Oral Proteasome Inhibitor Ixazomib for Switch-Maintenance Prophylaxis of Recurrent or Late Acute and Chronic Graft-versus-Host Disease after Day 100 in Allogeneic Stem Cell Transplantation.

Graft-versus-host disease (GVHD) is a frequent complication in the first year after allogeneic stem cell transplantation (allo-HCT). Recipients of reduced-intensity (RI) or nonmyeloablative (NMA) conditioning combined with calcineurin inhibitor (CNI)-based GVHD prophylaxis frequently develop GVHD in the context of immunosuppression taper. Ixazomib is an oral proteasome inhibitor with a wide safety profile that has demonstrated immunomodulatory properties, inhibition of pro-inflammatory cytokines, and anti-tumor activity. We hypothesized that switch-maintenance GVHD prophylaxis using ixazomib would facilitate CNI taper without increased GVHD frequency and severity while maintaining graft-versus-tumor (GVT) effect and an acceptable safety profile. We conducted an open-label, prospective, single-center pilot study in patients with hematologic malignancies who received an RI or NMA conditioning and CNI-based GVHD prophylaxis that were within day 100 to 150 after HCT (n = 18). Patients were treated with ixazomib once weekly on a 28-day cycle (3 weeks on, 1 week off). Treatment was safe; most adverse events were grade 1 or 2, with cytopenia and elevation in transaminases the most common. Five patients were removed from the study because of toxicity or side effects. Only 5 of 18 patients developed GVHD during the study, and its severity was driven by acute manifestations while chronic involvement was mild. The cumulative incidence of grade II-IV acute and chronic GVHD at 1-year after HCT was 33% (95% confidence interval [CI], 13-55). No patients died during the study, and only 1 had malignant relapse. An additional patient relapsed after completion of the study but within 1 year after HCT. The probability of progression-free survival and GVHD-free/relapse-free survival (composite endpoint) at 1 year were 89% (95% CI, 75-100) and 78% (95% CI, 61-100), respectively. Immune reconstitution analysis showed a rapid and sustained recovery in T-cell subpopulations and B cell reconstitution, and vaccine response in a subset of patients demonstrated continuing or de novo positive protective antibody titers. This study demonstrated low incidence of recurrent and late acute and chronic GVHD within 1 year after HCT possible associated with switch-maintenance GVHD prophylaxis using ixazomib. This approach allowed for CNI taper while preserving GVT effect, without aggravating GVHD. Our findings support further development of this approach and provide a proof-of-concept for switch-maintenance GVHD prophylaxis.