Zenas BioPharma (NASDAQ:ZBIO) Chief Executive Officer Lonnie Moulder outlined recent clinical progress and upcoming milestones for the company’s pipeline during a fireside chat at the Guggenheim Emerging Outlook Biotech Summit 2026, with much of the discussion centered on obexelimab in IgG4-related disease (IgG4-RD) and next steps toward regulatory filings.
Obexelimab IgG4-RD: Phase 3 results and early durability data
Moulder highlighted previously reported positive top-line results from the company’s INDIGO Phase 3 study of obexelimab in IgG4-RD. He said the trial design followed a framework used in a prior IgG4-RD program and accepted by regulators, enrolling patients in flare, bringing them into remission using steroids, then randomizing patients off steroids and tracking time to flare as the primary endpoint.
He also provided initial readouts from the study’s open-label extension (OLE). Of the 141 patients who entered the OLE, he said about half were evaluable at six months and that, among that cohort, 92% remained flare-free at six months. Moulder described the finding as supportive of durability for the mechanism of action.
Safety, administration, and market research feedback
On safety, Moulder said serious adverse events were not greater than placebo in the Phase 3 study, and he pointed to infection-related comparisons (including upper respiratory tract infections, urinary tract infections, and COVID-19) as “positioned really well.” He emphasized the relevance of safety in IgG4-RD because patients “tend to be older and at risk,” adding that investigators and key opinion leaders (KOLs) were encouraged by the potential to treat a generally frail population while offering at-home subcutaneous administration.
He noted that injection site reactions were “not much different than placebo.”
Moulder said the company conducted a market research survey to assess potential fit in IgG4-RD. According to his summary:
- The survey included 80 participants: about 60% rheumatologists and 20% gastroenterologists, with a mix of ~70% community and 30% academic clinicians.
- Participants reported treating an average of 18 IgG4-RD patients per year.
- When shown the INDIGO Phase 3 profile, 64% indicated they were likely to prescribe “product X” (obexelimab).
- In a three-year share allocation exercise, participants assigned obexelimab a 47% share, with the remainder split between Uplizna and rituximab.
- Just over 50% selected obexelimab as a first choice therapy in a line-of-therapy question.
Moulder also discussed switching behavior: in the survey, about half of respondents said that if a patient flared on obexelimab, they would add a course of steroids and continue the drug, rather than switch therapies.
On administration preferences, he said clinicians were shown a weekly subcutaneous option versus an every-six-month IV regimen. About 40% strongly preferred weekly subcutaneous dosing and about 50% were indifferent, while 5% preferred the every-six-month IV option. Moulder also referenced a separate patient preference survey of 20 IgG4-RD patients in which 75% preferred subcutaneous dosing.
How management views “inhibition” versus depletion
Responding to questions about why an inhibitory approach resonates, Moulder attributed it primarily to safety considerations. He said physicians and patients often focus on side effects and long-term risk, particularly in an older population with comorbidities. He cited clinician experiences during COVID-19, including concerns about patients on B-cell depleting therapy having poor vaccine responses and, in some cases, severe outcomes.
Moulder contrasted inhibitory therapy with B-cell depletion, noting that with a depleting antibody the decision is effectively set for months and can’t be easily reversed. He said an inhibitory approach can potentially be paused to manage comorbidities or vaccinations, an area the company is investigating in the open-label extension.
On cross-trial comparisons, Moulder said KOLs pushed back on comparing hazard ratios or flare-free rates across different studies, emphasizing that clinicians prioritize an overall risk-benefit profile over single-study benchmarks.
IgG4-RD commercial outlook, pricing dynamics, and filing timeline
Moulder said the company is confident there are about 20,000 diagnosed and managed IgG4-RD patients in the U.S. today, with a similar number in Europe. He added that the company believes there may be 30,000–40,000 total patients in the U.S., but emphasized the 20,000 figure for diagnosed patients. He suggested education efforts could expand diagnosis and the treatable population over time.
Using treatment-rate assumptions from the survey (he cited 80% treated, while acknowledging uncertainty), Moulder said applying current market pricing suggests a $3 billion to $4 billion U.S. opportunity. Based on the share assumptions from the market research, he said the company would expect obexelimab to be “significantly greater than a $1 billion drug in the US” for Zenas, though he said it was too early to project a sales ramp.
He also discussed payer dynamics, estimating Medicare exposure at roughly 40%–45%. On pricing considerations, he described differences in how costs are incurred for a monthly shipped subcutaneous product versus a regimen with large upfront dosing. Using an illustrative annual wholesale acquisition cost example of $280,000, he contrasted a monthly payment structure (about $23,000 per month) with an alternative approach that concentrates spend into early doses and additional dosing six months later.
On timing, Moulder said the company plans to file a U.S. BLA in the second quarter and file in Europe in the second half of the year. He said the initial launch would use prefilled syringes, followed by an autoinjector “within a year,” which he characterized as an sBLA as soon as the original BLA is approved.
For commercial build, he said Zenas already has medical affairs teams in the U.S. and Europe and has maintained a presence at rheumatology and gastroenterology meetings. He estimated that a U.S. sales force build could be just under 50 sales representatives, supported by additional strategic engagement and market access roles, for a total U.S. commercial organization of roughly 70 people. In Europe, he said the company would launch initially in Germany, with Italy and France following, and that reaching a similar scale could take about three years.
Lupus, BTK inhibition in progressive MS, and earlier-stage programs
Moulder said the company’s Sunstone lupus (SLE) study is expected to report in the fourth quarter, with a 24-week BICLA primary endpoint. He said biomarker analyses will be run alongside the top-line readout, allowing the company to describe outcomes in both the overall population and a biomarker-positive group. He described the biomarker as a published gene-expression pattern, adding that about 30% of SLE patients have the profile based on the company’s analysis.
To address placebo response challenges in SLE trials, he said Zenas is using strict screening criteria with investigator screening followed by committee rescreening, which he said has led to a high screen failure rate designed to ensure a “pure population.”
On BTK inhibitors in progressive multiple sclerosis, Moulder said the landscape had “cleared up” following disclosures around tolebrutinib and that fenebrutinib data presented at ECTRIMS was received “extremely well.” He said fenebrutinib met non-inferiority versus Ocrevus in PPMS and was numerically better across measures, while noting transaminase elevations and discontinuations but no clinical sequelae and normalization of labs. Moulder said Zenas is conducting a PPMS trial for orelibrutinib and is about to begin a non-active SPMS study, emphasizing the need for brain penetration and potency in progressive MS.
Finally, he outlined two oral programs: a brain-penetrant TYK2 inhibitor expected to enter Phase 1 at the end of the year with PK/PD data next year, and an oral IL-17 program (ZB021) expected to enter the clinic mid-year. He said ZB021 would move quickly through SAD/MAD and into psoriasis patients by year-end, with psoriasis outcomes expected next year.
About Zenas BioPharma (NASDAQ:ZBIO)
Zenas BioPharma, Inc is a clinical-stage biotechnology company focused on the discovery and development of novel therapies in oncology and infectious diseases. The company’s proprietary platform integrates structure-guided design, computational modeling and high-throughput screening to address challenging protein-protein interactions. Zenas BioPharma is advancing multiple preclinical and clinical-stage candidates aimed at providing new treatment options where current modalities may be limited by efficacy or safety concerns.
Founded in 2021 and headquartered in Cambridge, Massachusetts, Zenas BioPharma was built to streamline the drug discovery process from target identification through to IND-enabling studies.
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