Clinical Study to Investigate the Biological Activity, Safety, Tolerability, and Pharmacokinetics of ACT-334441 in Subjects With Systemic Lupus Erythematosus

Inclusion Criteria:

- Male and female subjects aged 18 to 65 years with established SLE. Subjects must have
active SLE, Systemic Lupus Erythematosus Disease Activity Index-2000 (SLEDAI-2K) score
of at least 2 points for musculoskeletal or mucocutaneous manifestations and history
or presence at Screening of positive anti-nuclear antibodies (ANA) or
anti-double-stranded DNA (anti-dsDNA) antibodies.

- Enrolled subjects must be treated with background SLE medications.

Exclusion Criteria:

- Subjects with significant medical conditions or therapies for such conditions (e.g.,
cardiovascular, pulmonary, immunological, hepatic, ophthalmological, infection and
infection risks, history or presence of malignancy, history or presence of bone marrow
or solid organ transplantation) or lactating or pregnant women.

- Subjects with severe SLE disease or with clinically relevant medical or surgical
conditions that, in the opinion of the investigator, would put the subject at risk by
participating in the study.