Abstract: Abstract LBA-3 Mutations in the transcription factor genes, RUNX1 and CEBPA, can lead to an autosomal dominant familial predisposition to MDS/AML. Using a candidate gene approach, we have detected domain specific heterozygous mutations in the GATA2 gene in 4 MDS/AML families which predispose to MDS/AML. The same novel heterozygous T354M missense mutation was observed in 3 families and a 355delT mutation in 1 family, all with multigenerational transmission of MDS and/or MDS/AML. Importantly, these genetic variants segregate with all affected members in each of the families. The 2 mutated threonine residues are in 5 consecutive highly conserved threonine residues at the DNA-binding, protein-protein interacting second zinc finger (ZF2) of GATA2. Neither these mutations, nor any other variants in the GATA2 coding sequence, were seen in a population screen of 695 normal individuals. Haplotype analysis suggests that the T354M mutation has multiple ancestral origins. While mutations in RUNX1 and CEBPA, can also lead to familial predisposition to MDS/AML, these patients with GATA2 mutations are unique in that there is no obvious pre-MDS or pre-leukaemic phenotype such as thrombocytopenia (RUNX1) and eosinophilia (CEBPA) in predisposed carriers. Most patients in these families have had a rapid disease course “appearing out of the blue” leading to death, with a variety of ages of onset from teenagers to early 40s. Yet remarkably, there are still asymptomatic carriers in their 60s. One of these carriers, and his 2 children, has had bone marrow prophylactically stored over 15 years ago in case of disease onset. No pathogenic GATA2 coding sequence changes were found in 268 sporadic MDS/AML patient samples. Additionally, GATA2 mutations were not found in germline samples from 35 other families predisposed to AML and various other hematological malignancies. Both the T354M and 355delT mutants appear to localize appropriately to the nucleus and maintain at least some DNA binding in electrophoretic mobility shift assays. We used the known murine Gata3 ZF2 structure bound to DNA to model the effects of the observed mutations and demonstrated that the T354 residue does not contact DNA but makes polar contact with the adjacent threonines, and via its amino group, with C349 which coordinates the zinc atom. Replacement of the T354 side-chain with the bulky methionine moiety may affect the zinc contacts and is predicted to alter the overall structure of this ZF2. In contrast, 355delT will shorten the conserved threonine string which is predicted to impact on the orientation and position of L359 which directly contacts DNA. Thus, 355delT is likely to have an effect on DNA binding. Luciferase reporter assays indicate that T354M and 355delT greatly reduce the transactivation ability of GATA2 on multiple response elements, impacting on downstream target genes such as RUNX1 and CD34. Of note, T354M shows a markedly lesser synergistic effect than wildtype (WT) GATA2 with PU.1 on the CSF1R promoter. Competition assays show that these mutations may be acting in a dominant negative fashion in some biological contexts. In stable promyelocytic HL-60 cell lines expressing regulatable GATA2 (WT or T354M), T354M allows proliferation to proceed even under stimulus to differentiate with all-trans retinoic acid. Microarray studies indicated that the down regulation of proapoptotic BCL-xS by T354M, but not WT, may be responsible for this phenotype. GATA2 is considered to be a hematopoietic “stemness” gene, highly expressed in haematopoietic stem cells and is required for megakaryocyte and mast cell production. GATA2 is down regulated during myeloid differentiation and forced overexpression prevents such differentiation. Discovery of GATA2 mutants in MDS/AML predisposed families provides new tools for probing the mechanism of GATA2 induced leukemogenesis, and possibly also for clarifying its role in maintenance of stemness. Our findings highlight the power of investigating familial predispositions to cancer identifying specific mutations with unique biological effects. They have immediate implications for diagnostic genetic testing, and longer term therapeutic implications through identification of drugable biological pathways such as apoptosis. The poor outcome associated with these mutations may suggest that an aggressive strategy is appropriate in the treatment of affected individuals in families found to be carrying GATA2 mutations. Disclosures: No relevant conflicts of interest to declare.

