Apilimod mesylate is primarily used in research and clinical settings as a selective inhibitor of phosphoinositide 3-kinase delta (PI3Kδ) and PIKfyve. It has shown potential in the treatment of autoimmune diseases and inflammatory disorders, such as rheumatoid arthritis and Crohn's disease, by modulating immune responses. Additionally, it is being investigated for its anti-cancer properties, particularly in B-cell malignancies, due to its ability to inhibit cell proliferation and induce apoptosis. Apilimod mesylate is also explored for its role in combating viral infections, including Ebola, by interfering with viral replication processes. Its application in these areas highlights its versatility as a therapeutic agent in both immunology and oncology.