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The familial occurrence of hematological malignancies has been underappreciated. Recent studies suggest that up to 15% of adults with myeloid neoplasms carry germline pathogenic variants in cancer-predisposing genes. This study aimed to identify the underlying germline predisposition variant in patients with a strong family or personal onco-hematological history using whole exome sequencing on sixteen uncharacterized individuals. It was carried out in two groups of patients, one with samples available from two affected relatives (Cohort A) and one with available samples from the index case (Cohort B). In Cohort A, six families were characterized. Two families shared variants in genes associated with DNA damage response and involved in cancer development (CHEK2 and RAD54L). Pathogenic or likely pathogenic germline variants were also found in novel candidate genes (NFATC2 and TC2N). In two families, any relevant pathogenic or likely pathogenic genomic variants were identified. In Cohort B, four additional index cases were analyzed. Three of them harbor clinically relevant variants in genes with a probable role in the development of inherited forms of hematological malignancies (GATA1, MSH4 and PRF1). Overall, whole exome sequencing is a useful approach to achieve a further characterization of these patients and their mutational spectra. Moreover, further investigations may help improve optimization for disease management of affected patients and their families.

We report a corona virus disease (COVID‐19) case with unprecedented viral complexity. In the first severe episode, two different severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) strains (superinfection) were identified within a week. Three months after discharge, the patient was readmitted and was infected in a nosocomial outbreak with a different strain, suffering a second milder COVID‐19 episode.

3 páginas, 1 figura, 1 tabla., This work was supported by Instituto de Salud Carlos III (Ref COV20/00140: SeqCOVID—Consorcio para la epidemiología genómica de SARSCoV-2 en España) and by Consejo Superior de Investigaciones Científicas (CSIC; PTI Salud Global). L.P.L. has a Miguel Servet Contract (CPII20/00001).

We report a COVID-19 case with unprecedented viral complexity. In the first severe episode, two different SARS-CoV-2 strains (superinfection) were identified within a week. Three months after discharge, patient was readmitted and was infected in a nosocomial outbreak with a different strain, suffering a second milder COVID-19 episode.

Conventional cytogenetics are the gold standard for the identification of chromosomal alterations recurrent in myeloid neoplasms. Some next-generation sequencing (NGS) panels are designed for the detection of copy number variations (CNV) or translocations, however, their use is far from being widespread. Here we report on the results of a commercial panel including frequent mutations, CNVs and translocations in myeloid neoplasms. Frequent chromosomal alterations were analyzed by NGS in 135 patients with myeloid neoplasms and three with acute lymphoblastic leukemia. NGS analysis was performed using the enrichment-capture Myeloid Neoplasm-GeneSGKit (Sistemas Genómicos, Spain) gene panel including 35 genes for mutational analysis and frequent CNVs and translocations. NGS results were validated with cytogenetics and/or MLPA when possible. A total of 66 frequent alterations included in NGS panel were detected, 48 of them detected by NGS and cytogenetics. Ten of them were observed only by cytogenetics (mainly trisomy 8), and another eight only by NGS (mainly deletion of 12p). Aside from this, 38 secondary CNVs were detected in any of the genes included mainly for mutational analysis. NGS represents a reliable complementary source of information for the analysis of CNVs and translocations. Moreover, NGS could be a useful tool for the detection of alterations not observed by conventional cytogenetics.

A new SARS-CoV-2 variant, B.1.1.7, emerged in September in the UK, and is responsible for 76.6% of COVID-19 cases.1 This variant has also been reported in another 45 countries, 17 of them European.2,3 B.1.1.7 is considered to have higher transmissibility.4 It carries an unusually high number of specific mutations/deletions, 18, mostly non-synonymous and eight concentrate in the S gene,5 including several which might have relevant functional roles. The 69/70 deletion may be associated to immune response evasion6 and the N501Y substitution increases the affinity to the ACE2 receptor.7 These findings have raised the alarm of having to face a new variant with the potential to accelerate the spread of the pandemic. A recent report finds a realistic possibility that B.1.1.7 is associated with an increased risk of death., This work was supported by Instituto de Salud Carlos III (Ref COV20/00140: SeqCOVID—Consorcio para la epidemiología genómica de SARS-CoV-2 en España) and by Consejo Superior de Investigaciones Científicas (CSIC) (PTI Salud Global). LPL holds a Miguel Servet Contract CP15/00075).

