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Biomedical subjects

C A Boucher

Publications and source records attributed to C A Boucher.

At least 73 records · Page 4Linked to original sources
PubMed1997

Overshoot of HIV-1 viraemia after early discontinuation of antiretroviral treatment.

OBJECTIVE: To determine whether, as predicted by predator-prey dynamics, early withdrawal of antiretroviral therapy, i.e. when the number of CD4+ lymphocytes is still elevated, results in an overshoot of HIV-1 viraemia due to infection of increased numbers of available target cells at that time. DESIGN AND METHODS: Five HIV-1-infected individuals were identified who discontinued antiretroviral therapy for various reasons after 8-19 days, and from whom stored serum samples obtained before, during, and shortly after treatment were available for measurement of HIV-1 RNA load. A mathematical model was designed to assess whether increased target cell availability could quantitatively explain the clinical observations. RESULTS: After therapy withdrawal, increases in the HIV-1 RNA load to levels exceeding pretreatment values by log10 0.6-1.5 copies/ml were observed after 2-17 days in all four of the individuals who had treatment-induced increases in CD4+ cell counts at the time of therapy withdrawal. Increases in viraemia were maximal within a few days, and subsequently seemed to wane until the pretreatment equilibrium between virus and its target cells was attained. Mathematical modelling confirms that these transient increases in viraemia can be explained by increased availability of target cells at the time of therapy withdrawal. CONCLUSIONS: Transient rises in HIV-1 viraemia do occur following early therapy withdrawal. These rises especially warrant consideration in short-term antiretroviral regimens for prevention of mother-to-child transmission, as are being studied in developing countries, since they could result in an increased transmission risk during the post-partum period through breast-feeding. This possibility needs to be investigated urgently.

Anti-HIV Agents↗
PubMed1997

Clinical data sets of human immunodeficiency virus type 1 reverse transcriptase-resistant mutants explained by a mathematical model.

Treatment of human immunodeficiency virus type 1 (HIV-1) infection during the clinical latency phase with drugs inhibiting reverse transcriptase (RT) reduces the HIV-1 RNA load and increases the CD4+ T-cell count. Typically, however, the virus evolves mutations in the RT gene that circumvent the drugs. We develop a mathematical model for this situation. The model distinguishes quiescent from activated CD4+ T cells, incorporates the fact that only activated cells can become productively infected by HIV-1, embodies empirical estimates for the drug resistance and the mutation frequency for each of the HIV-1 drug-resistant mutants, and assumes the antiviral immune response to remain constant over the course of the experiments. We analyze clinical data on the evolution of drug-resistant mutants for the RT inhibitors lamivudine and zidovudine. The results show that the evolutionary sequence of the drug-resistant mutants in both data sets is accounted for by our model, given that lamivudine is more effective than zidovudine. Thus, current empirical estimates of the mutation frequencies and the drug resistances of the mutants suffice for explaining the data. We derive a critical treatment level below which the wild-type HIV-1 RNA load can rebound before the first drug-resistant mutant appears. Our zidovudine data confirm this to be the case. Thus, we demonstrate in the model and the data that the rebound of the HIV-1 RNA load in the case of zidovudine is due to the outgrowth of wild-type virus and the first drug-resistant mutant, whereas that in the case of lamivudine can only be due to the drug-resistant mutants. The evolution of drug resistance proceeds slower in the case of zidovudine because (i) zidovudine is not as effective as lamivudine and (ii) the first zidovudine drug-resistant mutant is competing with the rebounding wild-type virus.

Drug Resistance, Microbial↗
PubMed1997

Initial appearance of the 184Ile variant in lamivudine-treated patients is caused by the mutational bias of human immunodeficiency virus type 1 reverse transcriptase.

