Abstract: |
For over a century, dating back to William Coley's initial experiments with bacterial toxins in cancer patients [1], investigators have been trying to harness the power of the immune system as a means of fighting cancer. The rationale for cancer immunotherapy derives from a number of pre-clinical and clinical observations, including but not limited to: 1) the ability of the immune system to recognize and eliminate tumors of diverse histological types in animal models; 2) the increased incidence of tumor formation in immunodeficient mice; 3) the modest but reproducible response rates seen in melanoma and renal cell carcinoma for cytokine immunostimulants such as interleukin 2 and interferon-alpha; and 4) the identification and isolation of antibodies and tumor-infiltrating lymphocytes from cancer patients which recognize a host of tumor antigens. This rationale has been bolstered further by the success, particularly in patients with hematologic malignancies, of passive immunotherapies such as donor leukocyte infusion following allogeneic stem cell transplantation and monoclonal antibodies such as rituximab. Less successful clinically to date have been attempts at active immunotherapy, despite a number of different immunization strategies designed to induce antitumor immunity in recipients (reviewed recently in ref. [2]). DNA vaccination, in which recipients are immunized with bacterially-derived plasmids encoding one or more antigens of interest, represents a relatively novel approach to the active immunotherapy of cancer, and will be reviewed in detail here. |