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INTRODUCTION In good risk patients (historic inhibitor peak

Congenital thrombotic thrombocytopenic purpura (cTTP) is an ultra-rare thrombomicroangiopathy caused by an inherited deficiency of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13). There are limited data on genotype-phenotype correlation; there is no consensus on treatment. We reviewed the largest cohort of cTTP cases, diagnosed in the United Kingdom, over the past 15 years. Seventy-three cases of cTTP were diagnosed, confirmed by genetic analysis. Ninety-three percent were alive at the time of review. Thirty-six percent had homozygous mutations; 64% had compound heterozygous mutations. Two presentation peaks were seen: childhood (median diagnosis age, 3.5 years) and adulthood, typically related to pregnancy (median diagnosis age, 31 years). Genetic mutations differed by age of onset with prespacer mutations more likely to be associated with childhood onset (P = .0011). Sixty-nine percent of adult presentations were associated with pregnancy. Fresh-frozen plasma (FFP) and intermediate purity factor VIII concentrate were used as treatment. Eighty-eight percent of patients with normal blood counts, but with headaches, lethargy, or abdominal pain, reported symptom resolution with prophylactic therapy. The most common currently used regimen of 3-weekly FFP proved insufficient for 70% of patients and weekly or fortnightly infusions were required. Stroke incidence was significantly reduced in patients receiving prophylactic therapy (2% vs 17%; P = .04). Long-term, there is a risk of end-organ damage, seen in 75% of patients with late diagnosis of cTTP. In conclusion, prespacer mutations are associated with earlier development of cTTP symptoms. Prophylactic ADAMTS13 replacement decreases the risk of end-organ damage such as ischemic stroke and resolved previously unrecognized symptoms in patients with nonovert disease.

Patients with an ABL-class fusion have a high risk of relapse on standard chemotherapy but are sensitive to tyrosine kinase inhibitors (TKI). In UKALL2011, we screened patients with post-induction MRD ≥1% and positive patients (12%) received adjuvant TKI. As the intervention started during UKALL2011, not all eligible patients were screened prospectively. Retrospective screening of eligible patients allowed the outcome of equivalent ABL-class patients who did and did not receive a TKI in first remission to be compared. ABL-class patients who received a TKI in first remission had a reduced risk of relapse/refractory disease: 0% vs. 63% at four years (P = 0·009).

Methodology This guideline was compiled according to the British Society for Haematology (BSH) process at (http://www.bcshguidelines.com). The Grading of Recommendations Assessment, Development and Evaluation (GRADE) nomenclature was used to evaluate levels of evidence and to assess the strength of recommendations. The GRADE criteria can be found at http://www.gradeworkinggroup.org. Literature review details Ovid MEDLINE and Ovid EMBASE were searched systematically for publications in English from 1980 to the end of 2015 using the key words Transient Abnormal Myelopoiesis, Transient Myeloproliferative Disorder, Transient Leukaemia, and Down Syndrome. Specific searches relating to fetal disease and hepatic parameters were also performed. References from relevant publications were also searched. Working group membership The guideline group was selected to be representative of UK‐based medical experts with invited representatives from the British Association of Perinatal Medicine and the Royal College of Paediatrics and Child Health. Review Review of the manuscript was performed by the BSH Guidelines General Haematology Task Force, the BSH Guidelines Committee and the General Haematology sounding board of BSH. It was also placed on the members section of the BSH website for comment. Further comments were invited from a sounding board of the Childhood Leukaemia Clinicians'27 Network, the Childhood Cancer and Leukaemia Group (CCLG), the Royal College of Paediatrics and Child Health, the British Association of Perinatal Medicine (BAPM) and patient representatives identified through the Down Syndrome Association; these organisations do not necessarily approve or endorse the contents. The objective of this guideline is to provide healthcare professionals with guidance on the investigation and management of patients with Transient Leukaemia of Down Syndrome (TL‐DS). Individual patient circumstances may dictate an alternative approach. This is the first BSH guideline on this topic and is in date at time of publication. Any updates will be posted on the BSH Guidelines website (http://www.bcshguidelines.com).

