UM171-Expanded Cord Blood Transplantation in Adults with High- and Very High-Risk Acute Leukemia and Myelodysplastic Syndrome: Combined Results of Two Prospective Phase II Trials

Purpose: Adults with high- or very high-risk acute leukemia (AL) or myelodysplastic syndrome (MDS) face substantial relapse risk after allogeneic hematopoietic stem-cell transplantation. We evaluated single-unit cord blood (CB) transplantation after ex vivo expansion with UM171 in this population. Patients and Methods: Two prospective, single-arm phase II trials at four centers enrolled 64 adults with high- or very high-risk AL or MDS; 60 received a UM171-expanded CB transplant and comprised the analysis population. CB units were preferentially selected at a 5/8 HLA match to maximize the graft versus leukemia effect. Patients received intermediate- or high-intensity conditioning with tacrolimus/mycophenolate mofetil graft-versus-host-disease (GVHD) prophylaxis. Endpoints included safety, feasibility, non-relapse mortality (NRM), relapse-free survival (RFS), overall survival (OS), GVHD, GVHD-free relapse-free survival (GRFS), chronic GVHD-free relapse free survival (CRFS). Results: Thirty-two percent of patients had undergone previous transplantation, 17% of patients with AL were not in remission and 24% of those with AML/MDS had TP53 mutations. Of 62 patients who remained eligible for transplantation, 60 had a graft successfully manufactured and infused. Median times to neutrophil and platelet engraftment were 17 and 38 days, respectively. NRM was 5.1% at day 100 and 15.2% at 1 year. Two-year cumulative incidence of relapse was 22.3%. Two-year OS and RFS were 63.9% and 60.4%, respectively. Grade III-IV acute GVHD incidence was 20.3% at 1 year and moderate-to-severe chronic GVHD incidence was 6.8% at 2 years. Conclusion: UM171-expanded CB transplantation was feasible and provided prompt engraftment, durable disease control, and infrequent clinically significant chronic GVHD in adults with high- and very high-risk AL/MDS. Comparative studies are warranted to define its role relative to contemporary donor platforms.