ALBERT

Description: Objectives: In patients with refractory chronic lymphocytic leukemia (CLL), the potential to cure is unique to allogeneic stem cell transplantation (HSCT). Clearance of minimal residual disease by suspected graft-versus-leukemia effects has been described elegantly and documented in several independent patient cohorts. Yet data from large numbers of patients which support the concept of cure by allogeneic transplantation have not been published. With the advent of new targeted therapies for patients with advanced chemo-refractory CLL, this information becomes crucial for clinical decision making and patient counselling. Therefore, we aimed at the description of long-term survival outcomes, and the estimation of excess mortality compared to the age- and sex-matched general population. Patients and Methods: Data from patients with CLL who had received a first allogeneic HSCT from an HLA-identical sibling (SIB) or alternative donor between January 2000 and December 2010, and who were registered with the EBMT database, were analyzed. Patients with Richter's syndrome and with syngeneic donors were excluded from this analysis. Survival probabilities were calculated by means of the Kaplan-Meier estimator both in the total population, and in patients who passed the 2- and 5-year landmark without previous relapse or progression. Excess mortality of the landmark populations compared to an age-, sex- and calendar year-matched general population was estimated with a Cox regression model for relative survival using the R-package relsurv. Results: In total 2589 patients were included into the analysis. The median follow-up of patients alive at the end of follow-up was 4.0 years (range: 1 to 161 months). The median age at HSCT was 55 years (range: 12 to 74 years). One hundred and fifty eight patients (6.1%) were below 40 years of age at the time of transplantation. Seventy-four percent of patients were male. The remission status at the time of transplantation was reported as complete remission in 15%, partial remission in 47%, and stable disease or progressive disease in 32%. Information on the remission status was not available for 6% of the patients. Fifty-one percent of the patients had an HLA-matched sibling donor and seventy-seven percent of patients received reduced-intensity conditioning. For the whole cohort of patients, the 5- and 10-year overall survival (OS), progression-free survival (PFS), and non-relapse mortality (NRM) were 45%, 35%, 36%, and 35%, 28%, 40%, respectively. The cumulative incidence of relapse (CIR) was 21% at two years, 29% at five years, and 32% at ten years. A total of 1023 patients and 394 patients were alive without relapse or progression, and in follow-up at two and five years after HSCT. Five years after patients had passed the 2- and 5-year landmark, OS, CIR and NRM were 73%, 22%, 16%, and 83%, 11%, 10% respectively. Compared to the general population excess mortality of the 5-year landmark population in the subsequent five years was estimated to be 3% for male patients at an age of 45 years, 10% for male patients at an age of 55 years, and 24% for male patients at an age of 65 years (see Figure 1). For female patients in this 5-year landmark population, the corresponding excess mortality rates were 4%, 11%, and 27%. Patients without progression and with CR at any time from HSCT to the two and five-year landmarks had a slightly better outcome than those who had never had CR. Surprisingly, this was not a result of a lower CIR but of a lower NRM. Conclusion: Long-term follow-up data derived from the EBMT registry show a steady decline in hazard of relapse after allogeneic HSCT, yet relapse continues to be a threat. Moreover, even patients alive and disease-free after 5 years are still confronted with substantial NRM. These results show that there is room for improvement of long-term patient care. By comparing mortality of younger patients who passed the 5-year landmark with the general population, only marginal excess mortality was observed, while elderly patients still had substantial excess mortality beyond this landmark. Nevertheless, the results indicate that a significant fraction of patients can be cured by allogeneic HSCT. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Description: Patients with recurrent or refractory low-grade non-Hodgkin's lymphoma (NHL) are increasingly treated with myeloablative therapy and autologous stem cell transplantation. However, allogeneic bone marrow transplantation (BMT) is only sporadically performed in such patients. Therefore, we wish to compare treatment results of patients with recurrent or refractory low-grade NHL who underwent allogeneic BMT with those who underwent autologous BMT in our center. Twenty-eight patients were studied. The patients had received 2 to 5 lines of conventional chemotherapy before the BMT procedure. Eighteen patients, all with chemotherapy-sensitive disease at the time of transplantation, underwent autologous BMT and 10 patients, of whom 7 with chemotherapy-resistant disease at the time of transplantation, underwent allogeneic BMT. Furthermore, all allogeneic BMT patients had overt lymphoma infiltration of the BM at the time of transplantation. The conditioning regimen consisted of cyclophosphamide plus total body irradiation in all 28 patients. All allogeneic BMT patients achieved complete remission, 3 patients had a treatment-related death, and 7 patients are alive and disease-free with a median follow-up of 41 months. In contrast, none of the autologous BMT patients died of transplant-related complications. However, despite the fact that all autologous BMT patients had chemotherapy-sensitive disease and partial remission was converted to complete remission by the BMT procedure in 67% of them, only 3 of 18 patients are alive and disease-free. The probability of relapse or disease-progression among allogeneic BMT patients was 0% compared with 83% for autologous BMT patients (P = .002). Progression-free survival rates 2 years after BMT were 68% for allogeneic BMT patients and 22% for autologous BMT patients (P = .049). Although the numbers of patients are small, this study suggests that allogeneic BMT offers a better chance for cure than autologous BMT for patients with poor-prognosis low-grade lymphoma, and the difference in relapse or disease progression is strongly suggestive for the existence of a graft–versus–low-grade lymphoma effect.

Description: Double umbilical cord blood transplantation (dUCBT) has extended the applicability of UCBT for hematologic disorders especially to adult patients (pts) for whom the low cellular content of a single unit is a limiting factor. However the use of dUCBT has been, recently, associated with a higher incidence of acute graft-versus-host disease (aGVHD) when compared with single UCBT (sUCBT). Moreover, several retrospective and prospective studies have addressed risk factors for aGVHD with some conflicting results. Whether the number of total nucleated cells, HLA disparities, type of conditioning regimen or GVHD prophylaxis have an impact on aGVHD incidence in dUCBT is yet to be established in a larger series of patients. With this background, this report analyzed 921 adult recipients who underwent dUCBT for hematologic malignancies from 2005-2012 in EBMT centers. Median age was 46 (range, 18-72) years (yrs) and 59% were males. Diagnosis was acute leukemia in 56%, MDS/CML in 19% and lymphoid malignancies in 25%; 22% of pts received at least one prior autologous HSCT. Reduced-intensity conditioning (RIC) was used in 68% of pts and the most common regimen for both myeloablative conditioning (MAC) and RIC was Cyclophosphamide-Fludarabine-TBI (TCF) (40% and 78%, respectively). ATG was used in 30% of pts. GVHD prophylaxis consisted of a MMF based regimen in 774 pts (84%); cyclosporine±steroids in 103 (11%) and MTX-based regimen in 44 (5%). HLA incompatibilities were classified using the cord blood unit bearing the highest degree of mismatch with the recipient: 1% were HLA matched 6/6, 25% were 5/6, 67% were 4/6, and 7%

Description: Outcomes for adolescents and young adults (AYA) might be considerably different from children and older adults with acute leukemia (AL). Patients in this transitory period tend to be considered at higher risk for poorer outcomes. However, AYA is still underrepresented in most hematopoietic stem cell transplant (HSCT) studies. Recent evidence shows superior outcomes for AYA with acute lymphoblastic leukemia (ALL) using pediatric rather than adult first line chemotherapy regimens. The aim of this study is to analyze outcomes of umbilical cord blood transplant (UCBT) in AYA patients with ALL or acute myeloid leukemia (AML) after myeloablative conditioning regimen (MAC). Eligibility criteria included patients with AL aged 15-25 (median 19) years, transplanted between 2004 and 2016 in EBMT centers, with