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D D Ho

Publications and source records attributed to D D Ho.

At least 163 records · Page 9Linked to original sources
PubMed1992

Identification and characterization of a neutralization site within the second variable region of human immunodeficiency virus type 1 gp120.

Two monoclonal antibodies designated BAT085 and G3-136 were raised by immunizing BALB/c mice with gp120 purified from human immunodeficiency virus type 1 (HIV-1) IIIB-infected H9 cell extracts. Among three HIV-1 laboratory isolates (IIIB, MN, and RF), BAT085 neutralized only IIIB infection of CEM-SS cells, whereas G3-136 neutralized both IIIB and RF. These antibodies also neutralized a few primary HIV-1 isolates in the infection of activated human peripheral blood mononuclear cells. In indirect immunofluorescence assays, BAT085 bound to H9 cells infected with IIIB or MN, while G3-136 bound to H9 cells infected with IIIB or RF, but not MN. Using sequence-overlapping synthetic peptides of HIV-1 IIIB gp120, the binding site of BAT085 and G3-136 was mapped to a peptidic segment in the V2 region (amino acid residues 169 to 183). The binding of these antibodies to immobilized gp120 was not inhibited by the antibodies directed to the principal neutralization determinant in the V3 region or to the CD4-binding domain of gp120. In a competition enzyme-linked immunosorbent assay, soluble CD4 inhibited G3-136 but not BAT085 from binding to gp120. Deglycosylation of gp120 by endo-beta-N-acetylglucosaminidase H or reduction of gp120 by dithiothreitol diminished its reactivity with G3-136 but not with BAT085. These results indicate that the V2 region of gp120 contains multiple neutralization determinants recognized by antibodies in both a conformation-dependent and -independent manner.

Amino Acid Sequence↗
PubMed1992

Mapping genetic determinants for human immunodeficiency virus type 1 resistance to soluble CD4.

Neutralization of human immunodeficiency virus type 1 (HIV-1) infection with soluble CD4 (sCD4) can be achieved over a broad range of concentrations for different virus strains. Laboratory virus strains passaged in transformed T-cell lines are typically sensitive to sCD4 neutralization, whereas primary virus isolates require over 100-fold-higher sCD4 concentrations. Using recombinant viruses generated from a laboratory strain, HIV-1NL4-3, and a primary macrophagetropic strain, HIV-1JR-FL, we mapped a region of gp120 important for determining sensitivity to sCD4 neutralization. This same region has previously been defined as important for macrophage and transformed T-cell line tropism and includes the V3 neutralization domain but does not include regions of gp120 that have been shown to be most important for CD4 binding.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Discontinuous, conserved neutralization epitopes overlapping the CD4-binding region of human immunodeficiency virus type 1 gp120 envelope glycoprotein.

Monoclonal antibodies have been isolated from human immunodeficiency virus type 1 (HIV-1)-infected patients that recognize discontinuous epitopes on the gp120 envelope glycoprotein, that block gp120 interaction with the CD4 receptor, and that neutralize a variety of HIV-1 isolates. Using a panel of HIV-1 gp120 mutants, we identified amino acids important for precipitation of the gp120 glycoprotein by three different monoclonal antibodies with these properties. These amino acids are located within seven discontinuous, conserved regions of the gp120 glycoprotein, four of which overlap those regions previously shown to be important for CD4 recognition. The pattern of sensitivity to amino acid change in these seven regions differed for each antibody and also differed from that of the CD4 glycoprotein. These results indicate that the CD4 receptor and this group of broadly neutralizing antibodies recognize distinct but overlapping gp120 determinants.

Antibodies, Monoclonal↗
PubMed1992

Distinction of human immunodeficiency virus type 1 neutralization and infection enhancement by human monoclonal antibodies to glycoprotein 120.

