Cancer vaccines: challenges and outlook in the field.

Therapeutic vaccination against cancer-associated antigens represents an attractive option for cancer therapy in view of its efficacy, the possibility of long-lasting immunity against the cancer, and safety profile. Nevertheless, it is now recognized that the same vaccination strategies used for prophylactic vaccinations against infectious diseases, cannot necessarily be used for therapeutic cancer vaccination. Cancer patients are usually immunosuppressed and most cancer-associated antigens are 'self-antigens', making it a significant challenge to vaccinate patients against a cancer-associated antigen. Various immunostimulation techniques are under investigation in an effort to bolster patients' immune systems and to overcome immune tolerance to self antigens. Strategies to stimulate antigen presentation, T-cell reactivity and innate immune activity are under investigation. Several clinical trials have been conducted to evaluate therapeutic cancer vaccines in patients, and attractive protocols, including those that combine the stimulation of specific T-cells and chemotherapy, or strategies to block immune regulation, are beginning to show some success. This feature review considers strategies for the development of effective therapeutic cancer vaccines, and highlights select vaccines that have already entered the clinic.