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Extracorporeal photopheresis (ECP) has been shown to be an effective treatment for graft-versus-host disease (GvHD). However, information regarding lymphocyte collection for ECP in children is limited. The aim of this study was to analyse and compare lymphocyte collection for ECP in children using different devices and protocols. Moreover, we have studied both safety and variables of the infused product related to treatment efficacy.This was a retrospective study of 91 patients who underwent 1524 apheresis procedures with either the COBE Spectra or Spectra Optia system. The comparison study between the Optia protocols (MNC and CMNC) was prioritized. We analysed 578 procedures using the Optia blood cell separator: 204 and 374 using the MNC and the CMNC protocol, respectively.The Optia CMNC protocol showed better collection efficiency, with increased lymphocyte collection per kg of body weight (p 0.001). On multivariate analysis, the type of protocol showed no relationship with haematocrit or platelet loss. Most procedures were well-tolerated, with the most frequent adverse events related to venous access (21.7%). Seventy-one percent of patients had either partial or complete clinical GvHD response. In the multivariate model, only two variables were associated with a better response to ECP, younger age and a greater increase of B lymphocytes after treatment.Lymphocyte collection for ECP is well-tolerated in most children, achieving complete or partial response in more than half of GvHD patients. CMNC is the optimal software to perform lymphocyte collection in children.

Introduction: In recent years, there have been changes in the management of patients with primary immune thrombocytopenia. In this study, a review is presented of the characteristics and outcomes of children with primary immune thrombocytopenia in a children’s hospital (Hospital Infantil Niño Jesús). Moreover, an analysis is made of the changes in the care of these patients diagnosed before and after 2011, when new guidelines were published by the Spanish Society of Paediatric Haematology Oncology (SEHOP). Material and methods: Data from a cohort of primary immune thrombocytopenia patients followed up in this hospital have been retrospectively reviewed. The statistical package used for the analysis was SPSS Statistics 22.0 (IBM Corp., Chicago, IL, USA). Results: A review is presented on the clinical data from 235 paediatric patients diagnosed with primary immune thrombocytopenia. It was observed that some features at diagnosis, such as age younger than five years and a previous history of infection, influenced the probability of cure. Regarding the changes in the management of patients since 2011, the steroid doses received during the first month and the first year, and the number of days corresponding to the patient’s first admission have both significantly decreased. Splenectomies were also significantly reduced. Conclusions: Since 2011, there have been changes in the medical care of our primary immune thrombocytopenia patients: they receive lower doses of steroids, they stay fewer days in the hospital, and the number of splenectomies has decreased without increasing bleeding or worsening the clinical evolution. Furthermore, it was observed that age younger than 5 years and a history of infection prior to diagnosis were related to higher chances of recovery. Resumen: Introducción: En los últimos años se han experimentado cambios en el manejo de los pacientes con trombocitopenia inmune primaria. En este estudio se revisan las características de los pacientes con trombocitopenia inmune primaria del Hospital Infantil Universitario Niño Jesús y su evolución. Además, analizamos los cambios en el abordaje de los pacientes diagnosticados antes y después del 2011, año en el que se publicó la guía de la Sociedad Española de Pediatría. Material y métodos: Se han revisado retrospectivamente los datos de pacientes con trombocitopenia inmune primaria en seguimiento en nuestro hospital desde el año 2000. El paquete estadístico utilizado para el análisis fue SPSS Statistics 22.0 (IBM Corp, Chicago, IL, EE.UU.). Resultados: Se han revisado 235 pacientes pediátricos con trombocitopenia inmune primaria observando que algunas características al diagnóstico, como la edad menor de 5 años y los antecedentes previos de infección, pueden influir en la probabilidad de recuperación. Con respecto al cambio de manejo de los pacientes, a partir de 2011 las dosis de esteroides recibidas durante el primer mes y el primer año se han reducido de forma significativa, así como el número de días del primer ingreso pasando de 5 a 3 días. Las esplenectomías también se han reducido significativamente. Conclusiones: Desde el año 2011 se han producido cambios en el abordaje de nuestros pacientes: reciben una menor dosis de esteroides, permanecen menos días ingresados y se ha reducido el número de esplenectomías sin aumentar los sangrados y sin disminuir la tasa de respuestas. Además, observamos que la edad menor de 5 años y el antecedente de infección previa al diagnóstico están relacionados con una mayor tasa de recuperación.

