Purine nucleoside phosphorylase (PNP) deficiency causes inadequate purine metabolite detoxification, which leads to combined immunodeficiency and variable neurologic symptoms. Hematopoietic stem cell transplantation (HSCT) cures the immunodeficiency, but large studies on the long-term outcomes are lacking. In a retrospective study of the European Society for Blood and Marrow Transplantation, we investigated 46 patients with PNP deficiency from 21 centers. We analyzed the presenting clinical signs and outcomes after HSCT. Cognition (0-3), hearing (0-3), interaction (0-4), movement (0-4), and occupation (0-3) (CHIMO) were scored at the last follow-up (FU) visit (no impairment, 17; mild, 15-16; moderate, 12-14; and severe impairment, <12). The median age at initial presentation was 7.5 (1-48) months. The patients presented with infections (41%), neurological dysfunction (39%), both (15%), or autoimmune disease (5%). At the time of HSCT (median age, 26 [2-192] months), neurological abnormalities were observed in 88% of patients. After a median FU of 7.9 (1.0-22.3) years, 40 patients were alive with a 3-year overall survival (OS)/event-free survival (EFS) probabilities of 86% (confidence interval [CI], 77%-97%)/75% (CI, 64%-89%), respectively. High-level (>50%-100%)/low-level donor chimerism (11%-50%) was observed in 85%/15% of patients, respectively, leading to resolution of T lymphopenia. The median overall CHIMO score was 14 (6-17), while the median scores for each component were 3 (0-3), 3 (1-3), 4 (1-4), 3 (1-4), and 2 (0-3), respectively. Patients who underwent HSCT before 24 months after the initial presentation demonstrated superior OS (P = .049). Neurological symptoms that occurred before 11 months of age were associated with reduced OS (P = .027). While the overall results were satisfactory, earlier diagnosis could further improve outcomes.

Anti-thymocyte globulin (ATG) is used in pediatric allogeneic hematopoietic cell transplantation (HCT) to prevent graft-versus-host-disease (GvHD) and graft failure (GF). Poor or delayed 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 II PARACHUTE trial investigating MBD-ATG, combined with real-world experience with identical MBD-ATG. Consecutive pediatric patients receiving a first T-cell replete HCT for any indication were evaluated. Results were compared to historical patients receiving conventional fixed ATG dosing (FIX-ATG). Primary outcome was overall survival (OS). The MBD-group consisted of 214 patients (58 trial patients, 156 real-world patients); 100 patients received FIX-ATG. MBD-ATG led to superior OS compared to FIX-ATG (hazard ratio [HR] for death 0.56, 95% confidence interval [CI] 0.34-0.93, p=0.026), mainly due to lower treatment related mortality (TRM; HR 0.51, 95% CI 0.29-0.92, p=0.025). Successful T-cell reconstitution (>0·05 × 10⁹ CD4+ T-cells/L twice within 100±3 days after HCT) was improved in MBD-ATG versus FIX-ATG (87%±2% versus 47%±5%, p<0.0001). The improved T-cell reconstitution led to lower TRM (HR 0.19, 95% CI 0.09-0.36, p<0.0001). Incidence of grade 2-4 acute GvHD was comparable, while chronic GvHD (HR 0.35, 95% CI 0.17-0.72, p=0.004) and GF (HR 0.36, 95% CI 0.13-0.97, p=0.044) were both less frequent in MBD-ATG compared to FIX-ATG. MBD-ATG results in improved OS and reduced TRM, while reducing chronic GvHD and GF. This easy-to-implement approach can improve outcomes after pediatric HCT though confirmatory studies are urgently needed.