Contains fulltext : 219893.pdf (Publisher’s version ) (Closed access) BACKGROUND: Treatment of venous thromboembolism in children is based on data obtained in adults with little direct documentation of its efficacy and safety in children. The aim of our study was to compare the efficacy and safety of rivaroxaban versus standard anticoagulants in children with venous thromboembolism. METHODS: In a multicentre, parallel-group, open-label, randomised study, children (aged 0-17 years) attending 107 paediatric hospitals in 28 countries with documented acute venous thromboembolism who had started heparinisation were assigned (2:1) to bodyweight-adjusted rivaroxaban (tablets or suspension) in a 20-mg equivalent dose or standard anticoagulants (heparin or switched to vitamin K antagonist). Randomisation was stratified by age and venous thromboembolism site. The main treatment period was 3 months (1 month in children /=1 dose), were centrally assessed by investigators who were unaware of treatment assignment. Repeat imaging was obtained at the end of the main treatment period and compared with baseline imaging tests. This trial is registered with ClinicalTrials.gov, number NCT02234843 and has been completed. FINDINGS: From Nov 14, 2014, to Sept 28, 2018, 500 (96%) of the 520 children screened for eligibility were enrolled. After a median follow-up of 91 days (IQR 87-95) in children who had a study treatment period of 3 months (n=463) and 31 days (IQR 29-35) in children who had a study treatment period of 1 month (n=37), symptomatic recurrent venous thromboembolism occurred in four (1%) of 335 children receiving rivaroxaban and five (3%) of 165 receiving standard anticoagulants (hazard ratio [HR] 0.40, 95% CI 0.11-1.41). Repeat imaging showed an improved effect of rivaroxaban on thrombotic burden as compared with standard anticoagulants (p=0.012). Major or clinically relevant non-major bleeding in participants who received >/=1 dose occurred in ten (3%) of 329 children (all non-major) receiving rivaroxaban and in three (2%) of 162 children (two major and one non-major) receiving standard anticoagulants (HR 1.58, 95% CI 0.51-6.27). Absolute and relative efficacy and safety estimates of rivaroxaban versus standard anticoagulation estimates were similar to those in rivaroxaban studies in adults. There were no treatment-related deaths. INTERPRETATION: In children with acute venous thromboembolism, treatment with rivaroxaban resulted in a similarly low recurrence risk and reduced thrombotic burden without increased bleeding, as compared with standard anticoagulants. FUNDING: Bayer AG and Janssen Research & Development. 01 januari 2020

Children with constitutional trisomy 21 (Down syndrome (DS)) have a unique predisposition to develop myeloid leukaemia of Down syndrome (ML-DS). This disorder is preceded by a transient neonatal preleukaemic syndrome, transient abnormal myelopoiesis (TAM). TAM and ML-DS are caused by co-operation between trisomy 21, which itself perturbs fetal haematopoiesis and acquired mutations in the key haematopoietic transcription factor gene GATA1. These mutations are found in almost one third of DS neonates and are frequently clinically and haematologcially 'silent'. While the majority of cases of TAM undergo spontaneous remission, ∼10 % will progress to ML-DS by acquiring transforming mutations in additional oncogenes. Recent advances in the unique biological, cytogenetic and molecular characteristics of TAM and ML-DS are reviewed here.

