Hongbing Yang

Late seroconversion in HIV-resistant Nairobi prostitutes despite pre-existing HIV-specific CD8 + responses

Resistance to HIV infection in a small group of Kenyan sex workers is associated with CD8+-lymphocyte responses to HIV cytotoxic T-lymphocyte (CTL) epitopes. Eleven prostitutes meeting criteria for HIV resistance seroconverted between 1996 and 1999. The occurrence and specificity of preexisting HIV-1 epitope-specific responses were examined using the IFN-gamma enzyme-linked immunospot assay, and any epitopes recognized were cloned and sequenced from the infecting viral isolate. Immunologic and behavioral variables were compared between late seroconverters and persistently uninfected sex worker controls. HIV-1 CTL epitope responses were present in four of six cases, 5-18 months before seroconversion, and their presence was confirmed by bulk CTL culture. A possible viral escape mutation was found in one of six epitopes. The key epidemiologic correlate of late seroconversion was a reduction in sex work over the preceding year. In persistently uninfected controls, a break from sex work was associated with a loss of HIV-specific CD8+ responses. Late seroconversion may occur in HIV-1-resistant sex workers despite preceding HIV-specific CD8+ responses. Seroconversion generally occurs in the absence of detectable CTL escape mutations and may relate to the waning of HIV-specific CD8+ responses due to reduced antigenic exposure.

Design and pre-clinical evaluation of a universal HIV-1 vaccine.

Background One of the big roadblocks in development of HIV-1/AIDS vaccines is the enormous diversity of HIV-1, which could limit the value of any HIV-1 vaccine candidate currently under test. Methodology and Findings To address the HIV-1 variation, we designed a novel T cell immunogen, designated HIVCONSV, by assembling the 14 most conserved regions of the HIV-1 proteome into one chimaeric protein. Each segment is a consensus sequence from one of the four major HIV-1 clades A, B, C and D, which alternate to ensure equal clade coverage. The gene coding for the HIVCONSV protein was inserted into the three most studied vaccine vectors, plasmid DNA, human adenovirus serotype 5 and modified vaccine virus Ankara (MVA), and induced HIV-1-specific T cell responses in mice. We also demonstrated that these conserved regions prime CD8+ and CD4+ T cell to highly conserved epitopes in humans and that these epitopes, although usually subdominant, generate memory T cells in patients during natural HIV-1 infection. Significance Therefore, this vaccine approach provides an attractive and testable alternative for overcoming the HIV-1 variability, while focusing T cell responses on regions of the virus that are less likely to mutate and escape. Furthermore, this approach has merit in the simplicity of design and delivery, requiring only a single immunogen to provide extensive coverage of global HIV-1 population diversity.

CD8+ T-cell selection, function, and death in the primary immune response in vivo

The primary immune response to Epstein Barr virus (EBV) is characterized by striking proliferation of EBV-specific CD8(+) T cells. In this study we have investigated the clonal composition and functional properties of the cells mediating this primary response and have analyzed the mechanisms that control the downregulation of the primary response and the selection of memory cells. We show that massively expanded T-cell clones often dominate the primary antigen-specific T-cell response. Despite the enormous extent of expansion, the virus-specific T cells express high levels of intracellular perforin and are potently cytotoxic. They are, however, functionally heterogeneous in their ability to secrete proinflammatory cytokines, with subpopulations of the antigen-specific T cells being hyporesponsive. The primary response is closely regulated, and the majority of cells are programmed to die via a cytokine-rescuable pathway, leaving only small populations of memory T cells surviving. Comparison of the clonal composition of primary and memory responses in vivo shows that the clones that dominate the primary response are relatively heavily culled during the downregulation of the primary response and the establishment of T-cell memory.

Cross-reactive cytotoxic T lymphocytes against a HIV-1 p24 epitope in slow progressors with B*57.

Objectives To determine whether CD8 T lymphocytes from HIV-1-infected patients expressing B*5701 and B*5703 show broad cross-reactivity against different variants of a conserved p24 epitope, which might account for the good prognosis of HIV-1-infected individuals with HLA-B*57. Design B*5701+ and B*5703+ were recruited from Nairobi, Kenya and from Oxford, UK. All patients had been HIV positive for at least 8 years and could be categorized as slow progressors. Methods CD8 cytotoxic T cell clones were generated from B*5701+ and B*5703+ donors and tested for their ability to recognize clade variants of an index p24 epitope in standard cytolytic assays. Cross-reactive responses in freshly isolated peripheral blood mononuclear cells (PBMC) were assessed by interferon-γ (IFNγ) production and tetramer binding. Results Broad cross-clade reactivity for both cytolysis and tetramer binding was observed in CD8 T cell clones from patients harbouring the index epitope sequence. Patterns of cross-reactivity were similar in freshly isolated PBMC but varied between individuals in terms of strength and breath of responses generated. One common variant induced an unusual response with tetramer binding but often failed to induce IFNγ production, and another was a weak stimulator of both IFNγ and cytolytic activity. Conclusion B*5701+ and B5703+ donors demonstrate broad functional cross-reactivity to both common and rare variants of a dominant p24 epitope, which could be relevant to the association of B*57 alleles with slow progression to AIDS.