Risk factors and outcomes of GF after TCD haploidentical transplantation in children with hematological malignancies were analyzed. 148 TCD transplants were included. 78 patients were diagnosed of ALL and 70 patients of AML. 22 out of 148 patients developed GF. MVA showed that patient

Introduction: Autoimmune hemolytic anemia (AIHA) is a rare and generally self-limiting disease in children. Material and methods: A descriptive cross-sectional study was performed in children under 18 years diagnosed with AIHA from January 1997 to July 2019. Clinical variables were collected and AIHA was classified according to the direct antiglobulin test (DAT) in warm AIHA (IgG+/-C3d) and cold AIHA (C3d). Response to treatment and evolution were analyzed. Results: 25 patients were included and 72% were males. The median age at diagnosis was 2 years (range 0.4–9). Fever (72%), pallor (68%), jaundice (64%), hepatosplenomegaly and coluria (48%) were the most common presenting symptoms. The median hemoglobin at diagnosis was 5.4 g/dl. DAT was positive in 96%, with detection of IgG antibodies in 76%. A single case presented negative DAT. 20% of the patients associated another cytopenia, one of which was subsequently diagnosed with common variable immunodeficiency. Concomitant viral infection was suspected or documented in 32%. Most of the cases were self-limiting and responded to corticosteroid treatment (72%). Those with partial response (24%), mainly those associated with other cytopenias, required other lines of treatment (rituximab, mycophenolate, immunoglobulins,…). Complications (32%) and relapses (26%) were detected only in warm AIHA. Conclusions: Our case series confirms that AIHA is a very rare disease in childhood. Most cases evolve favorably, although up to a quarter of them require second lines of treatment and, in exceptional cases, they need very aggressive treatments. These latter cases generally correspond to patients who present more than one cytopenia in the course of the disease. Resumen: Introducción: La anemia hemolítica autoinmune (AHAI) es una enfermedad rara en niños, generalmente autolimitada. Material y métodos: Estudio descriptivo transversal en menores de 18 años diagnosticados de AHAI desde enero 1997 a julio 2019. Se recogieron variables clínicas y se clasificaron según el test de Coombs directo (TCD) en AHAI por anticuerpos calientes (IgG+/-C3d) y fríos (C3d). Se analizó la respuesta al tratamiento y su evolución. Resultados: Se incluyeron 25 pacientes, siendo el 72% varones. La mediada de edad al diagnóstico fue 2 años (rango 0,4–9). Los síntomas predominantes fueron fiebre (72%), palidez (68%), ictericia (64%), hepatoesplenomegalia y coluria (48%). La mediana de hemoglobina al diagnóstico fue 5,4 gr/dl. En el 96% el TCD fue positivo, con detección de anticuerpos IgG en el 76%. Un solo caso presentó TCD negativo. Un 20% asociaron otra citopenia, uno de ellos fue diagnosticado posteriormente de inmunodeficiencia variable común. En un 32% se sospechó o documentó una infección viral concomitante. La mayoría de los casos fueron autolimitados y respondieron a tratamiento con corticoides (72%). Aquellos con respuesta parcial (24%), principalmente los que asociaban otras citopenias, precisaron otras líneas de tratamiento (rituximab, micofenolato, inmunoglobulinas,…). Se detectaron complicaciones (32%) y recaídas (26%) únicamente en AHAI por anticuerpos calientes. Conclusiones: Nuestra serie confirma que la AHAI es una enfermedad muy poco frecuente en la infancia. La mayoría de los casos evolucionan favorablemente, aunque hasta una cuarta parte precisan segundas líneas de tratamiento y casos excepcionales tratamientos muy agresivos. Estos últimos suelen corresponder a pacientes con más de una citopenia en la evolución de la enfermedad.