Introduction Osteopetrosis (OP) is a group of rare inherited conditions characterized by dysfunctional osteoclasts, leading to hypocalcemia, cytopenia, bone fractures, compression of cranial nerves and vision loss. Hematopoietic stem cell transplantation (HSCT) is the only curative approach for most children with OP but was historically complicated by high incidence of graft failure (GF), veno-occlusive disease (VOD) and transplant-related mortality (TRM). To define prognostic risk factors in this setting, the IEWP of the EBMT performed a registry study on HSCT in OP. Patients and Methods We analyzed the outcomes of children with OP receiving HSCT in EBMT centers between 1990 and 2022. The main endpoints of the study were overall survival (OS) and event-free survival (EFS; events: death and graft failure) according to year of HSCT, donor type, stem cell source and conditioning regimen. Results We studied 746 children affected by OP, with a median age at transplant of 0.7 years (range 0-15). Genetic results were available for 321 patients: TCIRG1 66.4%, CLCN7 12.9%, SNX10 6.6%, RANK 5.9%, and others 8.2%. Pre-HSCT OP-related complications included: bone fractures (16.9%), hypocalcemia (76.6%), splenomegaly (70.5%), transfusion-dependent anemia (53.6%), severe visual impairment or blindness (57.5%), intracranial hypertension (16.9%), and seizures (11.7%). The median follow-up was 7 years (range 0-33.8 years). Conditioning regimens were Busulfan/Fludarabine (n=310; 43.5% of known values), Busulfan/Cyclophosphamide (n=236; 33.1%), Treosulfan/Fludarabine/Thiotepa (n=132; 18.5%), or other (n=34; 4.8%). Donors were human leukocyte antigen (HLA) matched sibling donor (MSD; n=208, 29.2%), matched related (MRD; n=78, 10.9%), matched unrelated (MUD, 10/10 or 6/6; n=174; 24.4%), mismatched related (MMRD; n= 168; 23.6%), mismatched unrelated (MMUD, n= 85; 11.9%). Stem cell source was bone marrow (BM, n=470; 64%), peripheral blood (PB, n=201; 27.4%) or umbilical cord blood (UCB, n=63; 8.6%). The 3-year Kaplan-Meier estimate of OS was 69% (95% CI, 66-73%). Survival improved over time: 3-year OS was 50% (41-59%), 67% (60-73%) and 77% (73-82%) for patients transplanted between 1990-2000, 2001-2011 and 2012-2022, respectively (p<0.001). Risk factor analysis was performed for patients transplanted between 2007-2022 (n=491, 66%), reflecting adoption of modern transplant procedures. In this group, the 3-year OS, EFS and CI of graft failure (GF) was 75% (71-79%), 61% (56-66%) and 21% (17-25%), respectively. Second HSCT was performed in 65/491 patients and resulted in a 3-year OS and EFS of 63% (51-75%) and 45% (32-59%), respectively. The 180-day CI of grade II-IV and grade III-IV acute GvHD was 26% (22-31%) and 11% (8-14%), respectively. The 2-year CI of chronic and extensive chronic GVHD was 9% (6-12%) and 3% (2-5%), respectively. In multi-variate analysis (MVA), OS was lower in patients with HLA-mismatched donors (HR, 1.53; p=0.045), poor performance status (HR 2.69; p<0.001), splenomegaly (HR 2.89; p<0.001), and those undergoing UCB transplant (HR 1.92; p=0.036). Large center size (≥20 transplants) was associated with better OS (p<0.001), motivating the inclusion of center in the MVA. In MVA, EFS was lower in patients with poor performance score (HR 2.11; p<0.001), splenomegaly (HR 2.92; p<0.001), use of HLA mismatched donors (HR 1.85; p=0.001) and PB as stem cell source (HR 1.67; p=0.01). The 30-day CI of VOD was 20% (16-24%); this was (very) severe in 36.6% patients. In MVA exposure to Busulfan/Fludarabine (HR 5.87; p<0.001) and age <6 months (HR 1.23; p=0.005) were independent risk factors. Arterial pulmonary hypertension and hypercalcemia were described in 51/375 (13.6%) and 76/371 (20.5%) evaluable patients, respectively. OP-related clinical phenotypes improved significantly post-HSCT, with evidence of improved anemia (p<0.001), leukocytosis (p<0.001), thrombocytopenia (p<0.001), height (p<0.001), and intracranial hypertension (p<0.001). In UVA, earlier HSCT (<6 months) contributed to improved vision preservation (p<0.001). Conclusion This is the largest study to date describing HSCT outcomes in children affected by OP. Although challenges remain in terms of risk of GF, VOD and TRM, survival has significantly improved over the last decade, especially when an HLA matched donor is unavailable. Due to the complexity of OP patients, it is recommended that HSCT is performed in large and experienced centers.