Expansion and Diversification of Virus-Specific T Cells following Immunization of Human Immunodeficiency Virus Type 1 (HIV-1)-Infected Individuals with a Recombinant Modified Vaccinia Virus Ankara/HIV-1 Gag Vaccine

ABSTRACT Affordable therapeutic strategies that induce sustained control of human immunodeficiency virus type 1 (HIV-1) replication and are tailored to the developing world are urgently needed. Since CD8+ and CD4+ T cells are crucial to HIV-1 control, stimulation of potent cellular responses by therapeutic vaccination might be exploited to reduce antiretroviral drug exposure. However, therapeutic vaccines tested to date have shown modest immunogenicity. In this study, we performed a comprehensive analysis of the changes in virus-specific CD8+ and CD4+ T-cell responses occurring after vaccination of 16 HIV-1-infected individuals with a recombinant modified vaccinia virus Ankara-vectored vaccine expressing the consensus HIV-1 clade A Gag p24/p17 sequences and multiple CD8+ T-cell epitopes during highly active antiretroviral therapy. We observed significant amplification and broadening of CD8+ and CD4+ gamma interferon responses to vaccine-derived epitopes in the vaccinees, without rebound viremia, but not in two unvaccinated controls followed simultaneously. Vaccine-driven CD8+ T-cell expansions were also detected by tetramer reactivity, predominantly in the CD45RA− CCR7+ or CD45RA− CCR7− compartments, and persisted for at least 1 year. Expansion was associated with a marked but transient up-regulation of CD38 and perforin within days of vaccination. Gag-specific CD8+ and CD4+ T-cell proliferation also increased postvaccination. These data suggest that immunization with MVA.HIVA is a feasible strategy to enhance potentially protective T-cell responses in individuals with chronic HIV-1 infection.

Impaired IFN-γ-secreting capacity in mycobacterial antigen-specific CD4 T cells during chronic HIV-1 infection despite long-term HAART

Objective:To determine whether long-term HAART in chronic HIV-1 infection restores fully functional Mycobacterium tuberculosis (MTB)-specific CD4 T-cell responses. Design:A cross-sectional study of HIV-1-seropositive subjects on continuous HAART for over one year with CD4 cell counts greater than 300 cells/μl and undetectable viraemia, antiretroviral-naive individuals with primary HIV-1 infection (PHI), and healthy bacillus Calmette–Guérin-vaccinated low-risk controls. Methods:Purified protein derivative (PPD)-specific cytokine-secreting CD4 T cells were quantified ex vivo by enzyme-linked immunospot assay and intracellular cytokine staining. Lymphoproliferation was detected by [3H]-thymidine incorporation. Results:PPD-specific IFN-γ-secreting CD4 T cells were markedly reduced in chronic HAART-treated HIV-1-positive and PHI subjects compared with healthy controls [medians 30, 155 and 582 spot-forming cells/million peripheral blood mononuclear cells (PBMC), respectively, P < 0.0001 and P < 0.002], but the frequency of these cells was, nonetheless, significantly greater in viraemic PHI subjects than in aviraemic chronic HIV-1-positive subjects (P < 0.01). In the latter, low frequencies of PPD-specific IL-2 and IL-4-secreting CD4 T cells were also observed. However, lymphoproliferation was evident after the in-vitro stimulation of PBMC with PPD, indicating that MTB-specific T cells were present. The defect in IFN-γ secretion could be overcome by culture with IL-12. Conclusion:Despite an improvement in CD4 T-cell counts after HAART, MTB-specific CD4 T cells from chronically infected patients have impaired IFN-γ-secreting capacity. The early initiation of HAART might preserve functional CD4 T-cell responses to MTB, and warrants evaluation in populations with a high risk of dual infection.