Abstract: This study characterized the contribution of bone marrow-derived cells to human neoplasia and the perineoplastic stroma. The Australasian Bone Marrow Transplant Recipient Registry was used to identify solid organ neoplasia that developed in female recipients of male allogeneic stem cell transplants. Eighteen suitable cases were identified including several skin cancers, two gastric cancers, and one rectal adenoma. Light microscopy, fluorescence and chromogenic in situ hybridization, and immunohistochemistry were performed to determine the nature and origin of the neoplastic and stromal cells. In contrast to recent reports, donor-derived neoplastic cells were not detected. Bone marrow-derived neoplasia-associated myofibroblasts, however, were identified in the rectal adenoma and in a gastric cancer. Bone marrow-derived cells can generate myofibroblasts in the setting of human gastrointestinal neoplasia. Disclosure of potential conflicts of interest is found at the end of this article.

Abstract: Red cell and platelet transfusion requirements have been reported to be lower following reduced intensity conditioning allogeneic hematopoietic stem cell transplantation (RIC allo-HCT) when compared to myeloablative (MA) allo-HCT. However, previous studies examined RIC regimens with lower haemopoietic toxicity than many of the regimens in use today. We investigated risk factors for red cell and platelet transfusion in patients enrolled prospectively in an Australian study investigating the non-HLA immunogenetics of sibling allo-HCT. The transfusion requirements in the first year post transplant were reviewed for 122 patients transplanted between 2002 and 2006 in three Australian transplant centres. Seventy-one patients received MA and 51 RIC regimens. Using regression analysis, the outcome variables of total red cell and platelet units transfused were analysed. The factors age, transplant centre, disease, transplant type (RIC v MA), days of neutropenia, death within 12 months, disease risk (high risk (HR) v standard risk (SR)) and ABO mismatch underwent univariate analysis. Associated variables with p 〈 0.2 were included in a multivariable analysis. Duration of neutropenia, disease risk, death within 12 months and transplant centre were significantly associated with higher red cell and platelet usage (p 〈 0.0001). Transplant type was not associated with transfusion requirement. Each additional day of neutropenia resulted in a 9% increase in number of red cell units transfused and 11% of platelet units. HR MA patients used an estimated 17 units of red cells compared to 12 units for SR. HR RIC patients used an estimated 26 units compared to 10 for SR RIC patients. HR patients used an estimated 16.9 platelet units compared to 8.5 for low risk. These data highlight the importance of disease risk and degree of myelosuppression as key risk factors for blood product usage following allo-HSCT.

Abstract: Aim: Although allogeneic stem cell transplant (alloSCT) remains the only curative option for myelofibrosis, novel therapeutic agents, the application of new prognostic scoring systems and the emergence of molecular genetic analysis have lead to a new management landscape in myelofibrosis. In view of these recent advances, we aimed to review national practice in transplanting myelofibrosis patients and its outcomes. Methods: A retrospective study was conducted using the Australasian Bone Marrow Transplant Registry (ABMTRR) data on patients who underwent alloSCT for myelofibrosis at Australian/New Zealand transplant centres between 2006 and 2017. Participating centres completed an online questionnaire and responses were reviewed centrally by the ABMTRR. Results: 142 patients underwent alloSCT for myelofibrosis, primary (n=94) or secondary (n=48) (Table 1). 52% had HLA-identical sibling donors and 45% had matched unrelated donors (UD). Median follow-up was 51.8 months (range: 3.1-148). Cytogenetic abnormalities were identified in 29% of 120 patients who were tested pretransplant. JAK2 mutation testing was performed in 74% of patients whilst other mutations (CALR, MPL, EZH2, IDH, SRSF2, ASXL1) were rarely tested (1.4-8.4%). Only 4.2% of patients had next generation sequencing. Before transplant, 16% had splenectomy or splenic irradiation and 54 patients (38%) received JAK 1/2 inhibitors (JAKi), of whom 92.5% had Ruxolitinib. Median time to neutrophil engraftment was 20 (range: 10-43) days whereas median platelet recovery time was 28 (range: 13-230) days. 9 patients (6.3%) had primary graft failure and 11 patients (7.7%) had secondary graft failure. 