single or double UCBT as first allogenic transplantation after MAC regimen and reported to Eurocord. A total of 504 patients were included. Primary endpoint was overall survival (OS). Median follow-up for survivors was 38 months (1 month-11 years). Median time from diagnosis to UCBT was 11 months (1 month-17 years) (interquartile range 5-29 months). Diagnosis was ALL in 59% (n=297) and AML in 41% (n=207); 64% of patients were male. Disease status at UCBT were 42% in 1st complete remission (CR) (n=203), 2nd CR in 38% (n=183), and advanced disease in 20% (n=96). Fifty eight percent of patients (n=293) received single and 42% (n=211) double UCBT. Cyclophosphamide + TBI ± fludarabine (45%) was the most frequently used conditioning regimen. Anti-thymoglobulin (ATG) was used in 54% and GVHD prophylaxis was cyclosporine A + mycophenolate mofetil in 44% of patients. Median nucleated cell dose at collection was 3.63 (range 0.9-9.0) X107/Kg for single and 5.25 (range 2.3-10.6) X107/Kg for double UCBT. The 3-year OS was 45±2%; 3-year leukemia free survival (LFS) was 41±2% and refined GVHD free/relapse free survival (rGRFS) was 32±2%. OS was similar in ALL and AML (45±3% vs 45±4%, p-value=0.69). According to disease status at UCBT, 3-year OS was 54±4% for patients in CR1, 48±4% for CR2 and 20±4% for advanced disease (p-value

Description: Introduction Allogeneic stem cell transplantation (alloSCT) is the only potentially curative treatment for relapsed CLL patients with fludarabine refractory disease and/or a deletion 17p del(17p). Retrospective analyses identified bulky disease and lack of response to last treatment as predictors for poor survival. There is an unmet need for active salvage regimens for these high-risk patients, but so far prospective data on salvage regimens prior to alloSCT are lacking. Here we report our results with R-DHAP remission-induction studied in a prospective international multicenter phase 2 study. The rationale for R-DHAP is formed by in vitro studies showing that platinum induces p53 independent cell death. Patients up to the age of 70 years with fludarabine refractory CLL (defined, according to the EBMT consensus, as relapse within 1 year after fludarabine monotherapy or within 2 years after fludarabine plus a monoclonal antibody) and/or with relapsed CLL with a del(17p) , and with an indication for treatment were eligible for inclusion. Patients received at least 3 cycles of R-DHAP salvage therapy (rituximab on day 1 (375mg/m2 1st cycle, 500 mg/m2 later cycles), cisplatinum 100mg/m2 (day 1), cytarabine 2x2000mg/m2 (day 2) and dexamethasone 40mg days 1-4) every 4 weeks. Response to R-DHAP was determined according to 2008 IWCLL guidelines. Results Forty patients have been included from February 2009 till April 2012. One patient was ineligible because of Richter’s syndrome at the time of inclusion. The median age was 59 years (range 43-69) and the median number of prior therapies was 2 (range 1-5). Twenty-four patients completed at least 3 cycles of R-DHAP. Due to long donor search. two of these received 4 cycles, two 5 and 1 six cycles. Nine patients received only one or two cycles of R-DHAP because of toxicity, and two patients never received R-DHAP due to poor performance. Overall response rate (ORR) for all 39 eligible patients was 56%: 6 CR (15%), 16 PR (41%). Five patients had SD (13%) and 2 PD (5%). ORR rates in patients with bulky lymphadenopathy (〉5 cm, n=18) and in those having del(17p) (n=17) was 67% and 53% respectively. In the first 16 patients four infection related deaths occurred (3 septic shock and 1 encephalitis). After an amendment optimizing infection prophylaxis, no additional severe bacterial or fungal infections or infection related deaths were observed. Twenty-six patients proceeded to alloSCT (67%). With a median follow-up of 16 months (range 6-42 months) 2-years progression-free survival (PFS) and overall survival (OS) after transplantation is 63% and 72% respectively. Sixteen are free from progression and 3 progressed but are still alive. Seven patients died (3 from acute GVHD, 2 due to encephalopathy, 2 other reasons). Conclusion R-DHAP is an effective remission-induction regimen for fludarabine-refractory CLL patients even in those having bulky lymphadenopathy and/or del(17p), enabling a high percentage of patients to proceed to alloSCT resulting in a high PFS and OS at 2 years. Disclosures: No relevant conflicts of interest to declare.