espanolIntroduccion La anemia hemolitica autoinmune (AHAI) es una enfermedad rara en ninos, generalmente autolimitada. Material y metodos Estudio descriptivo transversal en menores de 18 anos diagnosticados de AHAI desde enero de 1997 a julio de 2019. Se recogieron variables clinicas y se clasificaron segun el test de Coombs directo (TCD) en AHAI por anticuerpos calientes (IgG+/-C3d) y frios (C3d). Se analizo la respuesta al tratamiento y su evolucion. Resultados Se incluyeron 25 pacientes, siendo el 72% varones. La media de edad al diagnostico fue de dos anos (rango 0,4-9). Los sintomas predominantes fueron fiebre (72%), palidez (68%), ictericia (64%), hepatoesplenomegalia y coluria (48%). La mediana de hemoglobina al diagnostico fue 5,4 g/dL. En el 96% el TCD fue positivo, con deteccion de anticuerpos IgG en el 76%. Un solo caso presento TCD negativo. Un 20% asociaron otra citopenia, uno de ellos fue diagnosticado posteriormente de inmunodeficiencia variable comun. En un 32% se sospecho o documento una infeccion viral concomitante. La mayoria de los casos fueron autolimitados y respondieron a tratamiento con corticoides (72%). Aquellos con respuesta parcial (24%), principalmente los que asociaban otras citopenias, precisaron otras lineas de tratamiento (rituximab, micofenolato, inmunoglobulinas). Se detectaron complicaciones (32%) y recaidas (26%) unicamente en AHAI por anticuerpos calientes. Conclusiones Nuestra serie confirma que la AHAI es una enfermedad muy poco frecuente en la infancia. La mayoria de los casos evolucionan favorablemente, aunque hasta una cuarta parte precisan segundas lineas de tratamiento y casos excepcionales tratamientos muy agresivos. Estos ultimos suelen corresponder a pacientes con mas de una citopenia en la evolucion de la enfermedad. EnglishIntroduction Autoimmune hemolytic anemia (AIHA) is a rare and generally self-limiting disease in children. Material and methods A descriptive cross-sectional study was performed in children under 18 years diagnosed with AIHA from January/1997 to July/2019. Clinical variables were collected and AIHA was classified according to the direct antiglobulin test (DAT) in warm AIHA (IgG+/-C3d) and cold AIHA (C3d). Response to treatment and evolution were analyzed. Results 25 patients were included and 72% were males. The median age at diagnosis was 2 years (range 0.4 to 9). Fever (72%), pallor (68%), jaundice (64%), hepatosplenomegaly and coluria (48%) were the most common presenting symptoms. The median hemoglobin at diagnosis was 5.4 g/dl. DAT was positive in 96%, with detection of IgG antibodies in 76%. A single case presented negative DAT. 20% of the patients associated another cytopenia, one of which was subsequently diagnosed with common variable immunodeficiency. Concomitant viral infection was suspected or documented in 32%. Most of the cases were self-limiting and responded to corticosteroid treatment (72%). Those with partial response (24%), mainly those associated with other cytopenias, required other lines of treatment (rituximab, mycophenolate, immunoglobulins). Complications (32%) and relapses (26%) were detected only in warm AIHA. Conclusions Our case series confirms that AIHA is a very rare disease in childhood. Most cases evolve favorably, although up to a quarter of them require second lines of treatment and, in exceptional cases, they need very aggressive treatments. These latter cases generally correspond to patients who present more than one cytopenia in the course of the disease. Previous article in issueNext article in issue

Classically, several variables have been related to the disease course of chronic primary immune thrombocytopenia (cITP), though to date, there is no consensus on their clinical relevance. In a recent systematic review, a meta-analysis was made and confirmed the existence of certain cITP-related variables that may be related to prognosis in pediatric patients. We retrospectively analyzed a cohort of patients diagnosed with ITP, identified prognostic variables, and compared our results to the variables described by the authors. A multivariate study revealed that older age at diagnosis and higher platelet count were the only independent variables related to cITP. Children up to age 4 years and those with lower platelet counts (below 20 × 109/L) were at lower risk for cITP.Conclusion: We therefore concluded that only age and platelet count at diagnosis are independent variables that should be considered when evaluating the risk of developing cITP. What is Known: • Around 20% of patients with immune thrombocytopenia progress to chronic disease as determined by a sustained platelet count below 100×109/L for more than 12 months. • A number of variables potentially related to the development of cITP are being studied, such as age, sex, cell count, and previous treatment. What is New: • This is a new group of patients diagnosed with ITP in which the platelet count and age at diagnosis are the only independent variables closely related to cITP. • In this new series, we could not confirm other variables previously related to cITP such as total leukocyte count or the absence of treatment at diagnosis.

