Metal-based nano-vaccines for cancer immunotherapy

Cancer vaccination is an effective way to prevent or cure cancers by inducing strong cellular and humoral immunity with the aid of delivery carriers or adjuvants. Increasing new delivery vehicles and vaccine adjuvants have been developed for immunotherapy as they can enhance immune responses with reduced doses and side effects. In spite of many advantages of cancer immunotherapy, the clinical outcomes of cancer vaccines are still not satisfactory due to insufficient induction of antigen specific T cells. Metalloimmunology may revitalize cancer vaccines and improve their clinical applications considering that nutritional metal ions such as Ca2+, K+, Fe2+/3+, Zn2+, Mn2+ play important roles in many key immune processes. As good adjuvants, a wide variety of metals can be incorporated in the formulations of nano-vaccines for the enhanced immunity. Metal-based nanomaterials can also efficiently deliver antigens to antigen-presenting cells for the generation of immunity. In this review, we comprehensively summarized different types of commonly-used metal nanomaterials, as adjuvants or delivery carriers, for the development of effective cancer vaccines. Other applications such as use as contrast agents for bioimaging were also briefly reviewed. Then, their applications for cancer immunotherapy, along with their action mechanisms were systematically discussed.