Japanese Journal of Clinical Oncology Advance Access originally published online on April 12, 2006
Japanese Journal of Clinical Oncology 2006 36(4):231-236; doi:10.1093/jjco/hyl005
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© 2006 Foundation for Promotion of Cancer Research
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
1 Department of Epidemiology and Health Care Research, Kyoto University Graduate School of Medicine, Kyoto, Departments of 2 Molecular Medicine, 3 Cancer Immunotherapy, 4 Neurosurgery, 5 Surgical Oncology, 6 Orthopaedics, 7 Functional Diagnostic Science, 8 Pathology, 9 Nuclear Medicine and Tracer Kinetics, Osaka University Graduate School of Medicine, Suita, Osaka, 10 Department of Immunology, Kochi Medical School, Nankoku, Kochi, 11 Department of Laboratory Medicine, National Hospital Organization, Osaka Minami Medical Center, Kawachinagano, Osaka and 12 Department of Epidemiological & Clinical Research Information Management, Kyoto University Graduate School of Medicine, Kyoto, Japan
For reprints and all correspondence: Satoshi Morita, PhD, Department of Epidemiology and Health care Research, Kyoto University Graduate School of Medicine, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan. E-mail: satoshi_morita{at}pbh.med.kyoto-u.ac.jp
Received September 7, 2005; accepted January 5, 2006
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Abstract |
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 TOP Abstract INTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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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.
Key Words: WT1 peptide vaccine • solid tumor • phase I trial • Bayesian approach • weekly schedule
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INTRODUCTION |
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Wilms' tumor gene WT1 is overexpressed in leukemias and a variety of solid tumors. As the WT1 protein has been identified as a tumor-associated antigen (1,2), such WT1 products may provide the basis for the development of a new peptide-based anti-cancer immunotherapy.
Oka et al. (3) performed a phase I clinical trial to examine the safety of a WT1-based vaccine and the clinical and immunological responses of patients with a variety of cancer types, including leukemia, non-small-cell lung cancer and breast cancer. Their study utilized an HLA-A*2402-restricted 9-mer WT1 peptide emulsified in Montanide ISA51 adjuvant (at 0.3, 1.0, and 3.0 mg per body) administered at 2-week intervals. Although all the patients with solid malignancies showed local inflammatory response with erythema at the WT1 vaccine injection sites, any damage to normal organs including bone marrow and kidney was not observed. Of the twenty-six patients who received the 3.0 mg WT1 treatment six completed the study. It was demonstrated that the 3.0 mg WT1 therapy can induce the generation of WT1-specific cytotoxic T lymphocytes without damaging normal tissues. The phase I study, however, failed to demonstrate evidence of any anti-tumor effect. While the number of residual leukemia cells within the bone marrow in two patients with acute myelocytic leukemia significantly diminished in the week of the first vaccination, the number of malignant cells increased again soon thereafter. WT1 treatment with a more intensive vaccination schedule, such as weekly vaccination, may provide higher efficacy by boosting the immune responses seen using a biweekly schedule. Although local toxicity should occur with extremely high frequency because of the intradermal injection, the probability of the occurrence of severe hematological/non-hematological toxicity was not expected to increase considerably by a change in the administration schedule to a more intensive one.
After completion of the phase I study using a biweekly schedule, a new phase I/II clinical study was considered to be necessary to determine a more effective vaccination schedule that would not compromise the safety of the patients. This phase I/II trial is designed to examine two questions raised in the phase I and phase II sections. The preset phase I study sought to determine an optimal vaccination schedule in terms of safety that could be used in the subsequent phase II trial. The objective of the phase II study was to estimate the response rate of the therapy using the treatment schedule determined in the phase I study.
This paper examined the safety of weekly WT1 therapy in patients with solid tumor who participated in the phase I study. This study was aimed at validating our decision to continue into phase II trials.