Treatment of human immunodeficiency virus type 1-infected patients with lamivudine (3TC) results in the appearance of drug-resistant virus variants with a mutation at the 184Met codon (ATG) of the reverse transcriptase (RT) gene. The 184Ile (ATA) variant appears first, but subsequently the 184Val (GTG) variant outcompetes the 184Ile variant. We demonstrated previously that the 184Val enzyme and the corresponding virus are more fit than 184Ile, thereby explaining eventual outgrowth of 184Val. In this study, we set out to determine why 184Ile is usually observed first after initiation of 3TC therapy. With a limiting dilution approach during in vitro selection with 3TC, we measured a significantly higher frequency of the G-->A substitution toward the ATA codon (184Ile; 56%) than the A-->G substitution toward GTG (184Val; 12.5%). This result indicates that the initial appearance of the 184Ile variant in patients is a consequence of the mutation bias of the RT enzyme. Interestingly, a novel 3TC-resistant variant which was generated by T-->C substitution (184Thr; 28%) was also observed. The RT enzyme of the 184Thr variant was less than 10% active compared with the wild-type enzyme, and the replication capacity of this variant was severely reduced. Selection of the 184Thr variant illustrates that the limiting dilution approach allows the selection of drug-resistant variants with suboptimal fitness.

Anti-HIV Agents↗
PubMed1997

HIV-1 RNA levels in the cerebrospinal fluid may increase owing to damage to the blood-brain barrier.

Human immunodeficiency virus type 1 (HIV-1) RNA can be detected in the cerebrospinal fluid (CSF) of 75-90% of all HIV-infected patients. However, it is not yet known which factors influence the amount of HIV-1 in the CSF, either qualitatively or quantitatively. We have analysed HIV-1 RNA in CSF samples from 24 HIV-infected patients using zidovudine who underwent lumbar puncture in order to establish a diagnosis for a neurological disorder. Several factors were examined for possible correlation with the amount of HIV-1 RNA in the CSF: age, gender, the medical indication for lumbar puncture, the most recent CD4 cell count in blood, zidovudine dose, duration of treatment with zidovudine, the zidovudine concentration in plasma and CSF, and the total protein concentration in plasma and CSF. The only statistically significant factor was the total protein level in the CSF, which showed a positive relation with the amount of HIV-1 RNA in the CSF. This study indicates that increased levels of HIV-1 RNA in the CSF of neurologically symptomatic patients are the result of damage to the blood-brain barrier.

AIDS Dementia Complex↗
PubMed1997

Results of long-term follow-up of HIV-infected patients treated with lamivudine monotherapy, followed by a combination of lamivudine and zidovudine.

The objective of this study was to determine the efficacy and safety of adding zidovudine to continuous treatment with lamivudine in symptomatic human immunodeficiency virus type 1 (HIV-1)-infected patients. Forty patients were monitored throughout lamivudine monotherapy and subsequent combination therapy with lamivudine and zidovudine, which was initiated because of disease progression, declining CD4 cell counts or prolonged use of lamivudine. Eleven of these patients had been treated with zidovudine before the start of the study. The median CD4 cell count at the start of lamivudine monotherapy was 200 x 10(6) cells/l. After a median interval of 69 weeks (range 23-102 weeks), the median CD4 cell count had dropped to 110 x 10(6) cells/l. Initial improvements in all laboratory markers for antiretroviral efficacy were observed after the addition of zidovudine. The median CD4 cell count remained 18% above baseline after 48 weeks of treatment with lamivudine and zidovudine, however plasma HTV-1 RNA load and CD4 cell counts returned towards baseline during prolonged treatment in most patients. The combination was well tolerated, although anaemia was observed in nine patients. Repeated measures analysis of variance suggested a superior effect of lamivudine monotherapy in patients who had previously used zidovudine. In conclusion, zidovudine was found to be effective in patients who have been treated with lamivudine. The study stresses the need to further define the mechanisms underlying this prolonged antiviral effect.

Anti-HIV Agents↗
PubMed1996

Reduced replication of 3TC-resistant HIV-1 variants in primary cells due to a processivity defect of the reverse transcriptase enzyme.