Introduction and Objective: Inhibitors to coagulation factor VIII (FVIII) are the most serious complication of haemophilia A treatment. Previously untreated patients (PUPs) are at the greatest risk of inhibitors, which generally occur within the first 20 exposure days (ED) to FVIII. Immune tolerance induction (ITI) is the only clinically proven strategy for eradication of inhibitors. We present a case series of six PUPs with severe haemophilia A and inhibitors who underwent ITI with simoctocog alfa (Nuwiq®), a 4th generation human cell-line-derived recombinant FVIII approved for treatment of haemophilia A. Materials and Methods: Six male PUPs with severe haemophilia A who developed FVIII inhibitors after treatment with simoctocog alfa were started on ITI with simoctocog alfa. Primarily, we assessed the success of simoctocog alfa in patients with inhibitors. Success of ITI was determined based on undetectable inhibitor titre (< 0.6 BU/ml), FVIII recovery ≥ 66% and half-life ≥ 6 hours. Secondary objectives were to assess bleeding rate, tolerability and safety in patients with inhibitors treated with simoctocog alfa ITI. Results: The age of the patients at the start of ITI ranged from 8 to 186 months. Four of the patients were Caucasian, and two were African. All patients had a F8 mutation associated with high risk of ITI failure and two patients had an additional risk factor for ITI failure. The number of EDs prior to inhibitor development ranged from 9 to 33, and the peak inhibitor titre ranged from 0.9 to 114 BU. For ITI, five patients were treated with 100 IU/kg simoctocog alfa daily, and one with 90 IU/kg every other day. One patient achieved complete tolerisation and is now on prophylaxis at normal doses, having achieved an undetectable inhibitor titre after 9 months. This was despite an inhibitor titre ≥ 10 BU/mL at ITI start, which is considered a poor prognosis factor for ITI success. Three other patients achieved an undetectable inhibitor titre after 1, 6 and 18 months of ITI, and FVIII recovery has normalised but half-life remains short and they are on weaning doses as the half-life extends. One patient discontinued ITI with simoctocog alfa after 15 months due to an increasing inhibitor level. This patient was 15 years old at ITI start, and older age is associated with poor ITI outcome. Additionally, his haemophilia A was untreated for 15 years, during which time he developed severe arthropathy. One patient, who started ITI 3 months ago, has an ongoing inhibitor titre and continues on ITI with simoctocog alfa. Conclusions: In a case series of six patients treated with simoctocog alfa for ITI, who all had poor prognosis factors for ITI success, four patients (67%) to date have achieved an undetectable inhibitor titre. These data suggest that ITI with simoctocog alfa may be an effective treatment approach in haemophilia A patients with inhibitors. Disclosures Khair: Shire, SOBI, Pfizer, Roche, Novo Nordisk, Octapharma: Speakers Bureau; shire, SOBI, Pfizer, Roche: Research Funding. Liesner:Roche: Research Funding; Novo Nordisk: Research Funding, Speakers Bureau; Baxalta: Consultancy, Research Funding; Bayer: Consultancy, Research Funding; Octapharma: Consultancy, Other: Clinical study investigator for NuProtect Study (Octapharma sponsored), Research Funding, Speakers Bureau; Sobi: Speakers Bureau. Belyanskaya:Octapharma AG: Employment.

We explored the feasibility of unrelated donor haematopoietic stem cell transplant (HSCT) upfront without prior immunosuppressive therapy (IST) in paediatric idiopathic severe aplastic anaemia (SAA). This cohort was then compared to matched historical controls who had undergone first-line therapy with a matched sibling/family donor (MSD) HSCT (n = 87) or IST with horse antithymocyte globulin and ciclosporin (n = 58) or second-line therapy with unrelated donor HSCT post-failed IST (n = 24). The 2-year overall survival in the upfront cohort was 96 ± 4% compared to 91 ± 3% in the MSD controls (P = 0·30) and 94 ± 3% in the IST controls (P = 0·68) and 74 ± 9% in the unrelated donor HSCT post-IST failure controls (P = 0·02).The 2-year event-free survival in the upfront cohort was 92 ± 5% compared to 87 ± 4% in MSD controls (P = 0·37), 40 ± 7% in IST controls (P = 0·0001) and 74 ± 9% in the unrelated donor HSCT post-IST failure controls (n = 24) (P = 0·02). Outcomes for upfront-unrelated donor HSCT in paediatric idiopathic SAA were similar to MSD HSCT and superior to IST and unrelated donor HSCT post-IST failure. Front-line therapy with matched unrelated donor HSCT is a novel treatment approach and could be considered as first-line therapy in selected paediatric patients who lack a MSD. © 2015 John Wiley & Sons Ltd.

HDAC inhibitors (HDACi) increase transcription of some genes through histone hyperacetylation. To test the hypothesis that HDACi-mediated enhanced transcription might be of therapeutic value for inherited enzyme deficiency disorders, we focused on the glycolytic and pentose phosphate pathways (GPPPs). We show that among the 16 genes of the GPPPs, HDACi selectively enhance transcription of glucose 6-phosphate dehydrogenase (G6PD). This requires enhanced recruitment of the generic transcription factor Sp1, with commensurate recruitment of histone acetyltransferases and deacetylases, increased histone acetylation, and polymerase II recruitment to G6PD. These G6PD-selective transcriptional and epigenetic events result in increased G6PD transcription and ultimately restored enzymatic activity in B cells and erythroid precursor cells from patients with G6PD deficiency, a disorder associated with acute or chronic hemolytic anemia. Therefore, restoration of enzymatic activity in G6PD-deficient nucleated cells is feasible through modulation of G6PD transcription. Our findings also suggest that clinical consequences of pathogenic missense mutations in proteins with enzymatic function can be overcome in some cases by enhancement of the transcriptional output of the affected gene.