Description: Introduction: We report the first analysis of a multicenter prospective single-arm phase I/II study that assesses the safety and feasibility of transplantation of TCRalpha/beta depleted stem cells from matched related or unrelated donors using the CliniMACS plus System (Miltenyi Biotec, Germany) in combination with a non-myeloablative conditioning in adult patients (trial nr NL48606.000.14). The conditioning regimen consisted of ATG (Thymoglobulin®) 1.5mg/kg i.v. days -12 to -9; fludarabine i.v. 40 mg/m2 days -5 to -2 and busulfan i.v. (Busivex®) days -5 to -2 (cumulative AUC of 80-90mg*h/L), followed by 28 days of mycophenolic acid. All 35 subjects were eligible to address the primary endpoint which is the incidence of acute GVHD at day 100. Results: 2 centers enrolled 10 female and 25 male patients (median age 59 years, range 19 - 69 years), including 9 AML, 4 ALL, 2 CML, 5 MM, 1 NHL, 10 MDS, 4 MPN. Diseases were in CR (n=17), VGPR (n=1), PR (n=5) or non-remission (n=12). 4 subjects had one or more previous allogeneic SCTs. Donors included 4 MRD, 24 10/10 matched MUD and 7 9/10 matched MUD. 8 male patients received stem cells of female donors. The median number of CD34+ cells and αβ TCR cells/kg was 6.1x 10^6 (range, 1.9-10) and 14.5x10^3 (range, 0-136), respectively. One primary graft failure was observed. Primary engraftment of ANCs 〉 500 cells/μL was reached at a median of 14 days (range 9 - 48 days) and of platelets 〉 20 at a median of 17 days (range 10 - 99) days. The median time of follow-up of this first analysis was 190 days (range 110-400 days). 3/35 patients developed acute GVHD grade III-IV during the first 100 days, 9/35 patients developed acute GVHD grade II-IV and 16/35 patients grade I-IV at day 100. At day 100 the cumulative incidence (CI) of CMV was 31%, of EBV 36% and of BK cystitis 20%. The combined CI of CMV/EBV/BK infections with a CTC-AE grade III-V was 53% at day 100. Immune reconstitution was rapid with a median of 227 (range 34 - 1626) CD3+ cells/µl on day 100 but varied substantially between patients. The median numbers of CD3/CD4+ and CD3/CD8+ at day 100 post transplant were 60 (range 30 - 120) and 124 (range 5 - 1450) cells/µl. The median numbers of NK were 289 (range 32-1140) at day 30 and 128 (range 24 - 1228) cells/µl at day 100 post transplant. The median numbers of γδ T cells were 38 (range 4-143) at day 30 and 50 (range 8-556) cells/µl at day 100 post transplant. 26 out of 35 patients were alive, 2 patients died of a relapse, 2 of GVHD and 5 of infectious complications. Kaplan Meier estimates of the OS are 88% (+/- 6%) at day 100 and 68% (+/- 9%) at 1Y. Kaplan Meier estimates of the EFS are 77% (+/- 7%) at day 100 and 52% (+/- 10%) at 1Y. 2 patients developed a relapse before day 100 and 5 patients before 1Y. It is noted that the outcome of 5 patients with MM was very poor in this cohort (3 patients developed a relapse and 2 patients died of complications). Conclusion: Allo-SCT of αβ T cell depleted PBMCs form matched related or unrelated donors, in combination with early ATG and a non-myeloablative conditioning regimen, resulted in favorable rates of primary engraftment (34/35), a CI of aGVHD II-IV of 26% with only minimal immuno-suppression and an encouraging early disease control (Fig 1). OS survival was mainly impacted by NRM (Fig 1), by which the majority of complications were of infectious nature. While all patients with MM suffered from NRM or relapse, all other disease categories had a rather favorable outcome. Reducing inter-individual variations in immune reconstitution early after transplantation will be key to further improve outcomes. Disclosures Minnema: Amgen: Consultancy; Takeda: Consultancy; Celgene: Consultancy, Research Funding; Janssen: Consultancy; Servier: Consultancy. Kuball:Novartis: Research Funding; Miltenyi Biotec: Research Funding; Gadeta (www.gadeta.nl): Consultancy, Equity Ownership, Patents & Royalties: on gd T cells and receptors and isolation strategies, Research Funding.

