Climb Bio Spotlights Budoprutug CD19 Strategy, Sets Up 2026 Data Readouts in pMN, ITP and SLE

Key Points

• Budoprutug is Climb Bio’s CD19‑targeting antibody being advanced across primary membranous nephropathy (PRISM Phase 2), immune thrombocytopenia and SLE, with a “data‑rich” 2026 planned for B‑cell, PLA2R, proteinuria and platelet response readouts.
• Early signals include complete peripheral B‑cell depletion and clinical remissions in a small pMN pilot (durability up to three years in some patients) and a Phase 1 subcutaneous study showing ~80% B‑cell reduction with comparable safety to IV, supporting further SC development.
• Management argues CD19 offers broader targeting than CD20 (including plasmablasts/plasma cells) for deeper, potentially more durable responses, and the company’s second program, CLYM116 (anti‑APRIL), is in Phase 1 with initial data expected mid‑2026.

Climb Bio NASDAQ: CLYM used an investor R&D spotlight event to outline its strategy around CD19-targeted B-cell depletion and to provide updates on development plans and timelines for its lead candidate, budoprutug, across primary membranous nephropathy (pMN), immune thrombocytopenia (ITP), and systemic lupus erythematosus (SLE). Management also briefly highlighted progress for a second program, CLYM116, an anti-APRIL monoclonal antibody being developed for IgA nephropathy (IgAN) and other B-cell-mediated diseases.

Company focus and portfolio updates

President and CEO Dr. Aoife Brennan said Climb’s strategy is to develop “differentiated monoclonal antibodies against validated B-cell targets” with “clear development paths” in immune-mediated diseases, including kidney-related indications. She described 2026 as a “data-rich period,” with readouts expected across ongoing studies.

Brennan noted that CLYM116 was in-licensed in January 2025 and is positioned as a “next-generation anti-APRIL monoclonal antibody” that the company believes could support “greater potency and longer dosing intervals with low immunogenicity” based on head-to-head preclinical work versus a first-generation anti-APRIL antibody. CLYM116 is being evaluated in two parallel Phase 1 studies in healthy volunteers (one run by Climb and one by partner MabWorks in China). The company expects to present non-human primate modeling data and initial safety data at the European Renal Association meeting in June, followed by additional biomarker data at a dedicated CLYM116 event mid-year.

Why CD19: physician perspective on CD19 vs. CD20

Guest speaker Dr. David Jayne, professor of clinical autoimmunity at the University of Cambridge and director of the Vasculitis and Lupus Service at Addenbrooke’s Hospital, discussed limitations of CD20-directed therapies in autoimmune disease and the rationale for CD19 targeting.

Jayne said CD20-directed treatment can result in incomplete removal of circulating autoantibodies and “incomplete removal of tissue-resident B cells,” which he described as important drivers of pathogenesis. He added that CD20 targeting can lead to only “partial efficacy” and “a high relapse rate” when effects wear off.

In contrast, Jayne said CD19 is expressed earlier and more broadly across the B-cell lineage than CD20, including on plasmablasts and “many plasma cells.” He pointed to clinical observations that CD19-positive plasma cells may persist in rituximab-refractory settings, and he said deep B-cell depletion—including disruption of follicular structures that support germinal centers—has been associated with durable remissions. Jayne also said available data suggest substantial tissue-level B-cell depletion can occur with conventional monoclonal antibodies and that “it is reasonable to hypothesize that even deeper B-cell depletion can be achieved by a monoclonal antibody that targets CD19.”

Budoprutug profile and clinical development plans

Chief Medical Officer Dr. Edgar Charles described budoprutug as an investigational CD19-targeting monoclonal antibody engineered with “low fucosylation” to enhance effector function, including antibody-dependent cellular cytotoxicity. Charles said the goal is “deep B-cell depletion,” including potential effects on tissue-resident and antibody-producing cells, within a conventional monoclonal antibody framework.

Charles also cited previously presented pilot data in pMN, where budoprutug at 100 mg or 200 mg achieved complete peripheral B-cell depletion in five of five evaluable patients, with depletion sustained to one year after two dose cycles. He said reductions in pathogenic autoantibodies and proteinuria were observed, with clinical remission in all five patients and complete remission in three. In long-term follow-up of four patients who received four doses, he said remission was maintained for up to three years, with three of the four not requiring further immunosuppression. Charles emphasized the small dataset but called the durability after four doses “particularly encouraging.”

