To assess incidence, characteristics, and changes in generalized myasthenia gravis (gMG)-specific scales in participants achieving minimal symptom expression (MSE) in the phase 3 study of intravenous efgartigimod, ADAPT, and its open-label extension, ADAPT+.

Efgartigimod, a human IgG1 antibody Fc-fragment, reduces IgG levels through neonatal Fc receptor blockade. A key efficacy indicator in gMG treatment is improvement in MG-ADL score. MSE (MG-ADL total score of 0 or 1) is explored as a novel proposed treatment target in gMG.

Post hoc analyses of acetylcholine receptor antibody-positive participants in ADAPT (n=129) and ADAPT+ (n=111) were performed.

In ADAPT participants, 44.6% treated with efgartigimod achieved MSE vs 10.9% of participants given placebo any time during the study. The difference between groups was noted as early as Week 4 and sustained throughout the study. In ADAPT+, 40.5% of participants achieved MSE. Eighty-one percent of participants from the efgartigimod arm who achieved MSE in ADAPT also achieved MSE during ADAPT+; 23% who had not achieved MSE in ADAPT did in ADAPT+. Baseline characteristics for efgartigimod-treated participants who achieved MSE during ADAPT were comparable to those who did not. Although mean (SD) baseline MG-ADL score was statistically significantly lower for those achieving MSE (8.2 [1.8] vs 9.7 [2.7]; P<0.0084), the difference was not clinically meaningful. Achieving MSE was associated with substantial improvements in QMG, MGC, and MG-QoL15r mean scores of 11.4, 16.0, and 12.4 points, respectively, from baseline to best score (across all visits). Researchers observed a 0.3-point increase in EQ-5D-5L utility score, resulting in quality of life (QoL) comparable to healthy populations. MSE achievement also resulted in sustained improvements of these disease-specific and QoL measures. Patients experienced clinically meaningful improvements over 60% of the visits during ADAPT.

Participants who achieved MSE had substantial improvement across multiple disease measures and experienced QoL comparable to healthy populations.