The classical treatment algorythm of idiopathic severe aplastic anemia (SAA) forsees, if a sibling donor is not available in the family, a first line option represented by immunosuppressive therapy (IST) with ATG and Cyclosporine A (CsA). IST provides a very good survival rate but a fairly high rate of failures (no response, relapse, need for transplant). This is particularly important in childhood and adolescence where faulty hematopoiesis represents a relevant limitation of quality of life. The option of haematopoietic stem cell transplantation (HSCT) from matched unrelated donor (MUD) as front line treatment with no prior failed IST, has never been investigated so far. This study provides for the first time the outcome analysis of 29 consecutive SAA patients who received an upfront unrelated donor HSCT without prior IST, in 9 UK Centres and compares each of these patient with 3 matched controls from the data base of the SAAWP of the EBMT who, in a similar time-span, underwent Matched Sibling Donor (MSD) HSCT. Twenty four patients received HLA-A,-B,-C,-DQ-,-DRB1 matched MUD HSCTs whilst 5 received single antigen/allele Mismatched Unrelated Donor (MMUD) grafts. The conditioning regimen was FCC (Fludarabine, Cyclophosphamide and Alemtuzumab) with the addition of low dose (3cGy) TBI for the MMUD HSCTs. GVHD prophylaxis was with CsA +-Mycophenolate. The primary endpoints were overall survival (OS) and event free survival (EFS). Events were death, disease recurrence, second HSCT, clinical PNH and post-transplant malignancies. Complete remission (CR) was defined as Hb > 10 g/dl, neutrophil count > 1x 109/l and platelet count > 100x109/l. The 87 (3 for each MUD/MMUD HSCT) patients from the EBMT data base who underwent MSD HSCT as first line treatment were matched to the upfront MUD/MMUD cohort by age, gender, time from diagnosis to HSCT and source of stem cells. Their median follow-up was 1.6 years (range 0.01-9.39). In the upfront MUD/MMUD cohort there were 12 males (41%) and 17 females (59%). Median age at HSCT was 8.46 years (range 1.73-19.11), 72% was aged below and 28% above 12 years; median interval from diagnosis to HSCT was 0.39 years (range 0.19-1.35) with 72 % receiving bone marrow and 28% peripheral blood stem cells. The median follow-up was 1.7 years (range 0.19-8.49). The median time to neutrophil recovery (>0.5 x 109/l) was 18 days (range 9-29) and the median time to platelet recovery (>50 x 109/l) was 19 days (range 10-40). The 100 day cumulative incidence (CI) of grade II-IV acute GVHD was 10 ± 6% ; there was only one case of grade III-IV acute GVHD (frequency of 3.5%). The 1 year CI of chronic GVHD was 19 ± 8%. There were 5/29 cases (frequency of 17,2 %), 4 in the MUD and 1 the MMUD subset. Chronic GVHD was limited in all cases and restricted to skin. There were only 2 events in this cohort; one primary graft failure following a HLA-A MMUD HSCT who has now successfully received a second HSCT and one death due to idiopathic pneumonia syndrome. No post-treatment malignancies occurred at last follow-up. The other 27 patients are in CR at last follow-up. The median interval diagnosis-neutrophil recovery was similar in MUD/MMUD (0.39 years; range 0.19-1.35) vs MSD transplants (0,31 years; range 0,1- 0,45) (p=0.93). The 2 year OS was 96%±4% in the upfront MUD/MMUD cohort vs 91%±3% of the MSD cohort (p=0.30). The 2 year EFS was 92%±5% in the upfront cohort vs 87%±4% in MSD (p=0.37) (Fig 1). The 2 year CI of rejection was 4%±4% in the MUD/MMUD vs .1%±1% in the MSD group (p=0.48). This is the first controlled study indicating that in idiopathic SAA of childhood and adolecence upfront MUD/MMUD HSCT using FCC as conditioning regimen, has similar outcome to MSD HSCT. MUD HSCT may be considered a feasible and successful treatment option when children lack a MSD and a MUD is readily available. Figure 1 Figure 1. Comparison of EFS between upfront MUD/MMUD and front-line MSD HSCT. Events were: death, disease recurrence, second HSCT, clinical PNH and post-transplant- malignancies. Table 1 EFS N events 2-yrs Pr (%) (SE) p-value MUD/MMUD 29 2 92 (5) 0.37 MSD 87 11 87 (4) Disclosures Dufour: Pfizer: Consultancy.

