RSLV-621 is a potent Interferon (IFN) antagonist that is comprised of a soluble IFN receptor fused to IgG1 Fc. The molecule demonstrates subnanomolar IC50 inhibition of major interferons including IFN- and IFN-. Interferon is a validated target in autoimmune disease with demonstrated efficacy in SLE, Lupus nephritis, and Systemic Sclerosis. Its smaller molecular weight, roughly 25% of a monoclonal antibody, may offer access to cellular compartments difficult to penetrate with a large 180 kDa monoclonal antibody. Since, inhibiting the IFN pathway has proven efficacy in SLE, there is a rapid path to clinical proof-of-concept and go/no-go decision into larger pivotal trials for RSLV-621.