Broad and potent cross clade neutralizing antibodies with multiple specificities in the plasma of HIV-1 subtype C infected individuals.

Broadly Cross clade Neutralizing (BCN) antibodies are recognized as potential therapeutic tools and leads for the design of a vaccine that can protect human beings against various clades of Human Immunodeficiency Virus (HIV). In the present study, we screened plasma of 88 HIV-1 infected ART naïve individuals for their neutralization potential using a standard panel of 18 pseudoviruses belonging to different subtypes and different levels of neutralization. We identified 12 samples with good breadth of neutralization (neutralized >90% of the viruses). Four of these samples neutralized even the difficult-to-neutralize tier-3 pseudoviruses with great potency (GMT > 600). Analysis of neutralization specificities indicated that four samples had antibodies with multiple epitope binding specificities, viz. CD4-binding site (CD4BS), glycans in the V1/V2 and V3 regions and membrane proximal external region (MPER). Our findings indicate the strong possibility of identifying highly potent bNAbs with known or novel specificities from HIV-1 subtype C infected individuals from India that can be exploited as therapeutic tools or lead molecules for the identification of potential epitopes for design of a protective HIV-1 vaccine

A comprehensive analysis of the naturally occurring polymorphisms in HIV-1 Vpr: Potential impact on CTL epitopes

The enormous genetic variability reported in HIV-1 has posed problems in the treatment of infected individuals. This is evident in the form of HIV-1 resistant to antiviral agents, neutralizing antibodies and cytotoxic T lymphocytes (CTLs) involving multiple viral gene products. Based on this, it has been suggested that a comprehensive analysis of the polymorphisms in HIV proteins is of value for understanding the virus transmission and pathogenesis as well as for the efforts towards developing anti-viral therapeutics and vaccines. This study, for the first time, describes an in-depth analysis of genetic variation in Vpr using information from global HIV-1 isolates involving a total of 976 Vpr sequences. The polymorphisms at the individual amino acid level were analyzed. The residues 9, 33, 39, and 47 showed a single variant amino acid compared to other residues. There are several amino acids which are highly polymorphic. The residues that show ten or more variant amino acids are 15, 16, 28, 36, 37, 48, 55, 58, 59, 77, 84, 86, 89, and 93. Further, the variant amino acids noted at residues 60, 61, 34, 71 and 72 are identical. Interestingly, the frequency of the variant amino acids was found to be low for most residues. Vpr is known to contain multiple CTL epitopes like protease, reverse transcriptase, Env, and Gag proteins of HIV-1. Based on this, we have also extended our analysis of the amino acid polymorphisms to the experimentally defined and predicted CTL epitopes. The results suggest that amino acid polymorphisms may contribute to the immune escape of the virus. The available data on naturally occurring polymorphisms will be useful to assess their potential effect on the structural and functional constraints of Vpr and also on the fitness of HIV-1 for replication

HIV-1 gp160 as a Modifier of Th1 and Th2 Cytokine Response: gp160 Suppresses Interferon-γ and Interleukin-2 Production Concomitantly with Enhanced Interleukin-4 Production in Vitro

Disease progression in HIV-1 infection is reported to be associated with a gradual shift in CD4 + T cell function from a Th type 1 to a Th type 2 of response, but the underlying mechanism remains unclear. In this study, the effect of HIV-1 envelope glycoprotein gp160 on secretion of cytokines IFN-γ/IL-2 (Th1 type) and IL-4 (Th2 type) was analyzed using freshly isolated unfractioned peripheral blood mononuclear cells (PBMC), CD4 + T cell lines, and PBMC depleted of CD8 + cells (CD8 - PBMC) as target cells. Pretreatment of these cells with HIV gp160 significantly reduced PHA-induced secretion of IFN-γ and IL-2 but augmented IL-4 production. This effect of gp160 was not observed when the target cells consisted of PBMC depleted of either CD4 + cells (CD4 - PBMC) or of CD2 + cells (CD2 - PBMC). Pretreatment of gp160 with soluble CD4-immunoglobulin chimeric molecules abrogated the observed effects of gp160, suggesting that CD4-gp120 interaction is required for modification of the cytokine secretion profile. Our results suggest that exposure of CD4 + T cells to HIV-1 envelope proteins may modify the responses evoked by additional stimuli in favor of a Th2-type dominant response

Inhibition of Functional Properties of Tetanus Antigen-Specific T-Cell Clones by Envelope Glycoprotein GP120 of Human Immunodeficiency Virus

