent manner. Assessment of direct antiviral T cell function by this assay provides additional information to guide vaccine design and the prioritizing of candidates for further clinical trials.

Increased proportion of CD16+ NK cells in the colonic lamina propria of inflammatory bowel disease patients, but not after azathioprine treatment

Aliment Pharmacol Ther 2011; 33: 115–126

Expression of PD-L1, a marker of disease status, is not reduced by HAART in aviraemic patients.

Anergy and defective immune responses are characteristic of chronic HIV-1 infection. The programmed death 1 (PD-1)/PD-1 ligand (PD-L1) pathway appears to be involved in downregulating T-cell functionality. We found raised levels of PD-L1 in aviraemic chronically infected HIV-1-positive patients, which may contribute to incomplete immune reconstitution after treatment with HAART.

CD8+/CD161++ mucosal-associated invariant T-cell levels in the colon are restored on long-term antiretroviral therapy and correlate with CD8+ T-cell immune activation.

Mucosal-associated invariant T (MAIT) cells are tissue-homing T cells recently implicated in HIV pathogenesis. We found that the proportion of MAIT cell in blood and colon of HIV+ patients are reduced in untreated infection. Antiretroviral therapy restored colonic but not blood MAIT cell percentages. We observed a negative correlation between colonic MAIT cells and T-cell activation in blood and suggest mucosal MAIT cell depletion may contribute to systemic immune activation in HIV infection.

Depletion of natural killer cells in the colonic lamina propria of viraemic HIV-1-infected individuals.

Background:HIV-1 infection is known to have a detrimental impact on peripheral blood natural killer cell phenotype and function. Chronic HIV-1 also causes a substantial depletion of CD4+ T cells in the gastrointestinal tract and the blood. Objective:To investigate the impact of chronic HIV-1 infection with on natural killer cell populations in the gastrointestinal tract and the effect of suppression of plasma viraemia with antiretroviral therapy. Methods:Lymphocyte populations were extracted from the lamina propria of biopsies taken from the sigmoid colon of HIV-1-infected and uninfected individuals. The proportions of natural killer cell subsets were compared in viraemic (n = 15) and aviraemic HIV-1-positive, HAART-treated individuals (n = 27) and HIV-1 negative control individuals (n = 26) using flow cytometry on gated subsets. Results:Natural killer cells are depleted in colonic biopsies from HIV-1-infected individuals with detectable plasma virus in comparison with HIV-1-negative individuals. A significant increase in the proportion of both natural killer and CD4+ T cells in the colonic lamina propria is observed in aviraemic individuals compared to viraemic individuals. Conclusions:Chronic HIV-1 infection results in depletion of both natural killer cells and CD4+ T cells in colonic tissue and antiretroviral therapy results in a recovery of these subsets in individuals with undetectable plasma viral load.

Elevated plasma lipopolysaccharide is not sufficient to drive natural killer cell activation in HIV-1-infected individuals.

Background:Lipopolysaccharide (LPS) is elevated in the plasma of individuals chronically infected with HIV-1 and is thought to contribute to chronic immune activation of myeloid cells and T-cells. Natural killer (NK) cells can also be stimulated by LPS in vitro. Objectives:To measure plasma LPS levels in individuals with HIV-1 infection, with or without suppressed plasma viral load, and in individuals with or without inflammatory bowel diseases (IBD). To compare the expression of NK cell receptors and activation markers in individuals with HIV-1 infection and in HIV-1-negative individuals with active IBD. Methods:NK cells were studied by flow cytometry in treatment-naïve viraemic HIV-1-positive individuals (n = 14), aviraemic HIV-1-positive individuals (n = 19), HIV-1-negative individuals with inflammatory bowel disease (n = 10) and HIV-1-negative healthy control individuals (n = 17). Plasma endotoxin (LPS) was measured using the limulus amoebocyte assay. Results:Viraemic and aviraemic HIV-1-positive individuals and patients with IBD have elevated levels of plasma LPS compared with HIV-1-negative individuals.HIV-1-positive individuals had significant changes in activation marker or NK cell receptor expression, whereas NK cells from IBD patients had similar levels to HIV-1-negative controls. NK cells from HIV-1-positive individuals are refractory to further stimulation by LPS in vitro. Conclusion:Elevated plasma LPS alone does not account for the chronic activation and receptor loss in NK cells from HIV-1-infected individuals.