Mobilization regimes in pediatric patients at high risk for poor mobilization are not standardized across different institutions. We present a retrospective analysis of our experience with a high-dose granulocyte colony-stimulating factor (G-CSF) regime of 12 μg/Kg per body weight (BW) twice a day for 4 days used in high-risk patients.We report the results of all pediatric patients mobilized with high-dose G-CSF between January 1999 and February 2021 in our center. A successful mobilization was defined as a peripheral blood (PB) CD34Of the 262 patients included in the analysis, mobilization failure was found in 27 (10.3%). In a univariate analysis, this was associated with age, weight, baseline diagnosis, and having undergone a previous mobilization cycle, the latter being the only factor that remained significantly associated in a multivariate analysis (P = 0.03). The 54 patients (20.6%) did not reach the minimum required CD34Although most high-risk pediatric patients are successfully mobilized with the high-dose G-CSF regime, this approach does not salvage all of them and significantly increases the presence of AEs in comparison to standard-dose regimes.

INTRODUCTION In order to propose risk-adapted mobilization algorithms, several authors have tried to look for predictive factors of the CD34+ yield in healthy pediatric donors. Donor recipient body weight ratio (D/R ratio) was identified as one of the main variables related with the success to achieve the target cell dose for transplantation. According to this variable we modified the mobilization schedule. MATERIAL AND METHODS We report the results of 46 mobilizations and apheresis procedures performed in our center with unfavorable D/R ratio. Mobilization was attempted by the standard regime of G-CSF (10 mcg/kg/24 hours) in 28 cases (60.9%), with high dose G-CSF (10 mcg/kg/12 hours) in 9 cases (19.6%), and with plerixafor and G-CSF single dose regime in 9 cases (19.6%). RESULTS CD34+ cell quantification before apheresis is closely related to CD34+ yield, being the only factor related to collected CD34+ cells (beta .71; P

Introduction: Symptomatic venous thromboembolism (VTE) is diagnosed in 3%14% of patients during pediatric acute lymphoblastic leukemia (ALL) therapy. There are well-known risk factors, but the role of others as inherited thrombophilia is still controversial. Prophylaxis with low molecular weight heparin (LMWH) has been described, but its use is not globally accepted. Methods: A retrospective multicentric study in ALL patients 1-18 years old following SEHOP-PETHEMA-2013 treatment guideline was performed to evaluate VTE rate, anticoagulant treatment, outcome, risk factors, and safety and usefulness of LMWH administration as primary thromboprophylaxis in children with inherited thrombophilia. Results: A total of 652 patients were included in the study. VTE incidence was 8.7%. Most of the cases occurred during induction therapy associated with central venous catheter. Univariant analysis showed that family history of thrombosis, presence of mediastinal mass, high-risk treatment group, and inherited thrombophilia were statistically significant risk factors. LMWH administration seemed to decrease VTE rate in patients with inherited thrombophilia and those with T-cell ALL phenotype. Conclusion: Most of the VTE cases occurred in patients without inherited thrombophilia, but when it is present, the VTE risk is higher. LMWH administration was useful to decrease VTE in these patients.

SUMMARY PARAGRAPH Fanconi anemia (FA) is a monogenic inherited disease associated with mutations in genes that encode for proteins participating in the FA/BRCA DNA repair pathway. Mutations in FA genes result in chromosomal instability and cell death, leading to cancer risks and progressive cell mortality, most notably in hematopoietic stem and progenitor cells (HSPC). Recently, we showed the first clinical evidence that gene therapy confers engraftment and proliferative advantage of gene-corrected HSPCs in FA patients1. Despite this and many other gene therapy advances, the question of whether the molecular pathways affected in monogenic diseases can be reverted by lentiviral-mediated gene therapy has never been addressed. This is even more challenging in DNA repair syndromes such as FA since in these cases, transcriptional defects in affected cells might not be restored due to DNA damage accumulated prior to gene therapy. Using single-cell RNA sequencing in HSPCs from FA-A patients previously treated by ex vivo gene therapy, we demonstrate that lentiviral-mediated gene therapy prior to severe bone marrow failure not only restores the expression of the defective gene, but also induces a long-term correction of the transcriptional program in FA HSPCs, which then acquire a signature characteristic of healthy HSPCs. Our results reveal new molecular evidence showing the potential of gene therapy to fully rescue phenotypic defects in FA, a devastating HSPC disease characterized by defective DNA repair.

