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Biomedical subjects

R Schuurman

Publications and source records attributed to R Schuurman.

At least 37 records · Page 2Linked to original sources
PubMed1999

Phenotypic assays and sequencing are less sensitive than point mutation assays for detection of resistance in mixed HIV-1 genotypic populations.

The sensitivity and discriminatory power of the 151 and 215 amplification refractory mutation system (ARMS) were evaluated, and their performance for the detection of drug resistance in mixed genotypic populations of the reverse transcription (RT) gene of HIV-1 were compared with T7 sequencing, cycle sequencing, the line probe assay (LiPA) HIV-1 RT test, and the recombinant virus assay (RVA). ARMS and the LiPA HIV-1 RT test were shown to be able to detect minor variants that in particular cases comprised only 1%. T7 sequencing on an ALF semiautomated sequencer could correctly score mixtures only when variants were present at 50%. Cycle sequencing on an ABI PRISM 310 improved the sensitivity for mixtures to about 25%. Using RVA, it was shown that at least 50% of the virus population needed to carry the resistance mutation at codon 184 to afford phenotypic resistance against lamivudine. The two point mutation assays therefore proved to be more sensitive methods than sequencing and RVA to reliably determine a gradual shift in HIV-1 drug resistance mutations in follow-up of patients infected with HIV-1. In 4 of 5 treated patients who were followed by ARMS, a gradual shift in resistant genotypic populations was observed during a period of 6 to 19 months. For 1 patient, a shift from wild to mutant type at position 151 occurred within 2 months, without mixed genotypic intermediate type's being detected.

DNA Mutational Analysis↗
PubMed1999

Incidence and risk factors for developing cytomegalovirus retinitis in HIV-infected patients receiving protease inhibitor therapy. Spanish CMV-AIDS Study Group.

OBJECTIVE: To assess the incidence and risk factors for cytomegalovirus (CMV) retinitis in HIV-infected patients who initiated protease inhibitor-containing antiretroviral therapy. DESIGN AND SETTING: Prospective, multicentre study. PATIENTS: A cohort of 172 HIV-infected patients with a CD4 cell count below 100x10(6) cells/l at the time of protease inhibitor introduction. MAIN OUTCOME MEASURES: Confirmed CMV retinitis and mortality, according to CD4 cell count, HIV load, and CMV viraemia. RESULTS: The cumulative incidence of CMV retinitis was 5% at 1 year and 6% at 2 years. Only a positive CMV polymerase chain reaction (PCR) test at therapy initiation was significantly associated with the development of disease (relative hazard, 4.41; 95% confidence interval, 2.12-8.93; P<0.00001). The 12-month Kaplan-Meier CMV retinitis event rate was 38% in patients who were CMV PCR-positive compared with 2% in those who were CMV PCR-negative (P<0.001). Mean CMV load was significantly higher in those individuals who went on to develop CMV retinitis (3700 versus 384 copies/ml, P = 0.002). Only 2% of patients remained CMV PCR-positive after 3 months of protease inhibitor therapy, and CMV viraemia was not associated with a worse therapy response or shorter survival. Transient CMV positivity without a higher risk of disease was observed in 7% of patients at the first month on therapy. CONCLUSIONS: Protease inhibitor-containing antiretroviral therapy significantly reduces the incidence of CMV viraemia and disease. Although a positive CMV PCR test identifies those patients on therapy at highest risk of CMV retinitis, it is not associated with an increased risk of death or a worse response to protease inhibitor therapy.

AIDS-Related Opportunistic Infections↗
PubMed1999

Increased polymerase fidelity of lamivudine-resistant HIV-1 variants does not limit their evolutionary potential.

