Rossum, A.M.C. van

Functional characterization of the RuvB homologs from Mycoplasma pneumoniae and Mycoplasma genitalium (Article)

2011-12-01T00:00:00Z

Homologous recombination between repeated DNA elements in the genomes of Mycoplasma species has been hypothesized to be a crucial causal factor in sequence variation of antigenic proteins at the bacterial surface. To investigate this notion, studies were initiated to identify and characterize the proteins that form part of the homologous DNA recombination machinery in Mycoplasma pneumoniae as well as Mycoplasma genitalium. Among the most likely participants of this machinery are homologs of the Holliday junction migration motor protein RuvB. In both M. pneumoniae and M. genitalium, genes have been identified that have the capacity to encode RuvB homologs (MPN536 and MG359, respectively). Here, the characteristics of the MPN536- and MG359-encoded proteins (the RuvB proteins from M. pneumoniae strain FH [RuvBFH] and M. genitalium [RuvBMge], respectively) are described. Both RuvBFHand RuvBMgewere found to have ATPase activity and to bind DNA. In addition, both proteins displayed divalent cation- and ATP-dependent DNA helicase activity on partially double-stranded DNA substrates. The helicase activity of RuvBMge, however, was significantly lower than that of RuvBFH. Interestingly, we found RuvBFHto be expressed exclusively by subtype 2 strains of M. pneumoniae. In strains belonging to the other major subtype (subtype 1), a version of the protein is expressed (the RuvB protein from M. pneumoniae strain M129 [RuvBM129]) that differs from RuvBFHin a single amino acid residue (at position 140). In contrast to RuvBFH, RuvBM129displayed only marginal levels of DNAunwinding activity. These results demonstrate that M. pneumoniae strains (as well as closely related Mycoplasma spp.) can differ significantly in the function of components of their DNA recombination and repair machinery.

Annual vaccination against influenza virus hampers development of virus-specific CD8 + T cell immunity in children (Article)

2011-11-01T00:00:00Z

Infection with seasonal influenza A viruses induces immunity to potentially pandemic influenza A viruses of other subtypes (heterosubtypic immunity). We recently demonstrated that vaccination against seasonal influenza prevented the induction of heterosubtypic immunity against influenza A/H5N1 virus induced by infection with seasonal influenza in animal models, which correlated with the absence of virus-specific CD8+T cell responses. Annual vaccination of all healthy children against influenza has been recommended, but the impact of vaccination on the development of the virus-specific CD8+T cell immunity in children is currently unknown. Here we compared the virus-specific CD8+T cell immunity in children vaccinated annually with that in unvaccinated children. In the present study, we compared influenza A virus-specific cellular and humoral responses of unvaccinated healthy control children with those of children with cystic fibrosis (CF) who were vaccinated annually. Similar virus-specific CD4+T cell and antibody responses were observed, while an age-dependent increase of the virus-specific CD8+T cell response that was absent in vaccinated CF children was observed in unvaccinated healthy control children. Our results indicate that annual influenza vaccination is effective against seasonal influenza but hampers the development of virus-specific CD8+T cell responses. The consequences of these findings are discussed in the light of the development of protective immunity to seasonal and future pandemic influenza viruses.

Sequence variation within the P1 gene of Mycoplasma pneumoniae (Article)

2011-10-01T00:00:00Z

Identification of amino acid residues critical for catalysis of holliday junction resolution by Mycoplasma genitalium RecU (Article)

2011-08-01T00:00:00Z

The RecU protein from Mycoplasma genitalium, RecUMge, is a 19.4-kDa Holliday junction (HJ) resolvase that binds in a nonspecific fashion to HJ substrates and, in the presence of Mn2+, cleaves these substrates at a specific sequence (5'-G/TC2C/TTA/GG-3'). To identify amino acid residues that are crucial for HJ binding and/or cleavage, we generated a series of 16 deletion mutants (9 N- and 7 C-terminal deletion mutants) and 31 point mutants of RecUMge. The point mutations were introduced at amino acid positions that are highly conserved among bacterial RecU-like sequences. All mutants were purified and tested for the ability to bind to, and cleave, HJ substrates. We found the five N-terminal and three C-terminal amino acid residues of RecUMgeto be dispensable for its catalytic activities. Among the 31 point mutants, 7 mutants were found to be inactive in both HJ binding and cleavage. Interestingly, in 12 other mutants, these two activities were uncoupled; while these proteins displayed HJ-binding characteristics similar to those of wild-type RecUMge, they were unable to cleave HJ substrates. Thus, 12 amino acid residues were identified (E11, K31, D57, Y58, Y66, D68, E70, K72, T74, K76, Q88, and L92) that may play either a direct or indirect role in the catalysis of HJ resolution.

