Systemic Delivery of Therapeutic Proteins by Intramuscular Injection of Plasmid DNA

In vivo delivery of a cytokine gene to treat a tumor has usually involved either injection of ex vivo transfected cells around the tumor site or direct intratumoral injection of a virus or plasmid DNA (pDNA) vector encoding the cytokine gene (1 ,2 ). In this manner, transfected cells in or around the tumor site may secrete cytokine locally and stimulate an antitumor immune response (3 ,4 ). Recently, a new method of cytokine gene delivery for treating tumors was described. In this method, a naked pDNA encoding a cytokine, in this case, interferon-α (IFN-α), was injected intramuscularly (im) into C57BL/6 mice bearing solid or metastatic B16F10 melanoma tumors (5). The mice treated in this manner had a striking inhibition of tumor growth.