The use of pharmacokinetic models in paediatric onco-haematology: effects on clinical outcome through the examples of busulfan and cyclosporine

Impact of a Bayesian Individualization of Cyclosporine Dosage Regimen for Children Undergoing Allogeneic Hematopoietic Cell Transplantation: A Cost-Effectiveness Analysis

BACKGROUND

Cyclosporine A (CsA) is the main drug used to prevent graft-versus-host disease in patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). CsA therapeutic drug monitoring (TDM) has been performed for ages, with studies revealing clinical benefits, but failing to examine its economic impact. In this article, the main objective was to evaluate the economic impact of the CsA TDM strategy, based on a Bayesian approach, by assessing costs related to its clinical impact. Furthermore, TDM effectiveness was analyzed for pharmacokinetics and clinical outcomes.

METHODS

A cost-effective, nonrandomized, retrospective, single-center study compared 2 CsA monitoring and dose adaptation strategies in pediatric patients undergoing HSCT. From 2014 to 2016, CsA TDM was performed using a population pharmacokinetics model-coupled Bayesian approach by a pharmacist ["pharmacist-assisted individualization" (PAI)]. From 2017 to 2018, CsA TDM was performed by the clinician without a Bayesian approach (non-PAI group). HSCT costs were evaluated from the French National Insurance perspective. Economic and clinical outcomes were assessed by measuring incremental cost-effectiveness ratios.

RESULTS

The study included 144 patients: 90 and 54 patients in PAI and non-PAI groups, respectively. Both groups were comparable for sociodemographic and clinical characteristics. The mean total cost per patient was significantly lower (P < 0.01) in the PAI group (€85,947) than in the non-PAI group (€100,435). Multivariate analysis revealed that TDM based on the Bayesian approach was a protective factor (odds ratio = 0.86) for severe acute graft-versus-host disease. We noted that pharmacist-based TDM was the dominant strategy. Bayesian method-based TDM allowed an increase in the percentage of target attainment at any period post-HSCT.

CONCLUSIONS

CsA TDM with a Bayesian approach is a cost-effective procedure, and highlighted clinical benefits encourage the development of new TDM strategies for HSCT.

A Clinical Decision Support Tool to Find the Best Initial Intravenous Cyclosporine Regimen in Pediatric Hematopoietic Stem Cell Transplantation

To optimize cyclosporine A (CsA) dosing regimen in pediatric patients undergoing hematopoietic stem cell transplantation (HSCT), we aimed to provide clinicians with a validated decision support tool for determining the most suitable first dose of intravenous CsA. We used a 10-year monocentric data set of pediatric patients undergoing HSCT. Discretization of all variables was performed according to literature or thanks to algorithms using Shannon entropy (from information theory) or equal width intervals. The first 8 years were used to build the Bayesian network model. This model underwent a 10-fold cross-validation, and then a prospective validation with data of the last 2 years. There were 3.3% and 4.1% of missing values in the training and the validation data set, respectively. After prospective validation, the Tree-Augmented Naïve Bayesian network shows interesting prediction performances with an average area under the receiver operating characteristic curve of 0.804, 32.8% of misclassified patients, a true-positive rate of 0.672, and a false-positive rate of 0.285. This validated model allows good predictions to propose an optimized and personalized initial CsA dose for pediatric patients undergoing HSCT. The clinical impact of its use should be further evaluated.

Pharmacokinetics and Safety of a Novel Oral Liquid Formulation of 13-cis Retinoic Acid in Children with Neuroblastoma: A Randomized Crossover Clinical Trial

