Thiamine-responsive megaloblastic anemia (TRMA) is a rare autosomal recessive disorder caused by biallelic loss of function variants in the SLC19A2 gene. It typically presents with a triad of megaloblastic anemia, diabetes mellitus, and sensorineural deafness. In this work, we analyzed ten children with suspected TRMA: nine exhibited the full triad and one, a younger sibling of a patient with full triad, did not develop hearing loss by the age of 18 months. All patients became transfusion-independent on high-dose thiamine therapy. Whole-genome sequencing identified homozygosity for the canonical splice variant SLC19A2 c.1223+1G>A in eight patients. One patient was homozygous for a known SLC19A2 c.196G>T variant, and the other was compound heterozygous for two novel variants, c.120C>G and c.584T>C. All patients with the SLC19A2 c.1223+1G>A variant were ethnic Ingush. In the reference Ingush cohort, 9/328 unrelated adults were c.1223+1G>A carriers (heterozygous carrier frequency 2.7%; carrier frequency ≈ 1/36), and shared a 2.3 Mb ATP1B1-FMO2 haplotype on chromosome 1, demonstrating a strong founder effect. These findings identify Ingushetia as a new TRMA-endemic region and support targeted SLC19A2 screening and early thiamine therapy in patients with macrocytic anemia and diabetes of unclear origin in this population.

Hematopoietic stem cell transplantation (HSCT) is a curative option for children with high-risk acute lymphoblastic leukemia (ALL). This retrospective single-center study analyzed 236 pediatric ALL patients in complete remission who underwent allogeneic HSCT using ex-vivo T cell depletion between 2012 and 2021. The majority received haploidentical grafts (n = 202), while the remainder received matched unrelated donor (MUD) grafts (n = 34). At four years, event-free survival (EFS) and overall survival (OS) were 57

Background aims: Hematopoietic stem cell transplantation (HSCT) from matched unrelated donor (MUD) is a curative option for severe aplastic anemia (SAA) patients, refractory to horse anti-thymocyte globulin (ATG) and cyclosporin A (CsA) mmunosuppression. Although the results of MUD HSCT in SAA have improved significantly, graft-versus host disease (GVHD) remains a serious problem, associated with significant morbidity and mortality. We investigated the role of alpha/beta T cell depletion of the graft as a way to improve the results of MUD HSCT in SAA. Methods: Forty-seven patients with SAA were treated since September 2012 till February 2022. Median age at HSCT was 12.4 (3-22.7) years, 26 males/21 females. All patients were either refractory or relapsed (35:12) after combined immune suppression therapy, 5 pts had concurrent severe hemolytic paroxysmal nocturnal hemoglobinuria (PNH). The median time from diagnosis to transplant was 1.2 years (0.5-11.8 years). Preparative regimen included cyclophosphamide 100 mg/kg, fludarabine 150 mg/kg, ATGAM at 100 mg/kg (27pts) or thymoglobulin 5 mg/kg (15 pts) and 6 Gy thoraco-abdominal irradiation. Thiotepa at 10 mg/kg and rituximab at 200 mg/m2 were used in a proportion of cases. Patients with PNH (n = 5) received eculizumab 600 mg once every 7 days from-7 to +14 days. Post-transplant GVHD prophylaxis included tacrolimus till day 180. Peripheral blood stem cell (PBSC) grafts were depleted of T cell receptor (TCR) alpha/beta cells and CD19 cells with CliniMACS device, as recommended by the manufacturer. Patients received a median of 9.2 (2.7-18.30) x106 CD34 per kg, 21.8 (0.85-316)x103 a$ T cells per kg. Results: Forty-six patients (cumulative incidence (CI) 0.96 (95% 0.9-1)) engrafted with a median of 14 (7-24) days for white blood cells (WBC) and 12 (9-18) days for platelets. In 8 patients after MUD transplantation secondary graft failure (rejection) developed, cumulative incidence was 0.15 (95% 0.08-0.3), three of them was successfully retransplanted. CI of acute graft-versus host disease (aGVHD) grade II-IV was 0.15 (95% 0.08-0.29). No cases of grade III-IV aGVHD were registered. CI of chronic graft versus host disease (cGVHD) was 0.11(95% 0.05-0.25). All were mild and off-IST at last follow-up. A median follow-up is 9 years. Ten patients died. At a median follow-up of 9 years, the overall survival was 79% (67-90). Failure-free survival was 72% (60-85) and the GRFS was 72% (60-85). Conclusions: TCR alpha/beta depletion is a robust platform for allogeneic HSCT from MUD in severe aplastic anemia. Results should be further improved by additional measures to control viral infections and prevent rejection.