Children with Down syndrome (DS; trisomy 21) have an increased risk of acute myeloid leukemia (ML-DS) in the first 5 years of life. In most cases ML-DS is preceded by Transient Abnormal Myelopoiesis (TAM), a fetal/neonatal pre-leukemic disorder unique to DS which regresses after birth. Both TAM and ML-DS harbor acquired N-terminal mutations in the hematopoietic transcription factor gene GATA1. In a prospective study of 200 DS neonates, we recently showed that 29% had acquired GATA1 mutations including 17/200 (8.5%) with clinical or hematologic evidence of TAM; the remaining 20.5% were clinically and hematologically 'silent', with smaller mutant GATA1 clones and lower blast frequency compared to overt TAM. The reasons why some DS neonates develop overt TAM and the factors which determine mutant GATA1 clone size are unknown. To address this, we analysed data from neonates in the prospective Oxford-Imperial DS Cohort Study and investigated the impact of 30 clinical and hematologic factors on clone size using statistical and mathematical modelling. Mutant GATA1 clones were determined in 54 neonates by targeted next generation sequencing of GATA1 exon 2 (mutation detection limit 0.3%). Clone size was determined by analysing original unprocessed reads using less stringent filtering parameters and counting reads containing mutated v total sequence. Correlation analysis identified 4 hematologic variables correlated with mutant GATA1 clone size: circulating nucleated red cells (r=+0.5003; p=0.0001), platelets (r=+0.436; p=0.001), total leukocytes (r=+0.7094; p150x109/L (p=0.019). Numbers of neutrophils, monocytes, basophils, eosinophils and lymphocytes did not correlate with GATA1 clone size. Clinical variables significantly correlated with clone size were hepatomegaly (p=0.0016), splenomegaly (p=0.0001) and rash (0.0174). The only pregnancy-related variables affecting mutant GATA1 clone size were intrauterine growth restriction and maternal diabetes (p=0.0156). Linear regression to determine the joint impact of all 30 variables on clone size (r2=0.88) followed by Lasso penalization identified the same 4 hematologic variables (nucleated red cells, platelets, total leukocytes and % blasts); Lasso penalized regression with these 4 variables gave a coefficient of determination of 0.63. Together these data suggest that chronic intrauterine hypoxia may affect expansion/differentiation of mutant GATA1 clones in DS. Consistent with this, nucleated red cells from 3 neonates with TAM all harbored GATA1 mutations identical to those in total circulating nucleated cells. Since neither perinatal infection nor gestational age at birth correlated with mutant GATA1 clone size, infection-related cytokines and the timing of acquisition of a mutant GATA1 clone during fetal development may not play a major role in determining clone size. Finally, a hierarchical model to investigate the impact of GATA1 mutation on hematopoietic stem and progenitor (HSPC) differentiation in DS neonates using a Bayesian approach also predicted increased erythroid cell output from GATA1 mutated HSPC v HSPC without a GATA1 mutation. In conclusion, in neonates with DS the size of the mutant GATA1 clone correlates with the presence of clinical signs of hepatomegaly, splenomegaly and skin rash; mutant GATA1 clone size correlates with the numbers of circulating nucleated red cells, platelets and blast cells suggesting that GATA1 mutant HSPC retain the ability to differentiate down the erythroid and megakaryocyte lineage; intrauterine hypoxia may be one of the factors driving expansion and/or maturation of the GATA1 mutant clone during fetal life in DS. Disclosures No relevant conflicts of interest to declare.

