The immune system uses both innate and adaptive responses to defend the body against infections, with innate immunity providing quick, nonspecific defense and adaptive immunity providing antigen-specific, long-lasting protection. Immunotherapy, which boosts or modifies immune responses, has revolutionized the treatment of cancer, autoimmune disorders, and infections by providing focused, effective alternatives to conventional therapies. Immune checkpoint inhibitors (ICIs) and CAR-T cell therapy have achieved remarkable success, but they face challenges such as immune evasion, variable efficacy, immune-related side effects, high costs, and limited durability. The tumor microenvironment and immune-desert characteristics have a substantial impact on treatment results, confounding patient selection and response prediction. Emerging approaches leveraging nanotechnology offer promising solutions by improving drug delivery, modulating immune cell activity, and enhancing therapeutic precision through nanoparticles, liposomes, and other nanostructures. These developments have resulted in improved pharmacokinetics, less toxicity, and tailored modulation of the tumor microenvironment. As nanomedicine advances, it has the potential to overcome existing limitations in immunotherapy, making therapies safer, more effective, and more accessible, resulting in a substantial advancement in the treatment of cancer and other immune-mediated diseases.