Background: Haploidentical hematopoietic cell transplantation (HCT) provides an alternative option for patients without HLA-matched donor. GVHD, engraftment failure, and infectious complications continue to be the main causes of non-relapse mortality (NRM). We hypothesized that selective depletion of TCRαβ+ and CD45RA+ naïve T cells subset will permit hematopoietic engraftment, while effectively reducing GVHD, and provide improved donor immune reconstitution through adoptive transfer of donor's mature NK cells, γδ T cells and CD45RO+ memory T cells. Methods: Mobilized PBSC product were divided into two fractions in 9:1 ratio, and depleted using CliniMACS device after labeling with TCRαβ and CD45RA reagents (Miltenyi Biotec, Bergish-Gladbach, Germany), respectively. The conditioning regimen consisted of fludarabine 160 mg/m2 divided daily over 4 days, thiotepa 10 mg/kg divided twice daily for 1 day and melphalan 70-140 mg/m2 for 1 day, in combination with total lymphoid irradiation 6 Gy (n=23), or 7.5 Gy (n=12) over 3 equal fractions, or total body irradiation of 2 Gy (n=2). Short term GVHD prophylaxis for 30 days was given to 1 patient using MMF, 25 patients using tacrolimus and 2 patients using sirolimus. Results: We transplanted 37 patients, including 32 adults (median age 47 years, range 20 - 69) and 5 children (median age 13 years, range 7-15 years) with high risk AML (n=17), ALL (n=11), MDS (n=5), myeloma (n=1), mast cell leukemia (n=1), acute undifferentiated leukemia (n=1) or NK/T lymphoma (n=1). The patients were infused with TCRαβ and CD45RA depleted graft containing a median of 8.65 x 106 (range, 3.54 - 20.78) CD34+ cells/kg, 0.00 x 104 (range 0 - 0.97) CD45RA+CD3+ cells/kg, and 2.4 x 106 (range, 0.15 - 11.67) CD45RO+CD3+ cells/kg. The TCRαβ depleted graft fraction contained a median of 0.19 x 104 (range 0 - 8.53) TCRαβ+ cells/kg, and 8.76 x 106 (range 1.73 - 30.00) TCRγδ+ cells/kg. Only 1 patient experienced primary graft failure. All others had engraftment of ANC > 500 cells/µL at a median of 10 day (range, 8 - 22) and PLT > 20,000 cells/µL at a median of 12 day (range, 7 - 19). There was no secondary graft failure. Four patients with high titers of donor-specific HLA antibodies (DSA) engrafted successfully after effective desensitisation with plasma exchange, rituximab and immunoglobulin. Fourteen patients (38%) developed acute GVHD of grade II-IV (Gd II n=9 ; Gd III n=4 ; Gd IV n=1 ). Only one patient experienced chronic GVHD, giving 2 year cumulative incidence (CI) of chronic GVHD of 3.9 %. Day 180 CI of NRM and relapse were 22.7 % (95% 10.5-37.7%) and 12.0 % (95% CI 3.7-25.7%), respectively. NRM was attributed to aGVHD in 3 of the 13 deaths. Viral reactivation included CMV (n=13), HHV6 (n=4), EBV (n=3) and adenovirus (n=4), with no fatal viral infection occurred within 180 days. Seven patients died of infection, including 3 patients who had fatal blood stream infection (bacteria n=2; fusarium n=1) within 180 days. With a median follow up of 436 days (range 20- 916 days) in surviving patients, the 6 month and 2 year overall survival (OS) were 77.2% (95% CI 59.4-87.9%) and 57.7 % (95% CI 37.6-73.4%), respectively (Figure 1). The 2-year OS for patients with intermediate risk and high/very high risk disease risk index (DRI) were 60% and 24%, respectively (p=0.07) (Figure 2). Conclusions: Our preliminary results suggest that RIC haplo-HCT with TCRαβ and CD45RA+ depleted grafts allows successful allograft in high-risk patients lacking a suitable matched donor, including patients with high level of donor-specific HLA antibodies. Acute GVHD was generally abortive, leading to chronic GVHD in <5% of the patients. Fatal viral infection was not observed. Further efforts are needed to lower the risk of death due to bacterial infection, and also relapse in patients with high risk DRI, such as antibiotic prophylaxis or repeated doses of memory-cell DLI. Disclosures Leung: Miltenyi Biotec: Employment.