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PATIENTS AND METHODS |
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TRIAL ELIGIBILITY
Patients with histologically confirmed solid malignancies were eligible if they exhibited a performance status of the Eastern Cooperative Oncology Group of 0–2 and had measurable disease. Additional inclusion criteria included: (i) age ranging from 16 to 80 years, (ii) overexpression of the WT1 gene in the cancerous tissue determined by RT–PCR and/or immunohistochemistry, (iii) HLA-A-2402 positivity, (iv) disease refractory to conventional chemotherapy, radiotherapy, and/or hormonal therapy, (v) no history of anti-tumor therapy within 28 days prior to enrolment, (vi) in patients not having primary brain tumor, absence of brain metastases should be confirmed by computed tomography or magnetic resonance imaging, (vii) sufficient organ function and (viii) written informed consent.
The Independent Data and Safety Monitoring Committee (IDSMC) independently reviewed the eligibility of each enrolled patient. Protocol compliance, safety and on-schedule study progress were also monitored by the IDSMC. This study's protocol was approved by the Ethical Review Board of the Faculty of Medicine, Osaka University.
WT1 PEPTIDE, VACCINE PREPARATION AND ADMINISTRATION
The modified 9-mer WT1 peptide (amino acids 235–243 CYTWNQMNL), in which Y was substituted at amino acid position 2 (anchor position) for M of the natural 9-mer WT1235–243 peptide (CMTWNQMNL), was used for vaccination of patients (4–7). The modified 9-mer WT1 peptide induces stronger CTL activity than the natural peptide against WT1-expressing tumor cells (5,6). We purchased WT1 peptides as lyophilized peptides from Multiple Peptide Systems (San Diego).
Skin-test-negative patients were intradermally injected once a week with 3.0 mg of the HLA-A*2402-restricted modified 9-mer WT1 peptide emulsified in Montanide ISA51 adjuvant (6–8). WT1 injection was scheduled for consecutive weekly administration for 12 weeks.
We examined the safety of the weekly treatment plan in the first patient cohort. If the weekly treatment plan was judged to be toxic or intolerable based on toxicity data observed during the first 4 weeks of WT1 treatment for the patients, we planned to sequentially include a new patient cohort to examine a less intensive schedule of biweekly. The decision criteria are described in the Statistical Methods in detail. The WT1 dose and administration schedules were established in light of the data compiled from a previous phase I trial (3). Toxicities were evaluated according to the National Cancer Institute Common Toxicity Criteria and independently reviewed by the IDSMC. The decision to discontinue therapy for each patient was based on the observation of grade 2 toxicities. In cases where therapy was discontinued, physicians confirmed that the patient had recovered from the toxicity prior to resuming treatment. Patients who experienced grade 3 or 4 toxicities were withdrawn from the study and followed until they recovered.
In addition, we performed an exploratory investigation of the anti-tumor effect of WT1 treatment by recording patients who experienced stable disease (SD) or who had complete or partial responses (PR) during treatment. The assessment of tumor response was based on the RECIST criteria. In addition, the tumor response data were reviewed extramurally.
STATISTICAL METHODS
Our decision criterion used Bayesian statistics, which are useful for monitoring data in clinical trials (9–13). The Bayesian paradigm treats parameters characterizing the important aspects of the phenomenon under study as random quantities. The parameter of primary interest was the probability that a patient experiences grade 3/4 toxicity during WT1 treatment. Bayes theorem was used to combine the observed toxicity data with the prior distribution that characterized our uncertainty or knowledge about the parameter prior to starting the trial. Given the data, the posterior distribution of the parameter was obtained through this Bayesian calculation.
We calculated the Bayesian posterior probability of the occurrence of grade 3/4 toxicity to provide the basis for making a decision with the following options: (i) terminating the phase I trial and continuing to phase II, (ii) continuing with phase I by optimizing the treatment schedule (weekly 
biweekly) and (iii) terminating the trial. A treatment schedule was considered acceptable if it was highly likely that the probability of developing grade 3 or 4 toxicities was below 20%. The cutoff probability of 0.90 was selected to quantify this criterion (9,10). The maximum level of 20% was chosen for WT1 immunotherapy, because 20% is the lowest value of target toxicity levels typically employed in phase I trials for solid tumors to estimate maximum tolerated doses of chemotherapy (14). We specified the 20% level before initiating the trial. For the Bayesian calculations, a beta distribution was used for the prior, while a binomial distribution was used for the observed data (14,15). A beta prior distribution is a conjugate family for a binomial distribution, which facilitates subsequent analysis. We employed the beta distribution that corresponded to the Bayes–Laplace uniform prior to beginning the study, reflecting the lack of knowledge of the probability of grade 3/4 toxicity following WT1 treatment.
