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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.