We conducted a prospective observational registry study at the Dmitry Rogachev National Medical Research Center aiming to evaluate acute myeloid leukemia (AML) treatment and its outcomes in children in regional oncology/hematology centers of Russia as well as to report the results. The study was approved by the Independent Ethics Committee and the Scientific Council of the The Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation. We enrolled a total of 380 patients (205 boys and 175 girls) with newly diagnosed AML with the median age of 6.6 years (52 days to 18 years) and the median white blood cell count at disease onset equaling 17.7 (0–540) × 109/L. Fifty-two patients (13.6%) had WBC count greater than 100 × 109/L (hyperleukocytosis), 55 patients (14%) presented with neuroleukemia, and 60 (16%) had extramedullary lesions. The enrolled patients were stratified into a standard risk (92 patients), intermediate risk (99) or high risk (189) group. The first clinical and hematological remission (CR1) was achieved in 324 patients (85%), with early mortality rate reaching 8.4%. The median follow-up of the survivors was 8.3 years (1.5 months to 11.5 years). The 5-year overall survival (OS) in the entire cohort was 0.60 ± 0.025, the 5-year event-free survival (EFS) – 0.42 ± 0.025, and the cumulative incidence of relapse (CIR) – 0.37 ± 0.027. Initial extramedullary lesions (OS 0.47 ± 0.06 and EFS 0,37 ± 0.06) and hyperleukocytosis (OS 0.47 ± 0.07 and EFS 0.25 ± 0.06) led to a poorer prognosis in the AML patients, but CIR was not affected by these factors. The lowest OS rate was observed in the patients with monosomy 7 and with t(10;11)(p11-15;q21)/PICALM::MLLT10, totaling 0.2 ± 0.2 and 0.14 ± 0.1, respectively. Hematologic stem cell transplantation (HSCT) performed in CR1 significantly improved OS (0.84 ± 0.05), EFS (0.77 ± 0.06) and CIR (0.18 ± 0.05) in the high-risk patients. The majority of allogeneic HSCTs were performed using cells from haploidentical (51%), unrelated (25%) and genoidentical donors (18%). In the 50 patients treated with HSCT while in active disease, the OS was 50%. Out of 189 high-risk patients, only 67 (35%) underwent HSCT in CR1. The OS and EFS of the patients from regions were 0.51 ± 0.033 and 0.38 ± 0.032, respectively. The CIR was 0.36 ± 0,04. Relapses were reported in 37% of the patients who had achieved СR1. A total of 157 (41%) patients died during the study, out of which 112 patients had been treated at regional hospitals. The OS in the AML pediatric patients in Russia was 60%. The main treatment failures were toxic deaths (16%) and relapses (37%). In 2018, healthcare professionals of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology developed the AMLMRD-2018 protocol that could also be implemented in regional clinics, aiming to reduce toxic (infectious) death rates and thus increase the OS by at least 10% as well as to ensure HSCT accessibility for all high-risk patients.

