Evaluation of treosulfan cumulative exposure in paediatric patients through population pharmacokinetics and dosing simulations.

AIM: To investigate the pharmacokinetics (PK) of intravenous treosulfan in paediatric patients undergoing haematopoietic stem cell transplantation (HSCT) for a broad range of diseases and to explore the impact of different dosing regimens on treosulfan exposure (area under the concentration-time curve, AUC0→∞ ) through dosing simulations. METHODS: A prospective multicentre PK study was conducted using treosulfan concentration data (n = 423) collected from 53 children (median age 3.5, range 0.2-17.0 years) receiving three daily age-guided doses (10-14 g/m2 ). Population PK modelling was performed using NONMEM software, utilising a stepwise forward selection backward elimination method and likelihood-ratio test for screening covariates to describe PK variability. Monte Carlo simulation was used to generate patient PK data for 10 000 virtual paediatric patients and cumulative AUC0→∞ values were evaluated using age, body surface area (BSA) and model-based dosing regimens, targeting 4800 mg*h/L. RESULTS: Treosulfan concentration data were described using a one-compartment PK model with first-order elimination. Population mean (95% CI) estimates for clearance (CL) and volume of distribution (V) were 16.3 (14.9-18.1) L/h and 41.9 (38.8-45.1) L, respectively. Allometrically scaled body weight was the best covariate descriptor for CL and V, and maturational age further explained variability in CL. Dosing simulations indicated that in young patient groups (<2 years), a model-based dosing regimen more accurately achieved the target AUC0→∞ (58.3%) over the age (42.6%) and BSA-based (51.3%) regimens. CONCLUSION: Treosulfan disposition was described through allometric body weight and maturational age descriptors. Model-informed dosing is recommended for patients under 2 years. Treosulfan PK parameters and AUC0→∞ were not influenced by patient disease.

High serum ferritin alone as a predictor of mortality and hemophagocytic lymphohistiocytosis.

We report here utility of high serum ferritin alone as a predictor of mortality and diagnosis of hemophagocytic lymphohistiocytosis (HLH). We compared mortality in patients with high serum ferritin >5000 ng/mL versus <5000 ng/mL and looked for presence of HLH. Mortality was significantly higher (P-value .0048) in patients with serum ferritin levels >5000 ug/dL. Of 21 patients with high serum ferritin, a median of three criteria were fulfilled to diagnose HLH. All patients had features of immune-activation, and 76.2% patients had features of immune-pathology favoring diagnosis of HLH. Serum ferritin can aid in prediction of mortality and help in the early diagnosis of HLH.

Successful Haploidentical Stem Cell Transplant With Posttransplant Cyclophosphamide for Hemophagocytic Lymphohistiocytosis.

Allogeneic hematopoietic stem cell transplant (HSCT) has been known to be a curative therapy for patients with hemophagocytic lymphohistiocytosis (HLH) but donor availability is an issue. Haploidentical HSCT with posttransplant cyclophosphamide (PTCy) has been investigated as a feasible option for various malignant and nonmalignant conditions with reduced incidence of acute graft versus host disease (GVHD) and graft rejection. However, its use has not been described in children with HLH and here we describe 2 boys who underwent successful haploidentical HSCT with PTCy. None had acute GVHD and 1 had limited chronic GVHD. Both are alive and disease-free at follow-up of 912 and 239 days, respectively. Haploidentical HSCT with PTCy is a feasible option for children with HLH lacking a matched sibling donor.

Reduced-toxicity alternate-donor stem cell transplantation with posttransplant cyclophosphamide for primary immunodeficiency disorders.

We describe here the outcomes of reduced-toxicity alternate-donor stem cell transplant (SCT) with posttransplant cyclophosphamide (PTCy) for primary immunodeficiency disorders (PIDs) in eight children (haploidentical-seven and matched unrelated donor-one). The conditioning was with serotherapy (alemtuzumab-3/rabbit-anti-thymoglobulin-5); fludarabine, cyclophosphamide, and total body irradiation-5 (additional thiotepa-3); fludarabine and treosulfan-2; and fludarabine and busulfan-1. All received PTCy 50 mg/kg on days 3 and 4 as graft versus host disease prophylaxis along with tacrolimus and mycophenolate. Mean CD34 dose was 13.8 × 106 /kg. Two children died because of PIDs. Acute graft versus host disease up to grades I and II was seen in three children. All six survivors are fully donor and disease free at median follow-up of 753 days. Alternate donor SCT with PTCy is feasible in PID and has good outcomes.

Successful Nonmyeloablative Allogeneic Stem Cell Transplant in a Child With Emberger Syndrome and GATA2 Mutation.

Emberger syndrome with underlying guanine-adenine-thymine-adenine 2 (GATA2) mutation is a rare disorder and very few successful nonmyeloablative allogeneic hematopoietic stem cell transplants (HSCTs) have been reported. We report a case of Emberger syndrome with GATA2 mutation in a 9-year-old girl who presented with congenital sensorineural deafness, warts, lymphedema, and Myelodysplastic syndrome. Her sister had died of a similar illness. She underwent a nonmyeloablative matched related donor peripheral blood HSCT with rabbit antithymoglobulin (5 mg/kg), fludarabine (160 mg/m), cyclophophamide (29 mg/kg), and total body irradiation (2 Gray). Graft versus host disease prophylaxis consisted of tacrolimus and mycophenolate moefetil. She had neutrophil engraftment on day+15 and fully donor chimerism by day+30. She developed limited chronic skin graft versus host disease on tapering off immunosuppression. She is disease free on day+475. The review of literature showed a total of 28 patients with GATA2 mutation have undergone HSCT mostly nonmyeloablative and overall survival is 75%. Nonmyeloablatove HSCT is feasible and safe for the patients with GATA2 mutation.

Successful Reduced Intensity Conditioning Alternate Donor Stem Cell Transplant for Wiskott-Aldrich Syndrome.

There are very few reports of reduced intensity conditioning (RIC) hematopoietic stem cell transplant (HSCT) with alternate donor for Wiskott-Aldrich syndrome (WAS) and there is no report of RIC with posttransplant cyclophosphamide (PTCy) in WAS. There is only 1 report of T cell receptor αß and CD19-depleted haploidentical HSCT for WAS. Here we report successful outcome in 3 children with WAS who underwent successful RIC alternate donor HSCT of whom 2 (matched unrelated donor and T-cell replete haploidentical) received PTCy and 1 underwent T cell receptor αß and CD19-depleted haploidentical HSCT. We modified conditioning used by Luznik for haploidentical HSCT by adding thiotepa 8 mg/kg and Campath or rabbit antithymoglobulin for 2 cases who received PTCy. In third case we gave fludarabine, thiotepa, and treosulfan-based conditioning. The mean duration of follow-up for these patients was 23.6 months posttransplant (range, 21 to 26 mo). All 3 patients are transfusion independent. Acute graft versus host disease (GVHD) grade I occurred in 1 and none had chronic GVHD. Chimerism of all 3 was fully donor (>95% donor) at D+30 and D+100 posttransplant. All are alive, healthy, and doing well. Our 3 cases highlight that with newer conditioning and GVHD prophylaxis approach alternate donor HSCT in WAS can become a safe and effective treatment option.