Immunoglobulin G4-related disease (IgG4-RD) is a chronic immune-mediated disorder characterized by inflammation, fibrosis, and involvement of multiple organs. Although glucocorticoids can effectively induce remission, many patients experience disease relapse after glucocorticoid tapering or discontinuation, and long-term glucocorticoid exposure may cause significant adverse effects. Therefore, new maintenance treatment strategies are needed to reduce relapse risk and minimize glucocorticoid-related toxicity.

This study is designed to evaluate the efficacy and safety of lenalidomide as a maintenance therapy in patients with stable IgG4-RD. This is a multicenter, randomized, double-blind, placebo-controlled phase III clinical trial.

Eligible participants will be adults with IgG4-RD who meet the 2019 ACR/EULAR IgG4-RD classification criteria and are in a stable disease state. Participants will be randomly assigned in a 1:1 ratio to receive either lenalidomide or matching placebo for 52 weeks. All participants will receive standardized glucocorticoid tapering according to the study protocol.

The primary objective of this study is to determine whether lenalidomide can reduce the risk of IgG4-RD relapse compared with placebo. The primary outcome is the proportion of participants experiencing disease relapse within 52 weeks after randomization.

Secondary objectives include evaluation of time to relapse, maintenance of remission, changes in disease activity, quality of life, and safety outcomes. Exploratory assessments will investigate changes in immunological biomarkers, peripheral blood immune profiles, transcriptomic characteristics, and gut microbiota.

This study aims to provide clinical evidence for a new maintenance treatment approach for patients with IgG4-RD and potentially reduce disease recurrence and glucocorticoid exposure.