In children without Down syndrome who have acute megakaryoblastic leukemia (AMKL), inv(16)(p13q24)/CBFA2T3::GLIS2 is the most frequent genetic aberration. Pediatric CBFA2T3::GLIS2-positive AMKL is strongly associated with a poor prognosis and a high cumulative incidence of relapse. One of the key laboratory signs of CBFA2T3::GLIS2-positive AMKL is the RAM immunophenotype, which looks very similar to that of solid-tumor bone marrow (BM) infiltration. For this reason, in cases of isolated extramedullary involvement of CBFA2T3::GLIS2-positive AMKL, excluding solid tumors may be challenging. We report a case of a girl with isolated extramedullary CBFA2T3::GLIS2-positive AMKL relapse, which was misdiagnosed as secondary Ewing sarcoma. The morphological differential diagnosis between Ewing sarcoma and AMKL presented significant challenges owing to their overlapping histological features (small, round blue-cell morphology and similar growth patterns). The tumor cells’ immunophenotype completely mirrored that at the initial diagnosis of AMKL. Additional cytogenetic and molecular studies confirmed the presence of the CBFA2T3::GLIS2 fusion, but no Ewing sarcoma-specific EWSR1, FUS and CIC fusion transcripts were found. Thus, extramedullary CBFA2T3::GLIS2-positive AMKL relapse was confirmed. The presented case demonstrates the difficulties in differential diagnosis between AMKL relapse and the development of a secondary tumor.

Background HLA-haploidentical relatives are increasingly used to transplant children with acute leukemia (AL) requiring an allograft. The 2 most widely employed platforms to overcome the bidirectional alloreactivity are in vitro a/b T- and CD19-cell depletion (a/b-TCD) and in vivo administration of post-transplant cyclophosphamide (PTCY). While a recent study compared the outcomes of children with inborn errors of immunity transplanted using either of the 2 platforms (Lum et al. Blood 2024), no large comparative analysis in children with AL has been conducted so far. This study includes pediatric patients with acute lymphoblastic leukemia (ALL) or acute myeloid leukemia (AML) transplanted from 2010 to 2022 and reported to the EBMT registry with either of the 2 approaches. Patients and methods The whole population included 1071 children with either AML (n=375) or ALL (n=696); among them, 541 received an in vitro a/b T- and CD19-cell depleted transplant, while 530 were treated with the PTCY approach. In order to evaluate the impact between the two groups, a 1:1 pair-match analysis was performed. Disease (AML or ALL) and disease status (complete remission, CR, or non-CR) were considered as exact matching, disease risk index (DRI), patient age, patient sex, donor sex, Lansky score and use of total body irradiation as part of the conditioning regimen were used for propensity score matching with a caliper set at 0.2. The different impact of the two groups were estimated using a Cox model including a cluster effect on matching subgroups. Results The pair-match cohort included 506 patients, 253 transplanted from each of the 2 HLA-haplo platform [median year of HSCT 2019 (interquartile range, IQR, 2016-2020)]. Median age at HSCT was 8.4 years (IQR 4.7-13); 278 children had ALL and 228 AML. As expected by the differences in the platform approaches, a/b-TCD patients received a significantly higher number of CD34+ positive cells/kg (but not different total nucleated cells), more serotherapy before transplant, less CD3+ cells/kg and the source of stem cells was more frequently peripheral blood, as compared to PTCY patients. Additionally, donor age was slightly higher for a/b-TCD patients (median 38.2 versus 36 for PTCY patients, p<0.001); all other transplant variables did not differ between the 2 groups. With a median follow-up of 4.4 years (95% CI 4.1-4.8), the 4-yr non-relapse mortality (NRM) and relapse incidence of the pair-match cohort were 13.4% and 37.1%, respectively, while cumulative incidence of grade III-IV acute graft-versus-host disease (GVHD) and extensive chronic GVHD were 10.1% and 14.6%, respectively. In the PTCY group, the 100-day cumulative incidence of grade III-IV acute GVHD and extensive chronic GVHD were 13.1% and 19.5%, respectively, while in the a/b-TCD group they were 7.2% and 10%, respectively. More patients in the PTCY group died of GVHD and infections (9 and 19, respectively) as compared to those given an a/b-TCD HSCT (3 and 