Description: Introduction: Cellular composition of grafts is believed to be one of the significant determinants of outcomes of reduced-intensity conditioning (RIC) allogenic hematopoietic cell transplantation (allo-HCT). However, inconsistent results of the influence of CD34+ cells dose on the incidence of graft-versus-host disease (GVHD), disease control and survival have been reported in studies published thus far. Allo-HCT remains the only potentially curative treatment modality for eligible patients with myelofibrosis (MF). As patients with this diagnosis were underrepresented or not included in the above mentioned analyses, this EBMT registry study aimed to determine impact of CD34+ cell counts on allo-HCT results in this population. Methods: Six hundred and fifty seven patients with primary or secondary MF transplanted with use of peripheral blood (PB) as a source of stem cells after RIC regimen (Fludarabine/Melphalan, N=536 (82%); Fludarabine/Busulphan, N=121 (18%)) between 2000 and 2016 were included. Stem cell donor type was HLA-identical sibling (MSD; N=249, 38%) or unrelated (UD; N=408, 62%). Use of ex vivo T-cell depletion and post-transplant cyclophosphamide to prevent GVHD were the exclusion criteria. Median patient age was 58 (range, 22-76) years. In-vivo T-cell depletion was used in 526 (80%) of cases. Median transplanted CD34+ dose was 6.6 (2-29) x 10^6 per kg of recipient body weight. Median follow-up was 46 (2-194) months. Patient and transplant characteristics are summarized in Table 1. Results: We did not observe any impact of CD34+ cells dose on outcome variables in the whole study group. However, in an analysis adjusted for donor type, among patients transplanted from a MSD, the 2yr overall survival (OS) probability was 77% for those transplanted with higher doses of CD34+ cells (defined as 〉7.0 x 10^6/kg) compared to 60% for lower CD34+ counts (below 7.0 x 10^6/kg), P=0.007 (Figure 1). The corresponding probabilities of 2yr non-relapse mortality (NRM) were 16% and 29% (P=0.04), respectively (Figure 2). In multivariate analysis, for patients transplanted from a MSD, higher CD34+ dose was an independent predictor for better survival (HR 0.56; P=0.01) and lower risk of NRM (HR 0.54; P=0.02). We did not find any association between CD34+ counts with probability of engraftment, the incidence of acute (aGVHD) and chronic (cGVHD) nor disease relapse. The effect of cell dose was not seen in the UD cohort. Factors associated independently with an unfavorable outcome in the whole study group were: older patient age and transplantation from CMV seronegative donors to seropositive recipients for OS and NRM and use of an UD and female donor for NRM. Allo-HCT from UD was also an independent predictor for higher incidence of aGVHD and lower probability of engraftment. Use of in vivo T-cell depletion was a protective factor for aGVHD. It was in turn associated with higher risk of relapse. Conclusions: Our analysis suggests a potential survival benefit for MF patients treated with RIC PB-allo-HCT from MSD with higher doses of CD34+ cells (threshold 〉 7.0 x 10^6/kg). We suggest that this factor should be taken into consideration when planning and performing hematopoietic cell apheresis. Disclosures Kröger: Celgene: Honoraria, Research Funding; DKMS: Research Funding; JAZZ: Honoraria; Medac: Honoraria; Neovii: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Riemser: Research Funding; Sanofi-Aventis: Research Funding. Robin:Novartis Neovii: Research Funding. Chevallier:Daiichi