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Opposing acute lymphoblastic leukemia, sparse data about AYAs with acute myeloid leukemia (AML) is available. Overall, 125 AYAs (age 10-35 years) treated during the last two decades were evaluated and compared to 385 older patients. CBF leukemia was more frequent in AYAs (21.6% vs. 8%

Transplant associated thrombotic microangiopathy (TMA) occurs in a significant percentage of patients after allogeneic stem cell transplantation (allo-SCT) and is associated with significant morbidity and mortality. The aim of the present study was to examine the association of serum angiopoetin-2 (Ang2) levels, and the presence of antibodies against Angiotensin II type 1 (AT1R) and Endothelin A Receptor (ETAR) with the outcome of patients with TMA and/or graft-versus-host disease (GVHD) after allo-SCT. Analysis of our data showed that elevated serum Ang2 levels at the time of TMA diagnosis are significantly associated with increased non-relapse mortality and decreased overall survival. To our knowledge this is the first study demonstrating an association between raised Ang2 levels and poor outcomes in patients with TMA. Antibodies against AT1R (AT1R-Abs) and ETAR (ETAR-Abs) were detected in 27% and 23% of the patients, respectively, but there was no association between the presence of autoantibodies and the outcome of patients with TMA. However, a significant finding was the strong positive correlation between the presence of AT1R-Abs with the occurrence of chronic fibrotic GVHD such as scleroderma and cryptogenic organizing pneumonia, raising the possibility of the contribution of autoantibodies in the pathogenesis of fibrotic GVHD manifestations.

Healthcare systems around the globe are still facing the evolving threat of the coronavavirus-19 (COVID-19) pandemic. Hemoglobinopathies include a group of genetic disorders, with the two main entities being thalassemias and sickle cell disease. Due to their immunocompromised status, such patients have been protected as extremely vulnerable to COVID-19 infection. We studied patients with different hemoglobinopathies, consecutively monitored at our center, who were infected with severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) during the second and third waves of the pandemic in Greece (September 2020-April 2021), and associated the outcomes of the infection with the following factors: age, employment, blood type, liver and heart hemosiderosis, splenectomy, concomitant endocrine disorders and transfusion dependency. Among 250 patients monitored at our center, 14 were infected with COVID-19. Nine of them were hospitalized but no one required intensive care unit support and all of them responded to the generally applied treatment plan, despite their comorbidities. Notwithstanding the slightly increased prevalence of COVID-19 in patients with hemoglobinopathies compared to the general population, self-applied measures are still thought to be effective, as our patients got infected through their already sick family members.

Background: Carfilzomib, an irreversible proteasome inhibitor approved for the treatment of relapsed/refractory Multiple Myeloma (MM) has been associated with Thrombotic Microangiopathy (TMA). Several pathogenetic mechanisms of carfilzomib-induced TMA have been proposed; however, recently, there has been a shift of focus on the potential contribution of complement dysregulation. Our aim was to explore whether patients with carfilzomib-induced TMA harbor germline variants of complement-related genes, which have been characterized as risk factors for TMA. Methods: We retrospectively recruited consecutive MM patients with carfilzomib-induced TMA and compared them to MM patients who received ≥4 cycles of carfilzomib and did not develop signs/symptoms of TMA, in a 1:2 ratio. Genomic DNA from peripheral blood was analyzed using next generation sequencing (NGS) with a complement-related gene panel; ADAMTS13 activity and soluble C5b-9 were measured using ELISA. Results: Complement-related variants were more common in patients with carfilzomib-induced TMA compared to non-TMA controls, regardless of patient and treatment characteristics; ADAMTS13 activity and C5b-9 were compatible with the phenotype of complement-related TMA. Conclusions: We confirmed the previous findings that implicated complement-related genes in the pathogenesis of carfilzomib-induced TMA. Most importantly, by incorporating a control group of non-TMA MM patients treated with carfilzomib-based regimens and functional complement assays, we enhanced the credibility of our findings.

Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are essential weapons to control the spread of the coronavirus disease-19 (COVID-19) pandemic and protect immunocompromised patients. With a greater susceptibility to infection, sickle cell disease (SCD) patients are considered as “high risk” patients during the current COVID-19 pandemic. In our study, we try to determine the immune response of adult SCD patients monitored at our center after the first and second dose of the qualified mRNA vaccines available and correlate them to several disease-specific markers, as well as complement activation. The results demonstrate that the levels of neutralizing antibodies (nAbs) against SARS-CoV-2 were adequate for most patients studied after the second dose and there seemed to be a certain association with complement activation. Further studies are critical to determine the durability of this immune response and the potential benefit of a third dose.

Introduction: Immunotherapy with Chimeric Antigen Receptor T cells (CAR-Τ) is a promising innovative treatment for refractory B cell malignancies offering a considerable chance for long-term survival in patients (pts) with an otherwise dismal prognosis. Since January 2020, two anti-CD19 CAR T cell products have been introduced into clinical practice in Greece: a) tisagenlecleucel (Kymriah) for adults with relapsed/refractory diffuse large B-cell Lymphoma (r/r DLBCL) including transformed follicular lymphoma (TFL), as well as for children or young adults with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL), and b) axicabtagene ciloleucel (Yescarta) for adults with r/r DLBCL including TFL and primary mediastinal B-cell lymphoma (PMBCL). The aim of this study was to present the real-world experience of the initial application of CAR T cell therapy in adult pts in Greece, with special focus on early toxicity and disease outcomes. Methods: Data from all consecutive pts were collected from the two transplant centers which were initially accredited for CAR T cell therapies in adult pts: Evangelismos Hospital, Athens and George Papanicolaou Hospital, Thessaloniki. Between November 2019 and July 2021, 51 pts were referred for CAR T cell treatment. In 41 pts lymphocyte collection was performed and product manufacturing was successfully completed in 35; in 2 pts insufficient cell expansion was noted and in 4 manufacturing was terminated due to disease progression and patient death. Results: From January 2020 until July 2021, CAR T cells were infused in 27 pts; 3 pts could not receive the product due to clinical deterioration/death and 5 pts are presently being scheduled for infusion. Of the 27 treated pts, 16 received tisagenlecleucel and 11 axicabtagene ciloleucel. The median age of infused pts was 49 (18-69) years. Diagnosis was DLBCL (n=16), PMBCL (n=3), TFL (n=2), B-ALL (n=6), and the median number of previous lines of treatment was 4 (2-5). Five pts with lymphoma had undergone autologous, and 4 pts with B-ALL allogeneic stem cell transplantation. In total 18/27 pts received bridging therapy, including radiotherapy (n=5), chemoimmunotherapy (n=9), steroids (n=3), and inotuzumab ozogamicin (n=1). The median time from leukapheresis to product delivery and infusion was 35 (15-81) and 59 (35-152) days, respectively. All pts received lymphodepleting therapy before CAR T cell infusion with combination of cyclophosphamide and fludarabine. For patient monitoring, prophylactic therapy and management of toxicity, the EBMT (Yakoub-Agha I, et al. Haematologica 2020) and MD Anderson (Neelapu S, et al. Nat Rev Clin Oncol 2018) guidelines were adopted. Twenty-six pts developed neutropenia (grade II: 2, grade IV: 24) and 20 thrombocytopenia (grade I: 7, grade II: 3, grade III: 1, grade IV: 9), with a median duration of 11 (4-132) and 20 (3-150) days, respectively. Cytokine release syndrome (CRS) and neurotoxicity (ICANS) were noted in 21 (grade I: 8, grade II: 7, grade