Variation in a surface-exposed region of the Mycoplasma pneumoniae P40 protein as a consequence of homologous DNA recombination between RepMP5 elements (Article)

2011-02-01T00:00:00Z

Mycoplasma pneumoniae is a human pathogen that causes a range of respiratory tract infections. The first step in infection is adherence of the bacteria to the respiratory epithelium. This step is mediated by a specialized organelle, which contains several proteins (cytadhesins) that have an important function in adherence. Two of these cytadhesins, P40 and P90, represent the proteolytic products from a single 130 kDa protein precursor, which is encoded by the MPN142 gene. Interestingly, MPN142 contains a repetitive DNA element, termed RepMP5, of which homologues are found at seven other loci within the M. pneumoniae genome. It has been hypothesized that these RepMP5 elements, which are similar but not identical in sequence, recombine with their counterpart within MPN142 and thereby provide a source of sequence variation for this gene. As this variation may give rise to amino acid changes within P40 and P90, the recombination between RepMP5 elements may constitute the basis of antigenic variation and, possibly, immune evasion by M. pneumoniae. To investigate the sequence variation of MPN142 in relation to inter-RepMP5 recombination, we determined the sequences of all RepMP5 elements in a collection of 25 strains. The results indicate that: (i) inter-RepMP5 recombination events have occurred in seven of the strains, and (ii) putative RepMP5 recombination events involving MPN142 have induced amino acid changes in a surface-exposed part of the P40 protein in two of the strains. We conclude that recombination between RepMP5 elements is a common phenomenon that may lead to sequence variation of MPN142-encoded proteins.

Neonatal Procalcitonin Intervention Study (NeoPInS): Effect of Procalcitonin-guided decision making on Duration of antibiotic Therapy in suspected neonatal early-onset Sepsis: A multi-centre randomized superiority and non-inferiority Intervention Study (Article)

2010-12-08T00:00:00Z

Background: Early diagnosis and treatment of the newborn infant with suspected sepsis are essential to prevent severe and life threatening complications. Diagnosis of neonatal sepsis is difficult because of the variable and nonspecific clinical presentation. Therefore, many newborns with nonspecific symptoms are started on antibiotic treatment before the presence of sepsis has been proven. With our recently published single-centre intervention study we were able to show that Procalcitonin determinations allowed to shorten the duration of antibiotic therapy in newborns with suspected early-onset sepsis.Methods/Design: The study is designed as randomized controlled international multicenter intervention trial on the efficacy and safety of Procalcitonin guided treatment. Term and near-term infants (gestational age ≥ 34 0/7 weeks) with suspected sepsis in the first 3 days of life requiring empiric antibiotic therapy will be included. The duration of antibiotic therapy in the standard group is based on the attending physician's assessment of the likelihood of infection (infection unlikely, possible, probable or proven). In the Procalcitonin group, if infection is considered to be unlikely or possible, antibiotic therapy is discontinued when two consecutive Procalcitonin values are within the normal range. Co-primary outcome measures are the duration of antibiotic therapy (superiority aspect of the trial) and the proportion of infants with a recurrence of infection requiring additional courses of antibiotic therapy and/or death in the first month of life (safety of study intervention, non-inferiority aspect of the trial). The number of infants to be included equals 800 per arm. With these numbers the power of the study to demonstrate superiority for duration of antibiotic therapy as well as non-inferiority regarding safety, i.e. excluding a disadvantage difference larger than 2% for the experimental arm, will both be greater than 80%.Discussion: Benefit of the study is a possible limitation of unnecessary use of antibiotics. The results of our first study suggest that there is a low risk on discontinuing antibiotic treatment too early, resulting in the development of a neonatal infection with its morbidity and mortality.

