Eligibility Criteria

All patients will be screened using the eligibility criteria detailed below:

Up to 12 months since diagnosis of SLE based on the 2019 EULAR and the American College of Rheumatology (EULAR-ACR) criteria.
Aged 5 years or older.
Starting their first immunosuppressant (e.g. methotrexate, azathioprine, mycophenolic acid analogue, cyclosporin, cyclophosphamide, leflunomide, tacrolimus) at screening or no more than 4 weeks earlier. Antimalarials and GCs are not considered as immunosuppressants.
Moderate-to-severe disease SLE activity (i.e. defined as a minimum of 1 x BILAG A OR 2 x BILAG Bs Grade, OR 1 x BILAG B in the mucocutaneous domain combined with physician intent to treat with an immunosuppressant).
Women of childbearing potential are required to use adequate contraception for the duration of the trial and for 12 months after the last treatment (see section 8.10 for details).
Written or online, informed consent, and where appropriate assent obtained from the participant, and consent from their legal representative/guardian.
In line with established prescribing guidelines, negative tests in the last 1 year for Human immunodeficiency virus (HIV), hepatitis B including past infection, and hepatitis C.

Pregnant or breastfeeding or planning to get pregnant in the near future.
Active infections, until treatment is completed and symptoms have resolved.
Serum immunoglobulin G (IgG) below the lower limit of the local laboratory range.
Receipt of a live attenuated vaccine within 4 weeks prior to screening visit.
History of cancer in the past 5 years except for squamous or basal cell carcinoma that has been completely excised or treated cervical carcinoma in situ.
Any other concomitant medical condition that, in the investigator’s opinion, or after discussion with the CI, places the participant at risk by participating in this study.
Any other criteria that would make the patient ineligible for rituximab or concomitant medications used in the FIRST trial under local routine prescribing guidelines.