III: 6) and 5 (grade I: 3, grade III: 2) pts, respectively. Tocilizumab was administered for CRS according to guidelines, and steroids were additionally required for CRS and/or ICANS in 12 pts. In 2 pts, persistent ICANS necessitated further treatment with anakinra (n=2), siltuximab (n=1), and cyclophosphamide (n=1). Hypogammaglobulinemia was encountered in 14/27 pts. With a median follow-up of 7.3 (1-17) months, overall response rate was 48% with 12 (45%) pts being currently in complete remission (CR). No treatment related mortality was observed. Disease-free (DFS) and overall survival (OS) were 52% and 85.3% at 1-year, respectively. DFS and OS were significantly associated with baseline LDH levels (p=0.017 and 0.050, respectively) and grade II/III CRS (p=0.041 and 0.015, respectively, Figure). Conclusions: Despite the limited experience in the real-world setting, CAR T cell therapy can be administered safely and may successfully rescue patients with DLBCL or B-ALL who lack alternative treatment options. Close monitoring of patients and prompt recognition and management of side effects are mandatory for achieving the benefits of therapy. Figure 1 Figure 1. Disclosures Baltadakis: WinMedica: Other: Travel Grants; Gilead: Other: Travel Grants; Genesis Pharma: Other: Travel Grants; Abbvie: Honoraria; Novartis: Honoraria; Gilead: Honoraria; Pfizer: Honoraria, Other: Travel Grants; Astellas: Honoraria; Alexion: Honoraria; Bristol-Myers Squibb: Honoraria; Amgen: Honoraria; Baxalta Hellas: Other: Travel Grants. Gavriilaki: Pfizer Corporation: Research Funding; Gilead Corporation: Honoraria; Alexion, Omeros, Sanofi Corporation: Consultancy. Tzannou: Allovir: Current equity holder in publicly-traded company; Gileas: Honoraria. Anagnostopoulos: Abbvie: Other: clinical trials; Sanofi: Other: clinical trials ; Ocopeptides: Other: clinical trials ; GSK: Other: clinical trials; Incyte: Other: clinical trials ; Takeda: Other: clinical trials ; Amgen: Other: clinical trials ; Janssen: Other: clinical trials; novartis: Other: clinical trials; Celgene: Other: clinical trials; Roche: Other: clinical trials; Astellas: Other: clinical trials .

Background: Complement dysregulation has been documented in the molecular pathophysiology of COVID-19 and recently implicated in the relevant pediatric patient inflammatory responses. Aims: Based on our previous data in adults, we hypothesized that signatures of complement genetic variants would also be detectable in pediatric patients exhibiting COVID-19 signs and symptoms. Methods: We prospectively studied consecutive pediatric patients from our COVID-19 Units (November 2020-March 2021). COVID-19 was confirmed by reverse-transcriptase polymerase chain reaction (RT-PCR). Patient data were recorded by treating physicians that followed patients up to discharge. DNA was obtained from peripheral blood samples. Probes were designed using the Design studio (Illumina). Amplicons cover exons of complement-associated genes (C3, C5, CFB, CFD, CFH, CFHR1, CFI, CD46, CD55, MBL2, MASP1, MASP2, COLEC11, FCN1, FCN3 as well as ADAMTS13 and ΤHBD) spanning 15 bases into introns. We used 10ng of initial DNA material. Libraries were quantified using Qubit and sequenced on a MiniSeq System in a 2x150 bp run. Analysis was performed using the TruSeq Amplicon application (BaseSpace). Alignment was based on the banded Smith-Waterman algorithm in the targeted regions (specified in a manifest file). We performed variant calling with the Illumina-developed Somatic Variant Caller in germline mode and variant allele frequency higher than 20%. Both Ensembl and Refseq were used for annotation of the output files. A preliminary analysis (A) for the identification of variants of clinical significance was based on annotated ClinVar data, while a further and more selective analysis (B) was performed to identify missense complement coding variants that may biochemically contribute to the deregulation