Rationale: The first descriptions of reinfection by SARS-CoV-2 have been recently reported. However, these studies focus exclusively on the reinfected case, without considering the epidemiological context of the event.Objectives: To perform a complete analysis of the sequential infections and transmission events around a SARS-CoV-2 reinfection, including the infection events preceding it, the exposure and subsequent transmissions.Methods: Our analysis was supported by host genetics, viral whole genome sequencing, phylogenomic viral population analysis, and refined epidemiological data obtained from interviews with the involved subjects.Results: The reinfection involved a 53-year-old woman with asthma (Case A), with a first COVID-19 episode in April-2020 and a much more severe second episode four months and a half later, with COVID-19 seroconversion in August, and requiring hospital admission. An extended genomic analysis allowed us to demonstrate that the strain involved in Case A´s reinfection was circulating in the epidemiological context of Case A and was also transmitted subsequently from Case A to her family context. The reinfection was also supported by a phylogenetic analysis, including 348 strains from Madrid, which revealed that the strain involved in the reinfection was circulating by the time Case A suffered the second episode, August/September-2020, but absent at the time range corresponding to Case A´s first episode.Conclusion: We present the first complete analysis of the epidemiological scenario around a reinfection by SARS-CoV-2, more severe than the first episode, including three cases preceding the reinfection, the reinfected case per se, and the subsequent transmission to another seven cases.

Background Bardet–Biedl syndrome (BBS) is a rare autosomal recessive ciliopathy disorder. Many BBS disease-causing genetic variants have been identified due to the advancement of molecular diagnostic tools. We report on a novel pathogenic variant in a consanguineous Pakistani family with an affected child. Case presentation Clinical exome sequencing was used to search for BBS causing variants in the affected individual and identified a novel homozygous splice-site variant in the BBS9 gene (c.702 + 1del). Sanger sequencing was performed for variant validation and segregation studies. Expression analysis using mRNA levels to assess the functional impact of the novel variant demonstrated skipping of exon 7 in the affected alleles, suggesting a truncating effect. Three-dimensional structural modelling was used to predict pathogenicity of the variant residue and the alteration leads to a partial deletion of the PHTB1_N domain and a total deletion of the PHTB1_C domain. Conclusion The study of this case expands the spectrum of biallelic variants in the BBS9 gene associated with BBS and increased the knowledge on the molecular consequences of splicing variation c.702 + 1del.

Development of de novo hematologic malignancies in donor cells after allogeneic stem cell transplantation (allo-SCT) provides a useful in vivo model to study the process of leukemogenesis. A systematic analysis of the cases reported in the literature was performed to identify risk factors and mechanisms involved in the pathogenesis of donor cell–derived hematologic neoplasms (DCHN) and leukemogenic transformation. Relevant data were extracted from 137 cases. Cases of DCHN show a wide heterogeneity with regard to recipient/donor age, sex mismatch, and conditioning regimen. Some characteristics, such as the type of primary disease, the type of hematologic malignancy of the DCHN, and the stem cell source used in the transplant procedure, differ from those expected. Mechanisms involved in the pathogenesis of DCHN are complex, and several hypotheses have been proposed, such as pre-existing hematologic neoplasms or premalignant clones in the donor, decreased immune surveillance, and damage to bone marrow microenvironment in the recipient. Most likely several if not all these mechanisms play a role in DCHN development. Novel approaches, such as next-generation sequencing to study consecutive samples after allo-SCT in these patients, appear to be promising to decipher the mechanisms of leukemogenesis.

