DSP-7888 is an immunotherapeutic cancer vaccine derived from the Wilms’ tumor gene 1 (WT1) protein. This phase 1/2 open-label study evaluated the safety and efficacy of DSP-7888 dosing emulsion in patients with myelodysplastic syndromes (MDS). DSP-7888 was administered intradermally (3.5 mg or 10.5 mg) every 2 weeks for 6 months then every 2─4 weeks until lack of benefit. Twelve patients were treated in the phase 1 part (3.5 mg, n=6; 10.5mg, n=6), with no dose-limiting toxicities reported. Thus, the 10.5 mg dose was selected as the recommended phase 2 dose, and 35 patients were treated in the phase 2 part. Forty-seven patients received ≥1 dose of study drug and comprised the safety analysis set. The most common adverse drug reaction (ADR) was injection site reactions (ISRs) (91.5%). Grade 3 ISRs were common (58.8%) in the phase 1 part, but occurred less frequently in the phase 2 part (22.9%) following implementation of risk minimization strategies. Other common ADRs were pyrexia (10.6%) and febrile neutropenia (8.5%). In the efficacy analysis set, comprising patients with higher-risk MDS after azacitidine failure in the phase 1 and phase 2 parts (n=42), the disease control rate was 19.0%, and median overall survival (OS) was 8.6 (90% CI, 6.8─10.3) months. Median OS was 10.0 (90% CI, 7.6−11.4) months in patients with a WT1-specific immune response (IR) (n=33) versus 4.1 (90% CI, 2.3−8.1) months in those without a WT1-specific IR (n=9) (P=0.0034). The acceptable safety and clinical activity findings observed support the continued development of DSP-7888 dosing emulsion.