Poxvirus-based vaccines for cancer immunotherapy: new insights from combined cytokines/co-stimulatory molecules delivery and "uncommon" strains

Poxvirus-based vaccines have a long record of efficacy as both anti-tumour agents and vectors for gene therapy in different human tumour models. Interestingly, several studies of these vaccines have now entered the clinical evaluation phase for safety and effectiveness. A desirable outcome of antigen specific cancer immunotherapy is the disruption of host self-tolerance against endogenous tumour-associated antigens (TAAs). Nonetheless, recent studies have found reductions in vaccine efficacy due to host anti-vaccine immune reactions. Thus, newer approaches bringing together poxvirus-based vaccination and immunostimulation are being developed, and new poxvirus strains are being examined in tumour therapy studies. Our review summarizes the current knowledge on the efficacy of poxvirus-based vaccination on human tumours, with a particular focus on approaches aimed at increasing innate and specific immune responses. Special attention will be devoted to the new poxvirus strains that are currently under consideration for tumour therapy; the current knowledge on clinical trials and outcomes will also be reviewed.