INTRODUCTION Allogeneic hematopoietic stem cell transplantation (alloHSCT) has been established as a powerful treatment modality for patients with hematological malignancies. The graft-versus-leukemia effect, however, is strongly associated with the occurrence of graft-versus-host disease (GVHD) and subsequent transplant-related mortality (TRM). Several strategies are applied in order to prevent GVHD, the post-transplant cyclophosphamide (PT-Cy) is one of the most used in Haploidentical HSCT (Haplo-HSCT). Cyclophosphamide (CY) is an alkylating agent with antineoplastic and immunosuppressive activities. CY is metabolized by highly polymorphic enzymes to produce phosphoramide mustard which is a bifunctional DNA alkylating agent, is the therapeutically active metabolite. Thus, the aim of our study is to identity polymorphisms in the genes of the CY metabolism and correlated with complications post-HSCT (GVHD, TRM, veno-occlusive disease (VOD) or hemorrhagic cystitis (HC)). METHODS We selected 182 consecutive patients who received an Haplo-HSCT from 2007 to 2019. Eleven genes related to CY metabolism were analyzed (Table 1). The genotyping was performed in peripheral blood samples for recipient using an enrichment-capture custom gene panels (IDT probes) in a MiSeq platform (Illumina, USA). The bioinformatic analysis was carried out with BaseSpace software (Illumina, USA). Variants located in coding region and splicing sites were analyzed. We selected polymorphisms corresponding to read depth ≥30X in the canonical isoform with an allele frequency ≥0.4 and represented in at least 5% in our cohort. The collected clinical variables were age/gender recipient and donor, pathology, pretransplant status, conditioning regimen, total body irradiation, basal ferritin and CMV reactivation. Fisher test was used to compare the differences among groups. Statistical Package for the Social Sciences (SPSS, Chicago, USA) was used for statistical test. RESULTS The cumulative incidence rates for aGVHD of II-IV and III-IV grades at 100 days was 39% and 12% respectively. The cumulative incidence rates for cGVHD, moderate or severe cGVHD and TRM at 1000 days were 37%, 19% and 29%, respectively. Among the cases analyzed, 9% developed VOD and 25% HC. Patients who received ablative conditioning regimen presented a higher incidence of TRM (p=0.005). No other clinical data was associated with complications post HSCT. Forty polymorphisms were detected in 9 genes by bioinformatic analysis. The variants that presents some correlation (p Overall, polymorphisms related with decrease activity of enzymes that active cyclophosphamide (level lor active metabolite) were correlated with higher aGVHD, cGVHD, TRM and VOD (Table 1). On the other hand, polymorphisms associated with low activity in detoxification enzymes were correlated with higher toxicity (TRM). As described in bibliography, GSTM1 null allele were correlated with higher probability of developing VOD. CONCLUSIONS Genetic analysis of CY metabolism genes correlated with several post HSCT complications. The analyses of this variants before transplant could facilitate personalized risk and clinical management of patients undergoing Haplo HSCT. Results must validated in others cohorts of patients. Disclosures Kwon: Gilead: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Jazz: Consultancy, Honoraria.

Molecular diagnosis of myeloid neoplasms (MN) is based on the detection of multiple genetic alterations using various techniques. Next-generation sequencing (NGS) has been proved as a useful method for analyzing many genes simultaneously. In this context, we analyzed diagnostic samples from 121 patients affected by MN and ten relapse samples from a subset of acute myeloid leukemia patients using two enrichment-capture NGS gene panels. Pathogenicity classification of variants was enhanced by the development and application of a custom onco-hematology score. A total of 278 pathogenic variants were detected in 84% of patients. For structural alterations, 82% of those identified by cytogenetics were detected by NGS, 25 of 31 copy number variants and three out of three translocations. The detection of variants using NGS changed the diagnosis of seven patients and the prognosis of 15 patients and enabled us to identify 44 suitable candidates for clinical trials. Regarding AML, six of the ten relapsed patients lost or gained variants, comparing with diagnostic samples. In conclusion, the use of NGS panels in MN improves genetic characterization of the disease compared with conventional methods, thus demonstrating its potential clinical utility in routine clinical testing. This approach leads to better-adjusted treatments for each patient.

