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D D Ho

Publications and source records attributed to D D Ho.

At least 19 recordsLinked to original sources
PubMed2004

Diverse hepatitis C virus glycoproteins mediate viral infection in a CD81-dependent manner.

We recently reported that retroviral pseudotypes bearing the hepatitis C virus (HCV) strain H and Con1 glycoproteins, genotype 1a and 1b, respectively, require CD81 as a coreceptor for virus-cell entry and infection. Soluble truncated E2 cloned from a number of diverse HCV genotypes fail to interact with CD81, suggesting that viruses of diverse origin may utilize different receptors and display altered cell tropism. We have used the pseudotyping system to study the tropism of viruses bearing diverse HCV glycoproteins. Viruses bearing these glycoproteins showed a 150-fold range in infectivity for hepatoma cells and failed to infect lymphoid cells. The level of glycoprotein incorporation into particles varied considerably between strains, generally reflecting the E2 expression level within transfected cells. However, differences in glycoprotein incorporation were not associated with virus infectivity, suggesting that infectivity is not limited by the absolute level of glycoprotein. All HCV pseudotypes failed to infect HepG2 cells and yet infected the same cells after transduction to express human CD81, confirming the critical role of CD81 in HCV infection. Interestingly, these HCV pseudotypes differed in their ability to infect HepG2 cells expressing a panel of CD81 variants, suggesting subtle differences in the interaction of CD81 residues with diverse viral glycoproteins. Our current model of HCV infection suggests that CD81, together with additional unknown liver specific receptor(s), mediate the virus-cell entry process.

Amino Acid Sequence↗
PubMed2001

Increased turnover of T lymphocytes in HIV-1 infection and its reduction by antiretroviral therapy.

The mechanism of CD4(+) T cell depletion in human immunodeficiency virus (HIV)-1 infection remains controversial. Using deuterated glucose to label the DNA of proliferating cells in vivo, we studied T cell dynamics in four normal subjects and seven HIV-1-infected patients naive to antiretroviral drugs. The results were analyzed using a newly developed mathematical model to determine fractional rates of lymphocyte proliferation and death. In CD4(+) T cells, mean proliferation and death rates were elevated by 6.3- and 2.9-fold, respectively, in infected patients compared with normal controls. In CD8(+) T cells, the mean proliferation rate was 7.7-fold higher in HIV-1 infection, but the mean death rate was not significantly increased. Five of the infected patients underwent subsequent deuterated glucose labeling studies after initiating antiretroviral therapy. The lymphocyte proliferation and death rates in both CD4(+) and CD8(+) cell populations were substantially reduced by 5-11 weeks and nearly normal by one year. Taken together, these new findings strongly indicate that CD4(+) lymphocyte depletion seen in AIDS is primarily a consequence of increased cellular destruction, not decreased cellular production.

Adult↗
PubMed2001

DNA-immunization with a V2 deleted HIV-1 envelope elicits protective antibodies in macaques.

Rhesus macaques immunized with the HIV-1 SF162DeltaV2 gp140 envelope using the DNA-prime plus protein-boost vaccination methodology, developed HIV envelope-specific T-cell lymphoproliferative responses and potent neutralizing antibodies. To evaluate the protective potential of these antibodies during acute infection, the animals were depleted of their CD8+ T lymphocytes using specific monoclonal antibodies and subsequently challenged intravenously with the pathogenic SHIV(SF162P4) isolate. As compared to non-vaccinated animals (one of which died from AIDS 16 weeks post-exposure) the vaccinated macaques had lower levels of peak viremia, rapidly cleared virus from the periphery and developed delayed seroconversion to SIV core antigens.

AIDS Vaccines↗
PubMed2001

SCH-C (SCH 351125), an orally bioavailable, small molecule antagonist of the chemokine receptor CCR5, is a potent inhibitor of HIV-1 infection in vitro and in vivo.

