A Study of Telitacicept for the Treatment of Generalized Myasthenia Gravis (UPSTREAM MG)

The purpose of this study is to evaluate the efficacy and safety of telitacicept in the treatment of generalized myasthenia gravis.

Myasthenia gravis (MG) is an autoimmune disease in which autoantibodies disrupt the postsynaptic membrane, impairing nerve-to-muscle signal transmission. The predominant manifestation is muscle weakness, which typically worsens with repeated muscle exertion, such that function is usually the best in the morning with more pronounced weakness at the end of the day. A major challenge in MG is the lack of therapies that effectively treat the disease. Telitacicept is a fully human TACI-Fc fusion protein that targets B-lymphocyte stimulator (BLyS) and A proliferating-inducing ligand (APRIL), neutralizing their interactions with receptors on B cells. The blockage of BLyS and APRIL interaction with their respective cell membrane receptors (transmembrane activator and CAML interactor \[TACI\], B-cell maturation antigen, and BLyS receptors) by telitacicept can inhibit B-cell proliferation and maturation. This suppression at the proximal portion of the immune response could alleviate autoimmune symptoms. This is a randomized, double-blind, placebo-controlled Phase 3 study with an open-label extension (OLE) to evaluate the efficacy and safety of telitacicept in a global patient population with gMG. The total duration of the study is variable but will include an approximately 4-week screening period, a 24-week double-blind treatment period (Week 0 through Week 24), a 48-week OLE (Week 24 through Week 72), followed by an extended OLE period (E-OLE), and an 8-week end-of-study follow-up period. The E-OLE is variable duration, defined as the period after the 48-week OLE period until telitacicept is approved for MG in the country or the further development in the indication is concluded.

Key Inclusion Criteria: 1. Male or female patient aged ≥18 years at screening. 2. Patients have prior confirmed diagnosis of gMG with generalized muscle weakness (typical pattern of weakness meeting the clinical criteria for diagnosis of MG as defined by the Myasthenia Gravis Foundation of America (MGFA) clinical classification II-IV. 3. Patients have positive antibodies against AChR or MuSK at screening. 4. MG-ADL score ≥6 points at screening and baseline with ocular-related score \<50% of the total score. 5. QMG score ≥8 points, and ≥ 4 items score at least 2 points at screening and baseline. Key Exclusion Criteria: 1. Patients have been diagnosed with any other autoimmune disease which can potentially pose a safety or efficacy confounding risk. 2. Patients having acute or chronic infection. 3. Patients having thymoma within 5 years or received thymectomy ≤6 months prior to screening. Patients with thymoma diagnosed 3-5 years prior to screening may be eligible if thymoma was at a localized stage and definitively treated with complete surgical resection. 4. Patients having current or history of primary immunodeficiency. 5. Patients having history of malignancy within the last 5 years. 6. Patient having prior or continuing diagnosis of serious cardiovascular, liver, kidney, respiratory system, endocrine or hematologic disease.