Risk factors and outcomes of GF after TCD haploidentical transplantation in children with hematological malignancies were analyzed. 148 TCD transplants were included. 78 patients were diagnosed of ALL and 70 patients of AML. 22 out of 148 patients developed GF. MVA showed that patient9 years (HR: 5.0; 95% CI: 1.1-23.0

© 2021 the Author(s)., Inherited bone marrow failure syndromes (IBMFSs) are a group of congenital rare diseases characterized by bone marrow failure, congenital anomalies, high genetic heterogeneity, and predisposition to cancer. Appropriate treatment and cancer surveillance ideally depend on the identification of the mutated gene. A next-generation sequencing (NGS) panel of genes could be 1 initial genetic screening test to be carried out in a comprehensive study of IBMFSs, allowing molecular detection in affected patients. We designed 2 NGS panels of IBMFS genes: version 1 included 129 genes and version 2 involved 145 genes. The cohort included a total of 204 patients with suspected IBMFSs without molecular diagnosis. Capture-based targeted sequencing covered > 99% of the target regions of 145 genes, with more than 20 independent reads. No differences were seen between the 2 versions of the panel. The NGS tool allowed a total of 91 patients to be diagnosed, with an overall molecular diagnostic rate of 44%. Among the 167 patients with classified IBMFSs, 81 patients (48%) were diagnosed. Unclassified IBMFSs involved a total of 37 patients, of whom 9 patients (24%) were diagnosed. The preexisting diagnosis of 6 clinically classified patients (6%) was amended, implying a change of therapy for some of them. Our NGS IBMFS gene panel assay is a useful tool in the molecular diagnosis of IBMFSs and a reasonable option as the first tier genetic test in these disorders.

Allogeneic hematopoietic cell transplantation (HCT) is the only curative option for bone marrow failure or hematopoietic malignant diseases for Fanconi anemia (FA) patients. Although results have improved over the last decades, reaching more than 90% survival when a human leukocyte antigen (HLA)-identical donor is available, alternative HCT donors are still less reported. We compared HCT outcomes using HLA-mismatched unrelated donors (MMUD; n = 123) or haplo-identical donors (HDs), either using only in vivo T cell depletion (n = 33) or T cells depleted in vivo with some type of graft manipulation ex vivo (n = 59) performed for FA between 2000 and 2018. Overall survival (OS) by 24 months was 62% (53–71%) for MMUD, versus 80% (66–95%) for HDs with only in vivo T cell depletion and 60% (47–73%) for HDs with in vivo and ex vivo T cell depletion (p =.22). Event-free survival (EFS) was better for HD-transplanted FA patients with only in vivo T cell depletion 86% (73–99%) than for those transplanted from a MMUD 58% (48–68%) or those with graft manipulation 56% (42–69%) (p =.046). Grade II-IV acute graft-versus-host disease (GVHD) was 41% (MMUD) versus 40% (HDs with no graft manipulation) versus 17% (HDs with T cell depleted graft), (p =.005). No differences were found for the other transplant related outcomes. These data suggest that HDs might be considered as an alternative option for FA patients with better EFS using unmanipulated grafts. © 2021 Wiley Periodicals LLC., The authors are particularly thankful to all centers from the Severe Aplastic Anemia Working Party and the Pediatric Diseases Working Party of the European Society for Blood and Marrow Transplantation, who kindly agreed to participate in this study (see Appendix S1). We would also like to thank Anne E. Lippinkhof, Study Coordinator, Severe Aplastic Anemia Working Party for her invaluable help.

Difficulties in the collection of hematopoietic stem and progenitor cells (HSPCs) from Fanconi anemia (FA) patients have limited the gene therapy in this disease. We have investigated (ClinicalTrials.gov, NCT02931071) the safety and efficacy of filgrastim and plerixafor for mobilization of HSPCs and collection by leukapheresis in FA patients. Nine of eleven enrolled patients mobilized beyond the threshold level of 5 CD34+ cells/μL required to initiate apheresis. A median of 21.8 CD34+ cells/μL was reached at the peak of mobilization. Significantly, the oldest patients (15 and 16 years old) were the only ones who did not reach that threshold. A median of 4.27 million CD34+ cells/kg was collected in 2 or 3 aphereses. These numbers were markedly decreased to 1.1 million CD34+ cells/kg after immunoselection, probably because of weak expression of the CD34 antigen. However, these numbers were sufficient to facilitate the engraftment of corrected HSPCs in non-conditioned patients. No procedure-associated serious adverse events were observed. Mobilization of CD34+ cells correlated with younger age, higher leukocyte counts and hemoglobin values, lower mean corpuscular volume, and higher proportion of CD34+ cells in bone marrow (BM). All these values offer crucial information for the enrollment of FA patients for gene therapy protocols., Graphical abstract, Mobilization and collection of HSPCs from FA patients with sufficient HSPC reserve is a safe and efficient procedure, incorporating filgrastim and plerixafor as mobilization agents. Adequate HSPC mobilization correlates with younger age, higher leukocyte counts and hemoglobin values, lower mean corpuscular volume, and higher BM CD34+ cell numbers.