(1) Background: 13-cis-retinoic acid (13-CRA) is a key component of neuroblastoma treatment protocols. This randomized crossover study compares the pharmacokinetics (PK), safety and palatability of a novel oral liquid formulation to the current method of extracting 13-CRA from capsules. (2) Methods: Pharmacokinetics was evaluated in two consecutive treatment cycles. Patients were randomized to receive either liquid or capsule formulation on cycle 1 and then crossed over to the alternative formulation on cycle 2. The daily dose was 200 mg/m², reduced to 160 mg/m² in patients with weight ≤ 12 kg. (3) Results: A total of 20 children, median (range) age 4.3 (1-11.6) y were recruited. Pharmacokinetic data were pooled and a population model describing the disposition of 13-CRA and 4-oxo-13-CRA was developed. Bioavailability of the liquid formulation was estimated to be 65% higher (95% CI; 51-79%) than the extracted capsule. CmaxSS and AUC(0-12)SS estimates were also significantly higher; mean (95% CI) differences were 489 (144-835) ng/mL and 3933 (2020-5846) ng/mL·h, respectively (p < 0.01). There were no significant differences in reported adverse effects. Parents found dosing considerably easier with liquid formulation. (4) Conclusions: The pharmacokinetics, safety and palatability of a new liquid formulation of 13-CRA compares favorably to 13-CRA extracted from capsules. Clinical Trial Registration: clinicaltrial.gov NCT03291080.

A decision support tool to find the best cyclosporine dose when switching from intravenous to oral route in pediatric stem cell transplant patients

PURPOSE

Managing the pharmacokinetic variability of immunosuppressive drugs after pediatric hematopoietic stem cell transplantation (HSCT) is a clinical challenge. Thus, the aim of our study was to design and validate a decision support tool predicting the best first cyclosporine oral dose to give when switching from intravenous route.

METHODS

We used 10-years pediatric HSCT patients' dataset from 2008 to 2018. A tree-augmented naïve Bayesian network model (method belonging to artificial intelligence) was built with data from the first eight-years, and validated with data from the last two.

RESULTS

The Bayesian network model obtained showed good prediction performances, both after a 10-fold cross-validation and external validation, with respectively an AUC-ROC of 0.89 and 0.86, a percentage of misclassified patients of 28.7% and 35.2%, a true positive rate of 0.71 and 0.65, and a false positive rate of 0.12 and 0.14 respectively.

CONCLUSION

The final model allows the prediction of the most likely cyclosporine oral dose to reach the therapeutic target specified by the clinician. The clinical impact of using this model needs to be prospectively warranted. Respecting the decision support tool terms of use is necessary as well as remaining critical about the prediction by confronting it with the clinical context.

Enhanced Dissolution and Oral Bioavailability of Cyclosporine A: Microspheres Based on αβ-Cyclodextrins Polymers

Cyclosporine (CsA) has a selective property of suppressing various T-lymphocyte functions. This is of utmost importance in preventing allograft rejection by several organ transplantations, as well as in the treatment of systemic and local autoimmune disorders. However, the poor water solubility of CsA can be a major hurdle for its absorption into the blood stream, which leads to low bioavailability and thus less efficacy. The aim of this study was to prepare, characterize, and evaluate in vitro as well as in vivo, the potential of the innovative CsA drug delivery system. The latter contains CsA in spherical amorphous solid dispersion (SASD) which is embedded in an original α-cyclodextrin and β-cyclodextrin polymer mixture (Poly-αβ-CD) as a multifunctional amorphous carrier. The new developed SASD formulation showed that CsA was molecularly dispersed in αβ-cyclodextrins in an amorphous form, as was confirmed by physicochemical characterization studies. Interestingly, the peptide secondary structure, and thus, the drug activity was not impacted by the preparation of SASD as was shown by circular dichroism. Furthermore, the in vitro CsA release profile kinetics was almost identical to the commercially available product Neoral^®. This study presents the first in vivo proof-of-concept for a novel drug delivery system based on Poly-αβ-CD containing CsA, with SASD allowing for increased bioavailibility. The pharmacokinetic parameters of cyclosporine A from the spherical spray-dried dispersion formulation was demonstrated in a “rat” animal model. For comparison, the commercially available Neoral® was studied. Importantly, the pharmacokinetic parameters were improved by extending T_max from 2 to 3 h after the oral administration in rats, and eventually preventing the enterohepatic circulation. All these results clearly demonstrate the improved pharmacokinetic parameters and enhanced bioavailability of CsA in the new developed drug delivery system. These data demonstrated the superiority of the newly developed Poly-αβ-CD formulation for oral administration of the poorly soluble CsA in vivo without altering its secondary structure. Poly-αβ-CD can be a very useful tool for the oral administration of poorly water-soluble drugs.