There is increasing evidence that sera from HIV-1-infected individuals contain antibodies that enhance infection by HIV-1 in vitro. Previous work has demonstrated that complement receptors on T lymphoid cells and Fc receptors for IgG (Fc gamma R) on monocytic cells are required for enhanced infection by antibody-complexed HIV-1. Characterization of such infection-enhancing antibodies is essential because immunogenic epitopes which induce enhancing antibodies should be excluded from HIV-1 vaccines. This study was conducted to identify enhancing antibodies involved in Fc R-mediated enhancement of HIV-1 infection employing IgG human monoclonal antibodies (HMAbs) reactive against gp120 of HIV-1, which were produced by B cell lines derived from an HIV-1-infected individual. A potent neutralizing HMAb N70-1.5e did not enhance infection by HIV-1 (IIIB and MN strains), whereas HMAb N70-2.3a mediated enhancement of HIV-1 infection, but had little neutralizing activity. A competition radio immunoassay demonstrated that the two antibodies bind to distinct epitopes. These results indicated that enhancing and neutralizing antibodies can be induced by different epitopes on gp120, suggesting the potential for development of safe vaccines against HIV-1 by exclusion of immunogenic epitopes for enhancing antibodies. We made attempts to identify the epitope on gp120 that is recognized by the enhancing antibody N70-2.3a by using recombinant HIV-1 proteins and found that the antibody binds to a conformational site of nonvariable sequences in the carboxyl half (aa 272-509) of gp120.

Animals↗
PubMed1992

Cooperativity of neutralizing antibodies directed against the V3 and CD4 binding regions of the human immunodeficiency virus gp120 envelope glycoprotein.

Human immunodeficiency virus type 1 (HIV-1) infection elicits neutralizing antibodies directed against two discrete regions of the gp120 exterior envelope glycoprotein: the third variable (V3) loop and the CD4 binding region. Monoclonal antibodies directed against these two regions demonstrated additive or, in some cases, weakly synergistic neutralization of HIV-1 infection. Cooperativity in virus neutralization was also observed for some gp120 mutants that, in the absence of anti-V3 loop antibodies, were relatively resistant to neutralization by antibodies directed against the CD4 binding region. Although the binding of some anti-V3 region monoclonal antibodies increased the recognition of the multimeric envelope glycoproteins by anti-CD4 binding antibodies, this enhanced binding was not predictive of the degree of cooperativity observed in virus neutralization. These results suggest that elicitation of both types of neutralizing antibodies should increase the efficacy of vaccine preparations.

Animals↗
PubMed1991

Anti-implantation activity of S(-)- and R(+)-camphor-yuehchukene in rats.

(+/-)-Yuehchukene is a dimeric indole alkaloid with potent anti-implantation activity in rats. Since (+/-)-yuehchukene occurs in nature as a racemate, it would be desirable to find out which enantiometer is the bio-active form. To this end, S(-)-camphor-yuehchukene and R(+)-camphor-yuehchukene were synthesised and tested in three bioassay models. It was found that the R(+) enantiomer was the active form. It was equipotent with (+/-)-yuehchukene in both anti-implantation and estrogenic activity tests. It seems fair to conclude that both activities reside in the same molecule.

Alkaloids↗
PubMed1991

Another discontinuous epitope on glycoprotein gp120 that is important in human immunodeficiency virus type 1 neutralization is identified by a monoclonal antibody.

To define the domains in the envelope glycoprotein important for antibody neutralization of the human immunodeficiency virus type 1 (HIV-1), monoclonal antibodies (mAbs) were generated by immunizing mice with purified glycoprotein gp120 of the IIIB isolate. One mAb, G3-4, reacted with the gp120 of homologous (IIIB) and heterologous (RF) isolates. In addition, mAb G3-4 efficiently neutralized both IIIB and RF viruses in vitro, as well as four of nine primary HIV-1 isolates. In competition immunoassays, mAb G3-4 and soluble CD4 were found to inhibit one another in binding to gp120. However, no competition was seen between mAb G3-4 and mAbs directed to the third variable region or the fourth conserved region of gp120. In particular, mAb G3-4 did not compete with our human mAb 15e, which identifies a discontinuous epitope on gp120 involved in group-specific neutralization of HIV-1 and in gp120-CD4 binding. Epitope-mapping studies on mAb G3-4 with synthetic or unglycosylated recombinant peptides were negative, suggesting that its epitope may be discontinuous. Indeed, this hypothesis was confirmed by showing the loss of mAb G3-4 serologic reactivity when gp120 was first denatured. We conclude that the site recognized by mAb G3-4 represents another discontinuous epitope on gp120 important for neutralization of HIV-1.