of innate responses during infection. This analysis was mainly based on the dbSNP and UniProt databases and available literature. Results: We studied 80 children and adolescents, 8 of whom developed inflammatory syndromes (MIS-C group). Among them, 41 were hospitalized and eventually all survived. In our preliminary analysis, patients exhibited heterogeneous variant profiles including pathogenic, benign, likely benign, and variants of unknown significance (median number of variants: 97, range: 61-103). We found a variant of ADAMTS13 (rs2301612, missense) in 39 patients. We also detected two missense risk factor variants, previously detected in complement-related diseases: rs2230199 in C3 (33 patients); and rs800292 in CFH (36 patients). Among them, 40 patients had a combination of these characterized variants. This combination was significantly associated with the presence of dyspnea (p=0.031) and cough (p=0.042). Furthermore, 27 patients had a pathogenic variant in MBL2 (rs1800450), and 7 a pathogenic deletion in FCN3 that have been previously associated with inflammatory syndromes.The results of our further analysis are summarized in Figure. We identified common variants, some well represented by relatively high frequencies (>70%) (rs11098044 in CFI, rs1061170 in CFH and rs12711521 in MASP2) and others less abundant, but varying considerably between the hospitalized group, the non-admitted group and the MIS-C individuals (rs2230199 in C3, rs1065489 in CFH, rs12614 and rs641153 in CFB, rs1800450 in MBL2, rs2273346 and rs72550870 in MASP2, rs72549154 in MASP3 and rs7567833 in COLEC11, all highlighted in Figure in red).). Structurally, the majority of these common variants of interest encode charge reversal mutations. These may influence protein-protein interactions in complex formations that are important for complement activation and/or regulation. Conclusion: In pediatric COVID-19 we have detected a novel set of complement missense coding variants some of which have been implicated earlier in inflammatory syndromes and endothelial stress responses. Certain combinations of mutations of alternative and/or lectin pathway components may increase the threshold dynamics of complement consumption and therefore alter COVID-19 phenotypes. Figure 1 Figure 1. Disclosures Gavriilaki: Alexion, Omeros, Sanofi Corporation: Consultancy; Gilead Corporation: Honoraria; Pfizer Corporation: Research Funding. Anagnostopoulos: Abbvie: Other: clinical trials; Sanofi: Other: clinical trials ; Ocopeptides: Other: clinical trials ; GSK: Other: clinical trials; Incyte: Other: clinical trials ; Takeda: Other: clinical trials ; Amgen: Other: clinical trials ; Janssen: Other: clinical trials; novartis: Other: clinical trials; Celgene: Other: clinical trials; Roche: Other: clinical trials; Astellas: Other: clinical trials .

Background. Hematopoietic cell transplant (HCT) recipients who develop coronavirus disease 2019 (COVID-19), have dismal prognosis with approximately 20% mortality. Given the lack of a specific and effective therapy, the availability of various vaccination platforms against SARS-CοV-2 has generated optimism towards the development of a robust herd immunity. Notwithstanding the prioritization of HCT recipients to COVID-19 vaccination, limited information is available on whether and to what extent, they mount an immune response to SARS-CοV-2 vaccination as they were generally excluded from vaccination trials. Aim. To gain insights in the immune responses developed to SARS-CoV-2 vaccines under immunosuppression, we studied the humoral and cellular immune responses to SARS-CoV-2 vaccination in HCT recipients. Methods. We prospectively studied (April-July 2021), adult patients who had undergone HCT in our Unit and received two doses of a SARS-CoV-2 vaccine (as per international guidelines) after providing written informed consent. Responses were studied before each vaccination dose and 12-51 days later after