Prostate cancer is the most common non-skin cancer in America, and the most commonly diagnosed cancer among males. When metastatic, the disease is ultimately incurable. Consequently, alternative strategies to current treatments are sought, especially in the area of immunotherapy. Vaccine immunotherapy using a specific antigen can be used to stimulate the body's immune response for targeted destruction of cancer cells and for prevention of tumor recurrence. Adenovirus-based vaccines have been successful in inducing an immune response to certain cancers and limiting tumor growth. To enhance this anti-tumor activity, we propose the combination of a viral system with a non-viral system, in the form of the cationic polymer poly ethylenimine (PEI). PEI complexes with DNA to form nanoparticles that can be used in gene delivery. We show that PEI can upregulate the CD80 and CD86 markers of maturation and activation in dendritic cells, a process necessary for launching a robust antigen-specific immune response in the body. We also show that PEI complexed with an antigen-specific adenovirus provides increased tumor protection in a murine tumor model.