Bayesian Networks: A New Approach to Predict Therapeutic Range Achievement of Initial Cyclosporine Blood Concentration After Pediatric Hematopoietic Stem Cell Transplantation

BACKGROUND

Pediatric hematopoietic stem cell transplantation (HSCT) allows the treatment of numerous diseases, both malignant and non-malignant. Cyclosporine, a narrow therapeutic index drug, is the major immunosuppressant used to prevent graft-versus-host disease (GVHD), but may also cause severe adverse effects in case of overdosing.

OBJECTIVE

The objective of this study is to predict the initial cyclosporine residual blood concentration value after pediatric HSCT, and consequently the dose necessary to reach the therapeutic range, using a mathematical individual predictive model.

METHODS

Clinical and biological data collected from the graft infusion for 2 months after transplantation in 155 pediatric patients undergoing HSCT between 2008 and 2016 were used to generate synthetic data for 1000 subjects which were used to build a Bayesian network model. We compared the characteristics and sensitivity to clinical or biological missing data of this model with four other methods.

RESULTS

The tree-augmented Naïve Bayesian network showed the best characteristics, with no missing data (area under the curve of the receiving operator characteristics curve [AUC-ROC] of 0.89 ± 0.02), 18.9 ± 2.6% of patients misclassified, and positive and negative predictive values of 85.9 ± 3.4% and 74.2 ± 5.1%, respectively, and this trend is found in the synthetic dataset from no to 10% missing data. The most relevant variables that could influence whether the initial residual cyclosporine concentration is in the therapeutic range are the last dose before measurement and the mean dose before measurement.

CONCLUSIONS

We developed and cross-validated an online Bayesian network to predict the first cyclosporine concentration after pediatric HSCT. This model allows simulation of different dosing regimens, and enables the best dosing regimen to reach the therapeutic range immediately after transplantation to be found, minimizing the risk of adverse effects and GVHD occurrence.

Personalised dosing of medicines for children

Objectives

Doses for most drugs are determined from population-level information, resulting in a standard ?one-size-fits-all’ dose range for all individuals. This review explores how doses can be personalised through the use of the individuals’ pharmacokinetic (PK)-pharmacodynamic (PD) profile, its particular application in children, and therapy areas where such approaches have made inroads.

Key findings

The Bayesian forecasting approach, based on population PK/PD models that account for variability in exposure and response, is a potent method for personalising drug therapy. Its potential utility is even greater in young children where additional sources of variability are observed such as maturation of eliminating enzymes and organs. The benefits of personalised dosing are most easily demonstrated for drugs with narrow therapeutic ranges such as antibiotics and cytotoxics and limited studies have shown improved outcomes. However, for a variety of reasons the approach has struggled to make more widespread impact at the bedside: complex dosing algorithms, high level of technical skills required, lack of randomised controlled clinical trials and the need for regulatory approval.

Summary

Personalised dosing will be a necessary corollary of the new precision medicine initiative. However, it faces a number of challenges that need to be overcome before such an approach to dosing in children becomes the norm.

Pharmacokinetics, Pharmacodynamics and Pharmacogenomics of Immunosuppressants in Allogeneic Haematopoietic Cell Transplantation: Part I

