Improved survival with model-based dosing of antithymocyte globulin in pediatric hematopoietic cell transplantation

Antithymocyte globulin (ATG) is used in pediatric allogeneic hematopoietic cell transplantation (HCT) to prevent graft-versus-host disease (GVHD) and graft failure (GF). Poor T-cell recovery, associated with increased mortality, is the main toxicity of ATG. Model-based precision dosing of ATG (MBD-ATG) minimizes toxicity while maintaining efficacy. We report updated results of the single-arm phase 2 PARACHUTE trial investigating MBD-ATG, combined with real-world experience using identical MBD-ATG. Consecutive patients receiving a first T-cell-replete HCT for any indication were evaluated. Results were compared with historical patients receiving conventional fixed ATG dosing (FIX-ATG). Primary outcome was overall survival (OS). The MBD-ATG group consisted of 214 patients (58 trial patients; 156 real-world patients); 100 patients received FIX-ATG. MBD-ATG led to superior OS compared with FIX-ATG (hazard ratio [HR] for death, 0.56; 95% confidence interval [CI], 0.34-0.93; P = .026), and lower treatment-related mortality (TRM; HR, 0.51; 95% CI, 0.29-0.92; P = .025). Successful T-cell reconstitution (&gt;0.05 × 109/L CD4+ T cells twice within 100 after HCT) was improved in MBD-ATG vs FIX-ATG (87% ± 2% vs 47% ± 5%; P &lt; .0001). The improved T-cell reconstitution led to lower TRM (HR, 0.19; 95% CI, 0.09-0.36; P &lt; .0001). Incidence of grade 2-4 acute GVHD was comparable, whereas chronic GVHD (HR, 0.35; 95% CI, 0.17-0.72; P = .004) and GF (HR, 0.36; 95% CI, 0.13-0.97; P = .044) were both less frequent in MBD-ATG compared with FIX-ATG. MBD-ATG results in improved OS and reduced TRM, while reducing chronic GVHD and GF. This easy-to-implement approach improves outcomes after pediatric HCT, confirmatory studies are needed. The PARACHUTE trial is registered with the Dutch Trial Register as #NL4836.</p

The Wiskott-Aldrich syndrome protein is required for iNKT cell maturation and function

The Wiskott-Aldrich syndrome (WAS) protein (WASp) is a regulator of actin cytoskeleton in hematopoietic cells. Mutations of the WASp gene cause WAS. Although WASp is involved in various immune cell functions, its role in invariant natural killer T (iNKT) cells has never been investigated. Defects of iNKT cells could indeed contribute to several WAS features, such as recurrent infections and high tumor incidence. We found a profound reduction of circulating iNKT cells in WAS patients, directly correlating with the severity of clinical phenotype. To better characterize iNKT cell defect in the absence of WASp, we analyzed was−/− mice. iNKT cell numbers were significantly reduced in the thymus and periphery of was−/− mice as compared with wild-type controls. Moreover analysis of was−/− iNKT cell maturation revealed a complete arrest at the CD44+ NK1.1− intermediate stage. Notably, generation of BM chimeras demonstrated a was−/− iNKT cell-autonomous developmental defect. was−/− iNKT cells were also functionally impaired, as suggested by the reduced secretion of interleukin 4 and interferon γ upon in vivo activation. Altogether, these results demonstrate the relevance of WASp in integrating signals critical for development and functional differentiation of iNKT cells and suggest that defects in these cells may play a role in WAS pathology

Anti-T-lymphocyte globulin exposure is associated with acute graft-versus-host disease and relapse in pediatric acute lymphoblastic leukemia patients undergoing hematopoietic stem cell transplantation: a multinational prospective study

Anti T-lymphocyte globulin (ATLG) is used in hematopoietic stem cell transplantation (HSCT) to prevent graft-versus-host disease (GvHD) and graft failure. To date, insight in ATLG pharmacokinetics and -dynamics (PK/PD) is limited, and population PK (POPPK) models are lacking. In this prospective study, we describe ATLG POPPK using NONMEM® and the impact of ATLG exposure on clinical outcome and immune reconstitution in a homogeneous cohort of pediatric acute lymphoblastic leukemia (ALL) patients transplanted with a matched unrelated donor and receiving uniform ATLG dosing. Based on 121 patients and 812 samples for POPPK analysis, a two-compartmental model with parallel linear and non-linear clearance and bodyweight as covariate, best described the ATLG concentrationtime data. The level of ATLG exposure (day active ATLG day 16 8.2%,

