Evaluating MOAs of Generalized Myasthenia Gravis Therapies

Key Takeaways:

• Broad immunosuppressants (corticosteroids and nonsteroidal agents) act slowly and non-specifically; nonsteroidal immunosuppressants may take months to reach full effect, and chronic immunosuppression carries cumulative infection and long-term toxicity risk.
• Three mechanistically targeted classes now act on defined steps of the disease – FcRn antagonists accelerate clearance of pathogenic immunoglobulin G (IgG), terminal complement inhibitors block C5-mediated damage at the neuromuscular junction, and CD19-directed B-cell depletion reduces the source of autoantibody production – generally with faster onset and more of the immune system preserved.
• Mechanism, antibody status, and each agent's distinct safety profile (such as meningococcal risk with complement inhibitors) should guide individualized therapy selection.

The treatment landscape for generalized myasthenia gravis (gMG) now spans 3 mechanistically distinct targeted approaches – FcRn antagonism, terminal complement inhibition, and CD19-directed B-cell depletion – layered on top of the broad immunosuppression that has long anchored care. Understanding how each class acts on the immune system – and where it does not – helps match therapy to the individual patient rather than to a one-size-fits-all strategy.^1,2

How broad immunosuppression works

Corticosteroids and nonsteroidal immunosuppressants remain a foundation of gMG management. These agents work broadly, suppressing lymphocyte proliferation or dampening cytokine-driven signaling across the immune system rather than targeting the antibodies that drive disease.^1,2

That breadth has 2 practical consequences. First, many nonsteroidal immunosuppressants have a delayed onset of action. Nonsteroidal immunosuppressants can take many months to reach full effect, so they are often paired with faster-acting therapy early in treatment.¹

Second, sustained, non-specific suppression of adaptive immunity raises the cumulative risk of infection and the toxicities associated with chronic corticosteroid and cytotoxic exposure.^2,3

Targeting pathogenic IgG

Neonatal Fc receptor (FcRn) antagonists take a narrower approach. By blocking FcRn-mediated recycling of immunoglobulin G (IgG), agents such as efgartigimod, rozanolixizumab, and nipocalimab accelerate the breakdown of circulating IgG – including the pathogenic anti-acetylcholine receptor (AChR) and anti-muscle-specific kinase (MuSK) antibodies – without depleting B or T lymphocytes. The result is a rapid, reversible reduction in disease burden while the cellular arm of adaptive immunity stays intact.^3-5

Labeled indications differ. Efgartigimod is approved for adults with gMG regardless of antibody status, whereas rozanolixizumab is approved for adults with AChR- or MuSK-antibody-positive gMG and nipocalimab is approved for AChR- or MuSK-antibody-positive gMG in patients 12 years of age and older. Because these agents transiently lower total IgG, infection risk is an important class safety consideration, although specific adverse-event profiles differ among agents.^2,5

Blocking complement at the junction

Terminal complement inhibitors act at the effector end of the disease. In AChR-antibody-positive gMG, antibody binding activates complement and drives formation of the membrane attack complex (MAC), which damages the postsynaptic membrane of the neuromuscular junction.⁶

Agents such as eculizumab, ravulizumab, and zilucoplan block complement protein C5, preventing MAC assembly while leaving the proximal complement pathway – important for opsonization and immune-complex clearance – intact.^2,6

This selectivity creates an important vulnerability to infection with encapsulated bacteria, particularly Neisseria meningitidis. These agents carry a boxed warning for meningococcal disease and require meningococcal vaccination according to current prescribing recommendations; vaccination does not eliminate the risk of meningococcal infection.^2,6

Because the mechanism depends on complement-mediated injury, this class is directed at AChR-antibody-positive disease rather than the largely non-complement-fixing MuSK-antibody subtype.^1,6

Depleting the B-cell source

B-cell-depleting therapy works further upstream, targeting B-cell populations involved in autoantibody generation rather than directly removing circulating pathogenic antibodies or blocking their downstream effects. Historically, this meant rituximab, an anti-CD20 monoclonal antibody used off-label; consensus guidance supports it particularly in MuSK-antibody-positive disease, where responses have been more consistent than in AChR-antibody-positive disease.^1,2

The class advanced with the December 2025 approval of inebilizumab, a CD19-directed monoclonal antibody, for adults with AChR- or MuSK-antibody-positive gMG. CD19 is expressed across a broader span of the B-cell lineage than CD20, including plasmablasts and some antibody-secreting cells, allowing CD19-directed therapy to target a broader B-cell population than CD20-directed therapy.⁷

In the phase 3 MINT trial, inebilizumab produced greater improvement in Myasthenia Gravis Activities of Daily Living (MG-ADL) scores than placebo over the study period, with the largest MuSK-antibody-positive cohort studied to date.⁷

Because depletion acts upstream of circulating autoantibodies, onset is more gradual than with IgG clearance or complement blockade, and the principal safety considerations are infection risk and reduced immunoglobulin levels with sustained B-cell suppression.^2,7

Matching mechanism to patient

Framing these therapies by mechanism clarifies the trade-offs. Broad immunosuppressants are familiar and low-cost but act slowly and tax host defense over time. Targeted biologics act on a defined step – clearing IgG, blocking complement, or depleting B cells – and preserve more of the adaptive immune system, but each carries class-specific risks, dosing routes, and cost considerations.^1,2

Antibody status narrows the field. Complement inhibitors are used in AChR-antibody-positive disease; rozanolixizumab, nipocalimab, and inebilizumab have indications that include AChR- and MuSK-antibody-positive disease, while efgartigimod is approved for adults with gMG regardless of antibody status. Rituximab has its clearest role in MuSK-antibody-positive disease.^1,5,7

Comorbidities, infection risk, onset expectations, dosing route, and monitoring capacity shape the final choice.^1,5,6

Increasingly, targeted agents are considered earlier in the disease course rather than reserved only for refractory cases, with treatment selection increasingly individualized based on disease severity, antibody status, comorbidities, treatment goals, and safety considerations.²