Safety Study of DNA Vaccine Delivered by Intradermal Electroporation to Treat Colorectal Cancer

The purpose of this study is to evaluate the safety and immunogenicity of a CEA DNA immunisation approach in patients with colorectal cancer. The DNA plasmid, tetwtCEA, encodes wild type human CEA fused to a tetanus toxoid T helper epitope. The vaccine will be delivered using an intradermal electroporation device, Derma Vax (Cyto Pulse Sciences). The following will be assessed: * The efficiency of priming immunological responses to CEA by intradermal administration of CEA DNA in combination with electroporation. * The efficiency of boosting immunological responses to CEA by intradermal administration of CEA DNA in combination with electroporation in subjects already vaccinated with CEA DNA. * GM-CSF will be administered to half of the subjects primed with CEA DNA in combination with electroporation and any possible adjuvant effects of GM-CSF will be evaluated.