PF-06651600 is primarily used in the treatment of autoimmune diseases due to its ability to selectively inhibit JAK3, a key enzyme involved in immune cell signaling. It has shown promise in conditions like rheumatoid arthritis, alopecia areata, and inflammatory bowel disease by modulating the immune response and reducing inflammation. The compound’s specificity for JAK3 minimizes off-target effects, making it a safer option compared to broader JAK inhibitors. Clinical trials have demonstrated its efficacy in promoting hair regrowth in alopecia patients and improving symptoms in autoimmune disorders, highlighting its potential as a targeted therapeutic agent.