This review describes the litifilimab (BIIB 059) development program to date for systemic lupus erythematosus (SLE) and cutaneous lupus erythematosus (CLE). Plasmacytoid dendritic cells (pDCs), major producers of type I interferons (IFN-I), play a key role in SLE pathogenesis. Litifilimab, a humanized monoclonal antibody, binds to BDCA2, a protein uniquely expressed on pDCs. The consequence of BDCA2 ligation is the inhibition of IFN-I as well as IFN-III, cytokine and chemokine production. Phase I and II LILAC trial parts A and B achieved primary end points in SLE and CLE patients, confirming the importance of pDCs and IFN-I in SLE and CLE. Litifilimab is currently being evaluated in phase III trials in both SLE and CLE.