CTLA-4 inhibitors are primarily used in immunotherapy to treat certain types of cancer. They work by blocking the CTLA-4 protein, which normally acts as a brake on the immune system. By inhibiting this protein, the immune system is activated to attack cancer cells more effectively. These inhibitors have shown significant success in treating advanced melanoma, often in combination with other therapies like PD-1 inhibitors. Additionally, they are being explored for use in other cancers, such as lung and kidney cancer, to enhance the body's natural ability to fight tumors. CTLA-4 inhibitors are also being studied in clinical trials for their potential in treating autoimmune diseases and improving outcomes in organ transplantation by modulating immune responses.