WELLESLEY HILLS, Mass. — Climb Bio, Inc. (Nasdaq: CLYM), a clinical-stage biotechnology company developing therapeutics for immune-mediated diseases, today announced results from a completed nonhuman primate (NHP) study comparing CLYM116 to sibeprenlimab, a first-generation anti-APRIL monoclonal antibody. The company is hosting a virtual investor event focused on CLYM116 today, Monday, September 29, 2025, at 8:00 a.m. ET. Climb Bio’s management team will be joined by leading nephrologist Craig E. Gordon, MD, MS, who has over 20 years of experience treating patients with IgA nephropathy (IgAN) and was a co-director of the Evidence Review Team for the recently issued 2025 KDIGO Clinical Practice Guideline for IgAN.
“We are highly encouraged by the differentiated profile observed with CLYM116, as highlighted in our newly shared nonhuman primate data,” said Aoife Brennan, President and CEO of Climb Bio. “CLYM116 is the only known ‘sweeper’ anti-APRIL monoclonal antibody in development, which we believe could provide a compelling clinical profile in IgAN. In this head-to-head preclinical study, our data have shown improvements in pharmacokinetic and pharmacodynamic measures – namely a longer half-life and deeper and more durable IgA reductions – as compared to sibeprenlimab, a first-generation anti-APRIL monoclonal antibody. These data highlight the potential for CLYM116 to provide a differentiated activity profile with less frequent dosing. Notably, the updated KDIGO treatment guideline published earlier this month highlights the need for more active management of IgAN, and we believe that the adoption of these approaches could expand the CLYM116 market opportunity. We are excited to advance CLYM116 development and look forward to initiation of a Phase 1 trial later this year, with initial data anticipated mid-year 2026.”
CLYM116 Data & Event Highlights
New CLYM116 NHP data demonstrate improvement versus sibeprenlimab (first-generation anti-APRIL monoclonal antibody)
- Subcutaneous formulation demonstrated high bioavailability (~85%), with a favorable tolerability profile
- Prolonged exposure observed compared to sibeprenlimab, with a ~2-3 times longer half-life across doses
- Deeper and more prolonged IgA reduction observed compared to sibeprenlimab after a single subcutaneous administration at equivalent doses (6 mg/kg), with >70% maximal reduction in IgA observed with CLYM116
- Additional in vivo studies in mice showed enhanced APRIL elimination and antibody recycling relative to sibeprenlimab
CLYM116 advancing towards planned Phase 1 trial in healthy volunteers
- Phase 1 trial expected to initiate in Q4 2025, subject to regulatory clearance, with initial data, including biomarkers and projected dosing interval, anticipated mid-year 2026
- Parallel execution by Mabworks in China expected to provide a complementary Phase 1 dataset
IgAN represents a high unmet need indication, with a well-defined development path
- Progressive autoantibody-mediated renal disease, caused by APRIL-mediated production of pathogenic IgA and deposition of immune complexes in the glomeruli
- Damage to glomeruli leads to proteinuria, kidney injury and loss of kidney function, with 30-40% of patients developing kidney failure within 10 years of diagnosis
- Prior product approvals in IgAN provide precedent regarding study design and registrational endpoints, including use of proteinuria for accelerated approval and estimated glomerular filtration rate (eGFR) for full approval
- Biomarkers (APRIL, IgA) enable rapid assessment of clinical profile during early development
IgAN is a significant market opportunity, estimated at $10-20B in US alone
- Most common primary glomerular disease worldwide, with ~170,000 patients in the US alone
- Typically diagnosed early in life and is likely to require lifelong management
- KDIGO 2025 guideline recommends a lower threshold for biopsy to enable earlier diagnosis and recommends aiming for stricter proteinuria control, with a goal of <0.5 g/day, ideally <0.3 g/day, which may result in earlier and more aggressive disease management
- Updated treatment guidelines highlight importance of reducing pathogenic IgA along with managing the consequences of existing nephron loss, potentially positioning anti-APRIL therapy as a core pillar in the future treatment of IgAN
Webcast Information
The live webcast will be accessible via the “Investors & Media” section of the Climb Bio website: https://ir.climbbio.com/, and an accompanying slide presentation will also be made available. A webcast replay will be available on the Climb Bio website beginning approximately two hours after the webcast event and will be archived for at least 30 days.
About Climb Bio, Inc.
Climb Bio, Inc. is a clinical-stage biotechnology company developing therapeutics for patients with immune-mediated diseases. The Company’s pipeline includes budoprutug, an anti-CD19 monoclonal antibody that has demonstrated B-cell depletion and has potential to treat a broad range of B-cell mediated diseases, and CLYM116, an anti-APRIL monoclonal antibody in development for IgA nephropathy. For more information, please visit climbbio.com.
About CLYM116
CLYM116 is a preclinical-stage monoclonal antibody targeting APRIL (A Proliferation-Inducing Ligand), a key driver of pathogenic B-cell activity in autoimmune diseases. CLYM116 employs a novel pH-dependent bind-and-release mechanism to potently block APRIL signaling, promote lysosomal degradation of APRIL and recycle the antibody to extend its half-life. This differentiated design offers the potential for rapid, deep and durable inhibition of APRIL with a favorable safety profile and less frequent dosing. CLYM116 is being advanced for the treatment of IgA nephropathy and may also have broader utility across other B-cell mediated diseases where APRIL plays a critical role.
Investors and Media
Carlo Tanzi, Ph.D.
Kendall Investor Relations
[email protected]