XmAb®5871 is currently in a Phase 1b/2a clinical trial for the treatment of moderate-to-severe rheumatoid arthritis and is in preparation for a clinical trial in IgG4-related disease. XmAb5871 is a first-in-class monoclonal antibody that targets CD19 with its variable domain and that uses our XmAb immune inhibitory Fc domain to target FcγRIIb, a receptor that inhibits B cell function. XmAb5871 is the first drug candidate that we are aware of that targets FcγRIIb inhibition. We have demonstrated in multiple animal models and in initial human clinical trials that XmAb5871 inhibits B-cell function without destroying these important immune cells.

B-cell inhibition has proven to be an effective strategy for a number of autoimmune diseases, ranging from rheumatoid arthritis and lupus to rare conditions such as IgG4-related disease. However, safety issues from other B-cell targeting therapies that attack and destroy B cells, such as rituximab, have limited market uptake. The ability of XmAb5871 to induce a broad blockade of B-cell activation without depleting B cells is a key differentiator.