OBJECTIVE: Anti HIV-1 therapy with nucleoside reverse transcriptase inhibitors can select for drug-resistant reverse transcriptase variants with altered enzyme properties. Some of the mutations, e.g. Met184Val and Met184Ile, result in an increase in polymerase fidelity of the enzyme as measured in biochemical assays; however, the effect of such changes on the fidelity during viral replication is largely unknown. In this study, the codon 184 variants were used to investigate whether the mutation at codon 184 affects the mutation spectrum and mutation rate of the mutant viruses. DESIGN AND METHOD: In vitro selection experiments with either wild-type or lamivudine-resistant viruses (Met184Val and Met184Ile) were performed using a protease inhibitor as the selective drug. In addition, a novel selection approach was developed using a mixture of viruses, instead of individual viruses, during the selection process. RESULTS: Comparison of a total of 108 protease-resistant variants revealed no significant difference in the mutational spectrum of the wild-type and the lamivudine-resistant variants. In addition, the selection experiments with the viral mixtures demonstrated no delay in the kinetics of mutation generation in response to an antiviral drug. CONCLUSION: This study demonstrates that the Met184Val and Met184Ile mutations in the HIV-1 reverse transcriptase enzyme do not significantly affect the evolutionary potential of the corresponding viruses.

Codon↗
PubMed1999

Randomized trial comparing saquinavir soft gelatin capsules versus indinavir as part of triple therapy (CHEESE study).

OBJECTIVE: To compare efficacy and tolerability of saquinavir soft gelatin capsule (SQV-SGC) formulation and indinavir, both given as part of a triple drug regimen containing zidovudine and lamivudine, in HIV-1-infected individuals. DESIGN: Randomized, open label, multicentre study. PATIENTS: A total of 70 patients who were antiretroviral-naive and who had a CD4 cell count < 500 x 10(6)/I and/or > 10000 HIV RNA copies/ml plasma and/or HIV-related symptoms. Subjects were assigned randomly to zidovudine 200 mg three times per day plus lamivudine 150 mg twice per day plus either SQV-SGC 1200 mg three times per day (SQV-SGC group) or indinavir 800 mg three times per day (indinavir group). Data are presented for all patients up to week 24. RESULTS: Mean baseline CD4 cell counts (+/- SE) were 301+/-29 x 10(6) cells/l and 310 +/-43 x 10(6) cells/l in the SQV-SGC and indinavir groups, respectively. The log10 median baseline HIV RNA load was 5.00 copies/ml in the SQV-SGC group and 4.98 copies/ml in the indinavir group. No difference in antiretroviral effect between the treatment arms could be demonstrated. Intention-to-treat analysis (last observation carried forward [LOCF]) at week 24 revealed that RNA levels decreased to < 50 copies/ml in 74.3% of patients in the SQV-SGC group and in 71.4% of the patients in the indinavir group (P = 0.78). In the on-treatment analysis the proportion of patients < 50 copies/ml at week 24 was 88.0% in the SQV-SGC group and 84.6% in the indinavir group (P = 0.725). Intriguingly, the mean increase of CD4 cells in the first 24 weeks was 162+/-20 x 10(6) cells/l in the SQV-SGC group and 89+/-21 x 10(6) cells/l in the indinavir group (P = 0.01), but preliminary data indicate that this difference in CD4 cell count gain may disappear after 24 weeks of treatment. Both regimens were generally well tolerated. CONCLUSION: During the first 24 weeks of the study, we found no difference in antiviral potency between the indinavir group and the SQV-SGC group. A significantly higher CD4 response in the SQV-SGC group was observed.

Adult↗
PubMed1999

Worldwide evaluation of DNA sequencing approaches for identification of drug resistance mutations in the human immunodeficiency virus type 1 reverse transcriptase.

A panel (ENVA-1) of well-defined blinded samples containing wild-type and mutant human immunodeficiency virus type 1 (HIV-1) reverse transcriptase was analyzed by automated DNA sequencing in 23 laboratories worldwide. Drug resistance mutations at codons 41, 215, and 184 were present in the panel samples at different ratios to the wild type. The presence of mutant genotypes was determined qualitatively and quantitatively. All laboratories reported the presence of sequence heterogeneities at codons 41, 215, and 184 in one or more of the panel samples, though not all reported the correct codon genotypes. Two laboratories reported a mutant genotype in samples containing only the wild type, whereas two and three laboratories failed to detect the mutant genotypes at codons 41 and 215, respectively, in a completely mutant DNA population. Mutations present at relative concentrations of 25% of the total DNA population were successfully identified by 13 of 23, 10 of 23, and 16 of 23 labs for codons 41, 215, and 184Val, respectively. For more than 80% of those laboratories that qualitatively detected the presence of a mutation correctly, the estimated wild type/mutant ratio was less than 25% different from the input ratio in those samples containing 25 to 50% or 75% mutant input. This first multicenter study on the quality of DNA sequencing approaches for identifying HIV-1 drug resistance mutations revealed large interlaboratory differences in the quality of the results. The application of these procedures in their current state would in several cases lead to inaccurate or even incorrect diagnostic results. Therefore, proper quality control and standardization are urgently needed.