Although immunosuppressive treatments and target concentration intervention (TCI) have significantly contributed to the success of allogeneic haematopoietic cell transplantation (alloHCT), there is currently no consensus on the best immunosuppressive strategies. Compared with solid organ transplantation, alloHCT is unique because of the potential for bidirectional reactions (i.e. host-versus-graft and graft-versus-host). Postgraft immunosuppression typically includes a calcineurin inhibitor (cyclosporine or tacrolimus) and a short course of methotrexate after high-dose myeloablative conditioning, or a calcineurin inhibitor and mycophenolate mofetil after reduced-intensity conditioning. There are evolving roles for the antithymyocyte globulins (ATGs) and sirolimus as postgraft immunosuppression. A review of the pharmacokinetics and TCI of the main postgraft immunosuppressants is presented in this two-part review. All immunosuppressants are characterized by large intra- and interindividual pharmacokinetic variability and by narrow therapeutic indices. It is essential to understand immunosuppressants' pharmacokinetic properties and how to use them for individualized treatment incorporating TCI to improve outcomes. TCI, which is mandatory for the calcineurin inhibitors and sirolimus, has become an integral part of postgraft immunosuppression. TCI is usually based on trough concentration monitoring, but other approaches include measurement of the area under the concentration-time curve (AUC) over the dosing interval or limited sampling schedules with maximum a posteriori Bayesian personalization approaches. Interpretation of pharmacodynamic results is hindered by the prevalence of studies enrolling only a small number of patients, variability in the allogeneic graft source and variability in postgraft immunosuppression. Given the curative potential of alloHCT, the pharmacodynamics of these immunosuppressants deserves to be explored in depth. Development of sophisticated systems pharmacology models and improved TCI tools are needed to accurately evaluate patients' exposure to drugs in general and to immunosuppressants in particular. Sequential studies, first without and then with TCI, should be conducted to validate the clinical benefit of TCI in homogenous populations; randomized trials are not feasible, because there are higher-priority research questions in alloHCT. In Part I of this article, we review the alloHCT process to facilitate optimal design of pharmacokinetic and pharmacodynamics studies. We also review the pharmacokinetics and TCI of calcineurin inhibitors and methotrexate.

Higher plasma bilirubin predicts veno-occlusive disease in early childhood undergoing hematopoietic stem cell transplantation with cyclosporine

AIM: To analyze the association between plasma bilirubin levels and veno-occlusive disease (VOD) in non-adult patients undergoing hematopoietic stem cell transplantation (HSCT) during cyclosporine therapy.

METHODS: A total of 123 patients taking cyclosporine were evaluated using an electronic medical system at the Seoul National University Children’s Hospital from the years 2004 through 2011. Patients were grouped by age and analyzed for incidence and type of adverse drug reactions (ADRs) including VOD.

RESULTS: The HSCT patients were divided into three age groups: G#1 ≥ 18; 9 ≤ G#2 ≤ 17; and G#3 ≤ 8 years of age). The majority of transplant donor types were cord blood transplantations. Most prevalent ADRs represented acute graft-vs-host disease (aGVHD) and VOD. Although the incidences of aGVHD did not vary among the groups, the higher frequency ratios of VOD in G#3 suggested that an age of 8 or younger is a risk factor for developing VOD in HSCT patients. After cyclosporine therapy, the trough plasma concentrations of cyclosporine were lower in G#3 than in G#1, indicative of its increased clearance. Moreover, in G#3 only, a maximal total bilirubin level (BILmax) of ≥ 1.4 mg/dL correlated with VOD incidence after cyclosporine therapy.

CONCLUSION: HSCT patients 8 years of age or younger are more at risk for developing VOD, diagnosed as hyperbilirubinemia, tender hepatomegaly, and ascites/weight gain after cyclosporine therapy, which may be represented by a criterion of plasma BILmax being ≥ 1.4 mg/dL, suggestive of more sensitive VOD indication in this age group.

Accurately Achieving Target Busulfan Exposure in Children and Adolescents With Very Limited Sampling and the BestDose Software

BACKGROUND

Busulfan dose adjustment is routinely guided by plasma concentration monitoring using 4-9 blood samples per dose adjustment, but a pharmacometric Bayesian approach could reduce this sample burden.

METHODS

The authors developed a nonparametric population model with Pmetrics. They used it to simulate optimal initial busulfan dosages, and in a blinded manner, they compared dosage adjustments using the model in the BestDose software to dosage adjustments calculated by noncompartmental estimation of area under the time-concentration curve at a national reference laboratory in a cohort of patients not included in model building.