Human immunodeficiency virus type 1 (HIV-1) variants with resistance mutations in the reverse transcriptase (RT) gene appear during drug therapy with the nucleoside analogue 2',3'-dideoxy-3'-thiacytidine (3TC). These resistance mutations alter the methionine (Met) residue of the conserved YMDD motif, which is part of the catalytic core of the RT enzyme. Isoleucine (Ile) variants are initially observed, followed by the appearance and eventual outgrowth of viruses encoding valine (Val). Similar replication kinetics were measured for wild-type and 3TC-resistant HIV-1 viruses in tissue culture infections of a T cell line, but we measured reduced polymerase activity for the two mutant RT enzymes compared with the wild-type enzyme (Ile = 43% and Val = 67%). Gel analysis of the reverse transcription products revealed that both 3TC-resistant RT mutants produce significantly shorter cDNA molecules than the wild-type enzyme [Met (wt)>Val>Ile], indicating that 3TC-resistant RT polymerases are less processive enzymes. Interestingly, these enzyme defects were more pronounced under limiting dNTP concentrations and we therefore assayed virus replication in primary cells that contain relatively low dNTP levels. Under these conditions, we measured significantly reduced replication kinetics for the 3TC-resistant HIV-1 variants [Met (wt)>Val>Ile]. If the level of virus replication can be similarly reduced in 3TC-treated patients that develop drug-resistant HIV-1 variants, this may be of considerable clinical benefit.

Antiviral Agents↗
PubMed1996

Anti-CD4 therapy for AIDS suggested by mathematical models.

HIV-1 infection typically involves a long clinical latency stage during which CD4 counts decline slowly. For the later part of the clinical latency stage it was found recently that this is a highly dynamic phase characterized by rapid turnover rates. Clinical latency can therefore be considered as a quasi-equilibrium state in which CD4 and HIV-1 turnover are in almost perfect balance. Here we consider this quasi-equilibrium to be the stable steady state of a simple host-parasite model in which the parasite (HIV-1) level is determined by the availability of infectable hosts (activated CD4+ T cells). Such models adequately account for the clinical data on the evolution of drug resistant mutants appearing after the administration of anti-HIV drugs. The model suggests a novel therapeutic approach for AIDS: reducing the CD4 count slightly will strongly reduce the HIV load. Combining this anti-CD4 treatment with conventional anti-HIV therapy would prevent the outgrowth of drug resistant mutants.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Host-parasite dynamics and outgrowth of virus containing a single K70R amino acid change in reverse transcriptase are responsible for the loss of human immunodeficiency virus type 1 RNA load suppression by zidovudine.

The association between human immunodeficiency virus type I (HIV-1) RNA load changes and the emergence of resistant virus variants was investigated in 24 HIV-1-infected asymptomatic persons during 2 years of treatment with zidovudine by sequentially measuring serum HIV-1 RNA load and the relative amounts of HIV-1 RNA containing mutations at reverse transcriptase (RT) codons 70 (K-->R), 41 (M-->L), and 215 (T-->Y/F). A mean maximum decline in RNA load occurred during the first month, followed by a resurgence between 1 and 3 months, which appeared independent of drug-resistance. Mathematical modeling suggests that this resurgence is caused by host-parasite dynamics, and thus reflects infection of the transiently increased numbers of CD4+ lymphocytes. Between 3 and 6 months of treatment, the RNA load returned to baseline values, which was associated with the emergence of virus containing a single lysine to arginine amino acid change at RT codon 70, only conferring an 8-fold reduction in susceptibility. Despite the relative loss of RNA load suppression, selection toward mutations at RT codons 215 and 41 continued. Identical patterns were observed in the mathematical model. While host-parasite dynamics and outgrowth of low-level resistant virus thus appear responsible for the loss of HIV-1 RNA load suppression, zidovudine continues to select for alternative mutations, conferring increasing levels of resistance.