Treosulfan-Based Conditioning in Pediatric Hematopoietic Stem Cell Transplantation: A Prospective Study on Pharmacokinetics and Early Clinical Outcomes

Abstract Introduction Treosulfan is an alkylating agent which is increasing applied in regimens prior to allogeneic hematopoietic stem cell transplantation (HSCT) in children. It has strong myeloablative and immunosuppressive activity and, in comparison with busulfan and total body irradiation, a relatively mild toxicity profile. The optimal dose of treosulfan in pediatric patients, remains to be established. To optimize the balance between treosulfan efficacy and toxicity, pharmacokinetic (PK) monitoring may be a valuable tool. With this purpose, we recently developed a PK and limited sampling model (LSM) which allows measurement of treosulfan exposure. We here report the first results of an ongoing prospective study on the relation between the pharmacokinetic profile of treosulfan in pediatric HSCT recipients and clinical outcome. Materials and Methods Children (n =26; ≤ 18 years) receiving treosulfan based conditioning prior to their first HSCT in the Leiden University Medical Center, The Netherlands were included. Patients ≥ 1 year of age received treosulfan in a dose of 42 g/m2, divided over 3 days. Two patients aged 1.5 and 7 months received 30 and 36 g/m2, respectively. Treosulfan was combined with fludarabine (30 mg/m2/day, 5 days) in all patients and in n=20 patients thiotepa (8 mg/kg) was added. Serotherapy consisted of anti-thymocyte globuline or alemtuzumab. Blood samples were collected at 1.5, 3.5, 4, 5, 7 and 9 or, when a LSM was applied, at 4-5 and 6-7 hours after the start of a three hour treosulfan infusion. The individual PK profile of each patient was determined by a population PK-model with a one-compartment model. Clearance and volume of distribution were allometrically scaled using body weight, with a fixed scaling exponent of 0.75 and 1.0, respectively. Clinical endpoints of this study were stem cell engraftment, chimerism, GvHD, organ toxicity, relapse and treatment related mortality. Results The median age, clearance, and volume of distribution were 6.5 (0.13-16.8) years, 7.8 L/h (1.2 - 44.7 L/h), and 13.8 L (3.0 - 42.9 L), respectively. Within the n=24 patients receiving 42 g/m2, the mean AUC of treosulfan was 1502 mg*h/L and the inter-patient variability was 14%. The inter-occasion variability was 5.4%, based on the day 1 and day 3 results of 12 patients. Two patients received a lower dose of 30 g/m2 and 36 g/m2, resulting in a day 1 AUC of 1578 mg*h/L and 1349 mg*h/L, respectively. A linear relationship was observed between age and treosulfan exposure (R2 = 24%) and body surface area and treosulfan exposure (R2 = 29%), resulting in a lower exposure in older patients (Figure 1.) In this cohort overall survival is 21/26 (81%). Four patients died prior to engraftment (≤18 days after HSCT), due to infection, toxicity (n = 2) and active malignant disease. Treosulfan exposure in these four patients was similar to the remaining patients of the cohort. Primary engraftment was seen in 95% of the 22 evaluable patients. Of the 21 survivors, 76% are disease free, four patients had a recurrence of initial disease, and one patient had a primary rejection followed by rapid autologous reconstitution. In 46% of the patients mucositis grade 2 or 3 was observed, 23% of the patients had skin toxicity grade 1-2 and 31% had a moderate and transient hepatic toxicity within 28 days after treosulfan administration. Acute GvHD ≥ grade II occurred in 3/26 patients. Severe hepatic toxicity occurred in three patients that received treosulfan as reduced toxicity conditioning because of their pre-existing organ toxicity. No association between treosulfan exposure and primary engraftment, survival and disease status at last follow-up was observed. Furthermore, the higher treosulfan exposure in the younger patients was not correlated with higher toxicity levels. Conclusion Our results demonstrate that PK monitoring provides novel insight in the level and inter-patient variability of treosulfan exposure in pediatric patients. To further improve early and long term clinical outcome in pediatric HSCT recipients individualized, age and possibly disease-specific dosing regimens may in the end be required. To achieve this goal, treosulfan PK monitoring as reported here will be a pivotal instrument to obtain further insight into the correlation between treosulfan dose and clinical outcome parameters. With this aim, we are currently performing a prospective multicenter pediatric study in disease-specific cohorts. Figure 1 Figure 1. Disclosures Off Label Use: Treosulfan in conditioning prior to allo-HSCT in pediatric patients. </jats:sec