We describe here the identification and properties of SCH-C (SCH 351125), a small molecule inhibitor of HIV-1 entry via the CCR5 coreceptor. SCH-C, an oxime-piperidine compound, is a specific CCR5 antagonist as determined in multiple receptor binding and signal transduction assays. This compound specifically inhibits HIV-1 infection mediated by CCR5 in U-87 astroglioma cells but has no effect on infection of CXCR4-expressing cells. SCH-C has broad and potent antiviral activity in vitro against primary HIV-1 isolates that use CCR5 as their entry coreceptor, with mean 50% inhibitory concentrations ranging between 0.4 and 9 nM. Moreover, SCH-C strongly inhibits the replication of an R5-using HIV-1 isolate in SCID-hu Thy/Liv mice. SCH-C has a favorable pharmacokinetic profile in rodents and primates with an oral bioavailability of 50-60% and a serum half-life of 5-6 h. On the basis of its novel mechanism of action, potent antiviral activity, and in vivo pharmacokinetic profile, SCH-C is a promising new candidate for therapeutic intervention of HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Evidence of two distinct subsubtypes within the HIV-1 subtype A radiation.

Members of HIV-1 group M are responsible for the vast majority of AIDS cases worldwide and have been classified on the basis of their phylogenetic relationships into nine roughly equidistant clades, termed subtypes. Although there are no known phenotypic correlates for these genotypes, the disproportionate spread of certain of these lineages has been taken to indicate that subtype-specific biological differences may exist. The subtype nomenclature thus remains an important molecular epidemiological tool with which to track the course of the group M pandemic. In this study, we have characterized HIV-1 strains described previously as unusual subtype A variants on the basis of partial sequence analysis. Six such strains from Cyprus (CY), South Korea (KR), and the Democratic Republic of Congo (CD) were PCR amplified from infected cell culture or patient PBMC DNA, cloned, and sequences in their entirety (94CY017, 97KR004, 97CDKTB48, and 97CDKP58) or as half genomes (97CDKS10 and 97CDKFE4). Distance and phylogenetic analyses showed that four of these viruses (94CY017, 97CDKTB48, 97CDKFE4, and 97CDKS10) were closely related to each other, but quite divergent from all other HIV-1 strains, except for subtype A viruses, which represented their closest relatives. In phylogenetic trees from gag, pol, env, and nef regions, the four newly characterized HIV-1 strains formed a distinct sister clade to subtype A, which was as closely related to subtype A as subsubtypes F1 and F2 are to each other. According to current nomenclature rules, this defines a subsubtype, which we have tentatively termed A2. The two other viruses, 97KR004 and 97CDKP58, as well as a full-length HIV-1 sequence from the sequence database (ZAM184), were found to represent complex A2/D, A2/G, and A2/C recombinants, respectively. These results indicate that HIV-1 subtype A is composed of two subsubtypes (A1 and A2), both of which appear to have a widespread geographic distribution. The A2 viruses described here represent the first reference reagents for this new group M lineage.

Cyprus↗
PubMed2001

DNA vaccination with the human immunodeficiency virus type 1 SF162DeltaV2 envelope elicits immune responses that offer partial protection from simian/human immunodeficiency virus infection to CD8(+) T-cell-depleted rhesus macaques.

DNA immunization of macaques with the SF162DeltaV2 envelope elicited lymphoproliferative responses and potent neutralizing antibodies. The animals were depleted of their CD8(+) T lymphocytes and then challenged intravenously with SHIV162P4. Compared to unvaccinated animals, the vaccinated macaques had lower peak viremia levels, rapidly cleared plasma virus, and showed delayed seroconversion.

AIDS Vaccines↗
PubMed2001

Genetic and functional diversity of human immunodeficiency virus type 1 subtype B Nef primary isolates.

