Argenx NV is set for a January 2022 U.S. commercial launch following FDA approval of Vyvgart (efgartigimod) in generalized myasthenia gravis (gMG), making it the first FcRn antagonist to cross the finish line. The Breda, Netherlands-based company reported in its third-quarter earnings in late October that a team of 70 sales reps were ready to go.

Shares of Argenx (NASDAQ:ARGX) rose 4.4% to $310.26 on Dec. 17 ahead of a trading halt triggered just ahead of the announcement.

Myasthenia gravis is a rare and chronic autoimmune disease characterized by debilitating and possibly life-threatening muscle weakness. More than 85% progress to gMG within a year and a half, which can result in extreme fatigue and, in addition to mobility, also cause difficulty with activities such as speech, swallowing and even breathing. Roughly 65,000 people in the U.S. are affected. In light of medical need more therapies, the FDA granted the efgartigimod program both fast track and orphan status.

Argenx’s Vyvgart is cleared for the treatment of adults who test positive for the anti-acetylcholine receptor (AChR) antibody, a group representing about 5% to 10% of all MG patients and the same patient group for with Soliris (eculizumab), the blockbuster terminal complement inhibitor developed by Alexion Pharmaceuticals Inc. was approved in 2017 in gMG. Astrazeneca plc acquired Alexion earlier this year.

Pricing for the new therapy wasn’t immediately clear. However, analysts have largely anticipated a higher price vs. the intravenous immunoglobulin (IVIG) treatments in MG, which run an average of $190,000 per patient per year, but well below Soliris, which has been criticized for its list price of about $470,000 annually per patient. In a final evidence report released in September, the Institute for Clinical Economic Review said the health-benefit price benchmark (HBPB) for Soliris in gMG would be $13,200 to $19,400 per year, which would require at least a 97% discount from the current price. For efgartigimod, the drug pricing watchdog listed the HBPB at between $18,300 and $28,400 per year.

H.C. Wainwright analyst Douglas Tsao indicated a lengthy payer process might lie ahead. In an Oct. 28 note to investors, he warned that efgartigimod was not expected to have a J code until the third quarter of 2022, “which is likely to slow initial uptake.” He modeled about $100 million in U.S. sales for the year, while another $11 million could come from ex-U.S. sales, depending on how those approvals pan out.

Applications are pending in Japan, where a decision is expected in the first quarter of 2022, and in Europe, which is expected to act in the second half of 2022, with commercialization there expected to roll out on a country-by-country basis due to national pricing negotiations. Regulatory application in Israel will be led by new partner Medison Pharma Ltd., of Petach Tikva, and in China by Zai Lab Inc.

The FDA nod was based on data from the pivotal Adapt study, which showed significantly more AChR antibody-positive gMG patients were responders on the Myasthenia Gravis Activities of Daily Living (MG-ADL) score vs. placebo (67.7% vs. 29.7%; p<0.0001), while 40% of patients treated with efgartigimod achieved minimal symptom expression defined as MG-ADL scores of 0 (symptom free) or 1, compared to 11.1% of patients who received placebo. Among AChR antibody-positive responders, 84.1% showed clinically meaningful improvement on the MG-ADL score within the first two weeks of treatment. And for those patients who met the primary endpoint, the majority showed a sustained response, including 88.6% who achieved a response for at least six weeks, 56.8% for at least eight weeks and 34.1% for at least 12 weeks.

Secondary endpoints yielded favorable responses, too, showing statistically significant differences vs. placebo in MG-ADL responders in the overall population, including both AChR antibody-positive and AChR antibody-negative patients (p<0.0001).

The most common side effects in the trial associated with the use of Vyvgart in the trial included respiratory tract infections, headache, and urinary tract infections.