Base Sequence↗
PubMed1996

Cloning of the human SIX1 gene and its assignment to chromosome 14.

The recently described murine homeobox genes, Six1 and Six2, which are expressed during development in limb tendons, have also been shown to be expressed in skeletal and smooth muscle, respectively. We have cloned and sequenced a human SIX1 cDNA and shown by Northern blotting that it is expressed in adult skeletal muscle. The cDNA sequence and predicted protein sequence of SIX1 and Six1 are highly homologous, with 98% similarity over the entire predicted amino acid sequence. SIX1 was mapped to human chromosome 14 using a rodent/human somatic cell hybrid panel.

Adult↗
PubMed1996

Ordered accumulation of mutations in HIV protease confers resistance to ritonavir.

Analysis of the HIV protease gene from the plasma of HIV-infected patients revealed substitutions at nine different codons selected in response to monotherapy with the protease inhibitor ritonavir. Mutants at valine-82, although insufficient to confer resistance, appeared first in most patients. Significant phenotypic resistance required multiple mutations in HIV protease, which emerged subsequently in an ordered, stepwise fashion. The appearance of resistance mutations was delayed in patients with higher plasma levels of ritonavir. Early mutants retained susceptibility to structurally diverse protease inhibitors, suggesting that dual protease inhibitor therapy might increase the duration of viral suppression.

Codon↗
PubMed1996

Changes in cellular virus load and zidovudine resistance of syncytium-inducing and non-syncytium-inducing human immunodeficiency virus populations under zidovudine pressure: a clonal analysis.

Zidovudine treatment preferentially benefits persons with only non-syncytium-inducing (NSI) human immunodeficiency virus type 1 (HIV-1) variants. To understand this differential efficacy, changes in cellular virus load, clonal composition of HIV-1 populations, and development of resistance-conferring reverse transcriptase mutations were studied in 17 persons initiating zidovudine therapy. Zidovudine treatment resulted in larger and more sustained decreases in cellular virus load in persons with NSI variants only compared with persons also carrying syncytium-inducing (SI) variants. Although the former group had a delayed emergence of resistance mutations, differences in initial responses between the 2 groups were independent of the emergence of resistance mutations. Changes in virus load in subjects also carrying SI variants were due mainly to loss of coexisting NSI virus. Resistance mutations emerged at similar rates in both coexisting variants. Data suggest that mechanisms other than drug resistance are necessary to completely explain the phenotype-dependent benefit of zidovudine.

Acquired Immunodeficiency Syndrome↗
PubMed1996

A controlled trial of nevirapine plus zidovudine versus zidovudine alone in p24 antigenaemic HIV-infected patients. The Dutch-Italian-Australian Nevirapine Study Group.

OBJECTIVES: Nevirapine is a non-nucleoside reverse transcriptase inhibitor of HIV-1 which exhibits synergy in vitro with zidovudine (ZDV) and also is active against ZDV-resistant HIV. We evaluated the activity and safety of nevirapine in combination with ZDV in patients receiving long-term ZDV therapy. METHODS: We conducted a randomized, open-label, controlled 28-week study of nevirapine (200 mg daily for 2 weeks followed by 200 mg twice daily for 26 weeks) and continued ZDV (500-600 mg daily) versus continued ZDV alone in 49 HIV-1 p24 antigenaemic patients with CD4+ lymphocyte counts < 500 x 10(6)/l and who had been treated with ZDV for at least 6 months. RESULTS: Addition of nevirapine to ZDV resulted in a significant and rapid reduction in circulating RNA load (mean, 0.65), a mean CD4+ lymphocyte rise of 34 x 10(6)/l, a reduction in serum beta 2-microglobulin and a median fall in immune complex dissociated p24 antigen levels of 69%. These changes remained statistically significant for 4, 4, 12 and at least 28 weeks, respectively. The principal adverse event due to nevirapine was a hypersensitivity reaction comprising rash with or without fever and mucositis in eight (32%) patients, which was dose-limiting in seven patients. CONCLUSION: Nevirapine exhibits significant although transient anti-HIV activity in ZDV-pretreated patients but its use is frequently associated with a hypersensitivity reaction.