Animals↗
PubMed1991

Resistance of primary isolates of human immunodeficiency virus type 1 to soluble CD4 is independent of CD4-rgp120 binding affinity.

The infection of human cells by laboratory strains of human immunodeficiency virus type 1 (HIV-1) can be blocked readily in vitro by recombinant soluble CD4 and CD4-immunoglobulin hybrid molecules. In contrast, infection by primary isolates of HIV-1 is much less sensitive to blocking in vitro by soluble CD4-based molecules. To investigate the molecular basis for this difference between HIV-1 strains, we isolated the gp120-encoding genes from several CD4-resistant and CD4-sensitive HIV-1 strains and characterized the CD4-binding properties of their recombinant gp120 (rgp120) products. Extensive amino acid sequence variation was found between the gp120 genes of CD4-resistant and CD4-sensitive HIV-1 isolates. However, the CD4-binding affinities of rgp120 from strains with markedly different CD4 sensitivities were essentially the same, and only small differences were observed in the kinetics of CD4 binding. These results suggest that the lower sensitivity of primary HIV-1 isolates to neutralization by CD4-based molecules is not due to lower binding affinity between soluble CD4 and free gp120.

Amino Acid Sequence↗
PubMed1991

Relative resistance of primary HIV-1 isolates to neutralization by soluble CD4.

Replication of the human immunodeficiency virus type 1 (HIV-1) underlies the pathogenesis and progression of the acquired immunodeficiency syndrome (AIDS). A soluble form of the virus receptor, CD4, has been developed as a potential therapeutic agent with good activity against laboratory strains of HIV-1 in vitro. However, quantitative virologic studies performed to date on the blood of patients receiving recombinant soluble CD4 (sCD4) demonstrated no efficacy in vivo despite good drug levels in serum. These results led us to examine the neutralizing activity of sCD4 against multiple primary HIV-1 isolates from infected patients. The findings demonstrate that primary isolates were significantly more resistant to sCD4 than were laboratory strains, which suggests a need to reevaluate CD4-based therapies and to conduct better designed preclinical studies that include experiments performed on patient viral isolates.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Transient high levels of viremia in patients with primary human immunodeficiency virus type 1 infection.

BACKGROUND: The rapidly evolving clinical picture of primary infection with the human immunodeficiency virus type 1 (HIV-1) suggests that a better understanding of the kinetics of viral replication in vivo during the short period before seroconversion may provide insight into the pathogenesis of the acquired immunodeficiency syndrome (AIDS). METHODS AND RESULTS: Titers of infectious HIV-1 were determined by end-point-dilution culture in sequential samples of plasma and peripheral-blood mononuclear cells from four patients with primary infection, with peak titers of 1000 to 10,000 tissue-culture-infective doses per milliliter of plasma and 100 to 10,000 infective doses per 10(6) peripheral-blood mononuclear cells. The high viral burden in mononuclear cells was confirmed by quantitative studies using a polymerase-chain-reaction method. In as little as 10 days, the high HIV-1 load in both plasma and cells decreased spontaneously and precipitously, at least 100-fold, in all four patients. CONCLUSIONS: Although p24 core antigenemia and viral isolation have previously been described during primary HIV-1 infection, this report documents the large viral burden during the acute phase of infection. The rapid and spontaneous decline in the viral load suggests an effective immune response in the host that, if understood, may be used to combat AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Conformational epitope on gp120 important in CD4 binding and human immunodeficiency virus type 1 neutralization identified by a human monoclonal antibody.

A human monoclonal antibody designated 15e is reactive with the envelope glycoprotein (gp120) of multiple isolates of human immunodeficiency virus type 1 (HIV-1). Antibody 15e also neutralizes HIV-1 with broad specificity and blocks gp120 binding to CD4. Characterization of the 15e epitope shows that it is conformation dependent and is distinct from previously recognized functional domains of gp120, suggesting that this epitope represents a novel site important for HIV-1 neutralization and CD4 binding. These findings have implications for the development of a vaccine for AIDS.

Antibodies, Monoclonal↗
PubMed1991

Virus burden in human immunodeficiency virus type 1-infected children: relationship to disease status and effect of antiviral therapy.

