Obexelimab
An investigational treatment for IgG4-Related Disease.
Drug facts
The same compound appears under different names depending on the context. Here is how to identify Obexelimab wherever you encounter it, plus the key facts at a glance.
- Generic name
- Obexelimab
- Development codes
- XmAb5871, ZB012
- Drug class
- Bifunctional anti-CD19 and FcγRIIb monoclonal antibody (non-depleting B-cell inhibitor)
- Manufacturer
- Zenas BioPharma
- How it's taken
- Injection under the skin once a week, under FDA review
Obexelimab is an investigational antibody that people inject under the skin once a week, under FDA review for IgG4-related disease[1][4].
- Zenas BioPharma said on August 13, 2026 that the FDA had accepted its Biologics License Application, with a target action date of May 27, 2027[4].
- In the Phase 3 INDIGO trial, 26.8% of people on obexelimab had a flare that needed rescue treatment over 52 weeks, against 54.6% on placebo, after both groups stopped steroids by week 8[1].
- Obexelimab holds B cells back without depleting them, which sets it apart from Uplizna (inebilizumab), the one FDA-approved IgG4-related disease treatment, which removes B cells[1][10][11].
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Where Obexelimab fits
Obexelimab is an investigational weekly self-injected antibody under FDA review for IgG4-related disease, designed to hold B cells back without depleting them, with a decision due May 27, 2027[4][1].
- Steroids (glucocorticoids) have long been the cornerstone of IgG4-related disease treatment, though their side effects limit long-term use and the disease often returns when they are stopped, according to the INDIGO investigators[1].
- Uplizna (inebilizumab), an IV infusion that removes B cells, became the first FDA-approved IgG4-related disease treatment for adults on April 3, 2025[10][11].
- Obexelimab has not been compared head to head with Uplizna or with steroids alone; INDIGO compared it with placebo after a steroid taper[1].
- A person with IgG4-related disease can ask their rheumatologist how a weekly self-injection that does not deplete B cells would compare in daily life with Uplizna infusions, and what the INDIGO flare results could mean for the organs affected in their own case.
How Obexelimab works
IgG4-related disease is a long-lasting condition in which inflammation and scarring build up in 1 or more organs, and it can affect almost any organ[1][2]. B cells, the immune cells that make antibodies, are the target the INDIGO investigators chose to test[2]. Obexelimab is a single antibody with 2 binding ends. One end grabs CD19, a marker found on B cells from early stages through maturity[11], and the other grabs FcγRIIb, a brake switch on the same cells. Holding the 2 together mimics the natural signal that tells a B cell to stand down[1][2].
Zenas says this dampens B cell activity, including antibody production, growth and presenting antigens to T cells, without killing the cells[7]. That is the main difference from B cell depleting drugs such as Uplizna, which target CD19 to remove B cells[10][11]. Zenas says B cells returned as soon as 6 weeks after obexelimab was stopped, compared with 6 months or longer after depleting anti-CD19 and anti-CD20 drugs[7].
Clinical trial results
INDIGO (NCT05662241) is a Phase 3, double-blind, placebo-controlled trial in adults with active IgG4-related disease[12][1]. From January 2023 through November 2024 it randomized 194 people, 97 to each group, to weekly obexelimab or placebo for 52 weeks; in both groups, steroids were tapered on a set schedule and stopped by week 8[1]. ClinicalTrials.gov lists 65 sites, 5 of them in the US[12].
The main measure was the time to a first flare that needed rescue treatment. Flares happened in 26 people on obexelimab (26.8%) and 53 on placebo (54.6%), a hazard ratio of 0.44, which Zenas describes as a 56% lower risk of flare[1][5]. Complete remission at week 52 was reached by 37.1% on obexelimab and 19.6% on placebo, and the cumulative dose of rescue steroids through week 52 was 329.5mg against 929.8mg[1]. The results were published in the New England Journal of Medicine in June 2026, and an open-label extension continues[1][12].