We have characterized the functional integrity of seven primary Nef isolates: five from a long-term nonprogressing human immunodeficiency virus (HIV)-infected individual and one each from two patients with AIDS. One of the seven Nefs was defective for CD4 downregulation, two others were defective for PAK-2 activation, and one Nef was defective for PAK-2 activation and major histocompatibility complex (MHC) class I downregulation. Five of the Nefs were tested and found to be functional for the enhancement of virus particle infectivity. The structural basis for each of the functional defects has been analyzed by constructing a consensus nef, followed by mutational analysis of the variant amino acid residues. Mutations A29V and F193I were deleterious to CD4 downregulation and PAK-2 activation, respectively, while S189R rendered Nef defective for both MHC class I downregulation and PAK-2 activation. A search of the literature identified HIVs from five patients with Nefs predominantly mutated at F193 and from one patient with Nefs predominantly mutated at A29. A29 is highly conserved in all HIV subtypes except for subtype E. F193 is conserved in subtype B (and possibly in the closely related subtype D), but none of the other HIV group M subtypes. Our results suggest that functional distinctions may exist between HIV subtypes.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Effects of in vivo CD8(+) T cell depletion on virus replication in rhesus macaques immunized with a live, attenuated simian immunodeficiency virus vaccine.

The role of CD8(+) T lymphocytes in controlling replication of live, attenuated simian immunodeficiency virus (SIV) was investigated as part of a vaccine study to examine the correlates of protection in the SIV/rhesus macaque model. Rhesus macaques immunized for >2 yr with nef-deleted SIV (SIVmac239Deltanef) and protected from challenge with pathogenic SIVmac251 were treated with anti-CD8 antibody (OKT8F) to deplete CD8(+) T cells in vivo. The effects of CD8 depletion on viral load were measured using a novel quantitative assay based on real-time polymerase chain reaction using molecular beacons. This assay allows simultaneous detection of both the vaccine strain and the challenge virus in the same sample, enabling direct quantification of changes in each viral population. Our results show that CD8(+) T cells were depleted within 1 h after administration of OKT8F, and were reduced by as much as 99% in the peripheral blood. CD8(+) T cell depletion was associated with a 1-2 log increase in SIVmac239Deltanef plasma viremia. Control of SIVmac239Deltanef replication was temporally associated with the recovery of CD8(+) T cells between days 8 and 10. The challenge virus, SIVmac251, was not detectable in either the plasma or lymph nodes after depletion of CD8(+) T cells. Overall, our results indicate that CD8(+) T cells play an important role in controlling replication of live, attenuated SIV in vivo.

Animals↗
PubMed2000

Modeling plasma virus concentration during primary HIV infection.

During primary HIV infection the viral load in plasma increases, reaches a peak, and then declines. Phillips has suggested that the decline is due to a limitation in the number of cells susceptible to HIV infection, while other authors have suggested that the decline in viremia is due to an immune response. Here we address this issue by developing models of primary HIV-1 infection, and by comparing predictions from these models with data from ten anti-retroviral, drug-naive, infected patients. Applying nonlinear least-squares estimation, we find that relatively small variations in parameters are capable of mimicking the highly diverse patterns found in patient viral load data. This approach yields an estimate of 2.5 days for the average lifespan of productively infected cells during primary infection, a value that is consistent with results obtained by drug perturbation experiments. We find that the data from all ten patients are consistent with a target-cell-limited model from the time of initial infection until shortly after the peak in viremia. However, the kinetics of the subsequent fall and recovery in virus concentration in some patients are not consistent with the predictions of the target-cell-limited model. We illustrate that two possible immune response mechanisms, cytotoxic T lymphocyte destruction of infected target cells and cytokine suppression of viral replication, could account for declines in viral load data not predicted by the original target-cell-limited model. We conclude that some additional process, perhaps mediated by CD8+ T cells, is important in at least some patients.

Cytokines↗
PubMed2000

Effect of recent thymic emigrants on progression of HIV-1 disease.

