Reduced Severe aGVHD and Improved Survival Using Post Transplant Cyclophosphamide/Tacrolimus/Methotrexate Graft Versus Host Disease Prophylaxis in AML Patients Receiving Myeloablative Fractionated Busulfan Conditioning Regimen
Authors: Popat Uday , Saliba Rima M. , Mehta Rohtesh S. , Olson Amanda L. , Chen Julianne , Ganesh Christina , Rondon Gabriela , Woodworth Glenda , McMullin Becky , Alousi Amin M. , Anderlini Paolo , Alatrash Gheath , Bashir Qaiser , Ciurea Stefan O. , Hosing Chitra , Im Jin S , Kebriaei Partow , Khouri Issa F. , Marin David , Nieto Yago , Oran Betul , Saini Neeraj , Srour Samer , Rezvani Katayoun , Qazilbash Muzaffar H. , Molldrem Jeffrey J. , Shpall Elizabeth J. , Andersson Borje S , Champlin Richard E. 
Published: November 2019

Background: Myeloablative conditioning can be given safely to older patients by simply administering busulfan over a longer period (fractionated busulfan regimen) than the standard four day regimen. (Popat et al Lancet Haematology 2018). Subsequently, we added post-transplant cyclophosphamide (PTCy) GVHD prophylaxis to our fractionated regimen with a hypothesis that it will reduce GVHD and improve outcomes. Herein, we report the results of our retrospective analysis comparing outcomes of patients with AML who received fractionated busulfan myeloablative conditioning and PTCy versus standard tacrolimus (Tac) and methotrexate (Mtx) GVHD prophylaxis.
Methods: Patients with AML between 18-70 years of age with adequate organ function and 8/8-HLA matched related or unrelated donor, who were treated on 4 consecutive protocols using fractionated busulfan were included in the analysis. All patients received two fixed doses of busulfan 80mg/m2 as outpatient either on days -13 and -12, or on days -20 and-13 followed by busulfan on day -6 to -3 dosed to achieve target area under the curve (AUC) of 20,000 mol/min for the whole course based on pharmacokinetic studies. Fludarabine ± cladribine were given on day -6 to -3. GVHD prophylaxis was PTCy 50mg/kg on days 3 and 4 and Tac ± mycophenolate mofetil in PTCy cohort (n=53), or standard Tac+ Mtx (n=53). Patients in both the cohorts were matched 1:1 by propensity score.
Results: Baseline characteristics were similar between the PTCy and Tac/Mtx cohorts. The median age was 60 (range, 18-70) and 58 (range, 24-70) years, respectively, (P=0.3). Forty-nine percent were in CR, and 30% had comorbidity index >3 in each arm. Similar proportion of patients had ELN adverse risk in both arms (43% vs 40%, respectively P=0.7).
The median follow up was 19 months (range, 3-36) in the PTCy and 46 months (range, 14-73) in Tac/Mtx cohort. Overall survival at 2-year was 78% vs 58% (P=0.03), non-relapse mortality was 6% vs 13% (P=0.2), incidence of grade 3-4 acute GVHD at 1-year was 6% vs 19% (P=0.07) and chronic GVHD at 2-year was 10% vs 29% (P=0.03) [Table 1 and figure 1]. The median time to neutrophil engraftment was prolonged by 3 days (15 vs 12 days; P<0.001) and platelet engraftment by 9 days (22 vs 13 days; P<0.001) in the PTCy cohort. Full donor chimerism at day 30 was noted in 79% vs 28% in the PTCy and Tac/Mtx cohorts respectively, (P<0.001).
Conclusion: As compared to Tac/Mtx, PTCy-based GVHD prophylaxis not only reduced severe acute GVHD and chronic GVHD, but also improved overall survival in AML patients up to the age of 70 years who received myeloablative fractionated busulfan conditioning. Prospective randomized trial is warranted to validate these findings.

Disclosures
Popat: Bayer: Research Funding; Incyte: Research Funding; Jazz: Consultancy. Bashir:Imbrium: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Spectrum: Membership on an entity's Board of Directors or advisory committees; Kite: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; StemLine: Research Funding; Acrotech: Research Funding; Celgene: Research Funding. Ciurea:Kiadis Pharma: Membership on an entity's Board of Directors or advisory committees, Other: stock holder; MolMed: Membership on an entity's Board of Directors or advisory committees; Spectrum: Membership on an entity's Board of Directors or advisory committees; Miltenyi: Research Funding. Kebriaei:Kite: Honoraria; Pfizer: Honoraria; Amgen: Research Funding; Jazz: Consultancy. Nieto:Astra-Zeneca: Research Funding; Affimed: Consultancy; Affimed: Research Funding; Novartis: Research Funding. Oran:Astex pharmaceuticals: Research Funding; AROG pharmaceuticals: Research Funding. Qazilbash:Genzyme: Other: Speaker; Amgen: Consultancy, Other: Advisory Board; Autolus: Consultancy; Bioclinical: Consultancy. Molldrem:M. D. Anderson & Astellas Pharma: Other: Royalties. Champlin:Johnson and Johnson: Consultancy; Actinium: Consultancy; Sanofi-Genzyme: Research Funding.