This is a randomized, double-blind, placebo-controlled multicenter clinical study to evaluate the efficacy, safety, and pharmacokinetics of SIM0278 in adult (18-75 years) subjects with active LN suitable for systemic therapy.

Approximately 60 subjects with active LN are planned to be enrolled and randomized 1: 1 to SIM0278 or placebo.

The study consists of 3 phases: screening, double-blind treatment, and safety follow-up.

Inclusion Criteria:

1. Weight ≥ 40.0 kg
2. SLE was diagnosed according to 2019 American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) classification criteria.
3. Subjects must be receiving or willing to initiate induction therapy for LN. Induction therapy, defined as including high-dose glucocorticoids and MMF, should be initiated within 60 days or on the same day prior to baseline.

Exclusion Criteria:

1. Previous or current nephropathy (except LN) that, in the opinion of the investigator, may interfere with the LN assessment and interfere with the assessment of disease activity (e.g., diabetic nephropathy). The subject was unable or unwilling to provide written informed consent and/or to comply with study procedures.
2. Severe renal impairment: a) oliguria (defined as recorded urine volume < 400 mL/24 h), or b) end-stage renal disease (ESRD) requiring dialysis or transplantation.
3. Previous induction therapy for MMF/MPS was considered by the investigator to have failed.