A phase I clinical trial of MVA expressing 5T4 and high-dose interleukin-2 (IL-2) for metastatic renal cell carcinoma

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Background: Metastatic renal cell carcinoma (RCC) is an immune responsive tumor. 5T4 is a tumor antigen expressed on the cell surface of clear cell and papillary RCC. We sought to evaluate the safety and immunologic effects of vaccination with modified vaccinia virus Ankara (MVA) expressing 5T4 followed by IL-2 in patients with advanced RCC. Methods: A single dose Phase I clinical trial was conducted in patients with metastatic RCC and who were eligible for high-dose IL-2. Vaccination was given every three weeks by intramuscular injection and was followed immediately by standard high-dose bolus IL-2 (600,000 IU/kg) after the second and third vaccinations. The regimen could be repeated if there was no evidence of disease progression. Peripheral blood and serum was collected before treatment and every three weeks for analysis. Routine blood counts, chemistry, and pituitary functions were monitored. Anti-5T4 antibody titers were determined by ELISA assay and 5T4-specific T cell responses were monitored by interferon-γ ELISPOT assay using overlapping peptides. Results: 25 patients with RCC are being sequentially enrolled. There have been no serious vaccine-related adverse events although typical Grade 3 IL-2 related toxicity has been seen in all patients. To date, all patients tested have developed an increase in 5T4-specific antibody titers following three initial vaccinations. T cell assays are currently in progress. Seven patients have completed the trial through at least one course of treatment (mean age 62.3 years). Of these 7, one patient who presented with a primary tumor in place and synchronous metastatic disease had an objective complete response of all metastatic disease and underwent a post-treatment nephrectomy; the primary tumor demonstrated highly necrotic tumor. Two additional patients have had stable disease and are receiving booster vaccinations every three months. Conclusions: These results demonstrate that local vaccination with an MVA virus expressing 5T4 administered in combination with high-dose IL-2 is safe and induces 5T4-specific antibodies in all patients. Additional T cell responses and clinical follow-up will be presented. The use of MVA-5T4 and IL-2 appears to be a promising approach for the treatment of advanced RCC.

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