The use of HAART has changed the clinical profile of HIV infection [1,2]. However, the chronic nature of HIV infection usually requires lifelong therapy, and the efficacy of treatment is strictly related to treatment adherence. High daily pill burden associated with dietary restrictions and HAART-related toxicities are factors compromising long-term adherence [3–5]. Furthermore, the potentially increased risk of lipodistrophy related to long-term exposure to protease inhibitors (PI) has attracted particular concern [6–8]. Noteworthy, PI-based regimens have been linked with a significant increase in dyslipidaemia and insulin resistance in children [9,10]. As a result, numerous strategies of simplified treatment have been explored in order to improve patient quality of life and adherence to treatment, as well as to manage drug-related toxicities while maintaining viral suppression [11–13].
Switching to a regimen of three nucleoside reverse transcriptase inhibitors (NRTI) has been shown to be an effective strategy of simplification in adult patients with no previous therapeutic history of suboptimal NRTI exposure or NRTI-related mutations [13–16].
Triple-NRTI regimens potentially present important advantages for long-term treatment of HIV-infected children, including good tolerability, decreased metabolic disturbances, low pill burden and reduced economic cost of antiretroviral treatment . Overall, NRTI drugs have relatively few serious drug–drug interactions and dosing can be independent from food intake. In addition, a triple-NRTI strategy allows other antiretroviral drug classes to be kept in reserve for further regimens .
Data on efficacy and tolerability of triple-NRTI regimens as simplified therapy in HIV-infected children are not yet available. The present study examines the extended follow-up (96 weeks) of a group of HIV-infected children switched from successful PI-based HAART to a triple-NRTI regimen.
Study design and patients enrolment criteria
This prospective, open-label, before–after study was approved by the Ethical Commission of the Children's Hospital Bambino Gesù. Inclusion criteria were: (1) HIV-1 infection as confirmed by at least two HIV-1 PCR assays; (2) age between 2 and 18 years; (3) first-line treatment with a stable PI-based HAART regimen for at least 12 months; (4) plasma HIV-1 RNA < 50 copies/ml for at least 12 consecutive months; (5) stable CD4 cell numbers over 25% in the last year before study entry; (6) no previous treatment with nonnucleoside reverse transcriptase inhibitors or NRTI or history of virological failure with other regimens. Patients with known opportunistic infections must have had no acute symptoms of infection within the last 24 months before study entry and must have been receiving a stable approved antimicrobial therapy or prophylaxis.
At study entry, the PI drugs were switched, preferentially to a fixed-dose combination of zidovudine plus lamivudine plus abacavir, or to another NRTI drug, didanosine or stavudine, at weight-dependent dosage as recommended by the HIV paediatric international guidelines . Patients were maintained on their preentry NRTI backbone throughout the duration of the study. Older children assuming zidovudine plus lamivudine or zidovudine plus lamivudine plus abacavir used Combivir or Trizivir tablets, respectively. Younger children used broken capsules, weighted to the prescribed dose, and packed as tiny pieces in special capsules. Written informed consent was obtained from each patient's legal guardian before study entry.
Adherence to treatment and difficulty of taking medications were assessed from week 0 onwards by the PENTA (Paediatric European Network for Treatment of AIDS) questionnaire, as previously described . Questionnaires were filled in at the time of scheduled clinic visits for the trial by caregivers (with children where appropriate) and with the help of the nurse or doctor if required.
The followings primary endpoints were defined: HIV-RNA load > 1000 copies/ml at two consecutive evaluations and a new AIDS-defining event. A ‘blip’ was defined as an intermittent plasma viraemia with plasma HIV-1 RNA levels 50–1000 copies/ml and a return to an undetectable level at the next determination. When a blip was detected, a new HIV RNA assessment was performed within 3 weeks. Secondary efficacy outcomes included immunological failure (considered as change in Centers for Disease Control and Prevention immunological classification) and the development of adverse events of grade 3–4. The severity of adverse clinical events and laboratory abnormalities were evaluated according to the standard Paediatric AIDS Clinical Trial Group (PACTG) toxicity grading scale.