BACKGROUND: The concentration of T-cell receptor-rearrangement excision DNA circles (TREC) in peripheral-blood T cells is a marker of recent thymic emigrant alphabeta T cells. We studied the predictive ability of measurements of TREC for clinical outcome in HIV-1-infected individuals. METHODS: We measured TREC in peripheral-blood mononuclear cells with a real-time PCR assay. We studied 131 Greek participants in the Multicenter Hemophilia Cohort Study who had known HIV-1 seroconversion dates. The prognostic value of baseline TREC, CD4 T-cell count, and HIV-1 RNA concentration was assessed by Kaplan-Meier and Cox's regression analysis. FINDINGS: Four participants had progressed to AIDS by first blood sampling. Among the remaining 127 individuals, the median value of TREC per 10(6) cells was 6900 (IQR 2370-15604). Baseline TREC values were lower in the 53 who progressed to AIDS than in those who did not (geometric mean 2843 [95% CI 1468-5504] vs 6560 [4723-9113] per 10(6) cells; p=0.017). The relative hazard of AIDS, adjusted for plasma viral load, CD4 T-cell count, and age at seroconversion was 1.44 (95% CI 1.04-2.01; p=0.031) per ten-fold increase in TREC; that for death was 1.52 (1.12-2.06; p=0.007). The adjusted relative hazards of death were 2.91 (1.91-4.44; p<0.001) per ten-fold increase in plasma HIV-1 RNA load and 1.20 (1.04-1.38; p=0.014) per 100-cell decrease in CD4 T-cell count. INTERPRETATION: The concentration of TREC in the peripheral T-cell pool complements HIV-1 RNA load and CD4 T-cell count in predicting the rate of HIV-1 disease progression. Recent thymic emigrants have a role in the pathogenesis of HIV-1 disease.

Adult↗
PubMed2000

Age-dependent changes in T cell homeostasis and SIV load in sooty mangabeys.

Sooty mangabeys (Cercocebus atys) showed age-dependent changes in T cell regeneration. Younger animals had a high percentage of CD4+ CD45RA + T cells and a high concentration of T cell receptor excisional circles (TRECs) in peripheral blood, which indicated active thymopoiesis. In contrast, older animals had an increased T cell turnover, which suggested that most T cell production occurred in the periphery. In addition, the number of peripheral CD4+ T cells naturally decreased with age. Non-pathogenic SIVsm infection did not significantly change the T cell proliferation rate or the TREC concentration, though it did cause a moderate loss of peripheral CD4 + T cells. The viral load correlated negatively with age, which could be accounted for by the reduced availability of CD4 + target cells in older mangabeys. Thus, the number of susceptible target cells may be a limiting factor in natural SIV infection.

Aging↗
PubMed2000

The decay of the latent reservoir of replication-competent HIV-1 is inversely correlated with the extent of residual viral replication during prolonged anti-retroviral therapy.

Replication-competent HIV-1 can be isolated from infected patients despite prolonged plasma virus suppression by anti-retroviral treatment. Recent studies have identified resting, memory CD4+ T lymphocytes as a long-lived latent reservoir of HIV-1 (refs. 4,5). Cross-sectional analyses indicate that the reservoir is rather small, between 103 and 107 cells per patient. In individuals whose plasma viremia levels are well suppressed by anti-retroviral therapy, peripheral blood mononuclear cells containing replication-competent HIV-1 were found to decay with a mean half-life of approximately 6 months, close to the decay characteristics of memory lymphocytes in humans and monkeys. In contrast, little decay was found in a less-selective patient population. We undertook this study to address this apparent discrepancy. Using a quantitative micro-culture assay, we demonstrate here that the latent reservoir decays with a mean half-life of 6.3 months in patients who consistently maintain plasma HIV-1 RNA levels of fewer than 50 copies/ml. Slower decay rates occur in individuals who experience intermittent episodes of plasma viremia. Our findings indicate that the persistence of the latent reservoir of HIV-1 despite prolonged treatment is due not only to its slow intrinsic decay characteristics but also to the inability of current drug regimens to completely block HIV-1 replication.

Adult↗
PubMed2000

Enhanced infectivity of an R5-tropic simian/human immunodeficiency virus carrying human immunodeficiency virus type 1 subtype C envelope after serial passages in pig-tailed macaques (Macaca nemestrina).

