Inhibition of human immunodeficiency virus type 1 gp120 presentation to CD4 T cells by antibodies specific for the CD4 binding domain of gp120.

Human immunodeficiency virus (HIV)-specific CD4 T-cell responses, particularly to the envelope glycoproteins of the virus, are weak or absent in most HIV-infected patients. Although these poor responses can be attributed simply to the destruction of the specific CD4 T cells by the virus, other factors also appear to contribute to the suppression of these virus-specific responses. We previously showed that human monoclonal antibodies (MAbs) specific for the CD4 binding domain of gp120 (gp120(CD4BD)), when complexed with gp120, inhibited the proliferative responses of gp120-specific CD4 T-cells. MAbs to other gp120 epitopes did not exhibit this activity. The present study investigated the inhibitory mechanisms of the anti-gp120(CD4BD) MAbs. The anti-gp120(CD4BD) MAbs complexed with gp120 suppressed gamma interferon production as well as proliferation of gp120-specific CD4 T cells. Notably, the T-cell responses to gp120 were inhibited only when the MAbs were added to antigen-presenting cells (APCs) during antigen pulse; the addition of the MAbs after pulsing caused no inhibition. However, the anti-gp120(CD4BD) MAbs by themselves, or as MAb/gp120 complexes, did not affect the presentation of gp120-derived peptides by the APCs to T cells. These MAb/gp120 complexes also did not inhibit the ability of APCs to process and present unrelated antigens. To test whether the suppressive effect of anti-gp120(CD4BD) antibodies is caused by the antibodies' ability to block gp120-CD4 interaction, APCs were treated during antigen pulse with anti-CD4 MAbs. These treated APCs remained capable of presenting gp120 to the T cells. These results suggest that anti-gp120(CD4BD) Abs inhibit gp120 presentation by altering the uptake and/or processing of gp120 by the APCs but their inhibitory activity is not due to blocking of gp120 attachment to CD4 on the surface of APCs.

An effective AIDS vaccine based on live attenuated vesicular stomatitis virus recombinants.

We developed an AIDS vaccine based on attenuated VSV vectors expressing env and gag genes and tested it in rhesus monkeys. Boosting was accomplished using vectors with glycoproteins from different VSV serotypes. Animals were challenged with a pathogenic AIDS virus (SHIV89.6P). Control monkeys showed a severe loss of CD4+ T cells and high viral loads, and 7/8 progressed to AIDS with an average time of 148 days. All seven vaccinees were initially infected with SHIV89.6P but have remained healthy for up to 14 months after challenge with low or undetectable viral loads. Protection from AIDS was highly significant (p = 0.001). VSV vectors are promising candidates for human AIDS vaccine trials because they propagate to high titers and can be delivered without injection.

Direct measurement of CD4+ and CD8+ T-cell responses to CMV in HIV-1-infected subjects.

Data from murine models of chronic viral infection suggest that CD4+ T-cell responses to viral pathogens are important in sustaining the number and/or function of CD8+ cytotoxic T-cell (CTL) effectors. In this study, we used cytokine flow cytometry (CFC), staining with HLA-A*0201-peptide tetramers, and peptide stimulation with epitopic peptides to study functional CD4+ and CD8+ T-cell responses to cytomegalovirus (CMV) in human subjects coinfected with CMV and the human immunodeficiency virus, type 1 (HIV-1). We show that strong CD4+ and CD8+ T-cell responses to CMV antigens are sustained over time in HIV-1-infected individuals. Those who maintain a strong CD4+ T-cell response to CMV are also likely to maintain higher frequencies of CD8+ T cells capable of binding to HLA-A*0201-CMV pp65 (A2-pp65) tetramers as well as responses to pp65 peptide stimulation with effector cytokine production. These data support the hypothesis that declines in frequencies of CD4+ T-cell responses to CMV are associated with an inability to sustain high levels of CMV-specific CD8+ T-cell responses in HIV-1-infected subjects. These declines may precede the onset of CMV-associated end organ disease.

Direct measurement of CD8+ T cell responses in macaques infected with simian immunodeficiency virus.

The simian immunodeficiency virus (SIV) macaque model system has been used extensively to study AIDS pathogenesis and to test candidate vaccines for their ability to protect against homologous or heterologous challenge with pathogenic SIV or SHIV. Recent studies suggest that stimulation of HIV-1-specific CTL responses is important for effective vaccination against HIV-1. While quantitative measurements of SIV-specific cytotoxic T lymphocyte (CTL) responses have been facilitated by the use of tetrameric peptide complexes, this technique is currently limited to the study of Mamu-A*01-positive rhesus macaques. Furthermore, very few SIV-specific CTL epitopes have been identified, and there is limited identification of other MHC alleles in macaques. In this study, cytokine flow cytometry (CFC) was used to quantify SIV-specific CD8+ antigen-reactive T cells in macaques infected with SIV. We found a strong correlation (r = 0.96, P < 0.001) between CD8+ antigen-reactive T cells stained with the Mamu-A*01 p11C, C-M tetramer and production of intracellular TNF-alpha in the CFC assay. Furthermore, the CFC assay was used to identify a novel SIV-specific CTL epitope in Envelope (SIV Env, a.a. 486-494, sequence AEVAELYRL). The use of the CFC assay facilitates the study of antigen-reactive T cell responses in SIV infection and vaccination.