10, respectively). The 4-yr overall survival (OS), leukemia-free survival (LFS) and GVHD/relapse-free survival (GRFS) of the whole cohort were 55.7%, 49.6% and 38.8%, respectively. In the a/b-TCD group, the 4-yr OS and LFS were 58.5% and 54.4%, respectively, while in the PTCY group they were 52.8% and 44.8%, respectively. The GRFS in the 2 groups were 46.7% for a/b-TCD and 30.8% for PTCY, respectively. According to the Cox model, in comparison to a/b T- and CD19-cell depleted recipients (reference), patients of the PTCY group had worse LFS (hazard ratio, HR, 1.31, 95% CI 1.02-1.67, p=0.03) and GRFS (HR 1.53, 95% CI 1.23-1.89, p<0.001) and higher NRM (HR 1.87, 95% CI 1.15-3.05, p=0.02), grade III-IV acute GVHD (HR 1.81, 95% CI 1.09-3.02, p=0.02), chronic GVHD (HR 2.35, 95% CI 1.41-3.94, p=0.001) and extensive chronic GVHD (HR 2.18, 95% CI 1.30-3.67, p=0.003). Conclusions These data indicate that both HLA-haploidentical transplant platforms are a suitable option for children with AL needing HSCT and lacking a suitable HLA-matched donor or with an urgent transplant indication. However, the a/b-TCD platform is associated with less severe acute and chronic GVHD, lower risk of NRM and better LFS and GRFS as compared to PTCY. The latter strategy for preventing bidirectional alloreactivity is easier to be performed and potentially more accessible, as compared to the a/b-TCD platform that requires a dedicated team with significant expertise in graft manipulation.

In the past decades, significant advancements have been made in the treatment of children with acute myeloid leukemia (AML) with the introduction of more effective treatment regimens, extended indications for hematopoietic stem cell transplantation as well as better supportive therapy and prophylaxis of infectious complications. Nevertheless, an improvement in treatment outcomes is still an important goal. One of the key ways to enhance treatment effectiveness is risk stratification of AML patients based on molecular and genetic characteristics of the disease. A multicenter treatment protocol (the AML-MRD-2018 protocol) was developed at the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation. Our study includes 525 patients from 54 Russian hospitals who underwent treatment from November 2018 to December 2023. A total of 205 patients with a median age of 8.9 years (1 month – 17.6 years) were re-stratified to the intermediate-risk group. The 3-year overall and event-free survival for this group was 77% and 47%, respectively. The patients with biallelic CEBPA (dCEBPA) mutations had the most favorable prognosis. In the intermediate-risk group, early death before remission occurred in 6% of the patients; 8% of the patients died in first remission. Death of progressive disease occurred in 32% of all the deceased patients. The study was approved by the Independent Ethics Committee and the Scientific Council of the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of Ministry of Healthcare of the Russian Federation.

Wiskott-Aldrich syndrome (WAS) is a life-threatening inborn error of immunity associated with bleeding risk due to profound thrombocytopenia. We previously demonstrated that romiplostim is effective for thrombocytopenia treatment in 60% of WAS patients. In this prospective trial, 28 WAS patients (aged 0-17 years) were treated with thrombopoietin receptor agonists (TPO-RAs) to evaluate the comparative efficacy and safety of romiplostim versus eltrombopag and to assess the benefit of switching these molecules in individual subjects. We demonstrate that both drugs are effective, with the probability of achieving an overall platelet response (complete response-platelet count of 100 × 109/L or more and partial response-platelet count increase of 30 × 109/L or higher above baseline) of 73% for romiplostim and 43% for eltrombopag. Switching to an alternative TPO-RA allowed the achievement of a complete platelet response in 33% of patients after switching to eltrombopag and in 43% after romiplostim initiation. The cumulative efficacy of TPO-RAs, taking into account alternative therapy, was 87%. There was a grade 2 adverse event (AE) and a severe grade 4 AE related to eltrombopag-reversible acute liver failure associated with metabolic acidosis and encephalopathy. TPO-RAs proved to be an effective treatment for WAS patients waiting for stem cell transplantation or opting for a conservative treatment.