the second dose. Neutralizing antibodies against SARS-CoV-2 (CoV-2-NAbs) were measured using an FDA approved methodology for diagnostic use (ELISA, cPass™ SARS-CoV-2 NAbs Detection Kit; GenScript, Piscataway, NJ, USA; cut-off value for a positive result set at ≥30%) and SARS-CoV-2 spike-specific T cells (spike-STs) by interferon-γ Elispot after pulsing peripheral blood mononuclear cells with spike pepmixes. Results. Humoral responses were studied on 65 patients, (50 allo-HCT/15 auto-HCT, Figure A). T cell responses were measured on 38/65 vaccinated patients (32 allo-HCT/6 auto-HCT) with a median of 3 (0.17-31) and 2 years (1.25-8) post allo- and auto-HCT respectively, and 19 healthy, unexposed vaccinees. One patient with prior COVID-19, was excluded from analysis. All patients were vaccinated with the Pfizer-BioNTech, except for 2 vaccinated with the AstraZeneca vaccine. Both CoV-2-NAbs and spike-STs were barely detectable before vaccination but could be detected in both allo- and auto-HCT patients after the first vaccination dose, reaching statistically significant increase after the second vaccination dose (p Conclusion . Herein, we report for first time humoral and T cell responses post SARS-CoV-2 vaccination in HCT recipients. Transplant recipients not under active and intense immunosuppression at the time of vaccination may benefit significantly from COVID-19 vaccination even though these responses are blunted compared to healthy individuals. However, for the severely immunocompromised patients it seems highly unlikely that they could be protected by vaccination and for this vulnerable population, different vaccination schemes or therapeutic platforms should be developed along with collateral measures including minimal exposure and immunization of caregivers and health care providers. Figure 1 Figure 1. Disclosures Gavriilaki: Alexion, Omeros, Sanofi Corporation: Consultancy; Pfizer Corporation: Research Funding; Gilead Corporation: Honoraria. Yannaki: SANDOZ: Speakers Bureau; Gilead: Speakers Bureau; Novartis: Speakers Bureau; bluebird bio, Inc.: Membership on an entity's Board of Directors or advisory committees, Research Funding. Anagnostopoulos: Abbvie: Other: clinical trials; Sanofi: Other: clinical trials ; Ocopeptides: Other: clinical trials ; GSK: Other: clinical trials; Incyte: Other: clinical trials ; Takeda: Other: clinical trials ; Amgen: Other: clinical trials ; Janssen: Other: clinical trials; novartis: Other: clinical trials; Celgene: Other: clinical trials; Roche: Other: clinical trials; Astellas: Other: clinical trials .

Chronic graft-versus-host disease (cGVHD) is the main cause of morbidity and transplant-related mortality following allogeneic hematopoietic stem cell transplantation (alloHSCT), however effective treatment options are limited. Lack of objective surrogates (biomarkers) for treatment response has hindered progress in this respect. T cells are considered the major effectors of cGVHD, yet the respective repertoires are insufficiently charted. Here, we investigated the dynamic architecture of T-cell repertoires in cGVHD by exploiting next-generation sequencing (NGS), aiming to uncover immunogenetic signatures linked with cGHVD occurrence and response to treatment. We analyzed 53 blood samples from 15 patients with hematological malignancies who underwent alloHSCT, with an intended bias towards patients who developed cGVHD (n=12). The remaining 3 patients had no cGVHD (control group). Patients with cGVHD were analyzed at cGVHD onset and/or prior to a new line of treatment (n=17 samples) as well as at clinically relevant timepoints following treatment: (i) partial response (PR, n=8), (ii) complete response (CR, n=3), (iii) stable disease (SD, n=18), (iv) progression (PD, n=1). Treatment modalities involved corticosteroids, mycophenolate myfetil, extracorporeal phototherapy, ruxolitinib and ibrutinib. Patients with no cGVHD were analyzed at 3 months (+3mo) and 