Intellia Therapeutics announced on October 27, 2025, a temporary suspension of dosing and screening activities in its pivotal Phase 3 clinical trials following a serious liver-related adverse event that led to patient hospitalization. The CRISPR gene-editing company paused enrollment in both the MAGNITUDE and MAGNITUDE-2 studies of nexiguran ziclumeran (nex-z) as it investigates the safety concerns.
The hospitalized patient, enrolled in the MAGNITUDE trial for transthyretin amyloidosis with cardiomyopathy (ATTR-CM), experienced a grade 4 increase in liver transaminase enzymes, indicating life-threatening liver injury that can signal acute liver failure. The patient also showed elevated total bilirubin levels, another biomarker for liver damage. According to Intellia, the individual "is being closely monitored and is receiving medical intervention."
Trial Scope and Patient Impact
The suspension affects two international Phase 3 studies evaluating nex-z in different patient populations. The MAGNITUDE trial had enrolled 650 patients with ATTR-CM, while MAGNITUDE-2 had enrolled 47 patients with transthyretin amyloidosis with polyneuropathy (ATTR-PN). Approximately 450 patients across both studies have already received doses of the experimental therapy.
Nex-z is administered as a one-shot intravenous infusion designed to inactivate the TTR gene that encodes the transthyretin protein. In ATTR conditions, this protein becomes unstable and forms amyloid fibril deposits that damage organs.
Strategic Implications for Intellia
The safety pause represents a significant setback for Intellia, which had positioned nex-z as one of its two priority late-stage programs. In January, the company reduced its workforce by more than 25% and discontinued other research and development initiatives to focus resources on nex-z and NTLA-2002, a hereditary angioedema candidate that completed Phase 3 enrollment in September.
"In line with our commitment to patient safety, we have taken immediate action to temporarily pause enrolment in MAGNITUDE and MAGNITUDE-2 as we investigate this recent event," stated John Leonard, Intellia's president and chief executive, ahead of a conference call with investors and analysts.
Market Response and Company Position
The announcement triggered a sharp market reaction, with Intellia's stock losing more than 45% of its value in pre-market trading. The company, co-founded by Nobel Prize winner Jennifer Doudna, had been building commercial operations in anticipation of its first product launch, previously projected for 2027.
Intellia ended the second quarter of 2025 with cash reserves of approximately $630 million, down from $862 million at the end of 2024. The company is now consulting with medical experts and regulatory authorities to develop risk-mitigation strategies and determine the path forward for resuming the trials.
The gene-editing specialist emphasized its commitment to patient safety and regulatory compliance as it works to address the safety concerns while maintaining progress toward potential approval of its CRISPR-based therapy for transthyretin amyloidosis.
