Bio’s Activin E Antibody IBIO-610 Shifts Semaglutide Weight Loss Toward Fat in Obese Primates

iBio, Inc. reported new body-composition data from an obese non-human primate (NHP) study. The data suggest its investigational Activin E antibody, IBIO-610, may shift semaglutide-driven weight loss toward fat. At week 8, lean mass made up 6% of the weight lost by animals given IBIO-610 plus semaglutide, compared with 22% for animals given semaglutide alone.¹ The data were discussed in an oral presentation at the European Association for the Study of Diabetes Annual Meeting on Oct. 1, 2026.¹

What did the primate study show?

The eight-week study included six obese NHPs per group.¹ Animals in the combination arm received a single dose of IBIO-610 alongside twice-weekly semaglutide, a GLP-1 receptor agonist used to treat obesity. At week 8, fat accounted for 93% of the weight lost with the combination, compared with 77% with semaglutide alone.¹

Earlier data from the same study showed that a single intravenous dose of IBIO-610 reduced serum levels of active Activin E by 97% at week 8. The antibody also had a 33.2-day half-life in NHPs. iBio said the projected human half-life could potentially support twice-yearly dosing.¹ In its fiscal third-quarter 2026 update, the company also reported results for IBIO-610 alone. Two once-every-eight-week doses reduced visceral fat by 6.7% and total fat mass by 5.2% compared with vehicle-treated obese NHPs. iBio described that study as small and not statistically powered.²

“While GLP-1 therapies have transformed obesity care, patients still need additional options to improve the quality of weight loss,” said Martin Brenner, DVM, PhD, chief executive officer and chief scientific officer of iBio, in the press release. “In this NHP study, IBIO-610 delivered durable, near-complete inhibition of active Activin E, and when combined with semaglutide, nearly all observed weight loss came from fat.”¹

How does Activin E blockade work?

Activin E suppresses the breakdown of stored fat in adipocytes by signaling through the activin receptor-like kinase 7 (ALK7)-Smad pathway.³ ALK7 is a type I receptor in the TGF-β superfamily, and it is preferentially expressed in adipose tissue. In mice, inactivating ALK7 signaling increases lipolysis and makes the animals resistant to both genetic and diet-induced obesity. A neutralizing monoclonal antibody against ALK7 also reduced adipose mass and improved glucose intolerance and insulin resistance in mouse obesity models.⁴

IBIO-610 targets the Activin E ligand itself. iBio describes it as potentially the first antibody in its class.¹

Why does lean mass matter with GLP-1 therapy?

In a body-composition analysis of the STEP 1 trial, semaglutide 2.4 mg reduced total fat mass by 19.3% from baseline at week 68. Total lean body mass fell by 9.7% over the same period.⁵ Semaglutide dosing options continue to expand. As BioPharm International® reported, the European Commission recently approved a 7.2 mg once-weekly Wegovy maintenance dose for adults with obesity.

Other antibody programs target muscle-regulating pathways directly. Scholar Rock’s phase 2 EMBRAZE trial enrolled 102 adults receiving tirzepatide. Lean mass accounted for 14.6% of total weight lost with apitegromab, a myostatin-targeting monoclonal antibody, compared with 30.2% with placebo.⁶ The trial did not show improvements in physical function, strength, or cardiometabolic outcomes over its 24-week treatment period.⁷ These clinical results cannot be directly compared with the IBIO-610 data. The IBIO-610 results come from a small preclinical primate study that used a different GLP-1 partner drug.

What happens next?

“We plan to begin first-in-human studies in the first half of 2027,” Brenner said.¹ In its forward-looking statements, iBio cautioned that findings in NHPs may not be replicated in humans.¹ The company is also developing IBIO-600, a myostatin antibody, and has received regulatory clearance to begin a phase 1 trial of that candidate in Australia.²

Developers of incretin drugs are also working on longer dosing intervals. Pfizer reported phase 2b VESPER-3 data supporting monthly maintenance dosing of its ultra-long-acting GLP-1 receptor agonist PF-08653944.

References

1. iBio, Inc. iBio Highlights Data from a Non-human Primate Study Supporting IBIO-610’s Potential to Preserve Muscle in Combination with GLP-1 Therapy. Press release. Published October 13, 2026. Accessed October 13, 2026.
2. iBio, Inc. iBio Reports Q3 Fiscal Year 2026 Financial Results and Provides Corporate Update. Press release. Published May 12, 2026. Accessed October 13, 2026.
3. ACROBiosystems. Next-Generation Obesity Target Spotlight: Activin E for Fat Loss with Muscle Preservation. Published May 18, 2026. Accessed October 13, 2026.
4. Zhao M, Okunishi K, Bu Y, et al. Targeting activin receptor–like kinase 7 ameliorates adiposity and associated metabolic disorders. JCI Insight. Published January 10, 2023. Accessed October 13, 2026
5. Patient Care Online. Semaglutide 2.4 mg Reduces Visceral Adiposity, Improves Lean Body Mass to Fat Mass Ratio. Published March 20, 2021. Accessed October 13, 2026.
6. Pratley RE, Denham DS, Trivedi R, et al. Apitegromab for lean mass preservation during tirzepatide-induced weight loss: a randomized, double-blind, placebo-controlled phase 2 trial. Nat Med. Published June 8, 2026. Accessed October 13, 2026.
7. Epocrates. New Approach Preserves Lean Mass During GLP-1 Weight Loss. Published June 10, 2026. Accessed October 13, 2026.