60% had chimerism studies using cytogenetic or molecular techniques at 3 months post transplant; 63% of those assessed achieved complete (≥95%) donor chimerism. CMV reactivation was detected in 32% and 10% had sinusoidal obstruction syndrome. The cumulative incidence of grade II-IV acute GvHD was 21.4% and grade III-IV acute GvHD was 8.7%. The cumulative incidences of limited and extensive chronic GvHD at 5 years were 11.1% and 18.1% respectively. Overall survival (OS) was 67% at 1 year and 57% at 5 years. GvHD free progression free survival was 54% at 1 year and 42% at 5 years (Figure 1). The cumulative incidence of non-relapse mortality (NRM) was 16% at 100 days and 25% at 1 year. In multivariate analysis, use of an UD was a significant independent unfavourable risk factor for OS (HR 2.26, 95%CI 1.17- 4.33, p=0.015) and NRM (HR 3.02, 95%CI 1.36-6.71, p=0.007), while splenic irradiation/splenectomy resulted in shortened neutrophil (HR 1.88, 95%CI 1.00-3.54, p=0.05) and platelet recovery time (HR 2.13, 95%CI 1.12-4.05, p=0.02). Use of UD significantly increased the incidence of grade II-IV acute GvHD in multivariate analysis (HR 5.66, 95%CI 1.99-16.11, p=0.001) whereas use of antithymoglobulin or alemtuzumab significantly reduced it (HR 0.27, 95% CI 0.09-0.79, p=0.017). Neither use of JAKi prior to alloSCT nor presence of JAK2 mutation had a significant impact on OS or NRM. 9 patients underwent a second alloSCT for myelofibrosis and median length of time from the first transplant was 22 (range: 1-132) months. 4 patients were transplanted for disease relapse and 3 patients for graft failure. For the second transplant cohort, NRM at day 100 and 1 year were 11.1% (95% CI, 0.4%-40.6%) and 33.3% (95% CI, 6.6%-64%) respectively, while 1-year and 5-year OS were 66.6% (95% CI, 42%-100%) and 44.4% (95% CI, 21.4%-92.2%). Conclusion: Survival rates in alloSCT for myelofibrosis in this Australasian cohort were comparable to international studies. There is a rise in the numbers of patients treated with JAKi pretransplant (Figure 2). Although this does not appear to have any effect on transplant outcomes, reduced symptom burden associated with increasing use of pre-transplant JAKi may increase the numbers of patients considered eligible for alloSCT. Although splenectomy/splenic irradiation had a positive impact on engraftment, it did not improve the survival outcomes. Our results show a negative influence of UD on OS and NRM, possibly related to an increased incidence of acute GVHD in the UD group. In light of the rise in utilization of alloSCT in the management of myelofibrosis, there is a need for further prospective studies incorporating molecular testing and the new comprehensive clinical-molecular myelofibrosis transplant scoring system. Disclosures Spencer: Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Haemalogix: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Secura Bio: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen Oncology: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Specialised Therapeutics Australia: Consultancy, Honoraria. Purtill:MSD: Honoraria; Novartis: Honoraria, Other: Travel for speaking and advisory boards; Gilead: Honoraria, Other: Travel for speaking and advisory boards; Janssen: Honoraria. Browett:Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Achillion: Research Funding; Beigene: Research Funding. Szer:Sanofi: Honoraria, Other: Travel, Research Funding; Takeda: Honoraria, Other: Travel, Research Funding; Pfizer: Honoraria, Other: Travel, Research Funding; Alexion: Honoraria, Other: Travel, Research Funding; Amgen: Honoraria, Other: Travel, Research Funding; Celgene: Honoraria, Other: Travel, Research Funding; MSD: Honoraria, Other: Travel, Research Funding; Novartis: Honoraria, Other: Travel, Research Funding; Prevail Therapeutics: Honoraria, Other: Travel, Research Funding. Ritchie:Amgen: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; BMS: Research Funding; Takeda: Research Funding; Beigene: Research Funding; Imago: Research Funding; Novartis: Honoraria; Sanofi: Honoraria. Greenwood:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Gottlieb:Merck: Consultancy; AbbVie: Consultancy; Gilead: Consultancy; Novartis: Consultancy; University of Sydney: Employment; Haemalogix P/L: Membership on an entity's Board of Directors or advisory committees, Research Funding.