6 months (+6mo) post-alloHSCT (n=6 samples). Starting material was PB mononuclear cells. TRBV-TRBD-TRBJ gene rearrangements were RT-PCR amplified and subjected to paired-end NGS and detailed bioinformatics analysis. Only productive TRBV-TRBD-TRBJ rearrangements were evaluated (n= 13,059,730, 89.9% of filtered-in sequences, median 219,063/sample). For repertoire characterization, clonotypes (i.e., TRB rearrangements with identical TRBV gene usage and amino acid complementarity-determining region 3 sequence) were considered (median 9,725 distinct clonotypes/sample). The 10 most frequent clonotypes/sample were defined as "major". To purge T cell clones expanded secondary to viruses common in the alloHSCT setting, we compared all major clonotypes against the GenBank TRB sequence database (n=18,402), as well as an extensive TR repertoire dataset from a previous study by our group, profiling tri-virus-specific (CMV, EBV, BK) T cell products generated from immunocompetent donors (n=947,298). Overall, we identified 289 unique major clonotypes; 38 were excluded due to match within the tri-VST database (no match within GenBank). All cases with cGVHD displayed significant clonal T cell expansions both pre- and post-treatment (overall median cumulative frequency of the 6 most expanded T cell clonotypes/sample 32.4%). However, clonality tended to decrease in PR samples compared to pre-treatment (19.8% vs 33.9%, respectively), although not reaching statistical significance possibly due to small sample size (p=0.06). Patients with no cGVHD, on the other hand, consistently displayed a clonality decrease overtime (31.8% at +3mo vs 18.4% at +6mo, p=0.02). Importantly, patients with no GVHD displayed TR repertoire reconstitution with few major T cell clones of the +3mo timepoint persisting at +6mo (median 20%). In clear contrast, cGVHD T cell repertoires were dominated by clones which persisted overtime (median 60%). In fact, repertoire persistence was most evident in SD (median 66.7%) and significantly lower in PR and CR (33.3% and 10.0%, respectively, p In conclusion, NGS immunoprofiling in cGVHD reveals expanded T cell clones with clonal dynamics that correlate with clinical response, indicating a causal relationship to cGVHD pathogenesis. Identification and longitudinal tracking of T cell clones associated with cGHVD could serve as a molecular surrogate marker for disease activity, with evident benefits for cGVHD monitoring and evaluation of response to various treatments. Disclosures Anagnostopoulos: Abbvie: Other: clinical trials; Sanofi: Other: clinical trials ; Ocopeptides: Other: clinical trials ; GSK: Other: clinical trials; Incyte: Other: clinical trials ; Takeda: Other: clinical trials ; Amgen: Other: clinical trials ; Janssen: Other: clinical trials; novartis: Other: clinical trials; Celgene: Other: clinical trials; Roche: Other: clinical trials; Astellas: Other: clinical trials . Chatzidimitriou: Janssen: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding.

The emergence of SARS-CoV-2, as of July 2021 has affected 469,042 individuals and accounted for 12,851 deaths nationally in Greece, according to WHO database. Mortality rate is higher in elderly patients (pts) and in pts with comorbidities, including malignancies. However, there is a growing interest on COVID-19 outcomes in pts with hematologic diseases. The aim of this study was to perform a systematic registration and analysis of the outcomes of pts with hematologic disease and COVID-19 in our center. The study is a single-center, retrospective study, conducted at a Hematology Department and HCT unit of a tertiary Hospital after approval from local Ethics Committee. We included pts with a hematologic disease and RT-PCR confirmed COVID-19 infection between October 2020 and July 2021. We reviewed hematological medical records to extract demographic and clinical data of COVID-19 infections. Most of the data have already been intergraded in ASH Research Collaborative Data Hub. Hematologic diseases were categorized to: Acute Myeloblastic Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Non-Hodgkin Lymphomas (NHL), Chronic Lymphocytic Leukemia (CLL), Hodgkin Lymphoma (HL), Multiple Myeloma (MM), Myelodysplastic Syndromes (MDS), Chronic Myeloid Leukemia (CML), Myeloproliferative Neoplasms (MPN, including all Philadelphia-negative MPN) and other hematologic conditions. We evaluated a total of 89 pts, 54% were male and 46% female, with a median age of 64.5 (20-86) and 59.5 (21-85) years respectively. 