Cemdisiran
An investigational treatment for Myasthenia Gravis.
Drug facts
The same compound appears under different names depending on the context. Here is how to identify Cemdisiran wherever you encounter it, plus the key facts at a glance.
- Generic name
- Cemdisiran
- Development code
- ALN-CC5
- Drug class
- Complement C5 siRNA
- Manufacturer
- Regeneron (under a global license from Alnylam)
- How it's taken
- In NIMBLE, cemdisiran on its own was given as 600mg injected under the skin every 12 weeks, about 4 times a year.
An investigational siRNA from Regeneron, injected under the skin every 12 weeks, that lowers the body's levels of complement protein C5.
- The FDA is reviewing it under priority review for adults with generalized myasthenia gravis who test positive for anti-acetylcholine receptor (AChR) antibodies, with a target action date in November 2026 on a day Regeneron has not disclosed[1].
- In the Phase 3 NIMBLE trial, cemdisiran improved scores on the MG-ADL daily-living scale by 2.3 points more than placebo at week 24[2].
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Where Cemdisiran fits
If approved, cemdisiran would be the first siRNA medicine approved for generalized myasthenia gravis, and the fourth way to block C5 in AChR antibody-positive adults, alongside Soliris (and its biosimilars), Ultomiris and Zilbrysq. It differs from them in how it is given: an injection under the skin every 12 weeks, against Soliris and Ultomiris infusions and daily Zilbrysq self-injections. FcRn blockers such as Vyvgart, Rystiggo and Imaavy treat the same disease a different way, by lowering antibody levels. No head-to-head trial has compared cemdisiran with any of these medicines, so NIMBLE's results cannot be ranked against theirs.
How Cemdisiran works
In AChR antibody-positive myasthenia gravis, the antibodies switch on complement, a chain of immune proteins in the blood, at the junction where nerve meets muscle. Complement protein C5 is split to build the membrane attack complex, which damages that junction and weakens the signal to the muscle. The C5 blockers already approved for myasthenia gravis, Soliris, Ultomiris and Zilbrysq, grab the C5 protein itself.
Cemdisiran works one step earlier. It is an siRNA, a short strand of RNA that tells cells to make less of one protein, so less C5 is made in the first place. BioPharma Dive reported on August 26, 2025 that cemdisiran alone cut complement activity by 74% on average in NIMBLE, and that adding the C5 antibody pozelimab pushed the cut to nearly 99%, though the combination appeared less effective than cemdisiran alone.
Clinical trial results
NIMBLE (NCT05070858) is a double-blind, placebo-controlled Phase 3 trial run at 86 centers in 13 countries in adults with generalized myasthenia gravis, anti-AChR or anti-LRP4 antibodies and an MG-ADL score of 6 or more[2][4]. It randomized 284 people to 4 groups for 24 weeks: cemdisiran 600mg every 12 weeks (79), pozelimab 200mg every 4 weeks (50), cemdisiran 200mg plus pozelimab 200mg every 4 weeks (80), or placebo (75).
In the main analysis of the first 245 patients treated, MG-ADL scores (0 to 24, lower is better) fell 4.5 points on cemdisiran, 4.0 on the combination and 2.2 on placebo, a placebo-adjusted improvement of 2.3 points for cemdisiran and 1.7 for the combination. Pozelimab alone was not formally tested against placebo. Of 277 people treated, 263 (95%) finished the double-blind period[2].
The results were published in The Lancet in April 2026[2], and Regeneron's FDA application covers cemdisiran alone in AChR antibody-positive adults[1]. ClinicalTrials.gov lists the trial as active, not recruiting, with its extension running to an estimated completion in November 2028[4].
Main registered trial: NCT05070858 on ClinicalTrials.gov. Check it for the current status, sites and contacts before asking about enrollment.
Side effects and safety
Cemdisiran has no US label yet, so the warnings an FDA label would carry are not set. In NIMBLE's 24-week double-blind period, 69% of people on cemdisiran (54 of 78) had at least 1 adverse event, against 77% on placebo (54 of 70). Upper respiratory infection was the most common in the cemdisiran group, at 12%, against 11% on placebo.
No serious infections and no meningococcal infections occurred in the cemdisiran group, and no one died during the double-blind period. After that period 2 deaths occurred, and the investigator judged 1 of them to be treatment related while Regeneron did not[2].
BioPharma Dive reported on August 26, 2025 that, according to Regeneron, 1 person on cemdisiran died of pneumonia and 1 person on the combination died of septic shock during the extension period, both while taking immune-suppressing medicines, and that serious adverse events in the double-blind period occurred in 3% on cemdisiran, 9% on the combination and 14% on placebo[3].
