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.

Inclusion Criteria:

• Histological confirmed AJCC stage II or III colorectal cancer
• Resection of the primary tumour without evidence of remaining macroscopic disease
• Allowable standard chemotherapy or radiotherapy in AJCC stage III completed minimum 2 months prior study entry
• Patients recruited from vaccination with CEA66 plasmid DNA must have completed trial at 18 months if immune response is proven or proven to be non-immune responders in two consecutive immunoassays.
• Age >18 years
• Karnofsky performance >80%
• Life expectancy of greater than 6 months
• Normal organ and marrow function
• Normal thyroid function as measured by serum T3, T4 and TSH
• Normal echocardiogram regarding arrhythmias (chronic or treated atrial fibrillation allowed)
• No concurrent treatment (chemotherapy or biological) may be planned during protocol treatment
• Women or men of reproductive potential must agree to use adequate contraception prior to study entry and for up to 3 months after the last injection
• Ability to understand and the willingness to sign an informed consent document

Exclusion Criteria:

• Immunotherapy or systemic corticosteroids within 8 weeks prior to entering the study
• Chemotherapy or radiotherapy within 2 months prior to entering the study
• Known hypersensitivity to GM-CSF
• Previous splenectomy or radiation therapy of the spleen
• Pregnancy or nursing
• HIV seropositivity
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic intracranial disease, congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements
• History of severe neurological, cardiovascular, renal, hepatic, respiratory, bone marrow dysfunction, organ graft or autoimmune disease (treated or not)
• Concomitant medication with an anticoagulant (acetylsalicylic acid and low-molecular weight heparin in prophylactic dose allowed)
• Other malignancy, except for the following: adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, adequately treated stage I or II cancer from which the patient is currently in complete remission, or any other cancer from which the patient has been disease-free for 5 years
• Cardiac demand pacemakers or surgically implanted defibrillators.
• Patients that has any metal implants in the area of the injection, (e.g. shoulder implant in the upper arm or shoulder girdle)