FT839 in Autoimmune Diseases

This is a multicenter, Phase 1/2, open-label trial designed to evaluate the safety, pharmacokinetics (PK), anti-B-cell activity, and clinical activity of FT839 in participants with moderate-to-severe ANCA-associated vasculitis (AAV), idiopathic inflammatory myositis (IIM), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc). Participants will receive FT839 as monotherapy or in combination with rituximab, with or without conditioning therapy and/or stable background therapy. Participants will be enrolled in 2 stages during the Phase 1 portion of the trial: a dose-escalation stage and a dose-expansion stage. In the dose-escalation stage, safety and tolerability will be assessed to define the MTD (or through the maximum assessed dose \[MAD\] in the absence of dose-limiting toxicities \[DLTs\] defining the MTD). The DLT evaluation period will extend from Day 1 through Day 29. Participants will be followed during the post-treatment follow-up period for up to 2 years after the first dose of FT839, followed by long-term-follow-up for safety and survival for up to 15 years after the first dose of FT839. In the dose-expansion stage, participants will be enrolled into disease-specific cohorts to further evaluate the safety and activity of FT839. Following completion of the Phase 1 portion, the Phase 2 portion of the trial will further evaluate the efficacy of FT839 within each disease cohort.