Macrolide resistance determination and molecular typing of Mycoplasma pneumoniae by pyrosequencing (Article)

2010-09-01T00:00:00Z

The first choice antibiotics for treatment of Mycoplasma pneumoniae infections are macrolides. Several recent studies, however, have indicated that the prevalence of macrolide (ML)-resistance, which is determined by mutations in the bacterial 23S rRNA, is increasing among M. pneumoniae isolates. Consequently, it is imperative that ML-resistance in M. pneumoniae is rapidly detected to allow appropriate and timely treatment of patients. We therefore set out to determine the utility of pyrosequencing as a convenient technique to assess ML-resistance. In addition, we studied whether pyrosequencing could be useful for molecular typing of M. pneumoniae isolates. To this end, a total of four separate pyrosequencing assays were developed. These assays were designed such as to determine a short genomic sequence from four different sites, i.e. two locations within the 23S rRNA gene, one within the MPN141 (or P1) gene and one within the MPN528a gene. While the 23S rRNA regions were employed to determine ML-resistance, the latter two were used for molecular typing. The pyrosequencing assays were performed on a collection of 108 M. pneumoniae isolates. The ML-resistant isolates within the collection (n = 4) were readily identified by pyrosequencing. Moreover, each strain was correctly typed as either a subtype 1 or subtype 2 strain by both the MPN141 and MPN528a pyrosequencing test. Interestingly, two recent isolates from our collection, which were identified as subtype 2 strains by the pyrosequencing assays, were found to carry novel variants of the MPN141 gene, having rearrangements in each of the two repetitive elements (RepMP4 and RepMP2/3) within the gene. In conclusion, pyrosequencing is a convenient technique for ML-resistance determination as well as molecular typing of M. pneumoniae isolates.

The Mycoplasma genitalium MG352-encoded protein is a Holliday junction resolvase that has a non-functional orthologue in Mycoplasma pneumoniae (Article)

2010-09-01T00:00:00Z

Recombination between repeated DNA elements in the genomes of Mycoplasma species appears to lie at the basis of antigenic variation of several essential surface proteins. It is therefore imperative that the DNA recombinatorial pathways in mycoplasmas be unravelled. Here, we describe the proteins encoded by the Mycoplasma genitalium MG352 and Mycoplasma pneumoniae MPN528a genes (RecUMgeand RecUMpnrespectively), which share sequence similarity with RecU Holliday junction (HJ) resolvases. RecUMgewas found to: (i) bind HJ substrates and large double-stranded DNA molecules and (ii) cleave HJ substrates at the sequence 5′-G/TC↓C/TTA/GG- 3′ in the presence of Mn2+. Interestingly, RecUMpn(from M. pneumoniae subtype 2 strains) did not possess obvious DNA binding or cleavage activities, which was found to be caused by the presence of a glutamic acid residue at position 67 of the protein, which is not conserved in RecUMge. Additionally, RecUMpnappears not to be expressed by subtype 1 M. pneumoniae strains, as these possess a TAA translation termination codon at position 181-183 of MPN528a. We conclude that RecUMgeis a HJ resolvase that may play a central role in recombination in M. genitalium.

Identification and classification of P1 variants of Mycoplasma pneumoniae (Article)

2010-02-01T00:00:00Z

The Mycoplasma pneumoniae MPN490 and Mycoplasma genitalium MG339 genes encode RecA homologs that promote homologous DNA strand exchange (Article)

2009-11-01T00:00:00Z

The P1, P40, and P90 proteins of Mycoplasma pneumoniae and the MgPa and P110 proteins of Mycoplasma genitalium are immunogenic adhesion proteins that display sequence variation. Consequently, these proteins are thought to play eminent roles in immune evasive strategies. For each of the five proteins, a similar underlying molecular mechanism for sequence variation was hypothesized, i.e., modification of the DNA sequences of their respective genes. This modification is thought to result from homologous recombination of parts of these genes with repeat elements (RepMp and MgPar elements in M. pneumoniae and M. genitalium, respectively) that are dispersed throughout the bacterial genome. Proteins that are potentially involved in homologous DNA recombination have been suggested to be implicated in recombination between these repeat elements and thereby in antigenic variation. To investigate this notion, we set out to study the function of the RecA homologs that are encoded by the M. pneumoniae MPN490 and M. genitalium MG339 genes. Both proteins, which are 79% identical on the amino acid level, were found to promote recombination between homologous DNA substrates in an ATP-dependent fashion. The recombinational activities of both proteins were Mg2+and pH dependent and were strongly supported by the presence of single-stranded DNA binding protein, either from M. pneumoniae or from Escherichia coli. We conclude that the MPN490- and MG339-encoded proteins are RecA homologs that have the capacity to recombine homologous DNA substrates. Thus, they may play a central role in recombination between repetitive elements in both M. pneumoniae and M. genitalium. Copyright

Sequence variations in RepMP2/3 and RepMP4 elements reveal intragenomic homologous DNA recombination events in Mycoplasma pneumoniae (Article)