RESULTS

Mean (range) age of the 53 model-building subjects was 7.8 years (0.2-19.0 years) and weight was 26.5 kg (5.6-78.0 kg), similar to nearly 120 validation subjects. There were 16.7 samples (6-26 samples) per subject to build the model. The BestDose cohort was also diverse: 10.2 years (0.25-18 years) and 46.4 kg (5.2-110.9 kg). Mean bias and imprecision of the 1-compartment model-predicted busulfan concentrations were 0.42% and 9.2%, and were similar in the validation cohorts. Initial dosages to achieve average concentrations of 600-900 ng/mL were 1.1 mg/kg (≤12 kg, 67% in the target range) and 1.0 mg/kg (>12 kg, 76% in the target range). Using all 9 concentrations after dose 1 in the Bayesian estimation of dose requirements, the mean (95% confidence interval) bias of BestDose calculations for the third dose was 0.2% (-2.4% to 2.9%, P = 0.85), compared with the standard noncompartmental method based on 9 concentrations. With 1 optimally timed concentration 15 minutes after the infusion (calculated with the authors' novel MMopt algorithm) bias was -9.2% (-16.7% to -1.5%, P = 0.02). With 2 concentrations at 15 minutes and 4 hours bias was only 1.9% (-0.3% to 4.2%, P = 0.08).

CONCLUSIONS

BestDose accurately calculates busulfan intravenous dosage requirements to achieve target plasma exposures in children up to 18 years of age and 110 kg using only 2 blood samples per adjustment compared with 6-9 samples for standard noncompartmental dose calculations.

Cyclosporine use in hematopoietic stem cell transplantation: pharmacokinetic approach

Cyclosporine is one of the most vital agents in the process of successful allogeneic hematopoietic stem cell transplantation. Despite a long history and worldwide extent of cyclosporine use for prevention of graft versus host disease, currently there are lots of uncertainties about its optimal method of application to reach the best clinical outcome. A major portion of this problem stems from complicated cyclosporine pharmacokinetics. Study of cyclosporine pharmacokinetic behavior can significantly help recognition of its effectiveness and consequently, optimization of dosing, administration, monitoring and management of adverse effects. In this review, highly accredited but sparse scientific data are gathered in order to provide a better insight for preparation of practice guidelines and directing future studies for allogeneic hematopoietic cell recipients.

Pharmacokinetic drug-drug interaction of calcium channel blockers with cyclosporine in hematopoietic stem cell transplant children

BACKGROUND

Cyclosporine (CsA) is frequently responsible for hypertension in bone marrow transplant children. Calcium channel blockers (CCBs) are considered to be the best treatment for CsA-induced hypertension, but they may alter the exposure and the effect of CsA by inhibiting the CYP3A4 pathway of CsA metabolism or P-gp. However, the inhibitory effect on CYP3A4 may vary among CCBs.

METHODS

This study aimed to quantify the pharmacokinetic drug-drug interaction between CsA and nicardipine, amlodipine, and lacidipine. In all, 51 children who received CsA and CCB concomitantly were included.

RESULTS

Dose-normalized CsA trough blood concentrations significantly increased in patients treated with nicardipine and amlodipine, whereas they remained stable in patients treated with lacidipine.

CONCLUSIONS

Because lacidipine appears to have no effect on CsA exposure, it may be the best option among CCBs for treating high blood pressure caused by CsA in children.

Development of multiplex PCR method for the analysis of glutathione s-transferase polymorphism

BACKGROUND

Busulfan is a key compound in myeloablative chemotherapy before hematopoietic stem-cell transplantation in children. Genetic polymorphisms of glutathione S-transferase (GST), which is involved in the metabolism of busulfan, have been implicated in interindividual variability in busulfan pharmacokinetics. Development of a rapid and simplified method for polygenic analysis of GST may facilitate large pharmacogenetic studies and clinical application of individualized busulfan dose adjustment. We previously introduced an effective PCR method for analyzing multiple genes using a small amount of DNA, termed 'TotalPlex amplification'.

OBJECTIVE

The aim of this study was to extend the application of the TotalPlex method to the specific GST gene families (A1, P1, M1, and T1) that are related to busulfan metabolism, and thereby facilitate pharmacogenetic analysis of GST polymorphisms.

METHODS

Seven genetic polymorphisms (GSTA1 promoter -52G>A, -69C>T, -567T>G, and -631T>G; GSTP1 313A>G; GSTM1 deletion; and GSTT1 deletion) were analyzed by multiplex PCR and genotyping, and the genotyping results from TotalPlex were verified with those from uniplex PCR.