Chimerism refers to the relative proportion of donor and recipient DNA after hematopoietic stem cell transplantation (HSCT) and its quantitative follow-up is of great clinical utility in this setting. PCR of short tandem repeats (STR-PCR) constitutes the gold standard method for chimerism quantification, although more sensitive PCR techniques (such as qPCR) have recently arisen. We compared the sensitivity and the quantification capacity of both techniques in patient samples and artificial mixtures and demonstrated adequate performance of both methods, with higher sensitivity of qPCR and better quantification skills of STR-PCR. By qPCR, we then prospectively followed up 57 patients that were in complete chimerism (CC) by STR-PCR. Twenty-seven patients (59%) showed 0.1&ndash, 1% recipient DNA in the bone marrow. Only 4 patients presented 0.1&ndash, 1% recipient DNA in peripheral blood (PB), and one of them relapsed. Finally, by qPCR, we retrospectively studied the last sample that showed CC by STR-PCR prior to relapse in 8 relapsed patients. At a median of 59 days prior to relapse, six patients presented mixed chimerism by qPCR in PB. Since both approaches have complementary characteristics, we conclude that different techniques should be applied in different clinical settings and therefore propose a methodological algorithm for chimerism follow-up after HSCT.

Low phospholipid-associated cholelithiasis (LPAC) syndrome is characterized by early intrahepatic and symptomatic gallstones leading to cholangitis, acute pancreatitis and biliary colic. It has been associated with loss of function variants in the ABCB4 gene. ABCB4 encodes for a phospholipid translocator at the canalicular membrane of the hepatocyte, which "flops" phosphatidylcholine into bile. The autosomal recessive form is the most common, although autosomal dominant forms have also been described. We report the first family with autosomal dominant LPAC syndrome due to heterozygosity of the loss of function mutation c.2932T>C in ABCB4, identified by targeted next generation sequencing.

Introduction: Non-Hodgkin B lymphomas (NHL-B) are a large group of heterogeneous diseases, with well-defined, histological and clinical features. Currently, the lymph node biopsy is essential for diagnosis, often obtained from hard to reach areas. Our aims with this study was to analyze genetics variants at diagnosis trying to discriminate between different NHL-B histologic subtypes using formalin fixed paraffin embedded (FFPE) tissue sections and circulating tumor free DNA (ctDNA) samples. Material and Methods: This is a retrospective, cross-sectional, single-center study. Sixty patients were selected with a diagnosis of different NHL-B subtypes: Diffuse large B cell lymphoma (DLBCL), follicular lymphoma (FL), marginal lymphoma (ML), mantle cell lymphoma (MCL) and plasmablastic lymphoma (PL). Sixty FFPE tissue samples and 23 ctDNA specimens obtained at diagnosis were selected. We performed an enrichment panel of 54 genes recurrently mutated in lymphomas (Lymphoma Solution; Sophia Genetics) by next generation sequencing (NGS; NextSeq; Illumina). The depth of 90% of the readings was greater than 2600x. Quantitative variables were expressed as median and range. Categorical variables were expressed as frequency and percentage. The Fisher exact test was used to compare the distribution of categorical variables. The Mann-Whitney test was used to compare differences between quantitative variables. Statistical significance was set at p < 0.05. Results: Our study shows that 97% (58/60) of patients presented any variant. The most frequently mutated genes were KMT2D, EP300 and SOCS1. Exclusive variants were detected in FL in the genes CCND1, PAX5, CREBBP, BCL2 and REL genes. In the same way, in DLCBL the variants detected in the BRAF, TCF3, XPO1, PIM1, CHD2, ID3 and BCL6 genes were exclusive of this subtype. Furthermore, the genes BCL2 (p=0.0021), CREBBP (p=0.0004), NOTCH2 (p=0.03), PAX5 (p=0.01) and TNFRSF14 (p=0.04) are more frequently altered in patients with FL, ATM (p=0.02) gene in MCL; NFKBIE (p=0.03), CIITA (p=0.02), MYC (p=0.009) and PIM1 (p=0.04) in DLCBL, among which it was found that high-grade lymphomas are more frequently associated with mutations in CHD2 (p=0.02), MYC (p=0.03) and MYD88 (p=0.02; data not shown). In the subgroup of 23 patients with paired samples (FFPE/ctDNA), 95% (22/23) of patients had mutations in any of the genes on the panel in FFPE tissue samples and 82% (19/23) in ctDNA specimens. The number of variants detected was different depending on the type of sample analysed, 52% of the variants were detected in both specimens, 39 only in FFPE tissue and 9% in ctDNA; Figure 1). In variants detected in both samples, the average value of the VAF was higher that when is detected only in one of the samples (FFPE: 28.1 vs 5.8 (p We did not find significant differences in the number of variants depending on the stage, classification, tumour burden or bulky mass (Table 1). Conclusion: In our study, we were able to identify genetic variables that could characterize different histological groups of NHL-B in FFPE tissue and ctDNA samples, by using a commercial gene panel of NGS. The mutational profile obtained from ctDNA and FFPE tissue is comparable in all histological subtypes, regardless tumour burden, aggressiveness or stage, throwing each one of them complemental information. These results support the hypothesis that could be possible to distinguish different histologies through non-invasive strategies, specially oriented to lesions where obtaining a tissue sample is difficult. We are working on the development of clinical-genetic algorithms that allow us to achieve our goal. Disclosures No relevant conflicts of interest to declare.

