Use of Post-Transplant Cyclophosphamide (PTCy) with Mycophenolate Mofetil and Tacrolimus in HLA Matched Allogeneic Hematopoietic Cell Transplant Is Safe and Associated with Acceptable Transplant Outcomes

Background: The use of post-transplantation cyclophosphamide (PTCy) as a single agent for graft-versus-host disease (GVHD) prophylaxis in HLA matched transplant patients has had varied results. Two recent studies at Johns Hopkins University noted favorable incidences of both GVHD and non-relapse mortality (NRM) in both matched related and unrelated donor allogeneic hematopoietic cell transplant (allo-HCT) recipients (Kanakry CG, et al, JCO, 2013 and Kanakry CG et al, Blood, 2014). In contrast to this data, a phase II study at MD Anderson reported higher rates of grade II-IV acute GVHD and NRM, with worse overall survival in patients receiving PTCy as the sole GVHD prophylaxis compared to their matched cohort receiving a calcineurin-inhibitor (CNI) and methotrexate (MTX) as immunosuppression (Alousi AM et al, BBMT, 2015). Another study in Australia had to be stopped for safety reasons due to high GVHD and NRM when using PTCy as sole GVHD prophylaxis (Bradstock KF, BBMT, 2015). There is no published data on the use of MMF plus tacrolimus in combination with PTCy in HLA matched allo-HCT recipients. We hypothesized that addition of MMF and Tacrolimus to PTCy in HLA matched allo-HCT recipients will lead to significantly improved transplant outcomes. To answer this question we retrospectively analyzed data from patients who received this regimen at a single institution.

Methods. We performed a retrospective analysis of 31 HLA matched allo-HCT patients who received PTCy at 50 mg/m2 on days +3 and +4 in addition to MMF and tacrolimus immunosuppression from December 2012 till June 2015 at Washington University School of Medicine in Saint Louis. All of these patients received G-CSF mobilized peripheral blood grafts. Patients included AML (n=13), ALL (n=5), MDS (n=5), CML (n=2), aplastic anemia (n=2) and NHL (n=1), myelofibrosis (n=1). Twelve of the patients underwent a matched related donor (MRD) transplant and 19 underwent a matched unrelated donor (MUD) transplant. Two of the MUD transplants had a HLA match grade of 8 of 10 and the other 17 were a 10 out of 10 match. Twenty-eight of the patients received a graft collected via peripheral blood stem cell mobilization and the other three had a donor graft collected via bone marrow harvest. Cumulative incidence of aGVHD was estimated using Gray's sub-distribution method to account for death without aGVHD as a competing event, and the cumulative incidences of non-relapse mortality (NRM) and relapse were estimated treating each other as competing event, while OS was estimated using Kaplan-Meier limit method.

Results: This regimen was associated with acceptable GVHD in our patients. Incidence of grade II-IV acute GVHD was 28% (21.3% for MRD; 31.5% for MUD) at day 100 and 28% at 1 year. Incidence of Grade III-IV acute GVHD was 13.5% at both 100 days and 1 year. Limited chronic GVHD was 25.9% and extensive GVHD was 14.8% at 1 year. Similarly we found acceptable NRM and relapse in these patients, NRM was 10.2% and 19.7% at 100 days and 1 year respectively and cumulative incidence of relapse at 100 days and 1 year were 17.8% and 29.0% respectively. Overall survival at 1 year for all patients was 52%.

Summary: Here we report favorable results from a regimen combining MMF and Tacrolimus on PTCy platform in HLA matched MRD and MUD transplant recipients. Relatively low GVHD and NRM results are particularly encouraging in view of almost exclusive use of G-CSF mobilized T cell replete grafts with much higher T cell content. Though limited by the relatively small number of patients, our results suggest combining MMF plus Tacrolimus with PTCy platform in HLA matched allogeneic transplant patients is safe and associated with acceptable transplant outcomes.