Codon↗
PubMed1999

Effect of weekly adefovir (PMEA) infusions on HIV-1 virus load: results of a phase I/II study.

The compound 9-(2-phosphonylmethoxyethyl)adenine (adefovir; PMEA) is a potent inhibitor of a number of viruses in vitro, such as human immunodeficiency virus (HIV) type 1 and 2, herpes simplex virus (HSV) type 1 and 2, human papillomavirus virus (HBV) and Epstein-Barr virus (EBV). Adefovir also proved to be effective in vivo against feline immunodeficiency virus (FIV) in cats and simian immunodeficiency virus (SIV) in rhesus monkeys. In an open, non-placebo-controlled trial the antiviral activity of weekly doses of adefovir in nine patients with AIDS or AIDS-related complex was studied for a period of 11 weeks. CD4 cell counts at baseline were between 10 and 450 cells/mm3, HIV-1 RNA levels at baseline were between 24,210 copies/ml and 406,197 copies/ml. The drug was administered intravenously at a dose of 1000 mg every week and plasma viral load was assessed at multiple points during the study. Administration of adefovir was tolerated well and no severe side effects were seen. The response to adefovir treatment differed widely between patients. The increase in CD4 cell count at end point ranged from -40 to 120 cell/mm3. The lowest HIV RNA levels were measured after 3-5 days, showing an increase thereafter. The nadir in viral load was achieved after 2 weeks, with a mean viral load decline of 0.7 from baseline. The decrease of the HIV RNA level at end point ranged from -0.3 log10 to 1.8 log10 with a mean decrease of 0.4 log10. Our results indicate that adefovir given intravenously once weekly has a short-lasting initial antiviral effect. The effect of more frequent dosing requires further evaluation. If adefovir is to be useful clinically, it needs to be combined with other antiviral agents.

Acquired Immunodeficiency Syndrome↗
PubMed1998

[Vertical HIV-I-transmission. II. HIV-diagnosis in a child].

In newborn children from HIV-infected women early establishment of HIV infection is of importance for optimal therapy of HIV-infected children and avoidance of unnecessary medication in uninfected children. A more than 95% reliable diagnosis of HIV infection can now be obtained at the age of four weeks by polymerase chain reaction (PCR) technology. Before this age a positive PCR result is relevant since it necessitates additional investigation such as measuring anti-HIV drug resistance and may lead to modification of anti-HIV treatment. Prophylaxis against Pneumocystis carinii is not needed if HIV infection can not be demonstrated by PCR after the age of four weeks.

AIDS-Related Opportunistic Infections↗
PubMed1998

Stochastic processes strongly influence HIV-1 evolution during suboptimal protease-inhibitor therapy.

It has long been assumed that HIV-1 evolution is best described by deterministic evolutionary models because of the large population size. Recently, however, it was suggested that the effective population size (Ne) may be rather small, thereby allowing chance to influence evolution, a situation best described by a stochastic evolutionary model. To gain experimental evidence supporting one of the evolutionary models, we investigated whether the development of resistance to the protease inhibitor ritonavir affected the evolution of the env gene. Sequential serum samples from five patients treated with ritonavir were used for analysis of the protease gene and the V3 domain of the env gene. Multiple reverse transcription-PCR products were cloned, sequenced, and used to construct phylogenetic trees and to calculate the genetic variation and Ne. Genotypic resistance to ritonavir developed in all five patients, but each patient displayed a unique combination of mutations, indicating a stochastic element in the development of ritonavir resistance. Furthermore, development of resistance induced clear bottleneck effects in the env gene. The mean intrasample genetic variation, which ranged from 1.2% to 5.7% before treatment, decreased significantly (P < 0.025) during treatment. In agreement with these findings, Ne was estimated to be very small (500-15,000) compared with the total HIV-1 RNA copy number. This study combines three independent observations, strong population bottlenecking, small Ne, and selection of different combinations of protease-resistance mutations, all of which indicate that HIV-1 evolution is best described by a stochastic evolutionary model.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Cellular proviral HIV type 1 DNA load persists after long-term RT-inhibitor therapy in HIV type 1 infected persons.

