To describe the efficacy of efgartigimod, a human immunoglobulin G1 (IgG1) antibody Fc-fragment that blocks the neonatal Fc receptor (FcRn), in anti-acetylcholine receptor antibody negative (AChR-Ab-) participants with generalized myasthenia gravis (gMG) receiving either efgartigimod IV or subcutaneous (SC) efgartigimod PH20 (coformulated with recombinant human hyaluronidase PH20).

Approximately 15% of patients with gMG are AChR-Ab-. The lack of approved treatment options for the AChR-Ab- gMG population represents an unmet need.

Post hoc analyses were conducted to examine the efficacy and safety of efgartigimod IV and/or efgartigimod PH20 SC in AChR-Ab- participants in the ADAPT/ADAPT+ and ADAPT-SC/ADAPT-SC+ trials. 

Among the pooled AChR-Ab- participants (n=56), the mean (SE) Myasthenia Gravis Activities of Daily Living (MG-ADL) total score improvement from baseline to Week 3 of Cycle 1 was -3.7 (0.44 [n=55]). Consistent improvements in MG-ADL were observed with repeated cycles. Clinically meaningful improvements (CMI; decrease of ≥2 in MG-ADL total score) in MG-ADL at week 3 of Cycle 1 were seen in 76.4% (n=42/55) of AChR-Ab- participants. Achievement of minimal symptom expression (MSE; MG-ADL total score of 0 or 1) at any time during Cycle 1 were seen in 23.2% (n=13/56) of AChR-Ab- participants. Similar CMI and MSE results were observed across all cycles. The overall safety profile was similar between AChR-Ab+ and AChR-Ab- participants.

Both efgartigimod IV and efgartigimod PH20 SC were well tolerated and led to clinically meaningful improvements in symptoms for participants with AChR-Ab- gMG.