ABSTRACT:Allogeneic hematopoietic cell transplantation (HCT) is a potentially curative treatment strategy for patients with inborn errors of immunities (IEIs). The objective of this study was to assess the optimal busulfan exposure before allogeneic HCT for patients with an IEI who received an IV busulfan-based conditioning regimen. Patients from 17 international centers were included. The main outcome of interest was event-free survival (EFS). Patients were categorized into 4 IEI subgroups: combined immunodeficiency (CID), severe combined immunodeficiency (SCID), neutrophil disorders, and hemophagocytic lymphohistiocytosis (HLH)-related disorders. Busulfan exposure was calculated by individual centers (area under the curve [AUC]CENTER) and re-estimated using a nonlinear mixed-effects model (NONMEM; exposure defined as AUCNONMEM). Overall, 562 patients were included: 173 (30.8%) with CID, 154 (27.4%) with SCID, 101 (18.0%) with HLH-related disorders, and 134 (23.8%) with neutrophil disorders. The median busulfan AUCNONMEM was 69.0 mg × h/L and correlated poorly with the AUCCENTER (r2 = 0.54). In patients with SCID, HLH-related, and neutrophil disorders with a busulfan AUCNONMEM of 70 to 90 mg × h/L, 2-year EFS was superior to <70 mg × h/L, and >90 mg ×h/L. Full donor chimerism increased with higher busulfan AUCNONMEM, plateauing at 90 mg × h/L. For patients with CID, the optimal AUCNONMEM for donor chimerism was found to be >70 mg × h/L. Improved EFS and higher donor chimerism may be achieved by targeting a cumulative busulfan AUCNONMEM of 80 mg × h/L (range, 70-90). Our study stresses the importance of uniformly using a validated population pharmacokinetic model to estimate AUCNONMEM.

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 concentration-time data. The level of ATLG exposure (day active ATLG <1 AU/mL, median 16 days post-HSCT) was strongly associated with aGVHD grade II-IV, with a lower incidence in patients with prolonged active ATLG exposure (≤day 16 50% vs. >day 16 8.2%; P<0.001). When stratified for remission state, patients transplanted in complete remission (CR) 2 or 3 with prolonged ATLG exposure had a higher relapse risk, while this effect was not seen in CR1 patients (P=0.010). High level ATLG exposure was associated with delayed CD4 T-cell recovery at 4 and 8 weeks post-HSCT, but not at 12 weeks, and overall and relapse-free survival were not influenced by CD4 recovery at 12 weeks post-HSCT. This study underlines the importance of individualized ATLG exposure with the use of model-informed precision dosing in order to optimize the HSCT outcome in pediatric ALL.

