ACT-128800 is primarily investigated for its potential therapeutic applications in the field of immunology and autoimmune diseases. It functions as a selective sphingosine-1-phosphate receptor 1 (S1P1) modulator, which plays a crucial role in regulating lymphocyte trafficking. By modulating this receptor, ACT-128800 can effectively reduce the migration of lymphocytes from lymph nodes into the bloodstream, thereby suppressing immune responses. This mechanism makes it a promising candidate for treating conditions such as multiple sclerosis, where controlling immune system activity is essential to prevent nerve damage. Additionally, its application is being explored in other autoimmune disorders and inflammatory conditions, offering a targeted approach to managing these diseases with potentially fewer side effects compared to broader immunosuppressive therapies.