Treatment of Systemic Lupus Erythematosus With Human Umbilical Cord Mesenchymal Stem Cells

patients will receive conventional therapy plus low dose hUC-MSCs treatment,The dosage is 1E6 cells/kg.

patients will receive conventional therapy plus medium dose hUC-MSCs treatment,The dosage is 3E6 cells/kg.

patients will receive conventional therapy plus high dose hUC-MSCs treatment,The dosage is 5E6 cells/kg.

patients will receive conventional therapy plus Placebo

Double dosing is selected by the investigators and the sponsor based on the data from the single-dose part of the study. One superior dose is chosen for multiple dosing (tentatively set at 3E6 cells/kg, administered twice with an interval of 4 weeks; the actual dose, frequency and interval of multiple dosing can be adjusted according to the available data). During the trial, stable standard treatment is allowed.