In order to propose risk-adapted mobilization algorithms, several authors have tried to look for predictive factors of the CD34We report the results of 46 mobilizations and apheresis procedures performed in our center with unfavorable D/R ratio. Mobilization was attempted by the standard regime of G-CSF (10 mcg/kg/24 hours) in 28 cases (60.9%), with high dose G-CSF (10 mcg/kg/12 hours) in 9 cases (19.6%), and with plerixafor and G-CSF single dose regime in 9 cases (19.6%).CD34Tailoring the mobilization regime we can reach the target cell dose, even in those cases with the worst D/R ratio.

Background: Fanconi anemia (FA) is a disorder of defective deoxyribonucleic acid (DNA) repair, progressive bone marrow failure (BMF), and a predisposition to hematologic malignancies and solid tumors. Approximately 60 to 70% of all cases result from a mutation in the Fanconi Anemia Complementation Group A (FANCA) gene (FA-A). 80% of FA patients experience BMF within the first decade of life. Allogeneic hematopoietic stem cell transplant (alloHSCT) is potentially curative for BMF; however, its efficacy is limited by human leukocyte antigen (HLA)-matched sibling donor availability and transplant-related toxicities. Lentiviral mediated gene therapy utilizing autologous FA-A CD34+ enriched hematopoietic stem and progenitor cells (HSPCs) confers a proliferative advantage to gene-corrected HSPCs as demonstrated in preclinical studies and the FANCOLEN-I clinical trial conducted in Madrid, Spain. We report results from ongoing RP-L102 studies using "Process B" manufacturing optimizations including transduction enhancers, commercial grade vector, and modified cell processing. Methods: Patients (pts) with a FANCA gene mutation, age ≥1 year with no HLA-matched sibling donor and at least 30 CD34+ cells/µL in bone marrow (BM) are eligible. Peripheral blood (PB) mononuclear cells are collected via leukapheresis on 2 consecutive days after mobilization with granulocyte-colony stimulating factor (G-CSF) and plerixafor. CD34+ HSPCs are enriched, transduced with a lentiviral vector encoding for the FANCA gene (PGK-FANCA-WPRE) and infused without cryopreservation or conditioning. Patients are followed for 3 years post-infusion for safety assessments (replication competent lentivirus [RCL], insertion site analysis [ISA]) and to ascertain evidence of efficacy (increasing PB and BM vector copy number [VCN] and mitomycin-C [MMC] resistance in BM colony forming units [CFUs]), along with stabilization/correction of cytopenias. Results: As of March 2021, 9 pts (aged 2 to 6 years) have received RP-L102. Evidence of engraftment has been identified in 6 pts with ≥6 months of follow up as indicated by PB VCN. 2 of 3 pts with follow up of ≥12 months have shown increased MMC resistance in BM CFUs. 1 pt developed BMF requiring alloHSCT after influenza B infection. 1 pt had a serious Grade 2 transient RP-L102 infusion-related reaction. Updated safety and efficacy data for pts with ≥12 months of follow-up will be presented. Conclusions: RP-L102's safety profile remains favorable. Increasing evidence of engraftment has been confirmed in 6 subjects as demonstrated by PB VCN; without conditioning, 12+ months of follow up is likely required to observe the proliferative advantage of transduced HSPCs. Disclosures Czechowicz: Editas Medicine: Current equity holder in publicly-traded company; Rocket Pharmaceuticals, Inc.: Research Funding; Global Blood Therapeutics: Current equity holder in publicly-traded company; Stemodontics: Consultancy, Current equity holder in publicly-traded company; GV: Consultancy, Current equity holder in publicly-traded company; Spotlight Therapeutics: Consultancy, Current equity holder in publicly-traded company; Beam Therapeutics: Consultancy, Current equity holder in publicly-traded company; Magenta Therapeutics: Current equity holder in publicly-traded company, Other: Intellectual property rights; Decibel Therapeutics: Current equity holder in publicly-traded company; Forty Seven Inc.: Divested equity in a private or publicly-traded company in the past 24 months; Gilead Sciences: Other: intellectual property rights; Jasper Therapeutics: Other: Intellectual property rights. Sevilla: Rocket Pharmaceuticals, Inc.: Consultancy, Other: J.Sevilla is an inventor on patents on lentiviral vectors filed by CIEMAT, CIBERER and Fundación Jiménez Díaz, and may be entitled to receive financial benefits from the licensing of such patents., Patents & Royalties: J. Sevilla is a consultant and has licensed medical products from Rocket Pharmaceuticals, Inc. ; Amgen: Consultancy; Novartis: Consultancy; Miltenyi: Consultancy; SOBI: Consultancy. Booth: GSK: Honoraria; Orchard Therapeutics: Consultancy, Honoraria; SOBI: Consultancy, Honoraria; Takeda: Honoraria; Rocket Pharmaceuticals, Inc.: Consultancy. Río: Rocket Pharmaceuticals: Current equity holder in publicly-traded company, Other: Paula Rio has licensed medicinal products and receives research funding and equity from Rocket Pharmaceuticals, Inc., Research Funding. Navarro: Rocket Pharmaceuticals, Inc.: Current equity holder in publicly-traded company, Other: Dr. Navarro has licensed medicinal products and receives research funding and equity from Rocket Pharmaceuticals, Inc., Patents & Royalties, Research Funding. Beard: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Law: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Choi: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Zeini: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Nicoletti: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Wagner: Magenta Therapeutics: Consultancy; Rocket Pharmaceuticals, Inc.: Consultancy, Current equity holder in publicly-traded company; Vertex Pharmaceuticals: Consultancy; ASC Therapeutics: Consultancy; Bluebird Bio: Consultancy. Rao: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Thrasher: Orchard Therapeutics: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; 4Bio Capital: Consultancy, Membership on an entity's Board of Directors or advisory committees; Generation bio: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Rocket Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees. Schwartz: Rocket Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Bueren: Rocket Pharmaceuticals, Inc.: Consultancy, Other: J.Bueren is an inventor on patents on lentiviral vectors filed by CIEMAT, CIBERER and Fundación Jiménez Díaz, may be entitled to receive financial benefits from the licensing of such patents and receives funding for research., Patents & Royalties, Research Funding.

