2574 Background: Oncofetal antigen 5T4 is expressed by most colorectal cancers. Administration of a vaccine combining a Modified Vaccinia Ankara (MVA) vector with 5T4 elicits immune responses in late-stage colorectal cancer patients. This trial seeks to investigate the immunological effects of the vaccine both in peripheral blood and locally in tumour tissue resected during potentially curative surgery for colorectal liver metastases. Some patients may have micrometastatic disease, a potential target for immunotherapy. Methods: Colorectal cancer patients selected for resection of liver metastases were eligible. Recruitment of up to 20 patients was planned. Following screening they received 2 vaccinations prior to, and 2 after, surgery. Primary endpoint was assessment of the immune response at time of surgery. Blood was taken for analysis at screening and 2 weeks after each vaccination. A tumour biopsy was obtained at surgery. T-cell responses were assessed using proliferation and gamma-interferon ELISPOT assays; ELISA used to assess serological response. Immunohistochemical analysis was used to confirm tumour antigen expression and the nature of T-cell infiltration into the liver. If 5T4-specific immune responses were demonstrated patients were offered further vaccinations at 20 and 28 weeks post surgery. Results: Of 20 patients recruited, 16 were eligible for assessment, 4 excluded, 1 due to hepatocellular carcinoma, 3 with inoperable disease. There was no grade III/IV toxicity related to vaccination. Tumour expression of 5T4 was confirmed in all cases, local T-cell infiltration consisted predominantly of CD4 cells. According to proliferation assays, 8 of 16 patients had T-cell responses at time of surgery and 12 of 16 in total to date. 14 patients have developed 5T4-specific antibody responses. At median follow up of 8.4 months 7 of 16 patients have disease recurrence. Conclusions: The MVA-5T4 vaccine (TroVax) was safe and well tolerated in all patients undergoing resection of colorectal liver metastases. 5T4 specific cellular and/or humoral immune responses were induced in the majority of patients following vaccination with TroVax. [Table: see text]
Regulatory T Cell Infiltration Predicts Outcome Following Resection of Colorectal Cancer Liver Metastases