IntroductionAnti-thymocyte globulin (ATG) is used in the conditioning for pediatric hematopoietic cell transplantation (HCT) to prevent graft-versus-host-disease (GvHD) and graft failure (GF). Toxicity includes poor T-cell recovery, associated with viral reactivations and higher mortality. The PARACHUTE-trial1 (non-randomized prospective trial investigating model-based dosing [MBD] compared to historical fixed dose of ATG Thymoglobulin) showed that MBD of ATG improves T-cell recovery compared to fixed dosing, while maintaining an anti-GvHD effect. We now evaluated outcome after 5-year follow-up combined with real-world data.MethodsWe included those enrolled on the PARACHUTE-trial and all consecutive real-world pediatric patients treated as per the trial protocol in Utrecht, the Netherlands (NL) and New York, USA. The cumulative MBD dose (based on body weight, lymphocyte counts and graft source) ranged 2-10 mg/kg, starting on day -9 before HCT. Results were compared to a historical cohort receiving fixed weight-based dose of 10 mg/kg starting 5±1 days before HCT (FIX)1. Primary endpoint was overall survival (OS); secondary endpoints included therapy-related mortality (TRM), successful CD4+ recovery (CD4IR; defined as >50/mm3 CD4+ twice within 100 days after HCT), acute and chronic GvHD and GF. Multivariable Cox proportional hazard and Fine-Gray competing risk models were used.ResultsA total of 214 patients were dosed according to MBD (58 trial patients and 124 (NL) and 32 (USA) real-world treated 2015-22); the historical controls included 100 patients (treated in NL 2004-12). Age (median 8.4 vs 6.1), graft source (bone marrow and cord blood) and conditioning (mostly BuFlu±Clo) was comparable in MBD and FIX, respectively. MBD led to superior OS (81%) as compared to FIX (63%; HR 0.56, 95% CI 0.34-0.93, p=0.026; Figure 1a), mainly due to lower TRM (HR 0.52, 95% CI 0.29-0.92, p=0.025; Figure 1b). Relapse incidence was comparable. Successful CD4IR was comparable amongst all MBD-groups, and significantly than FIX (87% vs 49%; HR 2.93, 95% CI 2.03-4.23, p=<0.0001). Successful CD4IR was strongly associated with improved survival (HR 0.28, 95% CI 0.17-0.47, p<0.0001) due to lower TRM, with no additional effect of MBD vs FIX (ie. historical patients), underlining the effect was CD4-driven rather than treatment-period driven (HR 0.18, 95% CI 0.09-0.34, p<0.0001; Figure 1c). Reducing the dose led to reduced toxicity with lower incidence of cGvHD (7% vs 17%; HR 0.35, 95% CI 0.17-0.72), p=0.004) and GF (5% vs 15%; HR 0.36, 95% CI 0.13-0.97, p=0.044) in MBD compared to FIX, and comparable rates of aGvHD (p=0.14).DiscussionMBD of ATG leads to improved OS and lower TRM, likely due optimized CD4IR, while also reducing cGvHD and GF. This approach can be a major breakthrough in improving outcomes after pediatric HCT and is easy to implement.

In the setting of hematopoietic stem cell transplantation (HSCT), Rituximab (RTX) is used for the treatment and prevention of EBV-associated post-transplantation lymphoproliferative disease or autoimmune phenomena such as autoimmune hemolytic anemia (AIHA). Persistent hypogammaglobulinemia and immunoglobulin substitution dependence has been observed in several patients after RTX treatment despite the normalization of total B cell numbers. We aimed to study whether this is a B cell intrinsic phenomenon. We analyzed four patients with different primary diseases who were treated with myeloablative conditioning and matched unrelated donor HSCT who developed persistent hypogammaglobulinemia after receiving RTX treatment. They all received RTX early after HSCT to treat EBV infection or AIHA post-HSCT. All patients showed normalized total B cell numbers but absent to very low IgG positive memory B cells, and three lacked IgA positive memory B cells. All of the patients had full donor chimerism, and none had encountered graft-versus-host disease. Sorted peripheral blood naïve B cells from these patients, when stimulated with CD40L, IL21, IL10 and anti-IgM, demonstrated intact B cell differentiation including the formation of class-switched memory B cells and IgA and IgG production. Peripheral blood T cell numbers including CD4 follicular T-helper (Tfh) cells were all within the normal reference range. In conclusion, in these four HSCT patients, the persistent hypogammaglobulinemia observed after RTX cannot be attributed to an acquired intrinsic B cell problem nor to a reduction in Tfh cell numbers.