Sustained Engraftment of Cryopreserved Human Bone Marrow CD34+ Cells in Young Adult NSG Mice

Hematopoietic stem cells (HSCs) are defined by their ability to repopulate the bone marrow of myeloablative conditioned and/or (lethally) irradiated recipients. To study the repopulating potential of human HSCs, murine models have been developed that rely on the use of immunodeficient mice that allow engraftment of human cells. The NSG xenograft model has emerged as the current standard for this purpose allowing for engraftment and study of human T cells. Here, we describe adaptations to the original NSG xenograft model that can be readily implemented. These adaptations encompass use of adult mice instead of newborns and a short ex vivo culture. This protocol results in robust and reproducible high levels of lympho-myeloid engraftment. Immunization of recipient mice with relevant antigen resulted in specific antibody formation, showing that both T cells and B cells were functional. In addition, bone marrow cells from primary recipients exhibited repopulating ability following transplantation into secondary recipients. Similar results were obtained with cryopreserved human bone marrow samples, thus circumventing the need for fresh cells and allowing the use of patient derived bio-bank samples. Our findings have implications for use of this model in fundamental stem cell research, immunological studies in vivo and preclinical evaluations for HSC transplantation, expansion, and genetic modification

Individualised dosing of anti-thymocyte globulin in paediatric unrelated allogeneic haematopoietic stem-cell transplantation (PARACHUTE): a single-arm, phase 2 clinical trial

Background: Anti-thymocyte globulin, which is used in the conditioning of haematopoietic stem-cell transplantation (HSCT) to prevent graft-versus-host disease (GVHD) and graft failure, has highly variable pharmacokinetics. Overexposure to anti-thymocyte globulin leads to poor CD4+ T-cell immune reconstitution, which is associated with inferior overall survival. We hypothesised that individualised anti-thymocyte globulin dosing would promote CD4+ immune reconstitution, while still preventing GVHD and graft failure. Methods: We report the results of a prospective, single-arm, phase 2 clinical trial done at the University Medical Center Utrecht and the Princess Máxima Center for Pediatric Oncology (Utrecht, Netherlands) to investigate individualised dosing of anti-thymocyte globulin for unrelated allogeneic HSCT in paediatric patients. Anti-thymocyte globulin dosing was based on bodyweight, absolute lymphocyte counts before the first dose, and the stem-cell source, with cumulative doses ranging from 2–10 mg/kg. Patients younger than 18 years receiving a first HSCT with a T-cell repleted graft for any indication and a Lansky/Karnofsky performance status of at least 70% were eligible for inclusion. The primary endpoint was CD4+ immune reconstitution (>0·05 × 109 CD4+ T-cells per L twice within 100 days [±3] after transplantation). The primary endpoint needed to be met in 38 of 53 evaluable patients (no death, relapse, or graft failure before day 100). Toxicity was registered according to Common Terminology Criteria for Adverse Events criteria version 4.0. The study is registered with the Dutch Trial Register, NL4836. Findings: Between July 1, 2015, and Aug 22, 2018, 58 patients were included in the study, of whom 51 were evaluable for the primary endpoint. Median follow-up was 25·6 months (IQR 15·0–37·0) and median age was 7·4 years (IQR 2·8–13·2). 29 (50%) of 58 patients were female. CD4+ immune reconstitution was reached in 41 (80%, 95% CI 67–90, in survival analysis) of 51 evaluable patients, hence the study met its primary endpoint. There was no difference in CD4+ immune reconstitution between patients who received different stem-cell sources (87% [95% CI 61–96] in cord blood, 77% [54–89] in bone marrow [p=0·62]). The most common grade 3–5 adverse events were infections (32 [50%] patients had grade 3, two [3%] patients had grade 4, and seven [11%] patients had fatal events) and immunological disorders (seven [11%] patients had grade 3, three [5%] patients had grade 4, and five [8%] patients had fatal events). Two (3%) of 64 patients died of GVHD, which might be indirectly related to the intervention. Interpretation: Individualised dosing of anti-thymocyte globulin led to a significant improvement in early CD4+ immune reconstitution without increasing GVHD and graft failure incidence. Promotion of early CD4+ immune reconstitution by individualising anti-thymocyte globulin dose might improve outcomes of allogeneic HSCT. Funding: Sanofi