The human immunodeficiency virus type 1 (HIV-1) was isolated from the plasma and peripheral blood mononuclear cells (PBMCs) from each of 21 infected children. The mean titers in plasma were 7 and 165 tissue culture-infective doses per milliliter in 9 children with asymptomatic (P-1) and 12 with symptomatic (P-2) infection, respectively (P = .0013). Significantly higher viral titers were found in PBMCs obtained from P-2 compared with P-1 children: 1920 vs 25 tissue culture-infective doses per 10(6) PBMC (P = .0018). In symptomatic patients at least 1 in 520 circulating mononuclear cells harbored HIV-1. No correlation was found between the viral burden and CD4+ lymphocyte counts. A decrease in the HIV-1 titers was noted both in PBMCs and plasma of symptomatic patients treated with zidovudine for 2 to 7 months. It is concluded that symptomatic children harbor a higher amount of the virus in plasma and PBMCs than asymptomatic children. Zidovudine treatment for 2 months or more decreased the amount of HIV-1 in PBMCs and plasma.

Acquired Immunodeficiency Syndrome↗
PubMed1990

High concentrations of recombinant soluble CD4 are required to neutralize primary human immunodeficiency virus type 1 isolates.

There is substantial evidence supporting the CD4 molecule as the principal cellular receptor for the human immunodeficiency virus type 1 (HIV-1). A number of truncated recombinant soluble CD4 (sCD4) molecules have been produced and shown to easily neutralize infection of laboratory strains of HIV-1 in vitro, and clinical trials using these sCD4 preparations have begun in patients with AIDS. Infectious HIV-1 titers in the plasma and peripheral blood mononuclear cells of five patients receiving sCD4 at 30 mg/day were sequentially monitored. No significant decrease in viral titers was found during therapy. Furthermore, plasma samples from eight patients with AIDS were titrated for HIV-1 with and without the addition of sCD4 ex vivo. Despite the addition of sCD4 at up to 1 mg/ml, there was little change in plasma viral titers. Subsequently, 10 primary HIV-1 isolates were tested for their susceptibility to neutralization in vitro by one preparation of sCD4. Neutralization of these clinical isolates required 200-2700 times more sCD4 than was needed to inhibit laboratory strains of HIV-1. Similar results were observed using one other monomeric sCD4 preparation and two multimeric CD4-immunoglobulin hybrid molecules. We conclude that unlike laboratory strains, primary HIV-1 isolates require high concentrations of sCD4 for neutralization. This phenomenon may pose a formidable problem for sCD4-based therapeutics in the treatment of HIV-1 infection.

AIDS-Related Complex↗
PubMed1990

Seroprevalence of human T cell leukemia viruses in selected populations of homosexual men.

This study sought to define the seroprevalence of human T cell leukemia virus (HTLV) types I and II in selected populations of homosexual men. Serum specimens were screened for antibodies to HTLV and to human immunodeficiency virus (HIV) by enzyme immunoassay; successive testing of specimens with positive results was done by Western blotting and radioimmunoprecipitation assay (RIPA) and then by polymerase chain reaction (PCR) assay on available peripheral blood mononuclear cells (PBMC). Of 1290 specimens, only 4 had antibodies against HTLV confirmed by RIPA. PCR analysis of DNA from PBMC from two subjects showed one to be HTLV-I and the other to be HTLV-II; both men also had HIV antibodies. These results demonstrate a lower seroprevalence rate for HTLV than some previous studies and emphasize the need for specific confirmatory tests.

Blotting, Western↗
PubMed1990

CD4-independent, productive infection of a neuronal cell line by human immunodeficiency virus type 1.

One neuronal cell line (SK-N-MC) was found to be susceptible to productive infection by multiple isolates of the human immunodeficiency virus type 1 (HIV-1). Characterization of SK-N-MC cells showed that these cells are neuroectodermal in origin in that they express dopamine hydroxylase, catecholamines, neuron-specific enolase, and neurofilaments. Despite their susceptibility to HIV-1 infection, SK-N-MC cells had no detectable CD4 and this infection was not blocked by anti-CD4 monoclonal antibodies (OKT4A, Leu3A) or recombinant soluble CD4. These experiments demonstrated that certain cells of neuroectodermal origin are susceptible to infection in vitro by HIV-1 via a CD4-independent mechanism.

Animals↗