Primary hemophagocytic lymphohistiocytosis (pHLH) is a group of genetically determined disorders characterized by severe and fulminant systemic inflammation, cytopenia, and multiple organ involvement. A dexamethasone-and-etoposide-based HLH-2004 protocol is widely used to treat pHLH, yet often fails to produce the disease control required for the next treatment step: hematopoietic stem cell transplantation (HSCT). We report on the use of the interferon gamma inhibitor emapalumab in seven children aged 6-39 months with pHLH. Three patients received emapalumab at an average starting dose of 1.7 mg/kg and had no active HLH by median day 28. Four patients received emapalumab at an average starting dose of 7.2 mg/kg and had no active HLH by median day 14 (P = 0,0015). We suggest that the higher starting dose of emapalumab, as well as its combination with Janus kinase inhibitors, might increase the remission rate in pHLH and the success of subsequent HSCT.

BACKGROUND AIMS:Hematopoietic stem cell transplantation (HSCT) from matched unrelated donor (MUD) is a curative option for severe aplastic anemia (SAA) patients, refractory to horse anti-thymocyte globulin (ATG) and cyclosporin A (CsA) mmunosuppression. Although the results of MUD HSCT in SAA have improved significantly, graft-versus host disease (GVHD) remains a serious problem, associated with significant morbidity and mortality. We investigated the role of alpha/beta T cell depletion of the graft as a way to improve the results of MUD HSCT in SAA. METHODS:Forty-seven patients with SAA were treated since September 2012 till February 2022. Median age at HSCT was 12.4 (3-22.7) years, 26 males/21 females. All patients were either refractory or relapsed (35:12) after combined immune suppression therapy, 5 pts had concurrent severe hemolytic paroxysmal nocturnal hemoglobinuria (PNH). The median time from diagnosis to transplant was 1.2 years (0.5-11.8 years). Preparative regimen included cyclophosphamide 100 mg/kg, fludarabine 150 mg/kg, ATGAM at 100 mg/kg (27pts) or thymoglobulin 5 mg/kg (15 pts) and 6 Gy thoraco-abdominal irradiation. Thiotepa at 10 mg/kg and rituximab at 200 mg/m2 were used in a proportion of cases. Patients with PNH (n = 5) received eculizumab 600 mg once every 7 days from -7 to +14 days. Post-transplant GVHD prophylaxis included tacrolimus till day 180. Peripheral blood stem cell (PBSC) grafts were depleted of T cell receptor (TCR) alpha/beta cells and CD19 cells with CliniMACS device, as recommended by the manufacturer. Patients received a median of 9.2 (2.7-18.30) х106 CD34 per kg, 21.8 (0.85-316)x103 αβ T cells per kg. RESULTS:Forty-six patients (cumulative incidence (CI) 0.96 (95% 0.9-1)) engrafted with a median of 14 (7-24) days for white blood cells (WBC) and 12 (9-18) days for platelets. In 8 patients after MUD transplantation secondary graft failure (rejection) developed, cumulative incidence was 0.15 (95% 0.08-0.3), three of them was successfully retransplanted. CI of acute graft-versus host disease (aGVHD) grade II-IV was 0.15 (95% 0.08-0.29). No cases of grade III-IV aGVHD were registered. CI of chronic graft versus host disease (cGVHD) was 0.11 (95% 0.05-0.25). All were mild and off-IST at last follow-up. A median follow-up is 9 years. Ten patients died. At a median follow-up of 9 years, the overall survival was 79% (67-90). Failure-free survival was 72% (60-85) and the GRFS was 72% (60-85). CONCLUSIONS:TCR alpha/beta depletion is a robust platform for allogeneic HSCT from MUD in severe aplastic anemia. Results should be further improved by additional measures to control viral infections and prevent rejection.