An earlier Phase 2 study run by Xencor (NCT02725476) gave the drug, then called XmAb5871, by IV infusion to 20 people with IgG4-related disease in 2016 and 2017[13]. The INDIGO protocol paper reports that 93% of them improved[2].
Obexelimab is also being studied in other diseases. SApHiAre (NCT05786573), a Phase 3 trial in warm autoimmune hemolytic anemia, is listed as active and no longer recruiting, with 7 sites outside the US; Zenas has not reported results, and its pipeline page does not list the trial[14][8]. In relapsing multiple sclerosis, Zenas reported that the Phase 2 MoonStone trial (NCT06564311) met its 12-week main goal, a 95% relative reduction in new gadolinium-enhancing brain lesions against placebo[6][15].
A Phase 2 trial in systemic lupus erythematosus, SunStone, had not reported results as of November 7, 2026[3]. Obexelimab is not under FDA review for any of these diseases.
Main registered trial: NCT05662241 on ClinicalTrials.gov. Check it for the current status, sites and contacts before asking about enrollment.
Side effects and safety
Obexelimab has no FDA label, so its official side effects and warnings are not set. In INDIGO, side effects more common on obexelimab than placebo included joint pain (19.6% vs 11.3%), allergic-type reactions called hypersensitivity (16.5% vs 11.3%) and diarrhea (11.3% vs 6.2%). Serious side effects were less common on obexelimab, 10.3% against 18.6% on placebo[1].
Zenas reported that infections occurred in 53.6% of people on obexelimab and 62.9% on placebo, that 3.5% of obexelimab injections caused an injection-site reaction against 2.3% of placebo injections, and that no one on obexelimab died, while 1 person on placebo did[5].
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Obexelimab
In INDIGO, people injected 250mg of obexelimab under the skin once a week for 52 weeks[1]. Zenas describes it as a self-given injection and says a single-dose prefilled pen matched the prefilled syringe in a bioequivalence study; Zenas plans to add the pen through a later supplement to the US application if obexelimab is approved[4]. The dose and device for any approved use would be set by the FDA label.
Development history
Xencor developed obexelimab under the code XmAb5871 and ran the first IgG4-related disease study in 2016 and 2017[13]. On November 21, 2021 Zenas BioPharma announced that it had acquired exclusive worldwide rights to develop, make and sell obexelimab from Xencor[9]. INDIGO began in January 2023[12], and Zenas announced on January 5, 2026 that it met its main goal and all 4 key secondary goals[6].
Full results were presented at the EULAR 2026 congress and published in the New England Journal of Medicine on June 2, 2026[5][1]. Zenas said on August 13, 2026 that the FDA had accepted the application with a May 27, 2027 target action date[4], and on November 5, 2026 that the European Medicines Agency had validated its EU application[3]. Bristol Myers Squibb holds the rights in Japan, South Korea, Taiwan, Hong Kong, Singapore and Australia[6]. The FDA had not announced a decision as of November 7, 2026.
Explore IgG4-Related Disease trials
Other IgG4-Related Disease treatments
Common questions about Obexelimab
▸What is Obexelimab?
Obexelimab is an investigational antibody that people inject under the skin once a week, under FDA review for IgG4-related disease[1][4]. Zenas BioPharma said on August 13, 2026 that the FDA had accepted its Biologics License Application, with a target action date of May 27, 2027[4]. In the Phase 3 INDIGO trial, 26.8% of people on obexelimab had a flare that needed rescue treatment over 52 weeks, against 54.6% on placebo, after both groups stopped steroids by week 8[1]. Obexelimab holds B cells back without depleting them, which sets it apart from Uplizna (inebilizumab), the one FDA-approved IgG4-related disease treatment, which removes B cells[1][10][11].
▸How does Obexelimab work?
IgG4-related disease is a long-lasting condition in which inflammation and scarring build up in 1 or more organs, and it can affect almost any organ[1][2]. B cells, the immune cells that make antibodies, are the target the INDIGO investigators chose to test[2]. Obexelimab is a single antibody with 2 binding ends. One end grabs CD19, a marker found on B cells from early stages through maturity[11], and the other grabs FcγRIIb, a brake switch on the same cells. Holding the 2 together mimics the natural signal that tells a B cell to stand down[1][2].
