PeptideInjectableMonoclonal antibodyActivin inhibitorAnti-activin A

Garetosmab (REGN2477)

Also known as REGN2477 · Garetosmab

Written by enwyReviewed 15 Jul 20261 sources0 comments

Garetosmab (REGN2477) is a fully human anti-activin A monoclonal antibody from Regeneron. Developed for fibrodysplasia ossificans progressiva, it is also studied alongside the anti-myostatin antibody trevogrumab as a body-composition combination to preserve lean mass during weight loss.

01 Overview

Garetosmab neutralises activin A, a TGF-beta ligand that, like myostatin, signals through activin type II receptors and suppresses muscle while contributing to abnormal bone formation. Its lead indication is fibrodysplasia ossificans progressiva, a rare disorder of heterotopic ossification, where a Phase 2 trial reduced new bone lesions.

In the muscle/body-composition arena, garetosmab is paired with trevogrumab (anti-myostatin) to block both major ActRII ligands at once, an approach explored to maintain or increase lean mass, including during GLP-1-driven weight loss. On its own it is not a muscle-building drug but is relevant to the same signalling axis.

02 Mechanism

A fully human monoclonal antibody that binds and neutralises activin A, blocking its activation of activin type II receptors; combined with anti-myostatin antibodies it broadens ActRII-ligand blockade.

03 Dosing

Tier	Dose	Route	Notes
Trial dosing	10–30 mg/kg	IV	Given roughly every 4 weeks in FOP trials; not marketed.

04 Effects

Effect	Magnitude	Evidence
Reduced heterotopic ossificationIn FOP, activin A blockade reduced new abnormal bone formation.	Fewer new lesions	Clinical
Lean-mass preservation (in combination)Paired with anti-myostatin antibody to help maintain muscle during weight loss.	Under study	Clinical

05 Side effects

Effect	Severity	Frequency	Evidence	Countermeasures
Epistaxis / bleedingNosebleeds and bleeding events were reported in FOP trials.	Moderate	Common	Clinical
Serious infections / deaths signalThe FOP programme reported a safety signal including deaths that prompted regulatory attention.	Severe	Uncommon	Clinical

06 Legal status

United States

Investigational biologic

Not approved; in clinical development. Activin/myostatin-axis agents are prohibited in sport by WADA (S4.5). · as of Jan 2026

07 References

Garetosmab (anti-activin A) in fibrodysplasia ossificans progressiva (LUMINA-1): a phase 2 trialNature Medicine, 2023

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.