Deficiency of adenosine deaminase-2 (DADA2) is an autosomal recessive autoinflammatory disease with an extremely variable disease presentation. This paper provides a comprehensive overview of the Dutch DADA2 cohort. We performed a retrospective cohort study in 29 ADA2-deficient patients from 23 families with a median age at inclusion of 26 years. All patients had biallelic pathogenic variants in the ADA2 gene. The most common clinical findings included cutaneous involvement (79.3%), (hepato)splenomegaly (70.8%) and recurrent infections (58.6%). Stroke was observed in 41.4% of the patients. The main laboratory abnormalities were hypogammaglobulinemia and various cytopenias. Patients presented most often with a mixed phenotype involving vasculopathy, immunodeficiency and hematologic manifestations (62.1%). In this cohort, malignancies were reported in eight patients (27.6%), of whom five presented with a hematologic malignancy and two with a basal cell carcinoma. Four patients developed hemophagocytic lymphohistiocytosis (HLH) or an HLH-like episode, of whom three passed away during or shortly after the occurrence of HLH. TNF-inhibitors (TNFi) were effective in treating vasculopathy-associated symptoms and preventing stroke, but were hardly effective in the treatment of hematologic manifestations. Three patients underwent hematopoietic cell transplantation and two of them are doing well with complete resolution of DADA2-related symptoms. The overall mortality in this cohort was 17.2%. In conclusion, this cohort describes the clinical, genetic and laboratory findings of 29 Dutch DADA2 patients. We describe the occurrence of HLH as a life-threatening disease complication and report a relatively high incidence of malignancies and mortality.

Alemtuzumab (anti-CD52 antibody) is frequently prescribed to children with nonmalignant diseases undergoing allogeneic hematopoietic stem cell transplantation (HSCT) to prevent graft failure (GF) and acute graft-versus-host disease (aGVHD). The aim of this multicenter study was the characterization of alemtuzumab population pharmacokinetics to perform a novel modelbased exposure-response analysis in 53 children with nonmalignant immunological or hematological disease and a median age of 4.4 years (interquartile range [IQR], 0.8-8.7). The median cumulative alemtuzumab dose was 0.6 mg/kg (IQR, 0.6-1) administered over 2 to 7 days. A 2-compartment population pharmacokinetics model with parallel linear and nonlinear elimination including allometrically scaled bodyweight (median, 17.50 kg; IQR, 8.76-33.00) and lymphocyte count at baseline (mean, 2.24 x 10(9)/L; standard deviation +/- 1.87) as significant pharmacokinetic predictors was developed using nonlinear mixed effects modeling. Based on the model-estimated median concentration at day of HSCT (0.77 mu g/mL; IQR, 0.33-1.82), patients were grouped into a low- (<= 0.77 mu g/mL) or high- (>0.77 mu g/mL) exposure groups. High alemtuzumab exposure at day of HSCT correlated with delayed CD4(+) and CD8(+) T-cell reconstitution (P value <.0001) and increased risk of GF (P value =.043). In contrast, alemtuzumab exposure did not significantly influence the incidence of aGVHD grade >= 2, mortality, chimerism at 1 year, viral reactivations, and autoimmunity at a median follow-up of 3.3 years (IQR, 2.5-8.0). In conclusion, this novel population pharmacokinetics model is suitable for individualized intravenous precision dosing to predict alemtuzumab exposure in pediatric allogeneic HSCT for nonmalignant diseases, aiming at the achievement of early T-cell reconstitution and prevention of GF in future prospective studies.