INTRODUCTION Allogeneic haematopoietic stem cell transplant (allo-HSCT) could be the only curative therapy for patients with hematological malignancies due to graft effect against tumor. However, approximately 40% of patients develop post-transplantation complications such as acute graft-versus-host disease (aGVHD). Cytokines and their receptors are involved in regulatory and inflammatory processes that occur during GVHD. Therefore, the analysis of polymorphisms (SNPs) that affect the expression or activity of these genes could be used as biomarkers to predict the development of these complication. The aim of this study was to select new polymorphisms in cytokine genes (interleukins, chemokines and their receptors) to build models to predict the development of aGVHD after allo-HSCT from an HLA-identical sibling donor. METHODS We retrospectively selected 88 patients with hematological malignancies who received an allo-HSCT from an HLA-identical sibling donor from 2000 to 2015. A total of 176 pre-transplant recipient (R) and donor (D) peripheral blood samples were collected. The genotyping was performed using an enrichment-capture gene panels (include 132 genes (73 interleukins, 59 chemokines) in a HiSeq platform (Illumina, USA). The bioinformatic analysis was carried out with the GeneSystemssoftware (Sistemas Genómicos, Spain). Variants located in coding region, splicing sites, and UTR, 5'upstream and 3'downstream zones (+ 200pb) were analyzed. We selected polymorphisms corresponding to non-synonymous variants, represented in at least 5% of our cohort, with readings ≥30X in the canonical isoformwith an allele frequency ≥ 0.4. Fisher test was used to compare the differences among groups. Multiple logistic regression models were performed using combination of interleukins and chemokines polymorphisms selected previously that could be applied to clinical practice to predict aGVHD. The models with the highest AUC value, sensitivity and specificity value and the lowest number of genetic variants used were selected.Statistical Package for the Social Sciences (SPSS, Chicago, USA) was used for statistical test. RESULTS The cumulative incidence rates for aGVHD of grades II-IV and III-IV at 100 days after transplantation were 48.93% and 18.08%, respectively. The clinical variables (age, gender, pathology, stem cell source and previous transplantation) were not correlated with II-IV or III-IV aGVHD. However, patients who received ablative conditioning regimen presented a lower incidence of III-IV aGVHD (p= 0.041). Using filters defined previously, we detected 481 polymorphisms (350 coincident, 68 specific R and 63 for D) in the interleukins group. On the other hand, we detected 339 polymorphisms (267 coincident, 29 specific R and 43 for D) in the group of chemokines. Finally, 17 polymorphisms were selected in the interleukin group and 10 in the chemokine group for its correlation with the aGVHD (p We developed multiple logistic regression models for II-IV and III-IV aGVHD in interleukins and chemokines genes (Table 3). The identification of these 15 polymorphisms could help us to prevent the developing II-IV and III-IV aGVHD. CONCLUSIONS We have identified new genetic polymorphisms correlate with the risk of developing aGVHD after allo-HSCT from an HLA-identical sibling donor. Based on these data, we have developed a genetic score that encompasses polymorphisms of greater relevance. In this way, patients at greatest risk for developing this type of post-transplantation complication who could benefit from personalized management through immunosuppression and other drugs. Disclosures No relevant conflicts of interest to declare.