The increasing prevalence of human immunodeficiency virus type 1 (HIV-1) subtype C infection worldwide calls for efforts to develop a relevant animal model for evaluating strategies against the transmission of the virus. A chimeric simian/human immunodeficiency virus (SHIV), SHIV(CHN19), was generated with a primary, non-syncytium-inducing HIV-1 subtype C envelope from a Chinese strain in the background of SHIV(33). Unlike R5-tropic SHIV(162), SHIV(CHN19) was not found to replicate in rhesus CD4(+) T lymphocytes. SHIV(CHN19) does, however, replicate in CD4(+) T lymphocytes of pig-tailed macaques (Macaca nemestrina). The observed replication competence of SHIV(CHN19) requires the full tat/rev genes and partial gp41 region derived from SHIV(33). To evaluate in vivo infectivity, SHIV(CHN19) was intravenously inoculated, at first, into two pig-tailed and two rhesus macaques. Although all four animals became infected, the virus replicated preferentially in pig-tailed macaques with an earlier plasma viral peak and a faster seroconversion. To determine whether in vivo adaptation would enhance the infectivity of SHIV(CHN19), passages were carried out serially in three groups of two pig-tailed macaques each, via intravenous blood-bone marrow transfusion. The passages greatly enhanced the infectivity of the virus as shown by the increasingly elevated viral loads during acute infection in animals with each passage. Moreover, the doubling time of plasma virus during acute infection became much shorter in passage 4 (P4) animals (0.2 day) in comparison to P1 animals (1 to 2 days). P2 to P4 animals all became seropositive around 2 to 3 weeks postinoculation and had a decline in CD4/CD8 T-cell ratio during the early phase of infection. In P4 animals, a profound depletion of CD4 T cells in the lamina propria of the jejunum was observed. Persistent plasma viremia has been found in most of the infected animals with sustained viral loads ranging from 10(3) to 10(5) per ml up to 6 months postinfection. Serial passages did not change the viral phenotype as confirmed by the persistence of the R5 tropism of SHIV(CHN19) isolated from P4 animals. In addition, the infectivity of SHIV(CHN19) in rhesus peripheral blood mononuclear cells was also increased after in vivo passages. Our data indicate that SHIV(CHN19) has adapted well to grow in macaque cells. This established R5-tropic SHIV(CHN19)/macaque model would be very useful for HIV-1 subtype C vaccine and pathogenesis studies.

Animals↗
PubMed2000

Normal T-cell turnover in sooty mangabeys harboring active simian immunodeficiency virus infection.

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) remain healthy though they harbor viral loads comparable to those in rhesus macaques that progress to AIDS. To assess the immunologic basis of disease resistance in mangabeys, we compared the effect of SIV infection on T-cell regeneration in both monkey species. Measurement of the proliferation marker Ki-67 by flow cytometry showed that mangabeys harbored proliferating T cells at a level of 3 to 4% in peripheral blood irrespective of their infection status. In contrast, rhesus macaques demonstrated a naturally high fraction of proliferating T cells (7%) that increased two- to threefold following SIV infection. Ki-67(+) T cells were predominantly CD45RA(-), indicating increased proliferation of memory cells in macaques. Quantitation of an episomal DNA product of T-cell receptor alpha rearrangement (termed alpha1 circle) showed that the concentration of recent thymic emigrants in blood decreased with age over a 2-log unit range in both monkey species, consistent with age-related thymic involution. SIV infection caused a limited decrease of alpha1 circle numbers in mangabeys as well as in macaques. Dilution of alpha1 circles by T-cell proliferation likely contributed to this decrease, since alpha1 circle numbers and Ki-67(+) fractions correlated negatively. These findings are compatible with immune exhaustion mediated by abnormal T-cell proliferation, rather than with early thymic failure, in SIV-infected macaques. Normal T-cell turnover in SIV-infected mangabeys provides an explanation for the long-term maintenance of a functional immune system in these hosts.

Aging↗
PubMed2000

Genetic characterization of rebounding HIV-1 after cessation of highly active antiretroviral therapy.