Adult↗
PubMed1996

Human immunodeficiency virus type 1 drug susceptibility determination by using recombinant viruses generated from patient sera tested in a cell-killing assay.

A simple approach for the determination of drug susceptibilities by using human immunodeficiency virus type 1 (HIV-1) RNA from the sera of patients is described. HIV-1 RNA was extracted from patient sera, and the 5' part of the reverse transcriptase (RT) gene was transcribed into DNA and amplified in a nested PCR. The amplified fragment covers the 3' part of the protease gene and amino acids 1 to 304 of the RT gene. This fragment can be introduced through homologous recombination, as described previously, into a novel HIV-1 reference strain (pHXB2 delta 2-261RT) from which amino acids 2 to 261 of RT have been deleted. The resulting recombinant virus expresses all properties of the HXB2 reference strain except for those encoded by the introduced part of the patient RT gene. Recombinant viruses were subsequently tested for drug susceptibility in a microtiter format killing assay [3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay] as well as in the standard HeLa CD4+ plaque reduction assay. Similar susceptibility profiles were obtained by each assay with recombinant viruses derived from patients receiving alternating nevirapine and zidovudine treatment or lamivudine-zidovudine combination therapy. In conclusion, this approach enables high-through-put determination of the drug susceptibilities of serum RNA-derived RT genes, independent of the patient's viral background, and generates the possibility of relating changes in susceptibility to changes in viral genotypes.

Anti-HIV Agents↗
PubMed1996

Safety, tolerance, and efficacy of atevirdine in asymptomatic human immunodeficiency virus-infected individuals.

Atevirdine is a nonnucleoside reverse transcriptase inhibitor of human immunodeficiency virus type 1 (HIV-1). In this study we investigated the effect of atevirdine in asymptomatic antiretroviral naive HIV-infected patients with CD4+ cell counts of between 200 and 750 cells per mm3. Patients were randomized to receive 600 mg of atevirdine (n = 15) or a placebo (n = 15) three times a day for 12 weeks. There was no statistically significant effect of atevirdine on viral loads (HIV p24 antigen and HIV-1 RNA levels by PCR) or CD4+ cell counts. The data do not support the use of atevirdine as a monotherapy in the treatment of HIV-infected patients.

Adult↗
PubMed1996

Multicenter comparison of three commercial methods for quantification of human immunodeficiency virus type 1 RNA in plasma.

Three procedures for the quantification of human immunodeficiency virus type 1 (HIV-1) RNA from plasma were compared at three laboratories. The comparison involved the Quantiplex branched DNA assay (version 1.0) by Chiron Diagnostics, the NASBA-QT assay by Organon Teknika, and the Amplicor Monitor assay by Roche Molecular Systems. The laboratories performed each of the three assays with the same sets of reconstructed HIV-1-infected human plasma samples, cross-sectionally collected clinical plasma samples and longitudinally collected plasma samples from patients starting zidovudine therapy. Analysis of the reconstruction panel results for interlaboratory variation demonstrated that no laboratory differences in results were detected for any of the assays. A comparison of the reproducibilities of duplicate samples analyzed by batch and in separate assay runs demonstrated that the reproducibilities of the test results were similar within one assay and appeared to be independent of the HIV-1 concentration. The best reproducibility was obtained with the Quantiplex assay, but all three assays demonstrated equal reliability, which was independent of batched or unbatched analysis of replicate samples. Differences in the absolute concentrations calculated were observed for the assays, in particular in the analysis of reconstructed samples. In all assays, similar changes in plasma HIV-1 RNA concentrations were determined for longitudinally collected clinical samples.

Biomarkers↗