Introduction: Allogeneic hematopoietic cell transplant (allo-HCT) is an effective consolidative treatment for patients with certain hematological malignancies and gives the best outcome when done in remission. However, patients with refractory acute myeloid leukemia (AML), certain forms of myeloproliferative neoplasia (MPN), and myelodysplastic syndrome (MDS) deemed unable to achieve remission with standard induction are often excluded from allo-HCT with conventional conditioning regimen as pre-transplant remission could not be achieved. Recently, a sequential transplant approach, as developed by the Munich group, comprising of intensive cytoreductive chemotherapy FLAMSA (fludarabine/amsacrine/cytarabine) to decrease leukemia cell burden shortly prior to conditioning regimen, had been successfully used for high-risk (HR) AML/MDS with promising results. Methods: We studied 56 patients (median age, 52 years; range 17-68) with HR AML (n=45), as defined by refractory, relapsed disease, secondary leukemia, complete remission with adverse-risk cytogenetics according to ELN criteria, or high/very high risk refined Disease Risk Index (DRI), MPN (n=2), and HR MDS (n=9) according to IPSS-R, undergoing allo-HCT using the sequential transplant approach in 2 transplant centers in Singapore between January 2009 and June 2020. The sequential transplant approach combined a cytoreductive chemotherapy, which consisted of either FLAMSA (n=17), FLAG +/- Ida [fludarabine/cytarabine/granulocyte colony stimulating factor (GCSF) +/- idarubicin] (n=23), or CLAG (clofarabine +/- cytarabine +/- GCSF) (n=15), followed by reduced intensity (RIC) (N=48) or myeloablative (MAC) (N=8) conditioning regimen. All patients received peripheral blood stem cell from matched related donors (N=30), mismatched related donors (N=3), matched unrelated donors (N=16), or mismatched unrelated donors (N=7). Post-grafting immunosuppression consisted of calcineurin inhibitor and mycophenolate mofetil in all patients. Thymoglobuline or post-transplant cyclophosphamide were added for GVHD prophylaxis in unrelated donor transplant and mismatched related donors, respectively. Results: The median time to neutrophil &gt; 1000/μL was 11 days (range, 8-19). With a median follow-up of 44 months (range, 1-123), the Kaplan-Meier estimate of overall (OS) and leukemia-free (LFS) survivals at 5 years were 49% (95% CI, 35-62) and 37% (95% CI, 23-52), respectively. The 2-years cumulative incidence of relapse and non-relapse mortality (NRM) were 47% (95% CI, 32-60) and 13% (95% CI, 6-24), respectively. Patients receiving FLAG or CLAG-based sequential regimen showed lower cumulative incidence of NRM (2-year cumulative incidence for NRM: 5% vs 29%; p=0.018), and similar relapse (2-year cumulative incidence for relapse: 49% vs 53%; p=0.64), as compared to patients given FLAMSA-based sequential regimen, resulting in a trend towards more favourable OS (5-year OS: 53% vs 41%; p=0.29) and LFS (5-year LFS: 46% vs 20%; p=0.08). In multivariable analysis, only refined DRI showed significant impact on OS (p=0.04), but has no significant impact on LFS, NRM, and relapse. The 5-year OS for patients with intermediate/high risk and very high risk DRI were 59% and 27%, respectively (p=0.017), and the corresponding 5-year LFS were 46%, and 20% (p=0.06), respectively (Figure 1 & Figure 2). The intensity of conditioning regimen did not significantly impact on OS, LFS, relapse, and NRM. Conclusions: Sequential transplant conditioning with FLAMSA, FLAG or CLAG followed by allo-HCT is an effective strategy in overcoming the dismal prognosis of HR AML, MDS and MPN, and enabling favourable long-term disease-free survival. More studies on effective strategies such as post-transplant maintenance therapy with prophylactic donor lymphocyte infusion, are needed to further eliminate the risk of relapse, without increasing risk of treatment related toxicity. Disclosures No relevant conflicts of interest to declare.

Introduction: There is currently no consensus on the optimal frontline therapy for patients with T cell Non-Hodgkin lymphomas (T-NHL). Consolidative autologous stem cell transplant (ASCT) is frequently offered to the patients with chemosensitive disease based on retrospective and prospective studies showing improved progression-free survival (PFS) when compared with historical controls getting chemotherapy alone. However, it remains unclear whether there is a good risk subset of patients who achieve first complete remission (CR1) following induction chemotherapy and who might not benefit from upfront ASCT. To date, no randomized control trials (RCTs) exist and available data is conflicting. We perform a systematic review/meta-analysis of the published literature to address this question. Methods A comprehensive, systematic search (from database inception - 9/2019) of MEDLINE/PubMed, EMBASE and Cochrane databases was performed. PRISMA and Meta-Analysis Of Observational Studies in Epidemiology (MOOSE) guidelines were followed. Studies were selected from a total of 2656, screened based on predefined inclusion/exclusion criteria, and were critically appraised for outcomes of interest [progression free survival (PFS) and overall survival (OS)]. Quality of studies was assessed using Newcastle-Ottawa Scale. Hazard ratios (HRs) and corresponding 95% Cis were calculated, and the meta-analysis was performed using the random-effects model. Test for heterogeneity was performed using I2 statistic. Results Of 2656 unique records, 13 studies (prospective = 3; retrospective = 10) were selected. In 8 studies, upfront ASCT was compared to NO ASCT in patients in first complete remission (CR1), while in 5, comparison was with patients achieving either PR1 (first partial remission) or CR1. 11 (of 13) studies reported PFS. Median follow-up in these studies ranged from 22 months to 7.8 years. Results from the meta-analysis showed that T-NHL patients who underwent ASCT had an improved 5-year PFS compared to those with NO ASCT (HR 1.62, 95% confidence interval (CI) 1.22 to 2.15, I² = 38%) (Figure 1). However, no benefit was observed in 5-year OS when ASCT was compared to NO ASCT (HR 1.32, 95% CI 0.82 to 2.12, I2 = 83%) (Figure 2). A sensitivity analysis including only studies with patients transplanted in CR1 showed similar findings, with a 5-year PFS (HR 1.54, 95% confidence interval (CI) 1.01 to 2.34, I² = 38%) and 5-yr OS (HR 1.11, 95% CI 0.41 to 3.02, I2 = 90%) when compared to No ASCT. Conclusions In the absence of RCTs, the results of this systematic review/meta-analysis represents the best evidence supporting long term PFS benefits of upfront ASCT consolidation in patients with T-NHL in CR1 or CR1/PR1 after frontline chemotherapy. Disclosures No relevant conflicts of interest to declare.