In a set of 42 antiretroviral naive HIV-1 infected persons who were treated with either Zidovudine (AZT) monotherapy, or a combination of AZT + ddC (Zalcitabine) or AZT + ddI (Didanosine), the HIV-1 DNA load was measured by competitive polymerase chain reaction (PCR) and related to the HIV-1 RNA load in plasma, the CD4+ counts and to clinical markers. The question was whether a reduction in the cellular HIV-1 DNA level contributes to clinical benefit, as predicted by a lasting response in HIV-1 RNA levels in plasma. No significant decline relative to baseline in HIV-1 DNA load was found in the AZT monotherapy arm. In this arm the differences from baseline for both HIV-1 RNA load and CD4+ T cell counts were small and transient. In both combination therapy arms, the maximum mean decline in HIV-1 DNA load was 0.6 log and it never differed significantly from baseline. This is in contrast to plasma HIV-1 RNA load that declined earlier and steeper (mean of 1.5 and 1.9 log for AZT + ddC and AZT + ddI, respectively) and that remained significantly below baseline for 80 weeks. Although 9 of 42 (32%) of the patients under combination therapy had prolonged decreased plasma RNA levels, the proviral HIV-1 DNA remained present in the cells throughout the total follow-up of 144 weeks. In conclusion, combination therapy showed better laboratory parameter responses than AZT monotherapy, in agreement with the clinical data. The HIV-1 DNA sequences did not disappear in any of the patients, heralding renewed active infection after cessation of therapy.

Anti-HIV Agents↗
PubMed1998

Efficient inhibition of both syncytium-inducing and non-syncytium-inducing wild-type HIV-1 by lamivudine in vivo.

OBJECTIVE: To determine the effect of lamivudine (3TC) on syncytium-inducing (SI) and non-SI (NSI) HIV-1 populations in vivo. DESIGN: Responses in virus load and 3TC resistance in 40 3TC-treated subjects were analysed in relation to the presence or absence of SI HIV-1 variants. METHODS: Peripheral blood samples were collected at regular intervals from 40 HIV-1-infected subjects during 3TC treatment. Virus isolates obtained at the start of treatment were typed for SI-capacity by coculture with MT-2 cells. Changes in levels of viral RNA in plasma were determined by quantitative reverse transcriptase PCR. The relative amount of wild-type and mutant virus at codon 184, associated with HIV resistance to 3TC, was determined using a primer-guided nucleotide incorporation assay after amplification of part of the reverse transcriptase gene. In five subjects the frequency of productively infected CD4+ cells with SI or NSI variants was determined in relation to codon 184 genotype. RESULTS: Twenty-six subjects harboured only NSI variants at baseline, whereas 14 subjects also harboured SI variants. Although baseline plasma viral RNA load and CD4 cell counts were different between the two groups, no differences in the response to 3TC therapy were observed for these parameters. In-depth analysis of five subjects showed that the kinetics of virus load changes and emergence of 3TC resistance mutations were similar in plasma and cells, and comparable for the SI and NSI populations present in one individual. CONCLUSIONS: These data show that, in contrast to didanosine and zidovudine, the pressure exerted by 3TC is similar for SI and NSI M184 populations.

Anti-HIV Agents↗
PubMed1997

HIV-1 viral load, phenotype, and resistance in a subset of drug-naive participants from the Delta trial. The National Virology Groups. Delta Virology Working Group and Coordinating Committee.

