Early IgG drops may signal response to generalized MG therapy, study finds

An early drop in immunoglobulin G (IgG), a type of antibody, may help predict how well patients with generalized myasthenia gravis (gMG) respond to a class of treatments called FcRn inhibitors, a study suggests. The analysis focused on patients with antibodies that mistakenly target acetylcholine receptors (AChRs).

Researchers analyzed data from a China-based Phase 3 clinical trial (NCT05039190) that tested batoclimab, an investigational FcRn inhibitor, against a placebo in more than 100 adults with gMG.

The researchers found that larger drops in blood IgG levels were significantly associated with a greater likelihood of improvements in daily activities, muscle strength, and function.

“The reduction rate in total IgG may serve as a valuable short-term indicator of clinical response in patients with [anti-AChR antibody-positive] gMG following [FcRn inhibitor] therapy,” the researchers wrote.

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The findings were described in the study “Rapid Serum IgG Reduction as a Potential Indicator of Short-Term Clinical Improvement in AChR-Ab-Positive Generalized Myasthenia Gravis: A Post Hoc Analysis of a Phase III Batoclimab Trial,” published in Neurology and Therapy.

MG occurs when self-reactive antibodies mistakenly attack proteins that help nerve cells communicate with muscles, most commonly AChRs. This causes symptoms such as muscle weakness and fatigue. Antibodies that target AChRs are a type of IgG.

Several FcRn inhibitors are approved to treat gMG. FcRn normally helps prevent IgG antibodies from being broken down. By blocking FcRn, these treatments lower IgG levels, including antibodies that contribute to MG.

Batoclimab was approved in China for adults with gMG who test positive for anti-AChR antibodies. The approval was supported by the China-based Phase 3 trial, in which batoclimab led to marked clinical improvements compared with a placebo. The treatment also rapidly reduced blood levels of IgG and anti-AChR antibodies.

However, Immunovant, which developed batoclimab for markets including the U.S., decided not to seek U.S. approval of the drug to treat gMG, instead prioritizing its next-generation FcRn inhibitor, IMVT-1402. In May, the company disclosed it had discontinued its own batoclimab development program across all indications.

“Given the complex [underlying mechanisms] of MG and the persistent need for reliable biomarkers to monitor treatment response, this exploratory analysis investigates the association between reductions in [blood] IgG and [anti-AChR antibody] levels and clinical outcomes in patients with [AChR-related] gMG treated with batoclimab,” the researchers wrote.

For this analysis, the researchers reviewed data from 65 patients who received batoclimab in the Phase 3 trial and tested positive for anti-AChR antibodies at the start. Their mean age was 43.4, and 60% were women.

The researchers tracked changes in blood IgG and anti-AChR antibody levels during the first treatment cycle. Patients received six injections of batoclimab under the skin, once a week from week 0 through week 5.

Batoclimab rapidly reduces IgG and AChR antibody levels

Among the 62 patients with complete blood test results, IgG levels fell by a median of 70.8%, while anti-AChR antibody levels fell by a median of 81.1%. All 62 patients had lower IgG levels, while 87.1% had lower anti-AChR antibody levels.

During the first treatment cycle, 31 patients had IgG reductions greater than 71% and were classified as fast IgG responders. The remaining 31, whose IgG levels fell by less than 71%, were classified as slow IgG responders.

Before treatment, fast IgG responders had significantly lower IgG levels, body weight, and body mass index (BMI) than slow IgG responders. BMI is a measure based on weight and height that is commonly used to estimate body fat.

After one treatment cycle, about 55% to 58% of patients in each group had a clinically meaningful improvement of at least three points on the MG Activities of Daily Living (MG-ADL) scale, which measures how the disease affects everyday tasks.

A clinically meaningful improvement of at least five points on the Quantitative MG (QMG) scale, which measures muscle weakness, was seen in 67.74% of fast IgG responders and 48.39% of slow IgG responders.

Early IgG reductions may help predict clinical improvement

Larger drops in both IgG and anti-AChR antibody levels were significantly linked to greater clinical improvements. However, IgG reductions were “more predictive of clinical improvement,” the researchers wrote.

Statistical modeling showed that an 80% drop in IgG levels was associated with a 59% probability of a clinically meaningful MG-ADL score improvement of at least three points and a 77% probability of a QMG score improvement of at least three points.

Further analyses found that lower body weight was independently associated with faster IgG reductions.

“Our findings demonstrated that a rapid decline in IgG level serves as a reliable biomarker for evaluating the short-term efficacy of FcRn [inhibitors], and potentially other therapies, in patients with [AChR-related] gMG,” the researchers wrote.

The researchers noted several limitations, including the small study population, which was predominantly Chinese, the focus on a single treatment cycle, and the lack of an established IgG reduction threshold for predicting clinical improvement.

“Future studies with larger, more diverse [patient groups] are needed to validate these findings,” the researchers concluded.