We investigated mechanisms by which the soluble native envelope glycoprotein gp120 of the human immunodeficiency virus (HIV-1) suppresses antigen-driven T cell responses. For this study, exogenous interleukin-2 (IL-2)-independent, antigen-specific, CD4 positive, human T-cell clones were developed by cyclic restimulation with soluble tetanus toxoid antigen. In the presence of soluble antigen and antigen-presenting cells (APC), T-cell clones proliferated and secreted IL-2. Purified gp120 suppressed the proliferative responses of the T-cell clones with concomitant suppression of IL-2 secretion; proliferative responses of CD8 + T cells preincubated with gp120 were not inhibited. A short pulse of 20 minutes with gp120 was sufficient to inhibit the proliferative response of the T-cell clones. Anti-CD3 monoclonal antibody (MoAb)-driven proliferation of the T-cell clones was also suppressed by gp120, but responses elicited by mitogens, phorbol myristate acetate (PMA) plus calcium ionophore, ionomycin, anti-CD2 MoAbs, and a combination of anti-CD3 plus anti-CD28 MoAb driven responses remained unaffected. Investigation of signal transduction events showed that antigen-driven early activation signals via translocation of protein kinase C (PKC), increase in intracellular inositol phosphates, and increase in intracellular calcium were suppressed in gp120 pretreated, tetanus toxoid antigen-stimulated T-cell clones. One mechanism of immune suppression by gp120 may involve interference with the initiation of signal transduction through the T-cell receptor complex

HIV-1 gp160 Induces Transforming Growth Factor-β Production in Human PBMC

Transforming growth factor-β (TGF-β) is a multifunctional cytokine secreted by many mononuclear cells in peripheral blood (PBMC) and has diverse effects on cellular and humoral immunity. Increased TGF-β mRNA expression has been reported in PBMC of HIV-infected patients, but the mechanism by which HIV induces TGF-β secretion is unknown. In this study, we observed that HIV gp160 could induce significant TGF-β secretion and TGF-β mRNA expression in PBMC from HIV-seronegative healthy donors. The cellular source of TGF-β was attributed to non-T cells, presumably monocytes. Specificity of secreted TGF-β was confirmed by the addition of anti-TGF-β mAb which abrogated the proliferative response of CCL-64 cells by gp160-treated culture supernatants. Soluble CD4 blocked the gp160-induced TGF-β production, suggesting that CD4–gp160 interaction is required to induce TGF-β production. Our results suggest that HIV-1 gp160 may contribute to the immune defects in HIV infection by inducing TGF-β secretion

The HIV Glycoprotein gp160 Has Superantigen-like Properties

HIV infection is characterized by paralysis of the immune system and a depletion of CD4 + cells. Recent studies demonstrating modulation of the Vβ T cell receptor (TCR) repertoire in HIV patients have suggested that some of these effects may be the result of action by one or more superantigens encoded by the virus. In order to determine whether the HIV envelope glycoprotein, gp160, displays properties reminiscent of a superantigen, the T cell receptor Vβ repertoire of T cells from healthy, seronegative individuals activated in vitro with gp160 was determined. In five individuals of disparate HLA type, activation by gp160 resulted in a marked skewing in the relative expression of a common set of Vβ gene segments. This activation was HLA class II-dependent and did not require antigen processing. Surprisingly, the Vβ segments affected by gp160 bore a striking similarity to those affected by the staphylococcal superantigen SEB. These observations suggest that exposure to superantigens produced by opportunistic infection might play an important role in disease progression

Envelope Glycoproteins of HIV-1 Interfere with T-Cell-Dependent B Cell Differentiation: Role of CD4-MHC Class II Interaction in the Effector Phase of T Cell Help

T-cell-dependent B cell differentiation involves two phases: an inductive phase of T cell activation followed by an effector phase, which involves stimulation of B cells by activated T cells. We have previously demonstrated that anti-CD3 mAb and antigen-induced T-cell-dependent B cell functions are inhibited by HIV-1 envelope glycoprotein, gp120, at the inductive phase of T-cell-dependent B cell response. In this study we have investigated whether gp120 also inhibits the effector phase of interactions involved in T-cell-dependent-B cell differentiation response. For these studies, CD4+ T cells were first activated with antigen or pokeweed mitogen, cultured with soluble HIV-gp120 or medium for 2 hr, and washed. Coculture of gp120-treated preactivated T cells with autologous B cells resulted in impairment of IgG secretion, but did not affect IgM secretion significantly. The IgG secretion was restored by the addition of PMA (activator of protein kinase C) or forskolin (activator of adenylate cyclase), but not by the addition of ionomycin (inducer of intracellular calcium) to the T plus B cell cultures. A similar pattern of Ig secretion (IgM, no IgG) was observed with B cells of a patient with bare lymphocyte syndrome, indicating a requirement for MHC class II molecule interaction with T cells. These studies suggest that the effector phase of T-B cell interactions are impaired by gp120, and that-the mechanism involves a signal transducing event(s), which is dependent upon cyclic AMP and/or protein kinase C. Furthermore, these latter reactions occur subsequent to TB cell contact-dependent interactions at the effector phase, which involve MHC class lI molecules on B cells and CD4 molecules on T cells