− Phase 1b, Open-Label Study Follow Up Shows Stable Kidney Function (eGFR) in Patients Treated with Investigational Mezagitamab Through Week 96 – 18 Months After Last Dose1

− Rapid Reductions in Proteinuria and Serum Gd-IgA1 Levels Were Sustained Through Week 961

− No Serious Adverse Events or Opportunistic Infections Were Observed Through Week 961

− Takeda Initiated Pivotal Phase 3 Clinical Trials Evaluating Mezagitamab in Primary IgA Nephropathy and Immune Thrombocytopenia with Patient Enrollment Ongoing

Takeda (TSE:4502/NYSE:TAK) today announced new interim data from the Phase 1b, open-label, proof-of-concept study of subcutaneous mezagitamab (TAK-079), an anti-CD38 monoclonal antibody with disease-modifying potential, in primary immunoglobulin A (IgA) nephropathy. Data from the study showed that kidney function (eGFR) remained stable in patients with IgA nephropathy through Week 96 – up to 18 months after the last mezagitamab dose.1 The results were presented at the American Society of Nephrology (ASN) Kidney Week 2025 in Houston.

IgA nephropathy is a lifelong progressive autoimmune disease often diagnosed in young people aged 10-30 years old that causes irreversible damage to the kidney function.2 It has no cure, and despite available treatments, approximately one in five patients experience renal failure within 10 years of diagnosis.3 By depleting cells that produce an abnormal protein called Gd-IgA1 implicated in the pathogenesis, mezagitamab targets early steps in the process leading to disease in IgA nephropathy.

“Mezagitamab targeted the underlying immune mechanisms of IgA nephropathy, with data showing that kidney function remained stable in patients after the last dose of treatment,” said Prof. Jonathan Barratt, M.D., Ph.D., principal investigator for the Phase 1b study and the presenting author. “This is especially critical given the progressive and often silent nature of the disease, with many patients already experiencing some degree of kidney damage by the time they’re diagnosed. Without effective intervention, the risk of renal failure – and the need for dialysis or transplant – remains alarmingly high.”

In the study, 17 patients with IgA nephropathy were treated with mezagitamab as an add-on to stable background therapy, and 13 patients continued into the long-term follow-up period. At Week 96 – 18 months after the last dose – kidney function remained stable (mean change in eGFR from baseline +2.5; 95% CI: −1.8, +7.6; n=12) and patients sustained a 55.2% (95% CI: 30.2, 72.6; n=13) mean reduction in proteinuria (protein in the urine) measured using a urine protein-creatinine ratio (UPCR).1 Sustained reductions of 50.1% in Gd-IgA1 and complete recovery toward baseline in IgG were observed by Week 96.1 Hematuria (blood in the urine) was resolved in 60% of patients by Week 96.1

In this study, mezagitamab was generally well tolerated with no new safety concerns identified. No serious adverse events (AEs), including no serious hypersensitivity or injection-related reactions, discontinuations due to AEs, opportunistic infections or grade ≥3 infections were reported.1

“These promising data reinforce our belief in the potential of mezagitamab to redefine how autoimmune diseases like IgA nephropathy are treated – by targeting their root cause,” said Obi Umeh, M.D., M.Sc., Vice President, Franchise Global Program Leader at Takeda. “With patient enrollment ongoing in our Phase 3 trials investigating mezagitamab in IgA nephropathy and immune thrombocytopenia, we are excited to advance these promising programs and remain committed to bringing innovative solutions to patients with high unmet need.”

Mezagitamab is currently in Phase 3 clinical development for the treatment of both primary IgA nephropathy (NCT06963827) and chronic immune thrombocytopenia (NCT06722235) with the first patients now enrolled. In October 2025, mezagitamab was granted Orphan Drug Designation by the European Medicines Agency for the treatment of primary IgA nephropathy. In August 2025, mezagitamab was granted Breakthrough Therapy Designation by the U.S. Food and Drug Administration for the treatment of adult patients with chronic immune thrombocytopenia who have had an insufficient response to previous treatment. Takeda is assessing additional indications for mezagitamab.

About Mezagitamab

Mezagitamab is a fully human, anti-CD38 IgG1 monoclonal antibody that depletes cells that are high expressors of CD-38, such as plasma cells, plasmablasts and natural killer cells. Depletion of these cells is predicted to decrease formation of immune complexes, reduce inflammation and thus the resulting proteinuria, ultimately preventing further injury to the kidneys and promoting stabilization of kidney function over time.

Mezagitamab is an investigational compound that has not been approved for use by any regulatory authority.

About the Mezagitamab Phase 1b Trial in IgA Nephropathy

The Phase 1b trial, open-label, single-arm, multicenter study (NCT05174221) evaluated mezagitamab as add-on to stable background therapy in patients with primary immunoglobulin A (IgA) nephropathy.

Eligible participants were adults with biopsy-proven disease and proteinuria with urine protein-to-creatinine ratio (UPCR) ≥1 g/g from a 24-hour urine collection or urine protein excretion ≥1g/24 hours and estimated glomerular filtration rate (eGFR) ≥45 mL/min/1.73m.1 Participants received subcutaneous mezagitamab 600 mg once weekly for 8 weeks, then 600 mg every two weeks for 16 weeks (16 total doses), followed by a 24-week safety follow-up.1 Participants with favorable proteinuria response by Week 48 could enter the long-term follow up with a 48-week observation period. The primary endpoint was the percentage of participants with adverse events (AEs), including grade ≥3 AEs and serious AEs, up to Week 96.1 Secondary and exploratory endpoints included serum IgA, IgG and Gd-IgA1 levels, percentage change from baseline in UPCR, change from baseline in eGFR and resolution of hematuria (blood in urine).1

About Immunoglobulin A Nephropathy

Immunoglobulin A (IgA) nephropathy is a lifelong progressive autoimmune disease often diagnosed in young people aged 10-30 years old that causes irreversible damage to the kidney function.2 It is caused by deposits of immune complexes inside the filters in the kidney, which trigger inflammation and damage to the kidney tissue, resulting in loss of renal function.2

There is no cure for IgA nephropathy.3 It is associated with a poor prognosis and can progress to kidney failure, which can lead to reduced quality of life or premature death.1 Approximately one in five patients experience renal failure within 10 years of diagnosis despite available treatments.3

About Takeda

Takeda is focused on creating better health for people and a brighter future for the world. We aim to discover and deliver life-transforming treatments in our core therapeutic and business areas, including gastrointestinal and inflammation, rare diseases, plasma-derived therapies, oncology, neuroscience and vaccines. Together with our partners, we aim to improve the patient experience and advance a new frontier of treatment options through our dynamic and diverse pipeline. As a leading values-based, R&D-driven biopharmaceutical company headquartered in Japan, we are guided by our commitment to patients, our people and the planet. Our employees in approximately 80 countries and regions are driven by our purpose and are grounded in the values that have defined us for more than two centuries. For more information, visit www.takeda.com.

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