To investigate the effect of treatment with efgartigimod [administered intraveniously (IV) or subcutaneously (SC, coformulated with recombinant human hyaluronidase PH20)], a human immunoglobulin G1 (IgG1) antibody Fc-fragment that reduces total and pathogenic IgG levels through neonatal Fc receptor blockade, on humoral immune responses to COVID-19 vaccination in participants with various antibody-mediated autoimmune diseases, including generalized myasthenia gravis (gMG).

Patients with gMG experience a greater risk of adverse outcomes from respiratory infections, including COVID-19. Some immunosuppressive therapies used in gMG management may increase risk of infection and impair vaccine responses.

In ADAPT-SC+, efgartigimod PH20 SC (1000 mg) was administered in cycles of 4 once-weekly injections. COVID-19 receptor binding domain-specific IgGs were assessed, nominally, at prevaccination, ≥4 weeks after vaccination, and subsequently at 1 week after the fourth efgartigimod PH20 SC injection (when total IgG levels were maximally reduced). One sample was collected if postvaccination time points coincided with each other. Responses to COVID-19 vaccinations were similarly assessed across clinical trials investigating efgartigimod IV or PH20 SC in various diseases.

Eighteen participants in ADAPT-SC+ received a COVID-19 vaccine during or after a cycle. For 78% (n=14/18) of participants, this was their second or third vaccine dose. A 35.9-fold increase in SARS-CoV-2-IgG-RBD levels occurred from prevaccination to ≥4 weeks postvaccination. Similarly, from prevaccination to 1 week after the fourth efgartigimod PH20 SC injection, a 33.8-fold increase was seen. Additional data across clinical trials assessing efgartigimod IV or PH20 SC will be presented at the congress.

Participants receiving efgartigimod PH20 SC were able to mount antigen-specific IgG responses to COVID-19 immunization.