Introduction Donor cell derived myeloid neoplasm (DCMN), defined as the development of de novohematological malignancies from cells of donor origin,is a late complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We report on seven cases of DCMN in which whole-exome sequencing (WES) at different time-points after allo-HSCT, as well as in a sample from each donor, was performed. The ultimate objective was to accurately described the clonal architecture, spatial heterogeneity and identify somatic mutations that are induced in the process of leukemogenesis and clonal evolution of myeloid neoplasm. Donors were also analyzed to detect underlying condition predisposing to the development of DCMN. Patient and Methods Seven patients with a confirmed diagnosis of DCMN and their donors were recruited from different Spanish institutions. This cohort included a total of 32 BM samples at different time points after allo-HSCTand one PB sample from each donor (one case received dual allo-HSCT, CB and PB from both donors were obtained), which provided a total of 40 samples. Genomic DNA samples were prepared according to Agilent SureSelect-XT Human exon 50Mb enrichment kit (Agilent Technlogies, Santa Clara, CA) preparation guide and libraries were sequenced on Illumina HiSeq platform (Illumina, San Diego, CA). DNA sequencing data from recipient post-transplant BM samples, were matched against their donor PB sample and previous post-transplant BM samples to identify the acquisition of mutations along the post allo-HSCT period.Germline variants in donors were studied in order to detect mutations that predisposed to the development of a myeloid neoplasm.The research protocol was approved by the Ethic Committee of Gregorio Marañón General University Hospital. Patients´ and donors´ information was collected from their medical records. Results Clinical and biological characteristics of the 7 patients with DCMN and their donors are shown in Table 1. Mutational profiles obtained from the follow-up samples at different time-points post-HSCT demonstrated high intra-tumor genetic heterogeneity and clonal dynamic for all cases. The number of variants are increased over time and at the moment of DCMN diagnosis, the median number of variants was 28, ranging from 18 to 92 variants (Figure 1). WES identified in DCMN patients gene mutations commonly seen in adult AML or MDS, such as in SETBP1, DNMT3A, TET2, RUNX1, CSF3R, EP300and IDH2.In addition, others non-silent variants were acquired in all cases. Among the additional novel alterated genes, we found 23 strong candidateswith oncogenic potential. LUC7L2, NOP14, LAMA5, SKOR2, EML1, SNX13, RHPN2, IRS1, MTG2, TENM2, MEFV, GSE1, NOTCH4, DTX1, CNOT4, PNKP, GRB7,SENP7,TAF1L, ZKSCAN2, ZBTB20, ZNF461 and MEGF10. Analysis of CNVs revealed numerical alterations across the post allo-HSCT samples in patients 1, 2, 3, 4, 5 and 7. The most common chromosomal alterations in DCMN were monosomy 7 and other chromosome 7 abnormalities, which detected in the 86% (6/7) of the patients. Although none of the donors developed a myeloid neoplasm at the moment of diagnosis of DCMN in recipient, donor 1 revealed an abnormal karyotype (45,XY,-7) at the moment of the allo-HSCT. All other donors harbored at least one pathogenic or probably-pathogenic variants, most probably of germline origin, in genes involved in hematological or solid tumor predisposition. Conclusions The development of DCMN involves dynamic genomic processes that begin months before the clinical onset. In this study, our integrated multi-step analysis revealed the intra-tumor heterogeneity and evolutionary history of seven DCMN. The present study reveals a process of sequential clonal expansions promoted by the acquisition of somatic mutations in donor hematopoietic cells. Detection of heritable or acquired gene mutations in donors associated with predisposition to haematological malignancies could have clinical implications for the patients undergoing to allo-HSCT. Leukemic transformation ofdonor hematopoietic stem cells provides a useful in vivomodel to study the mechanisms involved in leukemogenesis. Novel approaches based on high-depth next generation sequencing to study consecutive samples from post-transplant period in these patients, appear promising to discover new genes involved in myeloid neoplasm and to decipher the mechanisms of leukemogenesis. Disclosures No relevant conflicts of interest to declare.