In pMN, Charles said the company is running the PRISM trial, a global open-label, dose-escalation Phase 2 study in 45 patients with moderate-to-severe disease. Dosing starts at 200 mg and evaluates up to 1,000 mg, with the goal of maximizing B-cell depletion. He said PRISM includes roughly 45 sites across eight countries and is designed to use biomarkers such as B-cell depletion and PLA2R antibody levels to support dose selection for Phase 3. Brennan later said the company expects to share B-cell, PLA2R, and proteinuria data from the first cohort later in 2026 as those patients reach the three- to six-month time point.

In ITP, Charles outlined a multicenter open-label dose-escalation study in previously treated patients, including heavily pretreated individuals, across doses of 250 mg to 1,000 mg. He said enrollment in the first two cohorts is complete and cohort three is expected to begin in the second quarter. The company expects to present initial B-cell depletion and platelet response data from the low-dose cohort with follow-up out to 24 weeks at a medical meeting in June 2026, with additional higher-dose data expected by year-end.

For SLE, Charles said Climb is conducting two studies intended to generate translational insights about the relationship between dose, B-cell depletion, and biomarkers. Brennan said the global study starts at subtherapeutic single doses, while the China study uses higher repeated doses and is designed to provide complementary information, including potential ethnic differences in PK/PD and safety/tolerability.

Subcutaneous formulation: early healthy volunteer data

Charles presented top-line results from a Phase 1 placebo-controlled single ascending dose study of subcutaneous budoprutug in healthy volunteers. Participants received subcutaneous doses of 3 mg or 6 mg, intravenous budoprutug at 6 mg, or placebo. Charles said the low doses were selected to achieve measurable but submaximal B-cell depletion in healthy volunteers.

He reported comparable safety profiles between subcutaneous and IV groups. While PK interpretation was limited because most concentrations were below the limit of quantification, Charles said “robust” pharmacodynamic effects were observed, with all active groups showing rapid B-cell depletion to about an 80% reduction from baseline. He said depletion was similar between subcutaneous and IV administration arms, supporting further development of the subcutaneous formulation.

In Q&A, Brennan said dosing frequency for subcutaneous administration “remains to be determined,” describing two potential approaches: matching the IV regimen via a subcutaneous route or giving lower doses more frequently. Charles added the company plans to study higher subcutaneous doses in patients with autoimmune disease to evaluate safety, tolerability, and B-cell reductions with the aim of achieving comparable depletion to IV dosing.

Competitive landscape and dosing considerations

Chief Business Officer Dr. Perrin Wilson said rituximab is used off-label in pMN and ITP, but patients may not be served long term. He argued CD19’s broader expression across precursor cells, plasmablasts, and many plasma cells could provide a distinct advantage, including potentially in patients who have failed CD20-directed therapy.

On pMN competition, Wilson pointed to the “upcoming obinutuzumab MAJESTY readout at ERA” as a key near-term event, saying the company expects positive data but anticipates only incremental improvement versus rituximab based on other next-generation CD20 data. Charles said BAFF/APRIL inhibition addresses “more of a downstream pathophysiology rather than the root cause of disease,” and he contrasted budoprutug’s goal of deeper, durable responses with the need for “chronic regular dosing” in a monthly regimen cited for a BAFF/APRIL program.

Brennan also discussed why Climb is evaluating a broad dose range in pMN, noting that severe patients can have high baseline proteinuria and may lose antibody in urine, which could reduce exposure and affect B-cell depletion. She said the company is focused on selecting the right Phase 2 dose before advancing to Phase 3 and added that safety and tolerability “has not been a limitation” so far.

About Climb Bio NASDAQ: CLYM

Climb Bio Therapeutics, Inc is a clinical-stage biotechnology company focused on the discovery and development of engineered protein therapeutics for the treatment of cancer and immune-mediated disorders. The company's mission centers on designing biologics with enhanced specificity and functional activity to engage key cellular targets and improve patient outcomes in areas of high unmet need.

At the heart of Climb Bio's approach is its proprietary protein engineering platform, which combines mammalian cell display, directed evolution and computational modeling.

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