Evaluations were performed at baseline and at weeks 0, 2, 12, 24, 36, 48, 60, 72 and 96. At each evaluation, patients underwent a complete medical history and a physical examination that included weight, height and blood pressure measurements. Laboratory evaluations obtained after at least 8 h of fasting included complete blood count, blood chemistries (glucose, blood urinary nitrogen, creatine, electrolytes, total proteins, albumin, total and direct bilirubin, aspartate transaminase, lactate dehydrogenase, creatine kinase, amylase, lipase) and metabolic evaluations [total cholesterol, high density lipoproteins (HDL), low density lipoproteins (LDL), triglycerides, insulin and lactic acidaemia]. Dyslipidaemia was defined as cholesterolaemia and triglyceridaemia over the 95th percentile for age, race and gender .
In addition, T lymphocyte phenotyping, T cell receptor analysis, HIV-1-specific cytotoxic T cell assessment and plasma HIV-1 RNA measurements were carried out at study entry and every 12 weeks thereafter. HIV-1 DNA quantification was performed at baseline and at week 48 in 12 out of 20 patients.
Flow cytometry was performed on peripheral blood mononuclear cells (PBMC) in accordance with standard protocols with a FACScan flow cytometer (Becton Dickinson, San Jose, California, USA). Staining used antihuman monoclonal murine antibodies conjugated to fluoroscein isothiocyanate or phycoerythrin and specific for CD3 (clone UCHT-1), CD4 (clone RPA-T4), CD8 (clone UCHT-2), CD45RO (clone UCHL1) and CD45RA (clone HI 100) (Pharmingen, San Diego, California, USA).
T cell receptor Vβ repertoire analysis
To analyse the T cell receptor (TCR) Vβ repertoire, PBMC from patients were fractionated into CD4 and CD8 cells, and complementary DNA was synthesized and amplified from RNA extracted as previously described  using 24 different primers for unique 5′-Vβ sequences in combination with a primer for the TCR Vβ region 3′-Cβ primer (M-medical, Milan, Italy). Reverse transcriptase PCR products were run on a 6% polyacrylamide gel using the DNA Automatic Fluorescence Sequencer (Pharmacia ALF DNA Sequencer; Piscataway, New Jersey, USA) and analysed by specific software (Pharmacia DNA Fragment Manager 2.0). Two main patterns of distribution were observed: polyclonal profiles ‘p’ (five or more peaks) and skewed/perturbed profiles ‘sk’ (from one to four peaks, a multiple peak pattern with one solitary peak > 50% of the total area or one or more deleted peaks).
Analysis of HIV-1-specific CD8 T-lymphocytes
HIV-specific CD8 T lymphocytes were analysed as previously described, with minor modifications . Briefly, HIV-1 clade-independent and HLA class I promiscuous peptides designed on HIV-1 Gag, Tat and Nef proteins (Sigma-Genosys, Cambridge, UK) were used as specific stimuli. Fresh PBMC, 1 × 106 cells in 1 ml of complete RPMI medium, were incubated with 1 μg each of anti-CD28 and anti-CD49d monoclonal antibodies and a 1 μg pool of Gag, and Tat and Nef peptides. The interferon-γ (IFN-γ) release induced by phorbol 12-myristate 13-acetate (50 ng/ml) plus ionomycin (10 μg/ml) was used as a positive control. The cultures were incubated at 37°C in a 5% carbon dioxide incubator for 1 h, followed by an additional 5 h incubation with 10 μg/ml of the secretion inhibitor Brefeldin-A (Sigma, St Louis, Missouri, USA). Cells were washed and then stained with monoclonal antibodies specific for antihuman CD3 (IgG1, clone RPA-T3) and antihuman CD8 (IgG1 clone MOPC-21) (all antibodies from Becton Dickinson) for 15 min at 4°C. Samples were fixed in 1% paraformaldehyde for 10 min at 4°C before incubating with anti-IFN-γ monoclonal antibody diluted in phosphate-buffered saline 1×, bovine serum albumin 1% and saponin 0.5%. Cells were acquired by FACScalibur (Becton Dickinson). PBMC were obtained from 10 HIV-negative healthy children and used as negative controls. At least 200 000 live events were acquired, gated on small viable CD3+CD8+ lymphocytes. Data files were analysed using Cell Quest software (Becton Dickinson). An intracellular cytokine staining was considered positive when the percentage of cytokine-secreting cells was > 0.01%. Results are expressed as percentage of IFN-γ-producing CD3+CD8+ cells. A twofold increase of HIV-1-specific CD8 T lymphocytes frequency during the follow-up was considered significant.