Despite prolonged treatment with highly active antiretroviral therapy (HAART), infectious HIV-1 continues to replicate and to reside latently in resting memory CD4(+) T lymphocytes, creating a major obstacle to HIV-1 eradication. It is therefore not surprising to observe a prompt viral rebound after discontinuation of HAART. The nature of the rebounding virus, however, remains undefined. We now report on the genetic characterization of rebounding viruses in eight patients in whom plasma viremia was undetectable throughout about 3 years of HAART. Taking advantage of the extensive length polymorphism in HIV-1 env, we found that in five patients who did not show HIV-1 replication during treatment, the rebound virus was identical to those isolated from the latent reservoir. In three other patients, two of whom had been free of plasma viremia but had showed some residual viral replication, the rebound virus was genetically different from the latent reservoir virus, corresponding instead to minor viral variants detected during the course of treatment in lymphoid tissues. We conclude that in cases with apparent complete HIV-1 suppression by HAART, viral rebound after cessation of therapy could have originated from the activation of virus from the latent reservoir. In patients with incomplete suppression by chemotherapy, however, the viral rebound is likely triggered by ongoing, low-level replication of HIV-1, perhaps occurring in lymphoid tissues.

Adult↗
PubMed2000

An antigenic threshold for maintaining human immunodeficiency virus type 1-specific cytotoxic T lymphocytes.

BACKGROUND: Using the lymphocytic choriomeningitis virus (LCMV) model in mice, a number of studies show that memory cytotoxic T-lymphocyte (CTL) responses are maintained in the presence of continuous antigenic stimulation. Yet, other groups found that memory CTL specific for LCMV could last for a lifetime in mice without viral antigens. Thus, the extent to which an antigen is required for the maintenance of virus-specific CTL remains controversial. In humans, very few studies have been conducted to investigate the relationship between the quantity of antigen and the magnitude of CTL responses. MATERIALS AND METHODS: We quantified CTL precursors (CTLp) using a limiting-dilution analysis (LDA) and CTL effectors (CTLe) using a new Major Histocompatibility Complex (MHC) class I tetramer technology in six long-term nonprogressors (LTNPs) with human immunodeficiency virus type-1 (HIV-1) infection, as well as in eight patients whose viral loads were well suppressed by antiretroviral therapy. The viremia levels in these patients were measured using an reverse transcription polymerase chain reaction (RT-PCR) assay. The proviral DNA load in peripheral blood mononuclear cell (PBMC) was also measured by PCR in four LTNPs. RESULTS: The LTNPs had high levels of HIV-1-specific memory CTLp and CTLe, while maintaining a low plasma viral load. Despite also having low viral loads, patients whose plasma viremia was well-suppressed by effective therapy had low levels of CTLe. CONCLUSIONS: Our findings suggest that a complex, rather than a monotonic, relationship exists between CTL levels and HIV-1 viremia, including what appears to be an antigenic threshold for the maintenance of CTL at a measurable level. Under conditions of "antigen excess,", CTLe levels correlate inversely with viral load. On the other hand, under conditions that are "antigen limited," the correlation appears to be direct.

Adult↗
PubMed1999

Rapid production and clearance of HIV-1 and hepatitis C virus assessed by large volume plasma apheresis.

BACKGROUND: In chronic HIV-1 infection, dynamic equilibrium exists between viral production and clearance. The half-life of free virions can be estimated by inhibiting virion production with antiretroviral agents and modelling the resulting decline in plasma HIV-1 RNA. To define HIV-1 and hepatitis C virus (HCV) dynamics, we used plasma apheresis to increase virion clearance temporarily while leaving virion production unaffected. METHODS: Plasma virus loads were measured frequently before, during, and after apheresis in four HIV-1-infected patients, two of whom were also co-infected with HCV. Rates of virion clearance were derived by non-linear least-square fitting of plasma virus load to a model of viral dynamics. FINDINGS: Virion clearance rate constants were 0.0063/min (9.1/day) to 0.025/min (36.0/day; half-life 28-110 min) for HIV-1 and 0.0038/min (5.5/day) to 0.0069/min (9.9/day; half-life 100-182 min) for HCV. These values provided estimates of daily particle production of 9.3 log10-10.2 log10 particles for HIV-1 and 11.6 log10-13.0 log10 particles for HCV. INTERPRETATION: Our findings confirm that HIV-1 and HCV are produced and cleared extremely rapidly. New estimates for HIV-1 clearance are up to ten times higher than previous ones, whereas HCV clearance is similar to previous estimates.

DNA, Viral↗