IMAAVY - Overview of the Phase 2/3 Vibrance-mg Clinical Trial

SUMMARY

• The company cannot recommend any practices, procedures, or usage of IMAAVY that deviate from the approved labeling.
• IMAAVY is a fully human, aglycosylated, effectorless immunoglobulin G1 (IgG1) monoclonal antibody that binds with high affinity to the IgG-binding site on the neonatal Fc receptor (FcRn).^1-3
  • By interfering with the binding of IgG to FcRn, IMAAVY increases the lysosomal degradation of IgG, which reduces serum levels of total IgG and pathogenic IgG autoantibodies that cause myasthenia gravis (MG).
• A phase 2/3, open-label clinical trial (NCT05265273) is currently underway to evaluate the effect on total serum IgG, safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of IMAAVY in children and adolescents with generalized myasthenia gravis (gMG) who have an insufficient response to ongoing, standard of care (SOC) therapy.^3,4
  • Results through the active treatment (AT) phase (study day 1 through week 24) and long-term extension (LTE) phase in adolescents (aged 12 to <18 years) are summarized below.⁵

CLINICAL DATA

Phase 2/3 Clinical Trial

An ongoing, open-label, uncontrolled multicenter clinical trial is currently evaluating the effect on total serum IgG, safety, tolerability, PK, and PD of IMAAVY in children and adolescents aged 2 to <18 years with gMG and insufficient clinical response to ongoing, stable SOC therapy.^3,4

Study Design/Methods

The study consists of a screening period of up to 4 weeks, a 24-week open-label AT phase where patients will receive IMAAVY intravenous (IV) every 2 weeks (Q2W), and an optional LTE phase. A safety follow-up assessment will be conducted 8 weeks after the last dose. For study design/methods, see Figure: Vibrance-mg Study Design.

• Four patients switched from Q2W to Q4W at various times and were ongoing in LTE at data cutoff.
• The primary endpoints included the effect of IMAAVY on total serum IgG levels and safety and tolerability.
• Secondary endpoints included changes in Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) scores.

Results

Cohort 1

Strober et al (2025)⁵ presented results on PD (IgG), safety and efficacy through the AT phase (study day 1 through week 24) and LTE phase in adolescents (aged 12 to <18 years).

Baseline Demographics

• Baseline demographics of adolescent patients in cohort 1 (all with anti-AChR antibody positive gMG) are summarized in the following Table: Select Demographics and Baseline Characteristics.

Efficacy

• IgG reduction was observed in adolescent patients treated with IMAAVY.
• At the time of this analysis, of the 8 patients who had been enrolled, 7 completed the AT phase and 6 entered the LTE phase.
  • Reduction in median (interquartile range, IQR) serum IgG was observed from baseline (10.7, [8.9-13.1] g/L) to week 24 (3.2, [2.3-3.5] g/L) and week 72 (3.3 [2.8-4.3] g/L).
  • The median (IQR) percentage change from baseline (CFB) was -72.6% (-79.1 to -70.1) at week 2 and -73.3% (-78.7 to -62.8) at week 24. The effect was generally sustained in the LTE, with a median (IQR) CFB of -60.6% (-72.0 to 48.8) at week 72 (n=3). For details, see Figure: Median (IQR) Total Serum IgG Levels Over Time.

• The median (IQR) MG-ADL score decreased from a baseline score of 3.5 (3.0-5.0) to 1.5 (0.0-3.0) at week 4 and 1.0 (0.0-3.0) at week 24. For details, see Figure: Median (IQR) Total MG-ADL Score Over Time.
  • Of 3 patients who completed the LTE up to week 72, 2 maintained symptom improvement.
  • One patient reported worsening MG-ADL scores without any documented AE of MG worsening at week 72.
  • Minimal symptom expression defined as MG-ADL score of 0 or 1 was achieved in over half of patients at each time point during AT and/or LTE.

• The median (IQR) QMG score decreased from a baseline score of 14.3 (10.5-15.8) to 7.0 (4.0-13.5) at week 4 and 7.0 (2.0-11.0) at week 24. For details, see Figure: Median (IQR) Total QMG Score Over Time.
  • Of 3 patients who completed the LTE up to week 72, 2 maintained symptom improvement.
  • One patient reported worsening QMG scores without any documented AE of MG worsening at week 72.

Safety

• During the study, there were no reports of adverse events (AEs) or serious AEs (SAEs) leading to discontinuation reported in adolescent patients receiving IMAAVY. No treatment-emergent adverse events (TEAEs) leading to death or AEs of special interest were reported in the study. For details, see Table: Summary of Treatment-Emergent AEs in AT and LTE Phases.
• One patient reported with a SAE of worsened gMG after week 72 in LTE (at week 84).
• Another patient reported an AE of influenza at ~week 30 that led to temporary treatment discontinuation.

• The most common treatment-emergent AEs in the AT phase were nasopharyngitis (37.5%) and COVID-19 (25.0%), with a median (IQR) follow-up of 24.0 (18-31) weeks.
• The most common treatment-emergent AEs in the LTE phase were influenza (33.3%) and nasopharyngitis (33.3%), with a median (IQR) follow-up of 44.5 (12-79) weeks. For details, see Table: Patients with ≥1 Treatment-emergent AEs in AT and LTE Phases.

Literature Search

A literature search of MEDLINE^®, EMBASE^®, BIOSIS Previews^®, and DERWENT^® (and/or other resources, including internal/external databases) was conducted on
10 September 2026.