Plasma HIV-1 RNA determinations
Viral control was evaluated by plasma RNA determination, using a quantitative branched DNA assay (Quantiplex HIV-RNA 2.0 bDNA Assay, Chiron Diagnostic Corporation, Emerville, California, USA) with a detection limit of 50 copies/ml. Values between 50 and 999 copies/ml, preceded and followed by measurements < 50 copies/ml were defined as blips. Rate of blips was evaluated, as previously described , as the number of detected blips divided by the number of determinations.
Quantification of HIV-1 proviral DNA
To quantify the proviral HIV-DNA copy number in PBMC, the real-time TaqMan protocol was adapted for the Light Cycler (Roche Molecular Biochemicals, Indianapolis, Indiana, USA) as previously described . The standard curve was built by seven dilutions of 8E5 cells, known to contain one integrated copy of HIV DNA per cell, giving 75 000, 37 500, 3750, 375, 37.5, 3.75 and 1.87 copies. The sensitivity of the PCR allows 1 copy/reaction of HIV DNA to be detected, which is equal to 13.3 copies/106 PBMC). Replicates that scored negative for HIV DNA samples were considered to be undetectable or to have HIV DNA < 20 copies/106 PBMC. The HIV DNA target was hybridized with TaqMan probe and read on channel F1/F2 of the LightCycler.
To calculate the z-scores for lipids and T cell subsets for each patient at each time interval, normal means and SD for age [19,24] were used after controlling that all variables had a normal distribution. Average measures at multiple time points were compared with a reference (i.e. initial values) during follow up. Student t-test for paired samples was used for assessing statistical significance. Qualitative variables were analysed using the χ 2 test.
Between January 2003 and June 2005, the study enrolled 20 children aged 2 to 18 years (median, 7.9) who had been vertically infected with HIV. The children were followed for 96 weeks. Baseline characteristics of the cohort are summarized in Table 1. All patients were stably receiving a PI-based HAART regimen for a median duration of 4.4 years (range, 2–5), with a median period of 2.8 years (range, 1–4.4) with undetectable viral load before study entry.
As reported by Pensieroso et al. , no immunological failure was observed at week 96. In brief, the mean CD4 and CD8 cell percentages at baseline were 35.4 ± 7.1% (z-score, 0.11 ± 0.99) and 30.3 ± 7.7% (z-score, −0.1 ± 1.2), respectively. The percentage of CD4 cells slightly increased during the period of follow-up, reaching a mean value of 36.2% (z-score, 0.4 ± 1.8) at week 48 and 36.6 ± 5.4% (z-score, 0.81 ± 1.7) at week 96. The percentage of CD8 cells did not vary significantly over time, with a mean value of 30.2 ± 6.5% (z-score, −0.03 ± 1.4) at week 48 and 28.9 ± 5.6% (z-score, −0.14 ± 1.8) at week 96. Proportions of memory and naive CD4 and CD8 subsets were normal for age at study entry  and remained stable over time (data not shown).
At study entry, TCR Vβ repertoire distribution revealed relevant (≥ 25%) perturbed patterns of CD8 TCR Vβ families in 11 of 20 patients (patients 3, 5, 6, 7, 9, 11, 12, 13, 16, 19 and 20). In all but one patient (patient 4, who experienced virological failure at week 84) a significant (P < 0.001) trend toward a polyclonal pattern in TCR Vβ families of the CD8 subset was observed .
In addition, compared with the baseline, an increased percentage of HIV-specific IFN-γ-producing CD8 T cells was detected in 17/20 (85%) children (mean at baseline 0.12 ± 0.1% versus 0.78 ± 0.77%; P < 0.001; Fig. 1).
