Phase 1/2 study of the WT1 peptide cancer vaccine WT4869 in patients with myelodysplastic syndrome

WT4869 is a synthetic peptide vaccine derived from the Wilms' tumor gene 1 (WT1) protein. This phase 1/2 open-label study evaluated the safety and efficacy of WT4869, and biomarkers for response, in patients with myelodysplastic syndrome. WT4869 (5-1200g/dose) was administered intradermally every 2weeks, according to a 3+3dose-escalation method in higher-risk (International Prognostic Scoring System score 1.5) or lower-risk (score <1.5) red blood cell transfusion-dependent patients with myelodysplastic syndrome. Twenty-six patients were enrolled and treated (median age, 75years; range, 32 to 89). The most common adverse event was injection site reaction (61.5%). Main grade 3 or 4 adverse events were neutropenia (30.8%), febrile neutropenia, pneumonia, elevated blood creatine phosphokinase levels and hypoalbuminemia (all 7.7%). Dose-limiting toxicities occurred in 1patient in the 50g/dose cohort (pyrexia, muscle hemorrhage and hypoalbuminemia) and 1patient in the 400g/dose cohort (pneumonitis); however, the maximum tolerated dose could not be determined from this trial. The overall response rate was 18.2%, the disease control rate was 59.1% and median overall survival was 64.71weeks (95% confidence interval: 50.29, 142.86) as assessed by the Kaplan-Meier method. Subgroup analysis of azacitidine-refractory patients with higher-risk myelodysplastic syndrome (11patients) showed median overall survival of 55.71weeks (approximately 13months). WT1-specific cytotoxic T lymphocyte induction was observed in 11 of 25 evaluable patients. WT4869 was well tolerated in patients with myelodysplastic syndrome and preliminary data suggest that WT4869 is efficacious. This trial was registered at as JapicCTI-101374.