Zenas says this dampens B cell activity, including antibody production, growth and presenting antigens to T cells, without killing the cells[7]. That is the main difference from B cell depleting drugs such as Uplizna, which target CD19 to remove B cells[10][11]. Zenas says B cells returned as soon as 6 weeks after obexelimab was stopped, compared with 6 months or longer after depleting anti-CD19 and anti-CD20 drugs[7].
▸What are the side effects of Obexelimab?
Obexelimab has no FDA label, so its official side effects and warnings are not set. In INDIGO, side effects more common on obexelimab than placebo included joint pain (19.6% vs 11.3%), allergic-type reactions called hypersensitivity (16.5% vs 11.3%) and diarrhea (11.3% vs 6.2%). Serious side effects were less common on obexelimab, 10.3% against 18.6% on placebo[1]. Zenas reported that infections occurred in 53.6% of people on obexelimab and 62.9% on placebo, that 3.5% of obexelimab injections caused an injection-site reaction against 2.3% of placebo injections, and that no one on obexelimab died, while 1 person on placebo did[5].
▸How is Obexelimab taken?
In INDIGO, people injected 250mg of obexelimab under the skin once a week for 52 weeks[1]. Zenas describes it as a self-given injection and says a single-dose prefilled pen matched the prefilled syringe in a bioequivalence study; Zenas plans to add the pen through a later supplement to the US application if obexelimab is approved[4]. The dose and device for any approved use would be set by the FDA label.
▸Is Obexelimab FDA approved?
Not yet. Obexelimab is under FDA review for IgG4-Related Disease; Zenas BioPharma has filed an application and a decision is due May 27, 2027. The FDA calendar page tracks the outcome.
▸Is obexelimab FDA approved?
No. Obexelimab is under FDA review and has no approval for any use.
Status: Zenas said on August 13, 2026 that the FDA accepted its application for IgG4-related disease.
Decision date: The FDA's target action date is May 27, 2027.
Europe: The European Medicines Agency validated Zenas's EU application, Zenas said on November 5, 2026.
Source: Zenas BioPharma, August 13, 2026
▸What did the INDIGO trial of obexelimab show?
Fewer people on obexelimab had a flare needing rescue treatment over 52 weeks, 26.8% against 54.6% on placebo.
Risk: A hazard ratio of 0.44, which Zenas describes as a 56% lower risk of flare.
Remission: Complete remission at week 52 was reached by 37.1% on obexelimab, against 19.6% on placebo.
Steroids: Both groups stopped steroids by week 8, and rescue steroid use was lower on obexelimab.
Source: Della-Torre et al., New England Journal of Medicine 2026
▸How is obexelimab different from Uplizna?
Obexelimab and Uplizna both act on B cells through CD19, but obexelimab holds B cells back while Uplizna removes them, and no trial has compared them directly.
Schedule: Obexelimab was self-injected under the skin once a week in INDIGO; Uplizna is a 300mg IV infusion, a second 300mg infusion 2 weeks later, then 300mg every 6 months.
Status: Uplizna has been FDA approved for adults with IgG4-related disease since April 3, 2025; obexelimab is under review.
Source: Della-Torre et al., New England Journal of Medicine 2026; Amgen, April 3, 2025; Uplizna label, DailyMed
▸Is obexelimab being studied for other diseases?
Yes, in multiple sclerosis, lupus and warm autoimmune hemolytic anemia, though it is under FDA review only for IgG4-related disease.
Multiple sclerosis: Zenas reported that the Phase 2 MoonStone trial met its 12-week goal, a 95% reduction in new active brain lesions against placebo.
Lupus: The Phase 2 SunStone trial had not reported results as of November 7, 2026.
Warm autoimmune hemolytic anemia: The Phase 3 SApHiAre trial is listed as active and no longer recruiting, with no results reported.
