IL-15 is a type of cytokine, which is a protein that plays a crucial role in the immune system. It is primarily produced by dendritic cells, macrophages, and fibroblasts and helps in the growth and activation of T cells and natural killer (NK) cells. These immune cells are essential for fighting infections and tumors. IL-15 is known for its ability to enhance the survival and proliferation of memory T cells, which are important for long-term immunity. Research is ongoing to explore its potential in immunotherapy, particularly for treating cancers and enhancing vaccine responses.