Intellia Therapeutics’ stock has fallen nearly 23% following an announcement that a patient in its Phase III trial for a gene therapy targeting transthyretin amyloid (ATTR) cardiomyopathy suffered a serious adverse event (AE).
In a filing by the Securities and Exchange Commission (SEC), the company reported that one patient experienced Grade 4 liver transaminase elevations after treatment with nexiguran ziclumeran (nex-z) in the Phase III MAGNITUDE trial (NCT06128629). According to Intellia, the event is resolving without the need for hospitalisation or medical intervention.
Upon the announcement, Intellia’s stock, listed on the Nasdaq exchange, dropped by 22.87% from $9.66 a share at market close on 28 May to $7.45 at market close on 29 May.
Intellia emphasised that this is a single event from more than 200 patients dosed with nex-z in the MAGNITUDE study. Other AEs have been similar to those seen in the Phase I study, including infusion-related reactions and asymptomatic liver transaminase elevations.
The SEC filing added that Intellia said it will continue to monitor these events as the study progresses.
The trial has so far enrolled 365 patients out of an expected total enrollment of approximately 765 patients, which Intellia says is on track. The company aims to complete enrollment by early 2027.
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By GlobalDataIntellia is also investigating nex-z in the Phase III MAGNITUDE-2 study (NCT06672237), which is enrolling patients with hereditary ATTR amyloidosis with polyneuropathy (ATTRv-PN). Dosing has started, with investigators seeking data on whether the therapy will lead to a reduction in serum TTR.
Intellia will be waiting for data from MAGNITUDE-2 before filing a biologics licence application (BLA) to the US Food and Drug Administration (FDA) in 2028, with hopes for a 2029 commercial launch.
Another hurdle for gene therapy research
It has been a challenging time for gene therapy development, with several severe AEs and, in some instances, fatalities seeming to plague investors’ views on the therapeutic approach.
On 27 May, Rocket Pharmaceuticals announced that a patient died in its Phase II trial for a Danon disease gene therapy after suffering a serious AE.
In March 2025, Sarepta and Roche reported the death of a teenage patient dosed with its AAV gene therapy for Duchenne muscular dystrophy (DMD), Elevidys (delandistrogene moxeparvovec-rokl), causing agencies to pause ongoing clinical studies. This pause has since been lifted.
Last year, a fatality in Pfizer’s Phase II DMD gene therapy trial, as well as low efficacy in a Phase III study, caused the big pharma to drop the development of the AAV candidate, named fordadistrogene movaparvovec.
Earlier this month, the FDA shared that American haematologist oncologist Vinay Prasad will lead its Center for Biologics Evaluation and Research (CBER), the division responsible for regulating gene therapies and vaccines.
Prasad has openly criticised Elevidys, primarily about the clinical evidence and the FDA’s decision to approve the therapy, which raises questions about his overall opinion of the gene therapy approach.
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