Keith R. Fowke

Cytotoxic T cell responses to multiple conserved HIV epitopes in HIV-resistant prostitutes in Nairobi.

Many people who remain persistently seronegative despite frequent HIV exposure have HIV-specific immune responses. The study of these may provide information about mechanisms of natural protective immunity to HIV-1. We describe the specificity of cytotoxic T lymphocyte responses to HIV in seronegative prostitutes in Nairobi who are apparently resistant to HIV infection. These women have had frequent exposure to a range of African HIV-1 variants, primarily clades A, C, and D, for up to 12 yr without becoming infected. Nearly half of them have CTL directed towards epitopes previously defined for B clade virus, which are largely conserved in the A and D clade sequences. Stronger responses are frequently elicited using the A or D clade version of an epitope to stimulate CTL, suggesting that they were originally primed by exposure to these virus strains. CTL responses have been defined to novel epitopes presented by HLA class I molecules associated with resistance to infection in the cohort, HLA-A*6802 and HLA-B18. Estimates using a modified interferon-gamma Elispot assay indicate a circulating frequency of CTL to individual epitopes of between 1:3,200 and 1:50,000. Thus, HIV-specific immune responses-particularly cross-clade CTL activity- may be responsible for protection against persistent HIV infection in these African women.

Resistance to HIV-1 infection among persistently seronegative prostitutes in Nairobi, Kenya.

BACKGROUND There is indirect evidence that HIV-1 exposure does not inevitably lead to persistent infection. Heterogeneity in susceptibility to infection could be due to protective immunity. The objective of this study was to find out whether in highly HIV-1-exposed populations some individuals are resistant to infection. METHODS We did an observational cohort study of incident HIV-1 infection-among 424 initially HIV-1-seronegative prostitutes in Nairobi, Kenya, between 1985 and 1994. 239 women seroconverted to HIV-1 during the study period. Exponential, Weibull, and mixture survival models were used to examine the effect of the duration of follow-up on incidence of HIV-1 infection. The influence of the duration of exposure to HIV-1 through prostitution on seroconversion risk was examined by Cox proportional hazards modelling, with control for other known or suspected risk factors for incident HIV-1 infection. HIV-1 PCR with env, nef, and vif gene primers was done on 43 persistently seronegative prostitutes who remained seronegative after 3 or more years of follow-up. FINDINGS Modelling of the time to HIV-1 seroconversion showed that the incidence of HIV-1 seroconversion decreased with increasing duration of exposure, which indicates that there is heterogeneity in HIV-1 susceptibility or acquired immunity to HIV-1. Each weighted year of exposure through prostitution resulted in a 1.2-fold reduction in HIV-1 seroconversion risk (hazard ratio 0.83 [95% CI 0.79-0.88], p < 0.0001). Analyses of epidemiological and laboratory data, show that persistent seronegativity is not explained by seronegative HIV-1 infection or by differences in risk factors for HIV-1 infection such as safer sexual behaviours or the incidence of other sexually transmitted infections. INTERPRETATION We conclude that a small proportion of highly exposed individuals, who may have natural protective immunity to HIV-1, are resistant to HIV-1.

Influence of HLA supertypes on susceptibility and resistance to human immunodeficiency virus type 1 infection

Certain human leukocyte antigens, by presenting conserved immunogenic epitopes for T cell recognition, may, in part, account for the observed differences in human immunodeficiency virus type 1 (HIV-1) susceptibility. To determine whether HLA polymorphism influences HIV-1 susceptibility, a longitudinal cohort of highly HIV-1-exposed female sex workers based in Nairobi, Kenya, was prospectively analyzed. Decreased HIV-1 infection risk was strongly associated with possession of a cluster of closely related HLA alleles (A2/6802 supertype; incidence rate ratio [IRR], 0.45; 95% confidence interval [CI], 0.27-0.72; P=.0003). The alleles in this supertype are known in some cases to present the same peptide epitopes for T cell recognition. In addition, resistance to HIV-1 infection was independently associated with HLA DRB1*01 (IRR, 0.22; 95% CI, 0.06-0.60; P=.0003), which suggests that anti-HIV-1 class II restricted CD4 effector mechanisms may play an important role in protecting against viral challenge. These data provide further evidence that resistance to HIV-1 infection in this cohort of sex workers is immunologically mediated.