Introduction: Lymphomas continue to be a leading cause of death in HIV-positive patients (HIV+ pts) in the cART era. The aim of this study was to review our 15-year single institution experience in performing Autologous Stem Cell Transplantation (ASCT) for HIV-infected and non-HIV patients with high-risk or relapsed lymphomas, focusing on infectious complications. Patients and Methods: We retrospectively evaluated our cohort of 28 HIV+ pts who underwent an ASCT between 2000-2015, and compared it with a well-matched control group of 39 HIV-negative pts. Patient and ASCT characteristics are described in Table 1. All HIV+ pts were on cART. Chemomobilization was used in 60% of the HIV cohort and 84% of the controls. BEAM conditioning regimen was the most common. All transplants were performed in the same tertiary hospital JACIE-accredited SCT unit. The primary end points were first-year cumulative incidence (CI) of infection, total infectious episodes and infection-related mortality. For the analysis, we defined 3 different time frames: 1st Pre-engraftment; 2nd from engraftment to day +100 and 3rd from day +100 until 1 year after SCT. Events occurring during the first 2 periods were considered early infections as compared to late. Results: All patients received antiviral and anti-PJP prophylaxis, but a significantly higher proportion of HIV+ pts were given antibacterial and antifungal prophylaxis (2/3 vs 1/3 approximately, Table 1). G-CSF support was initiated in all HIV recipients and 66% of controls, and the median days of use was longer for the HIV group (7 vs 4 days, p= 0.04). Median time to neutrophil engraftment was similar in both groups (13 vs 11 days, p=0.55); 93% of HIV pts and all control pts reached ANC > 500c/uL by day +30. Infectious episodes (IE) are described in Table 2, divided by pathogen subtype and time frame. Globally, all infection subtypes were more common in the HIV-infected cohort at some point. The most significant findings from the analysis are as follows. CI of early global infections: HIV 75% vs non-HIV 25% (p= 0.04), Figure 1. Median number of global infectious events: HIV 65 vs non-HIV 39 (p= 0.002; OR 1.8 [1.2-2.8]). Bacteria: CI of pre-engraftment and early bacterial infections were not different among groups (42% vs 28%, p= 0.47), but the median number of bacterial episodes was clearly different: HIV 17 vs non-HIV 12 (p= 0.08; OR 2.16 [0.96-4.8]). Fungi: CI of early fungal infections: HIV 10.7% vs non-HIV 0% (p= 0.03); minor infections were not considered. Viruses: CI of early viral infections: HIV 46% vs non-HIV 15% (p= 0.004). Median nº of early viral IE: HIV 19 vs non-HIV 6 (p= 0.007; OR 4.16 [1.43-12]). CI of late viral infections: HIV 30% vs non-HIV 11.7% (p= 0.04). CMV reactivations were by far more common in the HIV cohort (p=0,01). HIV viral load bleeps were documented in 35% of the HIV patients (most commonly in the day +30 control) and one post-transplant virological failure was diagnosed, forcing HAART substitution. Of note, 1st year CI of infection-related mortality was 14% in the HIV group vs 0% in the non-HIV group (p= 0.01), Figure 2. Three HIV+ pts suffered early fulminant septic episodes (1 E. coli + Enterococcus, 1 Rothiamucilaginosa, 1 non-clarified - possible Stenotrophomonasmaltophilia) and a 29-year old woman in CR after a 1st line for a stage IVsB Burkitt-like lymphoma died due to a severe influenza A pneumonia. Length of admission was also significantly longer for the HIV+ pts (median days 34 vs 28, p=0.041). Regarding long-term outcome, median follow up as of July 2016 is 82 months for the HIV+ group and 70 months for the control group: 57% and 61% of the pts in each cohort are still alive, respectively. One HIV-infected pt and 3 controls have been lost to follow-up. EFS: 1 year 71.4% vs 81.9% (ns); 5 years: 63.9% vs 66.5% (ns). Overall Survival: 1 year 75% vs 84% (ns); 5 years 66.3% vs 74.6% (ns). Conclusion: Autologous stem cell transplantation has been proven to be feasible and effective in HIV-related lymphomas, but in our experience and despite great advances in cART and virological control, HIV+ patients are at high risk of infection and this might influence post-ASCT short-term survival. It is mandatory to focus on prophylactic and supportive measures and to choose carefully the optimal timing for transplantation. Table 2 Table 2. Disclosures No relevant conflicts of interest to declare.