Sankyo: Honoraria; Jazz Pharmaceuticals: Honoraria; Incyte: Consultancy, Honoraria. Mielke:Bellicum: Consultancy, Honoraria, Other: Travel (via institution); EBMT/EHA: Other: Travel support; Miltenyi: Consultancy, Honoraria, Other: Travel and speakers fee (via institution), Speakers Bureau; IACH: Other: Travel support; Jazz Pharma: Honoraria, Other: Travel support, Speakers Bureau; ISCT: Other: Travel support; GILEAD: Consultancy, Honoraria, Other: travel (via institution), Speakers Bureau; Celgene: Honoraria, Other: Travel support (via institution), Speakers Bureau; DGHO: Other: Travel support; Kiadis Pharma: Consultancy, Honoraria, Other: Travel support (via institution), Speakers Bureau. Snowden:Janssen: Honoraria; Mallinckrodt: Honoraria; Kiadis: Membership on an entity's Board of Directors or advisory committees; IDMC: Honoraria; Jazz: Honoraria; Gilead: Honoraria. Blaise:Sanofi: Honoraria; Pierre Fabre medicaments: Honoraria; Molmed: Consultancy, Honoraria; Jazz Pharmaceuticals: Honoraria. Hernandez Boluda:Incyte: Other: Travel expenses paid. McLornan:Jazz Pharmaceuticals: Honoraria, Speakers Bureau; Novartis: Honoraria.

Description: Abstract 363 Matched unrelated donor stem cell transplantation (MUD-SCT) has recently become a therapeutic option for patients with B cell diffuse large cell lymphoma (DLBCL) who fail other conventional therapies and do not have a matched sibling donor available. We present retrospective data of 473 DLBCL patients, 285 males and 188 females, aged 18 to 69 years (median 46 years), treated with matched sibling (n=301) or matched unrelated (n=172) SCT between January 2000 and December 2007 and reported to the EBMT registry. Median time from diagnosis to allograft was 25 months (range 2 – 203). Fifty-seven percent of the patients had failed previous autologous SCT, and 12% were transplanted in chemorefractory disease. After a median follow up of 41 months, the estimated 3-year non-relapse mortality (NRM), relapse rate (RR), progression free survival (PFS) and overall survival (OS) for the whole series were 37%, 32%, 31% and 40%, respectively. There were no statistically significant differences in patient age, disease status at transplantation, stem cell source and intensity of conditioning regimen between the Sib and the MUD cohorts (summarized in Table 1).However, a higher number of patients undergoing MUD have already failed an autograft (66% vs 52%, p=0.004), and T cell depleted grafts were more frequently used in the MUD cohort. Acute GvHD occurred in 48% of patients treated with a sib allograft vs 54% in those receiving a MUD (p=n.s). Interestingly, there were no statistically significant differences in NRM and RR between the Sib and the MUD groups (3 yr NRM=38% vs 37%, RR approached 38% vs 34%), resulting in a similar 3-year PFS and OS (32% vs 29% and 42% vs 35%, respectively). Multivariate analysis identified refractory disease (p = 0.001, RR 3.2; CI=1.3-3.5), poor performance status (p = 0.017, RR 1.9; CI=1.1-3.4) and age at transplantation 〉 50 years (p = 0.015, RR1.5; CI=1.1-2.1) as independent adverse prognostic factors for NRM and time from diagnosis to SCT 〈 36 months (p = 0.02, RR 1.5; CI=1.1-2.1), a previously failed autologous SCT (p = 0.026, RR .4; CI=1.1-1.9), refractory disease (p = 0.003, RR 2; CI=1.3-3.1), poor performance status (p = 0.0001, RR 3.5; CI=2.1-5.6) and T cell depletion (p = 0.001, RR 2; CI=1.3-2.9) as adverse prognostic factors for RR. A previous autologous SCT, poor performance status and refractory