The specific decisions listed below are based on the numeric values determined from the above calculations. The decision flow was presented in Fig. 1. If no grade 3/4 toxicities were observed in the first 10 patients, we would accept the weekly schedule and switch to phase II study. If 1 of 10 patients experienced grade 3/4 toxicity, the new patients would be assigned to the biweekly schedule. If one or more of the additional 10 patients experienced grade 3/4 toxicity, the trial would be terminated at that point, owing to the unacceptably high toxicity of WT1 therapy. Figure 2 details the Bayesian posterior distribution for the observation of no grade 3/4 toxicities (solid line) or one grade 3/4 toxicity (dashed line) in 10 patients. The estimated probabilities that the grade 3 and 4 toxicities would be below 20% are 0.914 and 0.678, respectively. According to these calculations, phase I study required at least 10 patients. The duration for patient enrollment was set at 1 year from January 2004.
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SAS for Windows release 8.02 software (SAS Institute Inc., Cary, NC, USA) was used to perform these statistical calculations. The SAS Probbeta function was used for the Bayesian calculations.
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RESULTS |
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PATIENT CHARACTERISTICS
Ten patients received a total of 114 vaccinations of WT1 according to a weekly schedule (Table 1). All patients had adequate follow-up to monitor toxicity and tumor response (Table 1). Patient listing was based on the order of enrollment in the study. Seven patients were male, while three were female. One and two patients had PS of 1 and 2 at baseline, respectively; all others had a PS of 0. The most frequent tumor types treated were glioblastoma (n = 5) and breast cancer (n = 2). All patients completed the 12 vaccination course, with the exception of one patient who received only six. All patients underwent conventional chemotherapy, radiotherapy and/or hormonal therapy prior to receiving WT1 therapy, with the exception of one patient with malignant fibrous histiocytoma (MFH). The patient with MFH did not undergo any prior treatment, because any standard therapy for the disease was not established.
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TOXICITY
Table 2 details the toxicities observed within the first and second 4-week treatment periods. No grade 3/4 toxicities were observed in either follow-up period. According to the Bayesian method, the lack of any grade 3/4 toxicities within the first 4 weeks in all 10 patients dictated that all patients were assigned to the weekly WT1 treatment schedule. After observing no grade 3/4 toxicities in 10 patients, the median and 90% quantile of the Bayesian posterior distribution were 6.1 and 18.9%, respectively (Fig. 1). One grade 1 and eight grade 2 toxicities occurred during the first four vaccinations. During the following four-week period, one grade 1 and seven grade 2 toxicities were observed. We did not withdraw WT1 treatment because of these toxicities. IDSMC review of these toxicities confirmed that these symptoms were not related to WT1 treatment. In addition, the individual patient physicians confirmed that all of the patients recovered from the toxicities completely or to the point at which these symptoms were not clinically a problem. Of the potential local toxicities, all treated patients experienced an inflammatory response with erythema at the WT1 vaccine injection site. These results indicated that a weekly schedule of WT1 treatment is sufficiently tolerable.
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RESPONSE TO TREATMENT
All 10 patients were assessed for their clinical responses to WT1 vaccination. One patient demonstrated a response to treatment during phase I study. The patient was a 33-year-old male with glioblastoma, previously treated with radiotherapy (60 Gy total dose). He exhibited a confirmed PR during WT1 treatment. An additional five patients demonstrated stable disease during the 12-week WT1 vaccination period.