NIMBLE required meningococcal vaccination before treatment[4], and the 3 C5 blockers approved for myasthenia gravis each carry a boxed warning for serious meningococcal infections[7][8][9]. Whether cemdisiran's label would carry the same warning is for the FDA to decide.
This is not a complete list of side effects. Talk to your doctor or pharmacist about what to expect and when to seek medical attention.
Taking Cemdisiran
In NIMBLE, cemdisiran on its own was given as 600mg injected under the skin every 12 weeks, about 4 times a year[2]. Participants had to complete meningococcal vaccination under the protocol, including a vaccine against groups A, C, W and Y within 5 years and a group B vaccine, where available, within 3 years before randomization[4]. The dose, schedule and vaccine rules for patients will be set by the FDA label if it is approved.
Development history
Cemdisiran came out of Alnylam's RNA interference work under the code ALN-CC5, first tested in healthy volunteers and people with paroxysmal nocturnal hemoglobinuria (PNH) in a Phase 1/2 study (NCT02352493)[5]. Regeneron and Alnylam signed a broad research alliance in 2019, and BioPharma Dive reported that a later amendment gave Regeneron a global license and responsibility for developing the drug[3].
NIMBLE began in December 2021[4], and Regeneron announced on August 26, 2025 that cemdisiran alone had met the trial's main and key secondary goals[3]. Full results appeared in The Lancet on April 21, 2026[2]. On June 22, 2026, Regeneron announced that the FDA had accepted its application for priority review, after Regeneron used a priority review voucher, with a target action date in November 2026, and that the European Medicines Agency had also accepted an application, with a European Commission decision anticipated in the second half of 2027[1].
Regeneron is also studying cemdisiran with pozelimab in PNH[6]. The FDA had not announced a decision as of November 6, 2026.
Explore Myasthenia Gravis trials
Other Myasthenia Gravis treatments
Common questions about Cemdisiran
▸What is Cemdisiran?
An investigational siRNA from Regeneron, injected under the skin every 12 weeks, that lowers the body's levels of complement protein C5. The FDA is reviewing it under priority review for adults with generalized myasthenia gravis who test positive for anti-acetylcholine receptor (AChR) antibodies, with a target action date in November 2026 on a day Regeneron has not disclosed[1]. In the Phase 3 NIMBLE trial, cemdisiran improved scores on the MG-ADL daily-living scale by 2.3 points more than placebo at week 24[2].
▸How does Cemdisiran work?
In AChR antibody-positive myasthenia gravis, the antibodies switch on complement, a chain of immune proteins in the blood, at the junction where nerve meets muscle. Complement protein C5 is split to build the membrane attack complex, which damages that junction and weakens the signal to the muscle. The C5 blockers already approved for myasthenia gravis, Soliris, Ultomiris and Zilbrysq, grab the C5 protein itself. Cemdisiran works one step earlier. It is an siRNA, a short strand of RNA that tells cells to make less of one protein, so less C5 is made in the first place. BioPharma Dive reported on August 26, 2025 that cemdisiran alone cut complement activity by 74% on average in NIMBLE, and that adding the C5 antibody pozelimab pushed the cut to nearly 99%, though the combination appeared less effective than cemdisiran alone.
▸What are the side effects of Cemdisiran?
Cemdisiran has no US label yet, so the warnings an FDA label would carry are not set. In NIMBLE's 24-week double-blind period, 69% of people on cemdisiran (54 of 78) had at least 1 adverse event, against 77% on placebo (54 of 70). Upper respiratory infection was the most common in the cemdisiran group, at 12%, against 11% on placebo. No serious infections and no meningococcal infections occurred in the cemdisiran group, and no one died during the double-blind period. After that period 2 deaths occurred, and the investigator judged 1 of them to be treatment related while Regeneron did not[2]. BioPharma Dive reported on August 26, 2025 that, according to Regeneron, 1 person on cemdisiran died of pneumonia and 1 person on the combination died of septic shock during the extension period, both while taking immune-suppressing medicines, and that serious adverse events in the double-blind period occurred in 3% on cemdisiran, 9% on the combination and 14% on placebo[3]. NIMBLE required meningococcal vaccination before treatment[4], and the 3 C5 blockers approved for myasthenia gravis each carry a boxed warning for serious meningococcal infections[7][8][9]. Whether cemdisiran's label would carry the same warning is for the FDA to decide.
▸How is Cemdisiran taken?
In NIMBLE, cemdisiran on its own was given as 600mg injected under the skin every 12 weeks, about 4 times a year[2]. Participants had to complete meningococcal vaccination under the protocol, including a vaccine against groups A, C, W and Y within 5 years and a group B vaccine, where available, within 3 years before randomization[4]. The dose, schedule and vaccine rules for patients will be set by the FDA label if it is approved.