2009-09-14T00:00:00Z

The gene encoding major adhesin protein P1 of Mycoplasma pneumoniae, MPN141, contains two DNA sequence stretches, designated RepMP2/3 and RepMP4, which display variation among strains. This variation allows strains to be differentiated into two major P1 genotypes (1 and 2) and several variants. Interestingly, multiple versions of the RepMP2/3 and RepMP4 elements exist at other sites within the bacterial genome. Because these versions are closely related in sequence, but not identical, it has been hypothesized that they have the capacity to recombine with their counterparts within MPN141, and thereby serve as a source of sequence variation of the P1 protein. In order to determine the variation within the RepMP2/3 and RepMP4 elements, both within the bacterial genome and among strains, we analysed the DNA sequences of all RepMP2/3 and RepMP4 elements within the genomes of 23 M. pneumoniae strains. Our data demonstrate that: (i) recombination is likely to have occurred between two RepMP2/3 elements in four of the strains, and (ii) all previously described P1 genotypes can be explained by inter-RepMP recombination events. Moreover, the difference between the two major P1 genotypes was reflected in all RepMP elements, such that subtype 1 and 2 strains can be differentiated on the basis of sequence variation in each RepMP element. This implies that subtype 1 and subtype 2 strains represent evolutionarily diverged strain lineages. Finally, a classification scheme is proposed in which the P1 genotype of M. pneumoniae isolates can be described in a sequence-based, universal fashion.

Indinavir/low-dose ritonavir containing HAART in HIV-1 infected children has potent antiretroviral activity, but is associated with side effects and frequent discontinuation of treatment (Article)

2007-06-01T00:00:00Z

We here present the study results of 21 HIV-1 infected children who were treated with indinavir plus low-dose ritonavir and two nucleoside reverse transcriptase inhibitors (NRTIs) for 48 weeks. Although this q12h HAART regimen had potent antiretroviral activity, it was frequently associated with side effects and discontinuation of therapy.

Challenges in the treatment of HIV-1 infected children with highly active antiretroviral therapy (Doctoral Thesis)

2002-04-03T00:00:00Z

Nobody could have predicted the tremendous implications of the headline in The New York Times of July 5, 1981: "Rare cancer in homosexuals". This article contained the first description of the disease "Acquired Immune Deficiency Syndrome" (AIDS) and marked the beginning of a pandemic by the Human Immunodeficiency Virus (HIV). (1) Three years after the first adults with AIDS were identified, similar disease features were reported in children. (2, 3) In general, HIV infection progresses more rapidly in children than in adults. This progression is associated with a higher viral burden, a more rapid depletion of CD4+ T-cell lymphocytes and impaired growth characteristics. (4- 8) HN infected children may be divided in three groups on the basis of disease progression: "rapid progressors" (±20%), "intermediate progressors" (±60%) and "slow progressors" (±20%). (9-12) The first group shows a rapid decrease in CD4+ T-cells and develops AIDS (CDC classification C (13)) within the first two years of life. In "intermediate progressors" a more gradual decrease in CD4+ T-cell counts is observed. These children don't have symptoms of serious immunosuppression until the age of 7-8 years. The "slow progressors" are asymptomatic at the age of 8 years and have a normal or slightly decreased CD4+ T-cell count. Symptoms associated with HIV infection in infants and children are dependent on the extent of immunosuppression. The Centers for Disease Control and Prevention have developed a pediatric classification system based on the seriousness of symptoms. (13) In children with intermediate and slow progression rates an asymptomatic medical history may be present possibly in combination with a slightly increased incidence of bacterial infections and lymphadenopathy. Pneumocystis carinii pneumonia (PCP) was the most frequently occurring opportunistic infection in HIV infected children during the initial period when HIV exposed and HN infected children in Europe and the USA did not routinely receive PeP-prophylaxis.

Treatment with highly active antiretroviral therapy in human immunodeficiency virus type 1-infected children is associated with a sustained effect on growth (Article)