RESULTS

Using five pairs of specific bulging-specific primers, seven specific gene fragments were successfully amplified by multiplex amplification coupled to a multiplexed bead array detection system, with a smaller amount of DNA and a shorter process time than is needed for the conventional approach. The genotypes of seven loci from 30 different genomic DNA samples derived using the multiplex system were consistent with the results of standard genotyping methods.

CONCLUSION

Our multiplex system provides a fast, inexpensive, and accurate method of detecting multiple GST polymorphisms (GSTA1, GSTP1, GSTM1, and GSTT1).

Clinical consequences of analytical variance and calculation strategy in oral busulfan pharmacokinetics

BACKGROUND

Busulfan pharmacokinetic (PK) monitoring of the area under the concentration-time curve (AUC) is necessary to minimize adverse events associated with both under- and over-dosing of busulfan during hematopoietic stem cell transplantation (HSCT). Three strategies are frequently used to calculate the AUC including in-house polynomial methods, the trapezoidal method (also called noncompartmental analysis), and the single compartment model with first-order elimination method. We compared these 3 methods, their clinical performance, and the relationship of AUC variance to analytical variance when each of these methods is used.

METHODS

Clinical busulfan PK data was reviewed from 159 patients receiving the first dose of oral busulfan while undergoing HSCT. These data were used as templates to simulate AUC results and actions with varying amounts of analytical precision.

RESULTS

Based on a predefined goal therapeutic target, the method for calculating AUC significantly changed the number of recommended busulfan dose adjustments (p<0.000001). Overall, the number of dose adjustments would be expected to drop by approximately 10% due to calibration optimization of the busulfan concentration measurement method.

CONCLUSION

Analytical variance and the AUC calculation method play a considerable role in the clinical management of busulfan dosing during HSCT. With better understanding and optimization of the analytical method, the reliability of clinically actionable information from busulfan PK can increase.

Population pharmacokinetics of busulfan in children: increased evidence for body surface area and allometric body weight dosing of busulfan in children

PURPOSE

To evaluate the best method for dosing busulfan in children, we retrospectively analyzed two different data sets from three different dosing regimens by means of population pharmacokinetics using NONMEM.

EXPERIMENTAL DESIGN

The development data set consisted of plasma samples from 94 children, in the age range of 0.4 to 18.8 years, receiving either oral or intravenous busulfan. The external model evaluation data set comprised 24 children, in the age range of 0.1 to 18.9 years, who belonged to the once-daily intravenous busulfan dosing regimen. A one-compartment model with first-order absorption using body surface area (BSA) or allometric body weight (BW) as covariate on clearance (CL) and BW as covariate on volume of distribution (V) were used to describe the results sufficiently. In addition to interindividual variability on all pharmacokinetic parameters, interoccasion variability was included for CL and V.

RESULTS

CL values in the present study did not reflect the shape of the CL versus weight curve reported in previous investigations. By external model evaluation, we were able to confirm these findings. Furthermore, bioavailability was calculated to be between 93% and 99% for the development data set. On the basis of the final models, we simulated two dosing schemes according to allometric BW and BSA showing that we estimated to include about 30% more patients into the proposed therapeutic area under the curve (AUC) range of 900 to 1,500 μM*min and could, furthermore, achieve a reduction in the AUC variability when dosed according to the labeled European Medicines Agency (EMA) dosing recommendation.

CONCLUSION

We recommend a BSA or an allometric BW dosing regimen for individualizing busulfan therapy in children to reduce variability in busulfan exposure and to improve safety and efficacy of busulfan treatment.

Therapeutic drug monitoring in cancer chemotherapy

For a select number of drugs, proper management of patients includes monitoring serum or plasma concentrations of the drugs and adjusting the doses accordingly - this practice is referred to as therapeutic drug monitoring (TDM). The need for TDM arises when pharmacokinetic variability of drugs is not easily accounted for by common clinical parameters. Many chemotherapeutic drugs have large interindividual variability, yet TDM is not commonplace in chemotherapy management. This review will discuss pharmacokinetics in the context of chemotherapeutic drugs, examine the few instances where TDM is currently used in the field of oncology and propose other drugs where TDM might be useful for dose adjustments in the management of chemotherapy.

