This open label trial will evaluate the safety of allogeneic MSCs for the treatment of adults with moderate to severely active systemic lupus erythematosus (SLE). MSCs will be derived from healthy donor umbilical cord cells and 1 dose of MSCs will be tested. MUSC has a good manufacturing practice (GMP) quality Clean Cell Facility to ensure the quality and safety of the MSCs prior to infusing into study participants. The goal of this study is to determine the safety of MSC infusion in patients with SLE when added to standard of care for SLE.