Source: Zenas BioPharma, January 5, 2026; ClinicalTrials.gov NCT05786573
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- New England Journal of Medicine · 2026-06-02. Obexelimab for the Treatment of IgG4-Related Disease.. https://pubmed.ncbi.nlm.nih.gov/42233621/
- Rheumatology and Therapy · 2026-03-16. Efficacy and Safety of Obexelimab to Treat IgG4-Related Disease: Protocol for a Global, Randomized, Placebo-Controlled Trial.. https://pubmed.ncbi.nlm.nih.gov/41840328/
- Zenas BioPharma via GlobeNewswire (BioSpace copy) · 2026-11-05. Zenas BioPharma Reports Third Quarter 2026 Financial Results and Provides Corporate Update. https://www.biospace.com/press-releases/zenas-biopharma-reports-third-quarter-2026-financial-results-and-provides-corporate-update
- Zenas BioPharma via GlobeNewswire (BioSpace copy) · 2026-08-13. Zenas BioPharma Reports Second Quarter 2026 Financial Results and Provides Corporate Update. https://www.biospace.com/press-releases/zenas-biopharma-reports-second-quarter-2026-financial-results-and-provides-corporate-update
- Zenas BioPharma via GlobeNewswire (BioSpace copy) · 2026-06-02. Zenas BioPharma Announces Data from the Registrational Phase 3 INDIGO Trial of Obexelimab in Immunoglobulin G4-Related Disease (IgG4-RD), Simultaneously Presented at the EULAR 2026 Congress and Published in the New England Journal of Medicine. https://www.biospace.com/press-releases/zenas-biopharma-announces-data-from-the-registrational-phase-3-indigo-trial-of-obexelimab-in-immunoglobulin-g4-related-disease-igg4-rd-simultaneously-presented-at-the-eular-2026-congress-and-published-in-the-new-england-journal-of-medicine
- Zenas BioPharma via GlobeNewswire (BioSpace copy) · 2026-01-05. Zenas BioPharma Announces Positive Results from Phase 3 INDIGO Registrational Trial of Obexelimab in Immunoglobulin G4-Related Disease (IgG4-RD). https://www.biospace.com/press-releases/zenas-biopharma-announces-positive-results-from-phase-3-indigo-registrational-trial-of-obexelimab-in-immunoglobulin-g4-related-disease-igg4-rd
- Zenas BioPharma. Our Science. https://zenasbio.com/our-science/
- Zenas BioPharma. Pipeline - Zenas BioPharma. https://zenasbio.com/our-science/pipeline/
- Zenas BioPharma and Xencor via GlobeNewswire (BioSpace copy) · 2021-11-21. Zenas BioPharma Acquires Exclusive Worldwide Rights to Obexelimab from Xencor. https://www.biospace.com/zenas-biopharma-acquires-exclusive-worldwide-rights-to-obexelimab-from-xencor
- Amgen · 2025-04-03. Uplizna (inebilizumab-cdon) Is Now the First and Only FDA-Approved Treatment for IgG4-Related Disease. https://www.amgen.com/newsroom/press-releases/2025/04/uplizna-inebilizumabcdon-is-now-the-first-and-only-fdaapproved-treatment-for-igg4related-disease
- U.S. National Library of Medicine, DailyMed. UPLIZNA (inebilizumab-cdon) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=834db232-afb0-4dcf-93e0-009ce8245c20
- ClinicalTrials.gov. A Phase 3 Study of Obexelimab in Patients With IgG4-Related Disease. https://clinicaltrials.gov/study/NCT05662241
- ClinicalTrials.gov. Study to Evaluate the Effect of XmAb®5871 on Disease Activity in Patients With IgG4-Related Disease (RD). https://clinicaltrials.gov/study/NCT02725476
- ClinicalTrials.gov. A Study of Obexelimab in Patients With Warm Autoimmune Hemolytic Anemia (SApHiAre). https://clinicaltrials.gov/study/NCT05786573
- ClinicalTrials.gov. A Study of Obexelimab in Patients With Relapsing Multiple Sclerosis (MoonStone). https://clinicaltrials.gov/study/NCT06564311