Introduction Dyskeratosis congenita (DKC) is a rare telomere disorder causing multi-organ dysfunction and bone marrow failure, with allogeneic hematopoietic cell transplantation (HCT) being the only curative option for hematologic complications. We previously reported 3- and 5-years overall survival (OS) rates of 66% and 59% in patients (pts) transplanted before 2016 (Fioredda et al., 2018). This study assesses outcomes in pts transplanted between 2016 and 2023 (new cohort) and compares long-term results with those of the pre-2016 cohort (old cohort). Methods This retrospective study was conducted by the Severe Aplastic Anemia Working Party (SAAWP) of the EBMT. Data were extracted from the EBMT registry, identifying pts diagnosed with DKC who underwent HCT. The following outcomes were analyzed in the new cohort: engraftment, graft failure (GF), acute and chronic graft versus host disease (GVHD), OS, event-free survival (EFS, defined as the absence of primary/secondary GF, relapse, second transplant, or death) and GVHD/relapse-free survival (GRFS; defined as survival without grade III–IV acute GVHD, extensive chronic GVHD, GF or lack of engraftment, relapse, or death). Causes of death were specifically investigated in both cohorts. Descriptive statistics were used for data analysis. Results Eighty-five DKC pts (63.5% males) underwent HCT between 2016 and 2023 in 55 EBMT centers. Median age at HCT was 11.7 (IQR, 5.9-21) years. Median time from diagnosis to HCT was 17.1 (7.6-38) months. Almost all pts (71.6%) had HCT- comorbidity index risk of 0 at HCT. Median follow-up was 1.7 (1.1-2.1) years. Pts were transplanted either from an HLA-matched sibling (17.6%), matched related donor (2.4%), mismatched related donor (14.1%), matched unrelated donor (36.5%), and mismatched-unrelated donor (18.8%). Number of mismatches was unknown in 10.6% of unrelated donor transplants. Graft sources included bone marrow (BM) in 51.8%, peripheral blood (PB) in 40%, cord blood in 5.9%, combination of BM and PB in 2.4%. Fludarabine-Cyclophosphamide (Flu-Cy) was the most used conditioning regimen (70.4%). GVHD prophylaxis was based on serotherapy (anti-thymocyte globulin 44.2%, alemtuzumab 41.6%), calcineurin inhibitors (5.2%), and post-transplant Cy (9.1%). HCT characteristics were not significantly different between the old and the new cohort, except for the time (in months) from diagnosis to transplant [22.1 (8.5–70.7) vs. 17.1 (7.6–38), p = 0.007], GVHD prophylaxis (increased use of alemtuzumab in the new cohort, p = 0.048), and conditioning regimen (greater use of Flu-based regimens in the new cohort, p = 0.002). Neutrophil recovery by day 28 and day 42 occurred in 67% and 82% of pts, respectively, with a median of 19 (95% CI 18-24) days post HCT, whereas platelet recovery by day 60 was achieved in 66% of pts, with a median of 26 (95% CI 21-39) days post HCT. Day 100 cumulative incidence of grade II-IV acute GVHD was 15%, whereas chronic GVHD at 1 and 2 years were 16% and 25%, respectively. Two-years GRFS was 46%; primary (at 42 days) and secondary (at 2 years) GF were 4% and 8%, respectively. One and 2-years EFS were 62% and 55%; 1- and 2-years OS were 74% and 68%, respectively. These outcomes were in line with those of the old cohort whose 5- and 10- years OS further declined to 59% and 42%, respectively. Moreover, early (0-2 years) mortality was mostly due HCT related causes in both cohorts (infections 58% and 53%, GVHD 5% and 11%, in old and new cohort, respectively). Late (3-5 years) mortality was similarly distributed in both cohorts between HCT (infections 33% and GVHD 25% in the old and new cohort, respectively) and DKC-related causes (organ dysfunction in both groups).In contrast, the very late (>5 years) mortality, observed (so far) only in the old cohort, was almost exclusively due to DKC-related causes (50% secondary malignancies, 40% lung/organ failure). Conclusions Despite general advances, post-HCT survival for DKC still has limited if any improvement, with persistent late and very late mortality driven by organ failure and malignancies. Future efforts should focus on identifying factors influencing long-term outcomes to mitigate non-hematological complications.

