Cancer immunotherapy strategies based on transition‑metal medical materials: Still a long way to go (Review).

Transition‑metal nanoparticles (NPs) have been extensively studied owing to their unique physical and chemical properties, ability to form a variety of nanostructures and targeting properties. After surgery, chemotherapy, radiotherapy and targeted therapy, immunotherapy has emerged as a major strategy for cancer treatment. In particular, immune checkpoint inhibition has attracted much attention in preclinical and clinical applications. The combination of transition‑metal NPs with tumor immunotherapy offers great potential. Therefore, the present review focused on four major transition‑metal NPs (Au, Ag, Cu and Fe NPs) and their respective categories, presented their characteristics and roles in the biomedical field and discussed their potential toxicities. In addition, the mechanisms of action of different tumor immunotherapies and the applications of transition‑metal NPs in tumor immunotherapy are discussed. The current status of, and challenges associated, with the clinical transformation of transition‑metal NPs in tumor immunotherapy are described to provide ideas for the subsequent development and clinical application of transition‑metal NPs.