A phase I/II trial of a WT1 (Wilms' tumor gene) peptide vaccine in patients with solid malignancy: Safety assessment based on the phase I data

Objective: We conducted a phase I study to investigate the safety of a weekly WT1 tumor vaccine therapy in patients with solid tumors that had been refractory to all other anti-cancer therapies. Methods: Skin-test-negative patients were intradermally injected weekly for 12 weeks with 3.0 mg of an HLA-A(*)2402-restricted modified 9-mer WT1 peptide emulsified in Montanide ISA51 adjuvant. We estimated the Bayesian posterior probability of the occurrence of grade 3 or 4 toxicity when receiving the weekly WT1 vaccination. This analysis provided the basis for making a decision to terminate the phase I study and switch to phase II. Moreover, we performed an exploratory assessment of the anti-tumor effects of WT1 treatment. Results: Ten patients received 114 vaccinations with WT1 on a weekly schedule. No grade 3 or 4 toxicities were observed. Based on the Bayesian approach, it was highly likely that the probability of grade 3 or 4 toxicity was below 20% (the posterior probability = 0.914). Fifteen grade 2 and two grade 1 toxicities were observed; all of these incidents, however, were determined by the Independent Data and Safety Monitoring Committee to be unrelated to the WT1 treatment. One patient exhibited a partial response; five additional patients had stable disease while receiving weekly WT1 treatment. Conclusion: This paper confirms that the potential toxicities of the treatment schedule of weekly WT1 vaccination are acceptable and suggested a potential anti-tumor effect. Consequently, we validated the decision to continue to the phase II trial.