Introduction Autologous chimeric antigen receptor (CAR) T cells induce high rate of deep remissions among children with relapsed/refractory B-precursor acute lymphoblastic leukemia (R/R B-ALL). In a significant proportion of cases cure is achieved only with HSCT as post-CAR-T consolidation. Seeking to combine the cytoreductive and curative power of HSCT with the antigen-specific activity of CAR-T we devised an approach with simultaneous infusion of hematopoietic stem cell graft and CAR-T cells, derived from the same donor. Two graft-versus-host disease prevention platforms were used: ex-vivo T cell depletion and post-transplant cyclophosphamide. We report here pooled analysis of prospective trial patients and compassionate use program. Patients and methods A total of 39 pts with R/R BCP-ALL (n=35), B-NHL/leukemia (n=3) and MPAL (n=1) (16 female, 23 male, median age 9,6 y) were enrolled. All patients had disease relapse after multiple lines of treatment including previous HSCT(n=13), blinatumomab (n=22), inotuzumab (n=2), blinatumomab+inotuzumab (n=6) and CAR-T cell infusion(n=12). The disease burden was above 5% for bone marrow blasts among 16 patients, with a median blast count of 50% (6 – 90%). MRD was detectable by flow cytometry among 13 patients with a median leukemia population of 0.15% (0.002 - 6.9%), and five patients had MRD-negative complete remission. The extramedullary disease was seen among 5 patients. The median proportion of CD19-positive cells in the leukemic population was 100% (0–100%), while the median proportion of CD22-positive cells was 100% (36–100%). Fourteen (36%) pts received treosulfan-based myeloablative preparative regimen and TBI-based regimen was used in 25 (64%) pts. Twenty-six patients received T-cell depleted graft, 25 from haploidentical donors and one from match related. In this subgroup CAR-T products included CD19 CAR- T (n=3), CD19-22 tandem CAR-T (n=20), and cocktail CD19 and CD22 CAR-T (n=2). Thirteen pts were transplanted with T-replete bone marrow with PtCy-based GVHD prophylaxis, 3 from matched sibling and 10 from haploidentical donors. In this subgroup CAR-T cells were infused on day +5 after HSCT and were represented by either by CD19-22 tandem CAR- T (n=1) or by CD19 and CD22 cocktail product (n=12). In the PtCy group GVHD prophylaxis included abatacept, vedolizumab and CsA or baricitinib Results There was no suspected conflict between the graft and CAR-T cells. Primary engraftment was observed in 37 of 39 pts (one pt died before engraftment and one relapsed early), the median time to neutrophil and platelet recovery was 13 and 17 days, respectively, all engrafted patients achieved MRD-negative CR at day +28 after HSCT. The median time to CAR-T cell peak expansion was 14 days. Cytokine release syndrome (CRS) occurred in 22 (56%) patients and only two pts had grade >2 CRS. Also 22 patients had neurologic events (ICANS grade 1, n=14, grade 2, n=6 and grade 3, n=2). Eleven patients had aGvHD, grade 2 (n=9), grade 3(n=1) and grade 4 (n=1), 5 patients had mild chronic GvHD. There were no significant differences in CAR-T toxicity between depletion and PtCy groups. Leukemia relapse was observed in nine children at a median time of 174 days (range, 95-1641 days) after allograft, 2 pts had CD 19 negative relapse. Twenty-four (62%) patients are alive (22 in CR, 2 with disease progression) with a median follow-up of 2,6 years (0,34-5,4), 15 patients died. Eight deaths were due to progressive disease. Six were in CR and one before engraftment. Causes of non-relapse mortality were VOD+pneumonia (n=1), CMV (n=1), Mucormycosis (n=1), septic event (n=3) and COVID19 (n=1). EFS and OS at 2,6 years are 59% (95%CI:42- 76) and 56% (95%CI:39- 72), respectively, without differences between T-cell depletion and ptCy groups. Conclusion Our early experience suggests that allogenic CAR-T cells can be safely infused simultaneously with the hematopoietic stem cell graft both on the platform of T cell depletion and PtCy-based GVHD prophylaxis. The infusions did not compromise engraftment and GvHD control, while specific CAR-T toxicity was mild and manageable. We have documented CAR-T expansion and persistence. Prospective testing of the approach is warranted.