Antiviral Inhibitory Capacity of CD8+ T cells Predicts the Rate of CD4+ T-Cell Decline in HIV-1 Infection

BACKGROUND Rare human immunodeficiency virus type 1 (HIV-1)-infected individuals who maintain control of viremia without therapy show potent CD8+ T-cell-mediated suppression of viral replication in vitro. Whether this is a determinant of the rate of disease progression in viremic individuals is unknown. METHODS We measured CD8+ T-cell-mediated inhibition of a heterologous HIV-1 isolate in 50 HIV-1-seropositive adults with diverse progression rates. Linear mixed models were used to determine whether CD8+ T-cell function could explain variation in the rate of CD4+ T-cell decline. RESULTS There was a significant interaction between CD8+ T-cell antiviral activity in vitro and the rate of CD4+ T-cell decline in chronically infected individuals (P < .0001). In a second prospective analysis of recently infected subjects followed for up to 3 years, CD8+ T-cell antiviral activity strongly predicted subsequent CD4+ T-cell decline (P < .0001) and explained up to 73% of the interindividual variation in the CD4+ T-cell slope. In addition, it was inversely associated with viral load set point (r = -0.68 and P = .002). CONCLUSIONS The antiviral inhibitory capacity of CD8+ T cells is highly predictive of CD4+ T-cell loss in early HIV-1 infection. It has potential as a benchmark of effective immunity in vaccine evaluation.

Epitope specificity of clonally expanded populations of CD8+ T cells found within the joints of patients with inflammatory arthritis

OBJECTIVE To investigate the hypothesis that clonality of synovial T cells from patients with rheumatoid arthritis is at least partly due to the presence of virus-specific T cells expressing a restricted repertoire of T cell receptors (TCRs). METHODS Using fluorescently labeled HLA class I-peptide tetramers, populations of virus-specific CD8+ T cells were identified in samples of peripheral blood and synovial fluid taken from 4 patients with inflammatory arthritis. The TCR repertoire of the virus-specific T cells in the synovial fluid was analyzed using a panel of TCR beta variable region-specific monoclonal antibodies. Where T cells expressing a particular Vbeta chain dominated the response to a viral epitope, the sequences of these Vbeta chains were derived from sorted populations of antigen-specific T cells by reverse transcription-polymerase chain reaction. RESULTS CD8+ T cells specific for Epstein-Barr virus, cytomegalovirus, and influenza virus were enriched in synovial fluid compared with peripheral blood. Clonal or oligoclonal populations of CD8+ T cells were found to dominate the responses to these viral epitopes in synovial fluid. CONCLUSION The results support the hypothesis that restricted T cell receptor usage by large populations of virus-specific T cells provides one explanation for the presence of clonally expanded CD8+ T cells within the joints of patients with inflammatory arthritis. Thus, T cell clonality at a site of inflammation may reflect enrichment for memory T cells specific for foreign antigens, rather than proliferation of autoreactive T cells specific for self antigens.

Immunisation with recombinant modified vaccinia virus Ankara expressing HIV-1 gag in HIV-1-infected subjects stimulates broad functional CD4+ T cell responses.

Virus‐specific CD4+ T cells with IL‐2‐secreting and/or proliferative capacity are detected readily in HIV‐1‐infected long‐term nonprogressors and rarely in persons with untreated progressive infection. The contribution of these cells to viraemia control is uncertain, but this question might be addressed in clinical therapeutic vaccination studies. However, the quality of T helper responses induced by currently available HIV‐1 vaccine candidates has not been explored in depth. We determined the effect of vaccination with modified vaccinia virus Ankara (MVA) expressing HIV‐1 gag p24/p17 (MVA.HIVA) on HIV‐1‐specific CD4+ T cell responses in 16 chronically infected, highly active antiretroviral therapy (HAART)‐treated subjects using CD8‐depleted IFN‐γ ELISPOT assays, intracellular cytokine staining assays for IL‐2 and IFN‐γ, and a CFSE‐based proliferation assay. Gag‐specific CD4+ T cell responses were significantly increased in magnitude and breadth after vaccination and targeted both known and new epitopes, several of which were also recognised by healthy HIV‐uninfected volunteers immunised with the same vaccines. The frequencies of CD4+ T cells expressing IL‐2 or IFN‐γ, alone or simultaneously, were also augmented. These findings indicate that functional virus‐specific T helper cells can be boosted by vaccination in chronic HIV‐1 infection. Further evaluation of their role in viraemia control is warranted.

Therapeutic immunization of highly active antiretroviral therapy-treated HIV-1-infected patients: safety and immunogenicity of an HIV-1 gag/poly-epitope DNA vaccine.

In view of the global emergency posed by lack of access to highly active antiretroviral therapy (HAART) and the limitations of current drug regimens, alternative therapeutic strategies are urgently needed. Cellular immune responses elicited by HIV-1 exert some control over virus replication, therefore the enhancement of HIV-1-specific responses by therapeutic vaccination might lead to viral containment without HAART. We evaluated the safety and immunogenicity, in HIV-1-infected individuals under HAART suppression, of a DNA vaccine, pTHr.HIVA.