disease at transplantation were found to be significantly associated with a shorter PFS (p=0.04, RR 1.3; CI=1-1.6; p=0.0001, RR 2.4; CI=1.6-3.4; p=0.000,RR 2.1; CI=1.5-2.9, respectively) and refractory disease (p=0.0001, RR 2.2; CI=1.6-3.1) and poor performance status at the time of SCT (p=0.0001, RR 2.5; CI=1.7-3.6) with a shorter OS. Patients allografted from MUD tended to have a slightly increased risk of overall mortality in multivariate analysis, but this was not statistically significant (p=0.06, RR 1.2; CI=0.95-1.6). In conclusion, MUD SCT provides a curative option, not significantly inferior to that obtained with a matched sibling transplant, for selected patients with DLBCL who have failed conventional therapies, including autograft. Similarly, the type of conditioning regimen was not found to have a significant impact on patient outcome. Table 1. Clinical characteristics Sib vs MUD Sib (n = 301) MUD (n= 172) p Age (median, years) 46 45 N.S. Previous ASCT 48% 33% 0.004 Refractory disease 12% 12% N.S. Poor P.S. 13% 7% 0.06 RIC/CC 57%/43% 56%/42% N.S. SC source BM/PB 20%/80% 22%/78% N.S. ATG/ALG 15% 46%

Description: To assess the impact of antithymocyte globulins (ATG), on patients' outcome after unrelated cord blood transplantation (UCBT) following a reduced-intensity regimen (RIC), we conducted a retrospective registry-based analysis on 661 adults with hematological malignancies who underwent unrelated single (s) or double (d) UCBT following RIC with the TBI/cyclophosphamide/fludarabine regimen (TCF) between 2004 and 2011 in EBMT centers. Participating centers were asked to provide additional information on type, timing and total dose of ATG used. Diagnosis was AML/ALL in 51%, MDS/CML in 19% and lymphoid malignancies in 30%; 28% of patients were transplanted in early disease status, 28% in intermediate and 44% in advanced disease. Thirty percent of patients had a previous autologous transplantation. Single UCBT was used in 226 (34%) patients, while 435 (66%) were transplanted with dUCBT. HLA matching was defined as low resolution for HLA-A and HLA-B, and high resolution for HLA-DRB1, and for dUCBT, the highest degree of HLA incompatibility was considered. Therefore, most of the HLA incompatibilities were 4/6 (n=435, 72%). Median number of collected total nucleated and CD34+ cells were 4.4x107/kg and 1.6x105/kg, respectively. All patients received TCF, with TBI 2Gy (86%), TBI 4Gy (12%) and TBI 6Gy (2%). Rabitt ATG (rATG) was used as part of RIC in 82 patients (12.4%) with a median total dose of rATG (Fresenius®) of 20mg/kg (5-60) and rATG (Genzyme®) of 8mg/kg (5-15). GVHD prophylaxis consisted of cyclosporine A (CsA)+ mycophenolate mofetil (MMF) in 91%, Csa alone±other in 9%. The median follow-up was 36.3 months. When compared to patients not receiving rATG-TCF, patients given rATG-TCF had more MDS/CML (30% vs 20%, p

Description: Abstract 3026 Background Double umbilical cord blood transplantation (UCBT) results in higher engraftment rates as compared to single UCBT in adult patients. Sustained hematopoiesis is usually derived from a single cord blood unit (CBU) after double UCBT. So far, the mechanism of predominance of a particular CBU is unresolved. In a prospective single-arm phase II study (HOVON-106) we monitored early engraftment kinetics to determine whether graft predominance after double UCBT is driven by specific leukocyte subpopulations. Methods 36 consecutive patients (pts) from 5 Dutch centers with high-risk hematological diseases received a double