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DISCUSSION |
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TOPAbstractINTRODUCTIONPATIENTS AND METHODSRESULTSDISCUSSIONCONCLUSIONReferences |
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The primary goal of the phase I part of the preset study was to determine a recommended schedule for the subsequent phase II trial; this study sought to determine if the weekly WT1 vaccination therapy satisfied safety criteria for clinical use. We employed the Bayesian posterior probability of occurrence of grade 3/4 toxicity to construct the criteria. While grade 1/2 toxicities do not necessarily prompt the termination of treatment, physicians usually consider withdrawing treatment if grade 3/4 toxicity develops. As WT1 treatment is a form of immunotherapy, the probability that a patient receiving WT1 treatment experiences grade 3/4 toxicity must be negligible. We specified the upper boundary of acceptable probability at 20%. To determine the most appropriate dose (the ‘target’ dose) to generate cytotoxic immunity, phase I trials typically use a value between 20 and 40% as the target toxicity level (14). The target dose is determined as the dose level at which 30% (the target toxicity level) of patients would experience grade 3/4 toxicities, which is defined as the dose-limiting toxicity. In this study, we used a value of 20% as the upper limit, not the target, of the acceptable toxicity level. In addition, we employed a probability cut-off of 0.90, which is frequently used in clinical trials for safety data monitoring (9,10). None of the 10 patients enrolled in the phase I section of this study experienced any grade 3 or 4 toxicities. Given these data, the probability of a grade 3/4 toxicity below 20% was estimated at 0.914, which is larger than the cut-off value. The Bayesian posterior distribution had a median of 6.1% and a 90% quantile of 18.9%. Consequently, the data observed in the phase I study indicated that this weekly WT1 treatment satisfied the safety criteria.
The toxicities observed in phase I study were all of grade 1 or 2. These toxicities were confirmed to be unrelated to WT1 treatment by the IDSMC. While some discontinuations of therapy were required owing to grade 2 toxicities, all of the patients, with the exception of one, completed the planned WT1 treatment. Withdrawal from WT1 therapy was necessary for one patient owing to progressive disease, despite receiving six vaccinations. The high compliance and the safety data indicate that the weekly schedule should be tolerable for the patients enrolled in phase II trial. In addition, the tumor responses of 1 PR and 5 SDs, observed in patients that were refractory to all other anti-cancer treatments, strongly support our decision to proceed to phase II trials.
We must stress, however, that the safety of weekly WT1 vaccination should be evaluated using larger numbers of patients, because our safety examination was performed using only a small number of patients. Phase II trial primarily seeks to evaluate the response rate to weekly WT1 treatments, only secondarily investigating safety, alterations in tumor markers, changes in performance status and immunological responses, such as delayed type hypersensitivity to WT1 peptide and numbers of cytotoxic T lymphocyte precursors. The phase II evaluation should be conducted in each of cancer types, which include glioblastoma, and breast, lung and colorectal cancers. The required sample size for each phase II study was estimated at 25 patients for 5% type I and 20% type II errors, assuming 5 and 25% response rates for the null and alternative hypotheses, respectively. We predict that the number of patients enrolled in these phase II trials should be at least 100 in total. Approximately 10 Japanese institutions will participate in the phase II trials, while the phase I trial was conducted in one institution. In addition to the goals of the phase II trials, the safety and efficacy of WT1 therapy should continually be examined. In addition, future studies should examine the efficacy of the combination therapy of WT1 administered in conjunction with GM-CSF (Granulocyte Macrophage colony stimulating factor) or other modalities. Such data will provide more convincing information concerning the safety and efficacy of vaccine treatment for cancer patients.
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CONCLUSION |
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This paper demonstrated that the weekly treatment schedule of WT1 injections is acceptable in terms of toxicity and may exhibit an anti-tumor effect in refractory patients. Consequently, we decided to proceed from phase I to phase II studies, in which the weekly WT1 therapy will be examined in a larger population of patients with solid cancer in the near future.
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Acknowledgments |
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We are grateful to Drs Hitoshi Shiozaki and Norio Arita for providing important advice and suggestions while serving as advisory committee members. This work was supported by Grant H16-TRANS-003 from the Ministry of Health, Labour, and Welfare of Japan, and the Kyoto University EBM Center.
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References |
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