In Down syndrome (DS), trisomy 21 (T21) causes perturbation of fetal liver (FL) hematopoiesis leading to expansion of megakaryocyte-erythroid (MK-E) progenitors. On this background, FL hematopoietic stem/progenitor cells (HSPC) may acquire GATA1 gene mutations which usually present as a neonatal preleukemic condition, Transient Myeloproliferative Disorder (TMD). TMD develops only in fetal life and most cases spontaneously regress after birth, suggesting unique features of the T21 fetal microenvironment may be important in driving both abnormal DS FL hematopoiesis and mutant GATA1 clones in TMD. Previous work showed activation of insulin-like growth factor (IGF) signalling in TMD and DS-AMKL and fetal-specific IGF dependence of murine MK development implicating T21 in altered fetal IGF signalling. To investigate the role of IGF signalling in fetal MK-E development in DS FL without GATA1 mutations, we performed gene expression profiling (GEP) of DS FL (n=5) and normal FL CD34+ cells (n=3). GSEA showed significant enrichment of IGF targets. We therefore measured expression of the principal IGF receptor, IGF1R, on DS FL HSPC (n=6). Surface IGF1R was uniformly expressed on all DS FL HSPC subpopulations. However, there was no difference in IGF1R surface or gene expression between DS and normal FL HSPC (n=8) suggesting that increased IGF1R expression on TMD and DS-AMKL cells is an early event and may reflect their fetal rather than T21 origin. To determine if the enrichment of IGF targets in DS FL HSPC might reflect increased IGF production in the FL microenvironment, we compared IGF expression in DS FL mesenchymal stromal cells (MSC)(n=4) and hepatocytes with normal FL MSC (n=4). Both DS and normal FL MSC expressed large amounts of IGF2, but little or no IGF1 with no difference between DS and normal MSC. Similarly, IGF2 was expressed by IHC at similar levels in both DS and normal fetal hepatocytes and MSC whereas IGF1 was barely detectable. Normal and DS fetal bone marrow (BM) MSC also expressed high levels of IGF2, but not IGF1 in contrast to adult BM MSC. Thus, IGF2 is the main IGF produced in the human fetal hematopoietic environment. Consistent with a specific role in DS FL hematopoiesis, IGF2 caused marked proliferation of DS FL clonogenic MK and MK-E cells (n=3) and stimulated MK proliferation in liquid culture while in normal FL, IGF2 stimulated EPO-independent BFU-E and Pre-BFU-E but had no effect on MK cells. Since differential effects of IGF2 on DS/normal FL HSPC might be due to altered expression of the Insulin Receptor (InsR), which binds IGF2 with low affinity, we compared InsR surface and gene expression in DS and normal FL HSPC but found no significant difference. IGF2 also binds to IGF2R, a negative regulator of IGF2, however there was no difference in IGF2R expression between DS and normal FL HSPC. Co-culture of normal FL CD34+ cells with DS or normal FL MSC (n=3) promoted MK and erythroid cell proliferation and differentiation. Since the effect of DS FL MSC on normal FL CD34+ cells was significantly greater (~4-fold) than that of normal FL MSC, the data above suggest this is unlikely to be due to IGF2 alone. To investigate whether T21 alters the MSC secretome, we performed GEP of DS FL MSC (n=3) and compared this with normal FL MSC (n=5). Both normal FL and DS FL expressed known hematopoietic cytokine genes, including SCF, CXCL12, G-CSF, M-CSF, Flt3 and IL-6, as well as IGF2 but not IGF1, EPO or TPO. Of the top 80 differentially expressed genes (Fold Change>2), ~40% encode secreted proteins, including several which affect IGF availability. Conclusion: T21 perturbs FL hematopoiesis through both HSPC-intrinsic mechanisms, including changes in IGF responsiveness, and through alterations to the FL microenvironment. Disclosures No relevant conflicts of interest to declare.