All but one patient (patient 4) maintained virological control until the end of the study. The median blip ratio observed during triple-NRTI treatment did not increase over time compared with previous PI-based HAART regimen [0.1 (range, 0–0.4) versus 0.05 (range, 0–0.3), respectively]. Ten patients did not present blips during the simplified regimen (patients 1, 2, 5, 9, 11, 12, 14, 15, 17 and 18) . Patient 4 experienced virological failure at week 84 after autonomous interruption of treatment. Genotypic analysis at failure identified mutation M184V and other secondary mutations such as V35M, S68GS, W88C, D123E, I178L, R211K.
Quantification of proviral DNA load was performed in 12 of the 20 children (60%) (Table 1). The median proviral DNA load remained stable between baseline and week 48 [2.5 log10 copies/106 PBMC (range, 1.6–3) and 2.6 log10 copies/106 PBMC (range, 1.8–2.9), respectively].
Safety and metabolic profile
Triple-NRTI regimens were well tolerated. A hypersensitivity reaction to abacavir was reported after 2 weeks of switching in one patient (patient 13). Discontinuation of abacavir and replacement with didanosine resolved the symptoms.
No clinical or laboratory signs of hyperlactatemia or other side effects were detected.
Cholesterol and triglycerides above the 95th percentile for age, race and gender were present in seven (35%) and five (25%) patients, respectively, at baseline. The number of patients with high cholesterol declined over time from seven at baseline to none at week 96. Mean total cholesterol decreased from 1.89 ± 0.51 g/l (z-score, 1.18 ± 2.08) at baseline to 1.57 ± 0.28 g/l (z-score, −0.07 ± 1.19) at week 48 (P < 0.01), and to 1.52 ± 0.30 g/l (z-score, 0.11 ± 0.99) at week 96 (Fig. 2a). LDL cholesterol significantly decreased from a mean of 1.14 ± 0.37 g/l at baseline to 0.84 ± 0.26 g/l at week 48, and to 0.76 ± 0.23 g/l at 96 weeks (P < 0.01) while HDL cholesterol did not change significantly over time (Fig. 3). The cholesterol:HDL ratio decreased significantly, from a mean baseline of 3.4 ± 0.6 to 2.2 ± 0.5 at 96 weeks (P < 0.01; Fig. 3).
Fasting triglycerides mean values declined from 0.93 ± 0.52 g/l (z-score, 1.18 ± 2.2) to 0.72 ± 0.38 g/l (z-score, 0.4 ± 1.2) at week 48, and to 0.55 ± 0.25 g/l (z-score, 0.06 ± 1.03) at week 96 (P < 0.01). Furthermore, the number of patients with high plasma triglycerides decreased from five to none at week 96 (Fig. 2b).
Detailed dietary history revealed no significant changes during the study period. None of the patients initiated therapy with lipid-lowering agents.
Lipodystrophy syndrome clinically diagnosed at baseline in two children as lipoatrophy (patients 5 and 11) and in one (patient 8) as lipoaccumulation remained stable over time. No new cases of lipodystrophy were clinically detected.
Adherence and difficulty of taking medications
The mean pill burden per patient decreased from 11.4 ± 2.8 to 2.5 ± 1.2 capsules after switching to triple-NRTI regimens. Compared with the previous PI-based HAART regimen, adherence remained high during the study follow-up. Full adherence was reported at baseline in 99 ± 3% of the children and in 98 ± 4% and 99 ± 2% at weeks 48 and 96, respectively.
The difficulty of taking medications significantly decreased (P < 0.01) under the simplified regimen. The proportion of patients reporting ‘some or great difficulty’ in taking drugs was 58 ± 2% under the PI-based HAART and 12 ± 3% after simplification to triple-NRTI combinations.
This prospective open-label trial in HIV-1 infected children receiving successful PI-based first-line HAART combinations shows, for the first time, the efficacy of a simplified treatment with triple-NRTI regimens in terms of maintenance of viral suppression (< 50 copies/ml) and immunological function for up to 2 years.