Background In hematopoietic transplantation, graft T lymphocytes play a determining role in promoting hematopoiesis, transferring immunity to pathogens and acting as mediators of the graft-versus-leukemia effect (GVL). However, they are also responsible for graft-versus-host disease (GVHD), the main cause of post-transplant morbidity and mortality. Depletion of CD45 RA lymphocytes, by eliminating naive T lymphocytes from inoculum, aims to conserve GVL without GVHD. Methods Since April 2016, 20 patients (12 boys and 8 girls), with a median age of 8 years, have undergone an allogeneic hematopoietic transplant from an HLA identical donor with CD45 RA depletion. Indication for transplant was: acute lymphoblastic leukemia (n=7), acute myeloblastic leukemia (n=7) and myelodysplasia (n=6). Donor was familiar in 7 cases and unrelated in 13. Conditioning regimen consisted on fludarabine, busulfan and thiotepa. Median of CD34 + cells infused was 6.82 × 106/ Kg. On day 0, +15 and +30 a programmed infusion of 1 × 106 / Kg lymphocytes CD45RA- was performed. Results All patients grafted with a median neutrophil (> 0.5 × 109/ L) and platelet (> 20 × 109/ L) engraftment time of 15 and 10 days, respectively. Only one patient has developed acute GVHD grade I and another patient has developed moderate chronic GVHD. Immune reconstitution was early and rapid in all lymphocyte subsets (see Figure 1). Four patient have relapsed so far. There was no case of toxic mortality. Overall survival was 77 ± 10% with a median follow-up of 1 year (2 months-2 years). At present, 17 patients are alive and doing well (Figure 2). Conclusions Allogeneic transplantation with CD45 lymphocytes RA depletion resulted on encouraging results, with a very low incidence of acute and chronic GVHD, but preserving the GVL effect by infusing CD45 RA- donor lymphocytes. Conflict of interest Miguel Angel Diaz, Marta Gonzalez-Vicent, Blanca Molina, Elena Sebastian, Josune Zubicaray, Julian Sevilla: Nothing to disclose. Keywords CD45RA depletion, Allogeneic transplant, Children