2002-01-01T00:00:00Z

INTRODUCTION: Growth failure is a common feature of children with human immunodeficiency virus type 1 (HIV-1) infection. Children who are treated with mono or dual nucleoside analogue reverse transcriptase inhibitor (NRTI) therapy show a temporary increase in weight gain and linear growth rate. In adults, protease-inhibitor-containing antiretroviral therapy is associated with a sustained weight gain and increased body mass index (BMI). Experience with protease inhibitors and growth in children is still limited. The data mainly deal with short-term effects on growth. OBJECTIVE: To evaluate the effect of highly active antiretroviral therapy (HAART) on growth in children with HIV-1 infection. DESIGN AND METHODS: We analyzed selected growth parameters, clinical data, and laboratory results as part of a prospective, open, uncontrolled, multicenter study to evaluate the clinical, immunologic, and virologic response to HAART consisting of indinavir, zidovudine, and lamivudine in children with HIV-1 infection. Height and weight were measured at 0, 12, 24, 36, 48, 60, 72, 84, and 96 weeks after initiation of HAART. Information about the children's growth before enrollment in the study was retrieved from the hospital medical records and/or the school doctor or health center. BMI was calculated. z Scores were used to express the standard deviation (SD) in SD units from the Dutch reference curves for age and gender. Viral loads and CD4+ T-cell counts were examined prospectively and related to these growth parameters. z Scores were also calculated for CD4+ T-cell counts to correct for age-related differences. A z score of 0 represents the P50, which is exactly the age/sex-appropriate median. A height z score of -1 indicates that a child's height is 1 SD below the age- and gender-specific median height for the normal population. Virologic responders were defined as those who either reached an undetectable viral load (<500 copies/mL) or had a >1.5 log reduction in viral load compared with baseline at week 12 after the initiation of HAART, which was maintained during the follow-up period. RESULTS. PATIENTS: Twenty-four patients were included (age: 0.4-16.3 years at baseline), with a median HIV-1 RNA load of 105 925 copies/mL (5.03 log), a median CD4+ T-cell count of 0.586 x 10(9)/L (median z score: -2.28 SD), a median height z score of -1.22, a median weight z score of -0.74, and a median baseline BMI z score of -0.32. Eleven patients were naive to antiretroviral therapy, and 13 patients had received previous treatment with NRTI monotherapy. Twenty children used indinavir and 4 children used nelfinavir as part of HAART. VIROLOGIC AND IMMUNOLOGIC RESPONSES TO HAART: Seventeen children were virologic responders, and 7 children were virologic nonresponders. In patients naive to NRTIs, median baseline viral loads were significantly higher than in pretreated patients. However, at weeks 48 and 96, there was no significant difference between the viral loads of both groups. At baseline, there was no significant difference in CD4+a T-cell z scores between virologic responders and nonresponders or between naive and pretreated patients. During 96 weeks of HAART, the increase of CD4+ T-cell z score was significantly higher in responders than in nonresponders. The increase in CD4+ T-cell z score was not significantly different for naive and pretreated patients. HEIGHT, WEIGHT, AND BMI z SCORE CHANGES: We found that there was a trend toward a significantly increased z score change during 96 weeks of HAART compared with the z score change before HAART initiation for height and weight, but not for BMI. GROWTH AND VIROLOGIC RESPONSE TO HAART: When the data were analyzed separately for virologic responders and nonresponders, virologic responders showed significant increases in height and weight. The height and weight of virologic nonresponders did not change significantly. The BMI did not change significantly in responders or in nonresponders. GROWTH AND IMMUNOLOGIC RESPONSE TO HAART: The increase of weight and BMI z scores from baseline correlated positively with the CD4+ T-cell z score increase from baseline. It did not correlate with absolute CD4+ T-cell count increase. Height z score increase did not correlate with CD4+ T-cell z score or with absolute CD4+ T-cell counts. GROWTH AND PREVIOUS NRTI TREATMENT: The height z score decrease from week -48 to baseline was significantly larger in naive than in pretreated patients. The weight and BMI z score change from week -48 to baseline was not significantly different for pretreated and naive patients. From baseline to week 96, the height and weight z score change increased significantly in naive patients but not in pretreated patients compared with the change from week -48 to baseline. The BMI z score did not change significantly over 96 weeks of HAART for naive or pretreated patients. GROWTH AND CLINICAL STAGE OF INFECTION: The clinical stage of infection according to the Centers for Disease Control and Prevention classification correlated negatively with the BMI z score and the weight z score at baseline but not with the height z score. Thus, children with the most severe clinical disease had the lowest BMI and weight z scores at baseline. The BMI z score increased more in children with more advanced clinical infection at baseline, who had lower BMI at baseline. The clinical stage of infection did not correlate with the change in weight z score from baseline to week 96. CONCLUSIONS: HAART has a positive influence effect on the growth of HIV-1-infected children. This effect is sustained for at least 96 weeks. Height and weight are favorably influenced in children in whom HAART leads to a reduction of the viral load of at least 1.5 log or to <500 copies/mL and to an increase in the CD4+ T-cell z score. In contrast to the increase of the BMI in adults on HAART, BMI did not increase in all children effectively treated with HAART. BMI increased more in children with an advanced stage of infection and a poor nutritional status at baseline. Data from pretreated and naive patients were difficult to interpret, because the baseline characteristics of these 2 groups differed too much.

