Emerging therapies
Although conventional treatments for MG are well-established, 10% to 20% of MG patients remain refractory to therapeutic intervention.21 These patients are more susceptible to myasthenic crisis, which can result in hospitalization, intubation, and death.21 As mentioned, rescue therapies, including plasmapheresis and IVIg, are imperative to achieve remission of refractory MG, but such remission is unsustainable. Risks associated with these therapies, including contraindications and patient comorbidity, and their limited availability have prevented plasmapheresis and IVIg from being reliable interventions.12
These shortcomings, along with promising results from randomized clinical trials of newer modes of pharmacotherapeutic intervention, have increased interest in new therapies for MG. For example, complement pathway and neonatal Fc receptor (FcRn) inhibitors have recently shown promise in removing pathogenic autoimmune antibodies.18
Efgartigimod. FcRn is of interest in treating generalized MG because of its capacity to recycle and extend the half-life of IgG.22 Efgartigimod is a high-affinity FcRn inhibitor that simultaneously reduces IgG recycling and increases its degradation.22 This therapy is unique: it is highly selective for IgG, whereas other FcRn therapies are nonspecific, causing an undesirable decrease in other immunoglobulin and albumin levels.22 In December 2021, the Food and Drug Administration approved efgartigimod for the treatment of AChR-positive generalized MG.23
Zilucoplan is a subcutaneously administered complement inhibitor that has completed phase 3 clinical trials.18,24 The drug works by inhibiting cleavage of proteins C5a and C5b in the terminal complement complex, a necessary step in forming cytotoxic pores on targeted cells.18,24 Zilucoplan also prevents tissue damage and destruction of signal transmission at the postsynaptic membrane.25 Clinical trials have already established improvement in the Quantitative MG Score and the Myasthenia Gravis Activities of Daily Living Score in patients with generalized MG.18,24
Zilucoplan is similar to eculizumab, but targets a different binding site, allowing for treatment of heterogeneous MG populations who have a mutation in the eculizumab target antigen.26 Additionally, due to specific drug-body interactions, parameters for treatment using zilucoplan are broader than for therapies such as eculizumab. In a Zilucoplan press-release, the complement inhibitor showed statistically significant improvement in the treatment group of generalized, AChR-positive MG patients compared to the placebo group. Tolerability and safety was also a favorable finding in this study. However, a similar rate of treatment-emergent adverse events were recorded between the treatment group (76.7%) and placebo group (70.5%) which could indicate that the clinical application of this treatment is still forthcoming.27 If zilucoplan is approved by the FDA, it will be used earlier in disease progression and for a larger subset of patients.26
Nipocalimab is another immunoglobulin G1, FcRn antibody that reduces IgG levels in blood.27,28 A phase 2 clinical study in patients with AChR-positive or MuSK antibody–associated MG showed that 52% of patients who received nipocalimab had a significant reduction in the Myasthenia Gravis Activities of Daily Living Score 4 weeks after infusion.28 Phase 3 studies for adults with generalized MG are underway and are expected to conclude in April 2026.29
Looking forward
Despite emerging therapies aimed at treating IgG in both refractory and nonrefractory MG, there is still a need for research into biomarkers that further differentiate disease. Developing research into new biomarkers, such as circulating microRNAs, gives insight into the promise of personalized medicine, which can shape the landscape of MG and other disorders.30 As of August 2022, only two clinical trials are slated for investigation into new biomarkers for MG.
Although the treatment of MG might have once been considered stagnant, newer expert consensus and novel research are generating optimism for innovative therapies in coming years.
Mr. van der Eb is a second-year candidate in the master’s of science in applied life sciences program, Keck Graduate Institute, Claremont, Calif.; he has an associate’s degree in natural sciences from Pasadena City College, Calif., and a bachelor’s degree in biological sciences from the University of California, Irvine. Ms. Toruno is a graduate from the master’s of science in applied life sciences program, Keck Graduate Institute; she has a bachelor’s degree in psychology, with a minor in biological sciences, from the University of California, Irvine. Dr. Laird is director of clinical education and professor of practice for the master’s of science in physician assistant studies program, Keck Graduate Institute; he practices clinically in general and thoracic surgery.
The authors report no conflict of interest related to this article.