Strategies of HAART simplification with triple-NRTI combinations have been recently suggested for the management of paediatric HIV [18,25]. In adults, an effective and safe simplification of standard PI-based HAART regimen can be achieved with triple-NRTI if this approach specifically targets patients with a low likelihood of harbouring nucleoside analogue-associated resistance mutations [13–16]. In agreement with these studies, our data suggest that this strategy can also be considered for HIV-infected children who reach a permanent and durable suppression of plasma viral replication (< 50 copies/ml) under an initial treatment regimen that contains a PI and who have a low likelihood to develop new viral mutations .
In this cohort, the ratio of intermittent episodes of detectable viraemia (blips) did not increase after the patients moved from the previous PI-based HAART treatment to the triple-NRTI regimens. Furthermore, proviral DNA, reported to be an informative marker to explore viral reservoirs and to assess the long-term impact of antiviral treatment [23,27,28], did not vary significantly during the first year of follow-up. HIV-specific cellular immune response, in addition to the stable good adherence reported in this group, might have contributed to the achievement of long-term viral control.
Indeed, we recently reported an enhancement of HIV-specific lymphoproliferative response in this cohort of children after switching to triple-NRTI therapy  and the current study also demonstrates an increased HIV-specific CD8 T cell response.
We argue that the improvement observed is possibly a result of removal of the PI component. In fact, PI drugs may cause immune suppression by interfering with antigen presentation . Specifically nelfinavir and ritonavir , which were mostly given to these patients, have been shown to modulate proteasome peptidase activity and cause intracellular accumulation of ubiquitin-tagged proteins, a hallmark of proteasome proteolytic inhibition in vivo . Supporting this hypothesis, Legrand et al.  recently reported increased T cell HIV-specific immune response, in terms of intracellular IFN-γ and tumour necrosis factor-α production, in a group of HIV-infected children who changed to a PI-sparing therapy owing to failure of viral control. The enhancement of the HIV-specific CD8 T cell response in our cohort of children is associated with a progressive trend to a polyclonal distribution of the TCR Vβ families in the CD8 cell subset. This broad TCR repertoire may support a multipotential ability to develop specific T cell responses against a variety of antigens including HIV [33,34].
Generally, the triple-NRTI regimen was well tolerated. The incidence of abacavir-related hypersensitivity in one patient (5%) was similar to the frequency reported in most other paediatric studies (3–5%) [35,36]. Neither clinical nor laboratory signs of hyperlactataemia were detected in our cohort, confirming that this event is more rare in children . Conversely, 8 of the 20 children presented signs of dyslipidaemia at the baseline. Lipid abnormalities improved early and in sustained fashion, in accordance with previous studies in children and adults, showing benefits of PI-sparing treatment on lipid metabolism [15,38–41]. Noteworthy, we have observed a significant decrease of the cholesterol:HDL ratio, that is an excellent predictor of future ischaemic heart disease [40,42]. This improvement is clinically important and implies a decrease in the need for dietary restrictions and lipid-lowering agents, and it is probably correlated with a decrease in the overall cardiovascular risk for the child [43–45]. No remarkable regressions in body fat redistribution were observed during the study. This can be partly explained by continuing mitochondrial toxicity through exposure to NRTI drugs, particularly stavudine and zidovudine [46,47].
Finally, although our data lack the statistical power to yield definitive conclusions, this pilot study demonstrates that simplification to triple-NRTI combinations in selected HIV-infected children is able to maintain viral suppression and immunological function, improve metabolic abnormalities and reduce the effort of taking medications in the long term. Larger randomized trials are necessary to investigate simplification strategies in HIV-infected children.
We thank all the patients' families for their kind collaboration, Professor M. Andreoni for his analysis of HIV-DNA load, Dr M. Amicosante for his test and analysis of HIV-1-specific CD8 T-lymphocytes, Professor A. Tozzi for his fundamental contribution in the statistical analysis and elaboration of the data of this study, Dr E. Freda for useful data discussions, and Miss J. Faudella for her precious secretariat work.
Sponsorship: The study was supported by IstitutoSuperiore di Sanita grant 30.F.45.
Note: M.L. Romiti and C. Cancrini contributed equally to this work.
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Keywords:© 2007 Lippincott Williams & Wilkins, Inc.
CD8 T lymphocytes; HAART; HIV-1 infected children; simplification; T cell Vβ