The US FDA granted breakthrough therapy status to Biogen's litifilimab (BIIB059) for the treatment of cutaneous lupus erythematosus (CLE).[1][3] CLE is a chronic autoimmune skin disease for which there are currently no targeted treatments.[1][3] Litifilimab is a first-in-class humanized IgG1 monoclonal antibody that targets BDCA2 in dendritic cells.[1][3] This status was granted based on data from the phase 2 LILAC trial, which demonstrated improvement in CLE skin disease activity.[1][6] In the LILAC study, there were greater decreases in CLASI-A scores compared to placebo, with apparent dose dependence and a higher proportion of patients achieving clinically significant responses.[6] Biogen continues to evaluate the efficacy and safety of litifilimb in the phase 3 AMETHYST study, with results expected in 2027.[1][3] Current treatments for CLE include antimalarials, immunosuppressants, and topical steroids, which relieve symptoms but do not alter the course of the disease.[3] CLE symptoms affect 70-85% of people with lupus.[5][7]