83% of pts were ≥40 years and 27% ≥70 years old. Most of them (92%) acquired infection outside a hospital setting. 13% of pts were asymptomatic and diagnosis was confirmed only with positive RT-PCR test. The most common represented malignancies were NHL 26%, CLL 20% and acute leukemias 13.5%, while 15% of pts underwent transplantation (HCT). Pts presented with moderate/severe COVID-19 were 55%, while 43% of hospitalized pts required Intensive Care Unit (ICU) admission. Overall, the death rate was 24%, while remarkably almost all pts required ICU support did not survive (mortality 94%). Higher mortality observed in patients with MDS (50%), MM (43%), CLL (39%), ALL (33%) and NHL (30%). Further analysis showed a positive correlation between mortality and male gender with 16 deaths out of 21 (p = .0245), as well as mortality and ICU admission (p < .001). A chi-square test of independence was performed to examine the relation between age and COVID-19 severity, without any statistically significant result [x 2 (2, N = 87) = 3.475, p = .176]. Whereas the only significant correlation between age and mortality was among age groups 18-39 and >70 years (p = .0146). Regarding treatment, pts were divided into two subgroups, 78% of them received anticancer therapy at least once in their lives, while 22% of them have never been on treatment, mainly pts with CLL and indolent NHL. 62% of the first subgroup manifested moderate/severe COVID-19 infection requiring hospitalization with 28% death rate, while the same rates in the 2 nd subgroup were 30% and 10% respectively. Although there was a significant correlation between the treatment status and the severity of COVID-19 infection (p = .020), the above was not translated in statistically higher death rate in the first subgroup (p = .14). There was also a correlation between HCT and COVID-19 severity in general (p = .005), with autologous HCT having statistically higher mortality than the allogeneic subgroup (p = .032). Α similar analysis in CLL and NHL groups showed no relation among treatment status, COVID-19 severity, and mortality (p values .638 and .115/ .34 and .62 respectively). As anticipated in hematological pts, the immunocompromised nature of the underlying disease makes them extremely vulnerable to COVID-19 infection regardless of their treatment status, a fact that is also reflected in mortality despite ICU admission and support. In general, the severity of infection is correlated to anticancer therapy, while mortality to male sex, ICU admission and autologous HCT. Larger number of pts are necessary for further studies to better understand the parameters that impact the outcome of COVID-19 in hematological pts. Hematology departments should remain COVID-19 free zones, dedicated only to hematologic treatment and pts should strictly comply with social distancing. It remains to see if vaccines can play a key role to protect this special group of pts. Figure 1 Figure 1. Disclosures Anagnostopoulos: Abbvie: Other: clinical trials; Sanofi: Other: clinical trials ; Ocopeptides: Other: clinical trials ; GSK: Other: clinical trials; Incyte: Other: clinical trials ; Takeda: Other: clinical trials ; Amgen: Other: clinical trials ; Janssen: Other: clinical trials; novartis: Other: clinical trials; Celgene: Other: clinical trials; Roche: Other: clinical trials; Astellas: Other: clinical trials .