Lymphocyte subset reconstitution after unrelated cord blood or bone marrow transplantation in children

We report the post-transplant lymphocyte subset recovery of 226 children treated with Unrelated Cord Blood transplant (UCBT) (n = 112) or Unrelated Bone Marrow Transplant (UBMT) (n = 114) for malignant or non-malignant diseases. Absolute numbers of natural killer (NK), B and T cells were monitored by flow cytometry up to 5 years post-transplant. Immunological endpoints were: time to achieve a CD3(+) cell count > 0·5 and 1·5 × 10⁹/l, CD4(+) > 0·2 and 0·5 × 10⁹/l, CD8(+) > 0·25 ×10⁹/l, CD19(+) > 0·2 × 10⁹/l, NK > 0·1 × 10⁹/l. These endpoints were analysed through the use of cumulative incidence curves in the context of competing risks. CD8(+) T cell recovery was delayed after UCBT with a median time to reach CD8(+) T cells > 0·25 × 10⁹/l of 7·7 months whereas it was 2·8 months in UBMT (P < 0·001). B cell recovery was better in UCBT, with a median time to reach CD19(+) cells > 0·2 × 10⁹/l of 3·2 months in UCBT and 6·4 months in UBMT (P = 0·03). Median time for CD4(+) T cell and NK cell recovery was similar in UCBT and UBMT. CD4(+) T cells recovery was negatively correlated to age (better reconstitution in younger patients, P = 0·002). CD8(+) T cells recovery was shorter in recipients with a positive cytomegalovirus serology (P =0·001).

Hepatic veno-occlusive disease: a chemotherapy-related toxicity in children with malignancies

Hepatic veno-occlusive disease (VOD) is a major manifestation of liver toxicity associated with conventional and high-dose chemotherapy in children affected by hematologic malignancies and certain solid tumors. Clinically, patients present with jaundice, painful hepatomegaly, and fluid retention, which may evolve into multi-organ failure, a hallmark of severe disease. The pathogenesis is complex and not completely understood, but the damage to sinusoidal endothelium, typically caused by toxic metabolites released from antineoplastic drugs, is thought to play a crucial role, together with cytokine activation, immune deregulation, and coagulopathy. Diagnosis is based on clinical criteria supported by characteristic ultrasound findings, with the gold standard investigation being hepatic-venous pressure gradient measurement and biopsy. Several treatment options have been tested; the most convincing approach to date is the use of defibrotide, a novel oligonucleotide with antithrombotic and antiplatelet aggregating properties, as well as endothelial-stabilizing effects. This agent, together with other specific forms of supportive care, has shown efficacy in the treatment of established VOD and promising results in the prevention of VOD in pediatric patients receiving chemotherapy.

Influence of GST gene polymorphisms on busulfan pharmacokinetics in children

Busulfan (BU) is a key compound in conditioning myeloablative regimens for children undergoing hematopoietic stem cell transplantation (HSCT). There are wide interindividual differences in BU pharmacokinetics, which increase the risk of veno-occlusive disease, graft rejection and disease relapse. As BU is mainly metabolized by glutathione S-transferase (GST), it is hypothesized that functional polymorphisms in GST genes may explain in part the variability in BU pharmacokinetics. We analyzed polymorphisms in GSTA1 (C-69T, A-513G, G-631T, C-1142G), GSTM1 (deletion) and GSTP1 (A1578G, C2293T) genes in 28 children undergoing HSCT. All patients had individualized dosing based on pharmacokinetics after the first dose of intravenous BU. GSTM1-null individuals had higher drug exposure (P(Cmax)=0.008; P(AUC)=0.003; P(Css)=0.02) and lower clearance (P(CL)=0.001). Multivariate regression models showed that, other than the drug dose and age, the GSTM1 genotype was the best predictor of first-dose pharmacokinetic variability. GSTM1-null patients also received lower cumulative BU doses (P=0.02). No association was found between BU exposure and major GSTA1 or GSTP1 gene variants. In children, GSTM1 polymorphism seems to modify BU pharmacokinetics after intravenous drug administration.