IntroductionSevere combined immunodeficiency (SCID) is one of the most severe forms of inborn errors of immunity (IEI), affecting both cellular and humoral immunity. Without curative treatment such as hematopoietic stem cell transplantation or gene therapy, affected infants die within the first year of life. Due to the severity of the disease, asymptomatic status early in life, and improved survival in the absence of pretransplant infections, SCID was considered a suitable candidate for newborn screening (NBS).Areas coveredMany countries have introduced SCID screening based on T-cell receptor excision circle (TREC) detection in their NBS programs. Screening an entire population is a radical departure from previous paradigms in the field of immunology. Efficient screening strategies are cost-efficient and balance high sensitivity while preventing high numbers of referrals. NBS for SCID is accompanied by (actionable) secondary findings, but many NBS programs have optimized their screening strategy by adjusting algorithms or including second-tier tests. Harmonization of screening terminology is of great importance for international shared learning.Expert OpinionThe expansion of NBS is driven by the development of new test modalities and treatment options. In the near future, other techniques such as next-generation sequencing will pave the way for NBS of other IEI. Exciting times await for population-based screening programs.

Epigenetic immune cell counting is a DNA (de)methylation-based technique which can be used to quantify lymphocyte subsets on dried blood spots (DBS). The foregoing techniques allow for a retrospective investigation of immune cell profiles in newborns. In this study, we used this technique for determining lymphocyte subcounts as a potential biomarker for necrotizing enterocolitis (NEC). We investigated whether this technique can be implemented in the field of neonatology, by testing whether regulatory T cell (Treg) levels are pre-existently low in preterms with NEC. Newborn screening (NBS) cards from 32 preterms with NEC and 32 age- and weight-matched preterm controls, and 60 healthy term newborns, were analyzed. Relative and absolute cell counts were determined for CD3+, CD4+, CD8+, Th17, and Treg T cells. For both relative and absolute cell counts of CD3+, CD4+, CD8+, and Th17 T cells, significant differences were found between healthy term controls and both preterm groups, but not between preterm groups. For Tregs, no significant differences were found in either relative or absolute counts between any of the newborn groups. This study demonstrates the principle of epigenetic immune cell counting to analyze lymphocyte subsets in preterm neonates.

Background:Alemtuzumab is a humanized monoclonal antibody that targets the CD52 glycoprotein expressed on most lymphocytes, subsequently inducing complement-mediated and antibody-mediated cytotoxicity. Owing to its ability to induce profound immune depletion, alemtuzumab is frequently used in patients before allogeneic hematopoietic stem cell transplantation to prevent graft rejection and acute graft-versus-host disease. In this clinical context, a stable immunoassay with high sensitivity and specificity to determine alemtuzumab levels is essential for performing pharmacokinetic and pharmacodynamic analyses; however, the available methods have several limitations. Here, we report the successful development and validation of an efficient and highly sensitive enzyme-linked immunosorbent assay technique based on commercially available reagents to quantify alemtuzumab in human serum or plasma.Methods:This enzyme-linked immunosorbent assay technique was developed and validated in accordance with the European Medicines Agency guidelines on bioanalytical method validation.Results:The assay sensitivity (lower limit of quantification) is 0.5 ng·mL−1, and the dynamic range is 0.78–25 ng·mL−1. To accommodate quantification of peak concentration and concentrations below the lympholytic level (<0.1 mcg·mL−1), patients' serum samples were prediluted 20–400 times according to the expected alemtuzumab concentration. The overall within-run accuracy was between 96% and 105%, whereas overall within-run precision (coefficient of variation) was between 3% and 9%. The between-run assessment provided an overall accuracy between 86% and 95% and an overall coefficient of variation between 5% and 14%.Conclusions:The developed assay provides accurate insight into alemtuzumab exposure and its effects on the clinical response to treatment, which is key to optimizing treatment strategies.

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 Maxima Center for Pediatric Oncology (Utrecht, Netherlands) to investigate individualised dosing of anti-thymocyte globulin for unrelated allogeneic HSCT in paediatric patients. Antithymocyte 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 (>0middot05 x 10(9) 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 25middot6 months (IQR 15middot0-37middot0) and median age was 7middot4 years (IQR 2middot8-13middot2). 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=0middot62]). 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.