Negative mucosal synergy between Herpes simplex type 2 and HIV in the female genital tract

Objective:There is substantial epidemiological evidence that infection by Herpes simplex virus type 2 (HSV2) enhances both HIV susceptibility and subsequent sexual transmission. Both infections are extremely common in female sex workers (FSWs) in sub-Saharan Africa, and up to 80% of new HIV infections in urban men in the region are acquired via transactional sex. The present study aimed to elucidate the mucosal immune interactions between HIV and HSV2 in the genital tract. Methods:Endocervical immune cell populations, cytokine/chemokine protein levels in cervico-vaginal secretions and cervical immune gene expression profiles were measured in a well-defined cohort of HIV-infected and uninfected Kenyan FSWs. Associations between the genital immune milieu and infection by and/or shedding of common genital co-pathogens were examined. Results:HIV-infected FSWs were much more likely to be infected by HSV2, and to shed HSV2 DNA in the genital tract. There was also a profound negative ‘mucosal synergy’ between these viruses. In HIV uninfected FSWs, HSV2 infection was associated with a ten-fold increase in cervical immature dendritic cells (iDC) expressing DC-SIGN, and a three-fold increase in cervical CD4+ T cells expressing CCR5. HIV infection was associated with iDC depletion in the cervix, and with increased HSV2 genital reactivation, which in turn was associated with HIV shedding levels. Conclusions:The findings suggest a mucosal vicious circle in which HSV2 infection increases HIV target cells in the genital mucosa, subsequent HIV infection impairs HSV2 mucosal immune control, and local HSV2 reactivation enhances both HSV2 and HIV transmission.

Isolation of rhododaurichromanic acid B and the anti-HIV principles rhododaurichromanic acid A and rhododaurichromenic acid from Rhododendron dauricum

Abstract—Two novel chromane derivatives (1 and 2) and the known chromene (3) were isolated from the leaves and twigs of Rhodo-dendron dauricum. The absolute stereostructure of 1 was established by spectroscopic examination and X-ray crystallographic analysis. Theabsolute stereostructures of 2 and 3 were also confirmed by photochemical conversion of 3 into 1 and 2. Daurichromenic acid (3)demonstrated potent anti-HIV activity with an EC 50 value of 0.00567 mg/mL and therapeutic index (TI) of 3,710. Rhododaurichromanicacid A (1) also showed relatively potent anti-HIV activity with an EC 50 value of 0.37 mg/mL, and a TI of 91.9, whereas rhododaurichromanicacid B (1) displayed no anti-HIV activity. q 2001 Elsevier Science Ltd. All rights reserved. 1. IntroductionRhododendron dauricum is distributed in the northern partof China, eastern part of Siberia, and Hokkaido. The driedleaves of this plant are known in China as ‘Manshanfong,’and are used medicinally as an expectorant and totreat acute–chronic bronchitis.

Decreased Immune Activation in Resistance to HIV-1 Infection Is Associated with an Elevated Frequency of CD4+CD25+FOXP3+ Regulatory T Cells

Human immunodeficiency virus (HIV)-resistant commercial sex workers provide a unique opportunity to study correlates of protection associated with natural resistance to HIV infection. Emerging data from studies of these individuals and other uninfected individuals who have been exposed to HIV suggest that low levels of immune activation may contribute to protection against infection. In the present study, HIV-resistant individuals were shown to have reduced frequencies of T cells expressing the activation marker CD69. They were also found to have elevated frequencies of regulatory T (T(reg)) cells, compared with HIV-negative control individuals. By controlling levels of T cell activation, T(reg) cells may contribute to HIV resistance by minimizing the pool of cells susceptible to infection.

Immunologic and virologic evaluation after influenza vaccination of HIV-1-infected patients

Objective: The present study was designed to determine the effect of immune activation, achieved by influenza vaccination, on plasma HIV RNA levels and immunological parameters including CD4 cell levels, antigen‐stimulated T‐cell function and apoptotic death of peripheral blood mononuclear cells. Design and methods: Thirty‐four HIV‐infected individuals and nine uninfected controls were immunized with influenza vaccine and blood was collected at weeks 0, 2, 4 and 16. Plasma was isolated and used for HIV RNA and influenza‐specific antibody quantifications. CD4 cell counts, activation and maturation markers of T‐lymphocyte subsets were determined by flow cytometry. In vitro T‐helper responses, spontaneous‐ and activation‐induced cell death assays were also performed. Results: Influenza‐specific humoral and cellular immune responses correlated with CD4 count. Only in patients with CD4 counts > 300 × 106/l there was a modest increase in T‐cell responses to influenza virus, which was less than control subjects, observed after vaccination. Immunization had no significant effect on CD4 counts or plasma viral levels in the HIV‐positive patients. Baseline apoptosis inversely correlated with CD4 counts and directly correlated with viral load. Activation‐induced apoptosis did not change appreciably after vaccination and spontaneous apoptosis increased only in the < 300 CD4 group. Conclusion: These results indicate that immune stimulation resulting from influenza vaccination did not significantly change the levels of plasma virus, CD4 cell counts, or activation‐induced apoptosis in HIV‐infected individuals, although an increase in the T‐cell response to influenza and spontaneous apoptosis was observed in the > 300 and < 300 CD4 groups, respectively.