▸Is Cemdisiran FDA approved?
Cemdisiran is currently in phase 3 clinical trials for Myasthenia Gravis. It has not yet received FDA approval.
▸When will the FDA decide on cemdisiran?
The FDA's target action date for cemdisiran in generalized myasthenia gravis is in November 2026, and Regeneron has not disclosed the exact day.
Review: Regeneron announced on June 22, 2026 that the FDA had accepted its application under priority review, after Regeneron used a priority review voucher.
Who it covers: Adults with generalized myasthenia gravis who test positive for anti-AChR antibodies.
Europe: Regeneron anticipates a European Commission decision in the second half of 2027.
Status: No FDA decision had been announced as of November 6, 2026.
▸How often is cemdisiran given for myasthenia gravis?
In the NIMBLE trial, cemdisiran alone was given as a 600mg injection under the skin every 12 weeks, about 4 times a year.
Vaccines: Trial participants had to complete meningococcal vaccinations before starting.
Once approved: The FDA label, if the drug is approved, will set the schedule for patients.
Source: Vu et al., The Lancet, 2026; ClinicalTrials.gov NCT05070858
▸What were the NIMBLE trial results for cemdisiran?
At week 24, cemdisiran improved MG-ADL daily-living scores by 2.3 points more than placebo.
Scores: MG-ADL scores fell 4.5 points on cemdisiran, 4.0 on cemdisiran plus pozelimab and 2.2 on placebo.
Combination: The combination improved scores 1.7 points more than placebo, against 2.3 for cemdisiran alone, and the 2 were not formally compared with each other. Regeneron's application covers cemdisiran alone.
Safety: No serious or meningococcal infections occurred in the cemdisiran group during the 24-week double-blind period.
Source: Vu et al., The Lancet, 2026
▸Is cemdisiran a complement inhibitor like Soliris and Ultomiris?
Yes, it targets the same complement protein, C5, but it works differently.
How it differs: Soliris, Ultomiris and Zilbrysq block the C5 protein in the blood, while cemdisiran, an siRNA, lowers how much C5 the body makes.
Dosing: Cemdisiran was given every 12 weeks under the skin in its trial; Soliris and Ultomiris are infusions and Zilbrysq is a daily self-injection.
Comparison: No trial has compared cemdisiran with these drugs directly.
Source: Vu et al., The Lancet, 2026
Sources and references
Every factual claim on this page is drawn from the public sources listed below. Click any reference to open the original document.
- Regeneron via GlobeNewswire · 2026-06-22. Cemdisiran Regulatory Submissions Accepted for Review by FDA and EMA for the Treatment of Generalized Myasthenia Gravis (gMG). https://www.globenewswire.com/news-release/2026/06/22/3315167/0/en/cemdisiran-regulatory-submissions-accepted-for-review-by-fda-and-ema-for-the-treatment-of-generalized-myasthenia-gravis-gmg.html
- The Lancet · 2026-04-21. Efficacy and safety of cemdisiran siRNA in myasthenia gravis (NIMBLE): a double-blind, randomised, placebo-controlled, phase 3 trial. https://pubmed.ncbi.nlm.nih.gov/42030965/
- BioPharma Dive · 2025-08-26. RNA drug from Regeneron, Alnylam succeeds in rare autoimmune disease trial. https://www.biopharmadive.com/news/regeneron-myasthenia-gravis-cemdisiran-alnylam-study-results/758607/
- ClinicalTrials.gov. A Study to Test How Safe Pozelimab and Cemdisiran Combination Therapy and Cemdisiran Alone Are and How Well They Work in Adult Patients With Generalized Myasthenia Gravis (NIMBLE). https://clinicaltrials.gov/study/NCT05070858
- ClinicalTrials.gov. A Phase 1/2 Study of an Investigational Drug, ALN-CC5, in Healthy Adult Volunteers and Patients With PNH. https://clinicaltrials.gov/study/NCT02352493
- ClinicalTrials.gov. A Study to Evaluate How Pozelimab + Cemdisiran Combination Therapy Works in Adult Patients With Paroxysmal Nocturnal Hemoglobinuria. https://clinicaltrials.gov/study/NCT07154745
- U.S. National Library of Medicine, DailyMed · 2026-06. SOLIRIS (eculizumab) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ebcd67fa-b4d1-4a22-b33d-ee8bf6b9c722
- U.S. National Library of Medicine, DailyMed · 2026-10. ULTOMIRIS (ravulizumab-cwvz) injection, for intravenous use: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a9a590d9-0217-43c7-908d-e62a71279791
- U.S. National Library of Medicine, DailyMed · 2026-01. ZILBRYSQ (zilucoplan) injection: prescribing information. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9f1d53d6-e495-4a3a-8bb9-680a15d25034