UCBT, preceded by a reduced-intensity conditioning regimen (Cy 60 mg/kg/ Flu 160 mg/m2/ TBI 2×2 Gy). CBUs were selected by intermediate resolution typing for HLA-A and -B loci and by high-resolution typing for HLA-DRB1. The minimal required HLA-match grade was 4/6. Chimerism analysis (STR-PCR) of unseparated peripheral blood (PB) and bone marrow (BM) cells was performed as from day +32 onwards. In addition, chimerism analysis in PB leukocyte subpopulations by flowcytometry using lineage-specific (CD45, CD3, CD4, CD8, CD19, CD16/56, CD14 and CD33) monoclonal antibodies (mAbs) in combination with human HLA-antigen specific mAbs (HLA-mAbs) was performed at day +11, +18, +25 and +32 if discriminating HLA-mismatches between recipient and CBUs were present. Day +32 flowcytometry results were compared to day +32 PB STR-PCR results. Results The median number of prefreeze total nucleated cells (TNC) per CBU was 2.3×107/kg (range: 1.5–5.5). Median numbers of post-thaw viable CD34+ cells, T-, B- and NK cells were 0.32 (range: 0–1.7), 4.4 (range: 0.4–36), 9.7 (range: 0.7–79) and 7.2 (range: 0.24–45) x105/kg, respectively. One pt was non-evaluable for engraftment due to insufficient follow up after early relapse. The cumulative incidence of neutrophil recovery (≥0.5×109/l) was 91% with a median time to neutrophil recovery of 33 days (range: 15–82). Primary graft failure occurred in 1 pt. Chimerism analysis, performed at day +32 by STR-PCR revealed single CBU predominance in all pts whereas residual non-engrafting CBU and recipient cells were detectable in only 3 and 7 pts, respectively. Simultaneous 3-donor-origin detection of leukocyte subpopulations by flowcytometry based on HLA disparities was possible in 12 pts. Flowcytometry using HLA-mAbs demonstrated single CBU predominance in various leukocyte subsets as from day +11 onwards in the majority of pts. Moreover, ultimate engraftment of a particular CBU was reliably predicted for by chimerism within the CD4+ (in 90% of pts) and NK cell (in 90% of pts) subsets at this early time point. In contrast, predominance of the engrafting CBU in monocytic en myeloid subsets was observed in only 70% and 33% of pts, respectively, at day +11. The numbers of CD8+ and B-cells were too low for analysis in the majority of pts. Predominance of the ultimate engrafting CBU was established in all subpopulations at day +18. Furthermore, the contribution of the non-engrafting CBU to the different leukocyte subsets was negligible or even absent as from day +18 onwards. Recipient hematopoiesis did not contribute to PB cell recovery either. The results of day +32 flowcytometry (CD45+ population) were similar to results of day +32 PB STR-PCR. The number of prefreeze TNC did not predict for the ultimately engrafting CBU, nor did the number of post-thaw CD34+, T, B or NK cells. Engraftment was not associated with the degree of HLA mismatches or presence of KIR ligand mismatches among recipient and CBUs. Conclusions These results show that single donor chimerism is rapidly established after double UCBT, preceded by a 4 Gy TBI-based conditioning regimen without ATG. In addition, our flowcytometry data suggest the occurrence of CBU predominance within 2 weeks post transplant, in the course of which both CD4+ and NK cell predominance at day +11 are highly predictive for ultimate single donor chimerism. That early engraftment pattern of leukocyte subsets might suggest a key role for either CD4+ T cells or NK cells in CBU predominance. Disclosures: Janssen: Novartis: Consultancy.