Individualised dosing of anti-thymocyte globulin in paediatric unrelated allogeneic haematopoietic stem-cell transplantation (PARACHUTE): a single-arm, phase 2 clinical trial

Background: Anti-thymocyte globulin, which is used in the conditioning of haematopoietic stem-cell transplantation (HSCT) to prevent graft-versus-host disease (GVHD) and graft failure, has highly variable pharmacokinetics. Overexposure to anti-thymocyte globulin leads to poor CD4+ T-cell immune reconstitution, which is associated with inferior overall survival. We hypothesised that individualised anti-thymocyte globulin dosing would promote CD4+ immune reconstitution, while still preventing GVHD and graft failure. Methods: We report the results of a prospective, single-arm, phase 2 clinical trial done at the University Medical Center Utrecht and the Princess Máxima Center for Pediatric Oncology (Utrecht, Netherlands) to investigate individualised dosing of anti-thymocyte globulin for unrelated allogeneic HSCT in paediatric patients. Anti-thymocyte globulin dosing was based on bodyweight, absolute lymphocyte counts before the first dose, and the stem-cell source, with cumulative doses ranging from 2–10 mg/kg. Patients younger than 18 years receiving a first HSCT with a T-cell repleted graft for any indication and a Lansky/Karnofsky performance status of at least 70% were eligible for inclusion. The primary endpoint was CD4+ immune reconstitution (>0·05 × 109 CD4+ T-cells per L twice within 100 days [±3] after transplantation). The primary endpoint needed to be met in 38 of 53 evaluable patients (no death, relapse, or graft failure before day 100). Toxicity was registered according to Common Terminology Criteria for Adverse Events criteria version 4.0. The study is registered with the Dutch Trial Register, NL4836. Findings: Between July 1, 2015, and Aug 22, 2018, 58 patients were included in the study, of whom 51 were evaluable for the primary endpoint. Median follow-up was 25·6 months (IQR 15·0–37·0) and median age was 7·4 years (IQR 2·8–13·2). 29 (50%) of 58 patients were female. CD4+ immune reconstitution was reached in 41 (80%, 95% CI 67–90, in survival analysis) of 51 evaluable patients, hence the study met its primary endpoint. There was no difference in CD4+ immune reconstitution between patients who received different stem-cell sources (87% [95% CI 61–96] in cord blood, 77% [54–89] in bone marrow [p=0·62]). The most common grade 3–5 adverse events were infections (32 [50%] patients had grade 3, two [3%] patients had grade 4, and seven [11%] patients had fatal events) and immunological disorders (seven [11%] patients had grade 3, three [5%] patients had grade 4, and five [8%] patients had fatal events). Two (3%) of 64 patients died of GVHD, which might be indirectly related to the intervention. Interpretation: Individualised dosing of anti-thymocyte globulin led to a significant improvement in early CD4+ immune reconstitution without increasing GVHD and graft failure incidence. Promotion of early CD4+ immune reconstitution by individualising anti-thymocyte globulin dose might improve outcomes of allogeneic HSCT. Funding: Sanofi