This is a Phase 2b, multicenter, randomized, double-blinded, placebo-controlled study to assess the efficacy and safety of IMVT-1402 in adult participants with moderate to severe systemic primary Sjogren's disease (SjD).

The primary objective is to evaluate the efficacy, safety, and tolerability of IMVT-1402 compared to placebo, as measured by the change from baseline of Clinical European League Against Rheumatism Sjogren's Syndrome Disease Activity Index (clinESSDAI) at Week 24.

The total duration of study participation is expected to be up to 105 weeks for an individual participant.

Inclusion Criteria:

• Participants with a diagnosis of primary SjD for at least 12 months prior to the Screening Visit and meet classification criteria for primary SjS according to the 2016 American College of Rheumatology/ European League Against Rheumatism Classification Criteria for Primary Sjogren's Syndrome at the time of screening.
• Participants with moderate to severe systemic disease activity as determined by a clinESSDAI total score ≥ 5 at the Screening Visit.
• Participants are seropositive for antibodies to Sjogren's Syndrome A (SSA)/Anti-Sjogren's Syndrome A (Ro) at the Screening Visit.
• Participants have residual salivary flow as measured by stimulated whole salivary flow rate ≥ 0.01 milliliters per minute (mL/min) at the Screening Visit.

Additional inclusion criteria are defined in the protocol.

Exclusion Criteria:

• Participants with a diagnosis of secondary SjD, inadequately treated fibromyalgia, other confirmed connective tissue, rheumatic, or systemic inflammatory autoimmune disease including but not limited to, rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis, dermatomyositis, or polymyositis, that in the opinion of the Investigator, is likely to interfere with the ability to assess primary SjD manifestations.
• Participants with a history of clinically significant monoclonal gammopathy, including but not limited to monoclonal gammopathy of undetermined significance, history of multiple myeloma or non-Hodgkin's lymphoma, or have an active malignancy or history of malignancy within 5 years prior to the Screening Visit.

Additional exclusion criteria are defined in the protocol.

The Sponsor will also be blinded in the study.