HIV-1-specific cellular immune responses among HIV-1-resistant sex workers.

The goal of the present study was to determine whether there were HIV‐1 specific cellular immune responses among a subgroup of women within a cohort of Nairobi prostitutes (n = 1800) who, despite their intense sexual exposure to HIV‐1, are epidemiologically resistant to HIV‐1 infection. Of the 80 women defined to be resistant, 24 were recruited for immunological evaluation. The HIV‐1‐specific T‐helper responses were determined by IL‐2 production following stimulation with HIV‐1 envelope peptides and soluble gp120. Cytotoxic T lymphocyte responses were determined by lysis of autologous EBV‐transformed B cell lines infected with control vaccinia virus or recombinant vaccinia viruses containing the HIV‐1 structural genes env, gag and pol. Resistant women had significantly increased HIV‐1 specific T‐helper responses, as determined by in vitro IL‐2 production to HIV‐1 envelope peptides and soluble glycoprotein 120, compared with low‐risk seronegative and HIV‐1‐infected controls (P ≤ 0.01, Students t‐test). Seven of the 17 (41%) resistant women showed IL‐2 stimulation indices ≥ 2.0. HIV‐1‐specific CTL responses were detected among 15/22 (68.2%) resistant women compared with 0/12 low‐risk controls (Chi‐squared test, P < 0.001). In the two resistant individuals tested, the CTL activity was mediated by CD8+ effectors. Many HIV‐1‐resistant women show evidence of HIV‐1‐specific T‐helper and cytotoxic responses. These data support the suggestion that HIV‐1‐specific T‐cell responses contribute to protection against HIV‐1 infection.

Invariant NKT Cells: Regulation and Function during Viral Infection

Natural killer T cells (NKT cells) represent a subset of T lymphocytes that express natural killer (NK) cell surface markers. A subset of NKT cells, termed invariant NKT cells (iNKT), express a highly restricted T cell receptor (TCR) and respond to CD1d-restricted lipid ligands. iNKT cells are now appreciated to play an important role in linking innate and adaptive immune responses and have been implicated in infectious disease, allergy, asthma, autoimmunity, and tumor surveillance. Advances in iNKT identification and purification have allowed for the detailed study of iNKT activity in both humans and mice during a variety of chronic and acute infections. Comparison of iNKT function between non-pathogenic simian immunodeficiency virus (SIV) infection models and chronic HIV-infected patients implies a role for iNKT activity in controlling immune activation. In vitro studies of influenza infection have revealed novel effector functions of iNKT cells including IL-22 production and modulation of myeloid-derived suppressor cells, but ex vivo characterization of human iNKT cells during influenza infection are lacking. Similarly, as recent evidence suggests iNKT involvement in dengue virus pathogenesis, iNKT cells may modulate responses to a number of emerging pathogens. This Review will summarize current knowledge of iNKT involvement in responses to viral infections in both human and mouse models and will identify critical gaps in knowledge and opportunities for future study. We will also highlight recent efforts to harness iNKT ligands as vaccine adjuvants capable of improving vaccination-induced cellular immune responses.

IL-7Rα expression on CD4+ T lymphocytes decreases with HIV disease progression and inversely correlates with immune activation

Many factors can influence the rate of HIV disease progression, including those that maintain T cell homeostasis. One key homeostatic regulator is the IL‐7 receptor (IL‐7R). Previous studies have shown IL‐7R expression levels decrease in HIV infection, but effects on memory subtypes, CD4+ T cells, and cell function have not been explored. The present study examined the expression of the IL‐7Rα chain on naïve and memory T lymphocyte subsets of both HIV‐positive and HIV‐negative individuals from Nairobi, Kenya to assess the role of IL‐7Rα in HIV disease. Expression of IL‐7Rα was significantly reduced in all CD4+ and CD8+ T cell subsets in HIV‐positive individuals. This reduction was further enhanced in those with advanced HIV progression. Expression of IL‐7Rα was inversely correlated to immune activation, and apoptosis, and was positively correlated with CD4 count in both bivariate and multivariate analysis. Expression of IL‐7Rα did not correlate with HIV viral loads, indicating the elevated immune activation seen in HIV‐infected individuals may be impacting expression of IL‐7Rα, independent of viral loads. Signaling via the IL‐7R is essential for T cell homeostasis and maintenance of T cell memory. Reduction of this receptor may contribute to the homeostatic disruption seen in HIV.