BACKGROUND: The Delta trial showed that combination therapy (zidovudine plus didanosine and zidovudine plus zalcitabine) substantially lengthened life and reduced disease progression compared with zidovudine monotherapy. We did a nested virological study in three countries (France, the Netherlands, and the UK) to investigate changes in markers for viral load and antiretroviral-drug resistance during therapy. METHODS: 240 zidovudine-naive HIV-1-infected patients were randomly assigned zidovudine only (n = 87), zidovudine plus didanosine (n = 80), or zidovudine plus zalcitabine (n = 73). Viral load in peripheral-blood mononuclear cells and plasma was measured by quantitative culture. Plasma HIV-1 RNA was measured by reverse-transcriptase PCR amplification, and serum p24 antigen by ELISA. Resistance to antiretroviral drugs was measured phenotypically by culture and genotypically by detection and quantification of drug-related point mutations in the pol gene. Analyses were done by intention to treat. FINDINGS: The reduction in viral load was greatest 4-12 weeks after the start of therapy and was most pronounced in the combination-therapy study groups (median reductions of RNA at 4 weeks 1.58, 1.28, and 0.49 log10 copies/mL for zidovudine plus didanosine, zidovudine plus zalcitabine, and zidovudine only, respectively). RNA levels at 8 weeks were predictive of disease progression and death after allowance for baseline values. At 48 weeks, the proportion of participants with phenotypic zidovudine resistance was similar in all three groups: didanosine and zalcitabine resistance were rare; zidovudine genomic resistance correlated with phenotypic resistance (r = 0.54, p < 0.0001) and developed earlier in the combined-therapy groups. However, participants in the zidovudine monotherapy group had higher circulating loads of resistant virus than those in the combined-therapy groups. INTERPRETATION: Combined antiretroviral therapy was more efficient at lowering virus load than monotherapy. Although zidovudine resistance was common in monotherapy and combined-therapy groups, circulating concentrations of resistant virus were substantially lower in the combination groups, which is likely to be a result of the continued antiviral activity of didanosine or zalcitabine.

Anti-HIV Agents↗
PubMed1997

Lamivudine-resistant human immunodeficiency virus type 1 variants (184V) require multiple amino acid changes to become co-resistant to zidovudine in vivo.

Exposure of human immunodeficiency virus to the nucleoside analogue lamivudine (3TC) rapidly selects for resistant variants with a valine at codon 184 (M184V) in the catalytic site of reverse transcriptase. In vitro, 184V demonstrated increased enzyme fidelity and suppressed zidovudine resistance. Clinical trials demonstrated that 3TC-zidovudine combination therapy results in a strong and sustained antiviral response. To investigate the role of 184V on in vivo virus evolution, the effect of zidovudine addition in 3TC-pretreated patients harboring 184V was studied. In vivo, no significant change in fidelity was observed with 184V, shown by generation of the classical pattern of zidovudine mutations. Of interest, in contrast to zidovudine monotherapy, in which just one substitution is sufficient for in vivo development of significant zidovudine resistance, multiple substitutions are required for the same level of zidovudine resistance in strains harboring 184V. This need for multiple substitutions may be one of the mechanisms explaining the sustained antiretroviral response of the 3TC-zidovudine combination.

Amino Acid Sequence↗
PubMed1997

In-vitro selection of HIV-1 variants resistant to non-nucleoside reverse transcriptase inhibitors in monocyte-derived macrophages.

Unlike the selection of HIV-1 variants resistant to anti-retroviral drugs in human peripheral blood mononuclear cells and T cell lines, induction of resistance in monocyte-derived macrophages has not been widely studied. Since macrophages serve as a potential HIV-1 reservoir in humans, knowledge of the effect of anti-retroviral drugs on macrophage-tropic HIV-1 isolates may help in the design of a strategy for prolonged suppression of viral replication. In-vitro selection and drug susceptibility testing of macrophage-tropic HIV-1 variants with reduced sensitivity to two non-nucleoside reverse transcriptase inhibitors, atevirdine and delavirdine (both bis-heteroarylpiperazines), is described here. The atevirdine-resistant isolate was cross-resistant to delavirdine, and the delavirdine-resistant isolate was cross-resistant to atevirdine. Interestingly, the atevirdine-resistant isolate, but not the delavirdine-resistant isolate, was also cross-resistant to nevirapin while the inhibition of viral replication of both isolates in macrophages by zidovudine was the same as that in the parental HIV-1 strain. Nucleotide sequence analysis of the resistant macrophage-tropic HIV-1 isolates showed that the atevirdine-induced resistance was due to a single amino acid change at codon 106 and that the delavirdine-induced resistance could be attributed to an amino acid change at codon 236. This study demonstrates that monocyte-derived macrophages can be used to investigate the phenotypic and genotypic acquisition of anti-retroviral drug resistance of macrophage-tropic HIV-1.

Amino Acid Sequence↗
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

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

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↗