Abstract 11 Stem cell transplantation (SCT) is currently the only curative option for sickle cell disease. Cerebrovascular disease (CVD) is one of the main indications to undertake this procedure as even with best conventional approaches there is a significant risk of recurrence or progression and there is evidence that SCT arrests disease progression, though more detailed study of outcomes is awaited. Early studies of SCT in sickle cell disease showed a high rate of neurological complications that led to the optimization of protocols. We conducted a retrospective analysis of related SCT in children with severe SCD between 2001 and 2010 at our institution to study the effect of transplantation. 20 patients (11 male, 9 female) received a BMT for sickle CVD (n=11) or recurrent vaso-occlusive crises (n=9). One patient with CVD was a second procedure following primary graft failure in a previous sibling transplant. CVD was investigated with clinical history and examination, transcranial Doppler ultrasound, magnetic resonance imaging/magnetic resonance angiography and psychometric testing using WISC-IV: 7 patients had no evidence of CVD, 5 had silent infarcts, 6 ischaemic stroke and 2 Moya-Moya disease. The median age at transplantation was 136 months (range 34 – 210 months). Donor source was HLA-matched siblings in 18 patients, one 9/10 mismatched sibling and HLA-matched relative in another. Bone marrow was used in all (n=19) but one patient who received combined bone marrow and umbilical cord. All patients (n=18) but two received conditioning with oral busulfan 14 mg/kg, cyclophosphamide 200 mg/kg and alemtuzumab 0.3 mg/kg; 1 patient received fludarabine 160 mg/m2, treosulfan 42 mg/m2, thiotepa 10mg/kg and ATG (Thymoglobulin) 11.25 mg/kg and 1 patient received oral busulfan 16mg/kg, cyclophosphamide 200 mg/kg and antilymphocyte globulin (45 mg/kg). GvHD prophylaxis was provided with ciclosporin and short course methotrexate (n=18), ciclosporin and MMF (n=1) and ciclosporin alone (n=1). Mean cell dose was 3.70 × 108 TNC/kg (range 1.45 – 6.16 × 108 TNC/kg). Neutrophil engrafment (>0.5 × 109/L) occurred at a median of 19.5 days (range 12 – 28 days) and platelet engrafment (>50 × 109/L) at median of 26 days (range 21 – 52 days). The median follow up is 974 days (range 270 – 3622 days). 18 patients achieved stable donor haemopoiesis, one patient suffered secondary graft failure due to Parvovirus B19 infection and one patient died on day +21 post-transplant due to sepsis and multi-organ failure. No significant sickle related neurological events occurred during these transplants. All 18 patients with long-term engraftment achieved radiological stabilization of the underlying CVD. Imaging performed at least 12 months post SCT showed no further changes from pre-transplant images. There were no clinical neurological events after SCT. Psychometric testing demonstrated improvements in all areas in patients transplanted for silent infarcts, particularly those affecting processing speed. In summary, SCT appears safe even in patients with severe CVD, arrests further progression and shows functional improvement. Disclosures: No relevant conflicts of interest to declare.

Abstract 1673 Introduction: Mature B-cell lymphoproliferative disorders that present with a leukemic phase may have overlapping morphological and immunophenotypic features. Accurate diagnosis is essential to determine prognosis and therapy. B-cell chronic lymphocytic leukaemia (B-CLL) and mantle cell lymphoma (MCL) both express CD5 but usually have divergent clinical courses. Conventional markers are able to discriminate in many cases but a significant proportion of cases require more detailed analysis. CD200 is a membrane glycoprotein that has been reported to differentiate between B-CLL and MCL. It is expressed on resting and activated T and B cells, but not on NK cells, monocytes, granulocytes or platelets. We prospectively assessed the utility of this antibody in a single centre, servicing haematology units in North London. Methods: Over a 12 month period we prospectively assessed the expression of CD200 (Clone MRC OX-104, BD Pharmingen) on neoplastic cells of patients with presenting with mature B-cell lymphoproliferative disorders. EDTA anti-coagulated peripheral blood and bone marrow underwent a lyse/wash technique before being acquired on a BD FACS Canto II flow cytometer equipped with DIVA 6.1.2 software. A lymphoid gating strategy was used to analyse the data and expression of more than 20% of nucleated cells referenced to a negative internal control was considered positive. A diagnosis was made using all available data according to the WHO classification of haematopoietic tumours, including the 5 point CLL score. The predictive value of CD200 expression was subsequently assessed. Results: There were 100 patients (58M: 42F) with a median age of 70 years (range 29–92). CD200 was present on the neoplastic cells of all 78 patients with B-CLL; in all 7 MCL patients CD200 was negative; 15 patients had CD5 negative B-cell lymphoproliferative disorder with variable expression of CD200. The specificity of CD200 negativity in the setting of CD5 positive B-cell clone was 100% for MCL. The positive predictive value of CD200 for CLL was 97.5% with a sensitivity of 100% and a Pearson's correlation coefficient of 1. Conclusion: Our results confirm CD200 expression in the neoplastic cells of B-CLL patients but not in MCL. This antibody may contribute to the accurate differentiation between B-CLL and MCL in patients presenting with the diagnostic problem of a CD5- positive lymphoproliferative disorder. We propose to add CD200 to our diagnostic B-cell lymphoma panel. Further studies are needed to determine whether CD200 could replace other immunophenotypic strategies currently used in this situation, such as CD23, FMC7 and intensity of CD22/CD79b expression. Disclosures: No relevant conflicts of interest to declare.