Background: Treosulfan has been increasingly used in reduced toxicity regimens, especially in older or frail patients. Different doses of treosulfan plus fludarabine have shown an advantage over reduced intensity regimens, confirmed by a randomized phase 3 trial utilizing treosulfan 30 g/m² (or FT10) in the majority of patients. However, data comparing fludarabine with higher doses of treosulfan (FT14) to fludarabine combined with myeloablative doses of busulfan are limited. Aims: We compared outcomes between treatment alternatives of similar conditioning intensity: FT14 (fludarabine 150 or 160 mg/m 2 and treosulfan 42g/m 2, or FT14) over FB4 (fludarabine 150 or 160 mg/m 2 and busulfan 12.8 mg/kg). Methods: We retrospectively studied consecutive patients from the European Society for Blood and Marrow Transplantation (EBMT) registry, meeting the following inclusion criteria: a) adults diagnosed with acute myeloid leukemia (AML), b) recipients of first allogeneic hematopoietic stem cell transplantation (HSCT) from a matched unrelated or sibling donor between 2010-2020, c) HSCT at first or second complete remission (CR), d) conditioning regimen with either FT14 or FB4. Patients with ex vivo manipulated grafts were excluded. A sub-group analysis was performed according to age ( Results: In total, 2703 patients were included in the analysis comprising 2025 (75%) transplanted with FB4, and 678 (25%) with FT14. In the sub-group of patients younger than 55 years (n=1676), FT14 recipients (n=236) had a significantly increased age (p Similar differences in patient characteristics were observed in patients aged ≥55 years (n=1027). FT14 recipients (n=442) had a significantly increased age (p Conclusion: With the limitations of a retrospective analysis, our large real-world multicenter study suggests that FB4 is associated with better outcomes compared to FT14 in younger patients with AML transplanted in first or second CR. The same was not true for older patients (≥55 years). It should also be noted that FT14 has been selected by treating physicians for higher risk HSCT, including patients who are older, have secondary disease, adverse cytogenetics, and unrelated donors. Therefore, further studies are needed to determine the optimal conditioning regimen for such patient populations. Figure 1 Figure 1. Disclosures Gavriilaki: Alexion, Omeros, Sanofi Corporation: Consultancy; Gilead Corporation: Honoraria; Pfizer Corporation: Research Funding. Labopin: Jazz Pharmaceuticals: Honoraria. Yakoub-Agha: Jazz Pharmaceuticals: Honoraria. Hilgendorf: Novartis: Honoraria; AbbVie: Honoraria; Jazz Pharmaceuticals: Honoraria, Other: Travel Support; Celgene: Other: Travel Support; SanofiGenzyme: Other: Travel Support. Kröger: Novartis: Research Funding; Riemser: Honoraria, Research Funding; Sanofi: Honoraria; Neovii: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Gilead/Kite: Honoraria; Celgene: Honoraria, Research Funding; AOP Pharma: Honoraria. Mielke: Gilead/KITE: Other: Travel support, Expert panel ; Novartis: Speakers Bureau; Immunicum: Other: Data safety monitoring board; Miltenyi: Other: Data safety monitoring board; DNA Prime SA: Speakers Bureau; Celgene/BMS: Speakers Bureau. Zuckerman: AbbVie: Honoraria; Orgenesis Inc.: Honoraria; Janssen: Honoraria; BioSight Ltd: Honoraria; Novartis: Honoraria; Gilead Sciences: Honoraria, Speakers Bureau; Cellect Biotechnology: Honoraria. Giebel: Janssen: Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau. Bazarbachi: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Hikma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Astra Zeneca: Membership on an entity's Board of Directors or advisory committees. Spyridonidis: Menarini: Current Employment. Mohty: Astellas: Honoraria; Amgen: Honoraria; Celgene: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding; Takeda: Honoraria; Jazz: Honoraria, Research Funding; Adaptive Biotechnologies: Honoraria; Pfizer: Honoraria; Novartis: Honoraria; Bristol Myers Squibb: Honoraria; Janssen: Honoraria, Research Funding; Gilead: Honoraria.

We have previously shown an advantage of a myeloablative conditioning regimen with reduced toxicity (Fludarabine 150 mg/m2, Treosulfan 42 g/m2, FluTreo) compared to a reduced-intensity regimen. We aimed to determine long-term safety and efficacy of FluTreo. We prospectively studied consecutive patients who received FluTreo in our center (2014-2019) on the basis of age (≥50 years), hematopoietic cell transplantation comorbidity index (HCT-CI) ≥2, or both. FluTreo recipients were then compared to a historical control group. We studied 68 FluTreo recipients, with a median age of 58.5 years and HCT-CI of 3. We calculated cumulative incidence (CI) of acute (grade 2-4) and moderate/severe chronic graft-versus-host disease (GVHD) (29.9% and 25%, respectively). The 3-year CI of treatment-related mortality was 19.1%, associated only with acute GVHD (P