Persistent sterile leukocyturia is associated with impaired renal function in human immunodeficiency virus type 1-infected children treated with indinavir (Article)

2002-01-01T00:00:00Z

BACKGROUND: Prolonged administration of indinavir is associated with the occurrence of a variety of renal complications in adults. These well-documented side effects have restricted the use of this potent protease inhibitor in children. DESIGN: A prospective study to monitor indinavir-related nephrotoxicity in a cohort of 30 human immunodeficiency virus type 1-infected children treated with indinavir. METHODS: Urinary pH, albumin, creatinine, the presence of erythrocytes, leukocytes, bacteria and crystals, and culture were analyzed every 3 months for 96 weeks. Serum creatinine levels were routinely determined at the same time points. Steady-state pharmacokinetics of indinavir were done at week 4 after the initiation of indinavir. RESULTS: The cumulative incidence of persistent sterile leukocyturia (> or =75 cells/ micro L in at least 2 consecutive visits) after 96 weeks was 53%. Persistent sterile leukocyturia was frequently associated with a mild increase in the urine albumin/creatinine ratio and by microscopic hematuria. The cumulative incidence of serum creatinine levels >50% above normal was 33% after 96 weeks. Children with persistent sterile leukocyturia more frequently had serum creatinine levels of 50% above normal than those children without persistent sterile leukocyturia. In children younger than 5.6 years, persistent sterile leukocyturia was significantly more frequent than in older children. A higher cumulative incidence of persistent leukocyturia was found in children with an area under the curve >19 mg/L x h or a peak serum level of indinavir >12 mg/L. In 4 children, indinavir was discontinued because of nephrotoxicity. Subsequently, the serum creatinine levels decreased, the urine albumin/creatinine ratios returned to zero, and the leukocyturia disappeared within 3 months. CONCLUSIONS: Children treated with indinavir have a high cumulative incidence of persistent sterile leukocyturia. Children with persistent sterile leukocyturia more frequently had an increase in serum creatinine levels of >50% above normal. Younger children have an additional risk for renal complications. The impairment of the renal function in these children occurred in the absence of clinical symptoms of nephrolithiasis. Indinavir-associated nephrotoxicity must be monitored closely, especially in children with risk factors such as persistent sterile leukocyturia, age <5.6 years, an area under the curve of indinavir >19 mg/L x h, and a C(max) >12 mg/L.

Clinical and virologic response to combination treatment with indinavir, zidovudine, and lamivudine in children with human immunodeficiency virus-1 infection: A multicenter study in The Netherlands. (Article)

2000-01-01T00:00:00Z

Abstract OBJECTIVE: To evaluate the clinical, immunologic, and virologic response to indinavir, zidovudine, and lamivudine in children with human immunodeficiency virus-1 (HIV-1) infection. STUDY DESIGN: Twenty-eight HIV-1-infected children (3 months to 16 years of age) with or without prior treatment with reverse-transcriptase inhibitors and a HIV-1 RNA >5000 copies/mL and/or a CD4 cell count less than the lower limit of the age-specific reference value were treated with indinavir, zidovudine, and lamivudine. Pharmacokinetics of indinavir were determined in each child. RESULTS: The combination treatment was well tolerated in the majority of patients. Clinical improvement was seen in all patients. After 6 months of therapy, 70% of the patients had an HIV-1 RNA load below 500 copies/mL, whereas 48% of the children had a viral load below 40 copies/mL. Relative CD4 cell counts in relation to the lower limit of the age-specific reference value increased significantly from a median value of 79% at baseline to 106% after 6 months of therapy. The doses of indinavir necessary to achieve area under the curve values comparable to adult values varied from 1250 mg/m(2)/d to 2450 mg/m(2)/d. CONCLUSIONS: Highly active antiretroviral therapy consisting of indinavir, zidovudine, and lamivudine in children reduced HIV-1 RNA to less than 500 copies/mL in 70% of the children within 6 months. Improved CD4 cell counts were observed in most patients, as was a better clinical condition (no invasive or opportunistic infections, increased weight gain). Side effects of the triple therapy were mild. Highly active antiretroviral therapy can be used as successfully in children as in adults.