Introduction Donor cell leukemia (DCL) is a rare complication of allogeneic stem cell transplantation (allo-SCT). The leukemic transformation of otherwise healthy donor stem cells provides a useful in vivo model to study the mechanisms involved in leukemogenesis. The objective of the present study is to study the dynamics of emergence of mutations that precede the development of DCL. Material and methods We report the case of a female patient diagnosed of acute lymphoblastic leukemia with t(1;19), who developed normal karyotype acute myeloid leukemia (AML) of donor origin 16 months after unrelated cord blood transplantation (UCBT). Whole exome sequencing(SureSelect-XT Human exon capture 50Mb Agilent Technologies) was performed by next generation sequencing (Hiseq 2000 Illumina) on bone marrow samples post allo-SCT, obtained in the days +98, +189, +350, +486 (DCL diagnosis) and + 569 (DCL relapse) as well as on the UCB unit used in SCT. The exome of bone marrow samples post allo-SCT were aligned to the human reference genome (NCBI build 37/hg19), non-synonymous variants in the coding regions of genes related to leukemia were selected and matched to the UCB exome to identify the acquired variants. Variants meeting such criteria were evaluated with three softwares (SIFT, Polyphen and Mutation Taster) to predict their functional effects. The UCB exome was aligned to the human reference genome (NCBI build 37/hg19). Results In silico variants analysis revealed progressive emergence of multiple mutations related to the development of leukemia in bone marrow samples post allo-SCT (Figure 1). Interestingly three of the mutated genes (PTPN11, NRAS, MAP2K1) are part of the same cellular pathway (RAS-MAPK). In addition, mutations in leukemic subclones that disappear after chemotherapy were indentified, as well as the acquisition of new mutations in resistant subclones (Figure 2). Finally a mutation in SH2B3 gene, a gene that encodes for a regulatory protein of the JAK-STAT pathway, which links strongly to JAK2 inhibiting the activation of the pathway, was detected in the CBU. Conclusions The present study reveals the acquisition of additional somatic mutations in donor cells during leukemogenesis, including mutations not previously described in AML initiation (POU2F2, CA9, POU4F1, FMN2, TLR9, ELF5). Although the cause of DCL onset seems to be multifactorial, the infusion of a CBU with pre-leukemic potential due to mutation in SH2B3 in a context of residual toxicity in recipient as a result of pre-transplant chemotherapy, a post-transplant environment characterized by a decreased immune surveillance may well have played role in the case here reported. The study of a greater number of DCL cases by next generation sequencing could help to understand the process of leukemogenesis. Figure 1 Mutations related to the onset of donor cell leukemia after hematopoietic transplantation. Figure 1. Mutations related to the onset of donor cell leukemia after hematopoietic transplantation. Figure 2 Dynamic of mutation acquisitions in leukemic clones.(DCL: Donor cell leukemia, CBU: Cord blood unit, CBT: Cord blood transplantation, Quim: Quimerism, CQ: Complete quimerism) Figure 2. Dynamic of mutation acquisitions in leukemic clones.(DCL: Donor cell leukemia, CBU: Cord blood unit, CBT: Cord blood transplantation, Quim: Quimerism, CQ: Complete quimerism) Disclosures No relevant conflicts of interest to declare.