To investigate the effect of efgartigimod treatment on immune responses to vaccination.

Treatment with some immunosuppressive and B-cell–depleting therapies may lead to increased risk of severe infections in patients and may reduce immunogenicity of vaccines. Previous studies have demonstrated that efgartigimod, a human IgG1 antibody Fc fragment that reduces levels of IgG (including pathogenic autoantibodies) through neonatal Fc receptor blockade, does not impair cellular and humoral immune responses to antigenic challenges. Rates and severities of severe infections have been similar between efgartigimod- and placebo-treated participants in placebo-controlled studies and have not increased during long-term open-label studies.

In participants receiving efgartigimod, antigen–specific IgG titers increased from prevaccination to postvaccination, even during maximal IgG reduction. Additional data demonstrating preservation of cellular immune responses during efgartigimod treatment will be presented.

Efgartigimod’s unique structure as an Fc fragment selectively reduces IgG antibodies and autoantibodies while preserving the ability to mount antigen-specific responses to immunization. This mechanism avoids both broader impacts on immunity and increased risk of infections observed with some immunosuppressive and B-cell–depleting therapies.