The Gene Therapy That Killed: How a Trial Slipped Past FDA Safeguards

On February 14, 2025, a research scientist at Helix Biotherapeutics sat in a coffee shop three blocks from the company's San Diego headquarters and slid a USB drive across the table. 'They knew,' she said. 'They knew the monkeys died, and they submitted the IND anyway.' The scientist, who spoke on condition of anonymity because she had signed a nondisclosure agreement and feared retaliation, had worked on preclinical trials for HLX-217, an experimental CRISPR-based gene therapy designed to treat Duchenne muscular dystrophy. What she was about to share would reveal how a startup biotech company concealed critical safety data from federal regulators—and how the Food and Drug Administration approved a clinical trial that would kill three patients within eighteen months.

The drive contained internal emails, toxicology reports, and meeting minutes from 2023 and 2024. Documents reviewed by The Editorial show that between August 2023 and March 2024, four of eleven cynomolgus macaques dosed with HLX-217 in a preclinical safety study died of acute liver failure within six weeks. Two others developed severe hepatotoxicity and were euthanised. The company's principal investigator, Dr. Rajesh Kumar, wrote in an internal memo dated March 18, 2024: 'Hepatic necrosis patterns are consistent across subjects. Recommend dose modification or alternative delivery vector before human trials.' That recommendation never reached the FDA.

Instead, Helix Biotherapeutics submitted an Investigational New Drug application to the FDA on June 3, 2024. The application, portions of which were obtained by The Editorial through a Freedom of Information Act request filed in January 2026, described the macaque study but characterised the deaths as 'adverse events within acceptable parameters for this disease model' and attributed them to 'pre-existing conditions and study stress.' The toxicology summary submitted to the agency made no mention of Dr. Kumar's findings. It stated that 'no treatment-related mortality was observed.'

What the FDA Didn't See

The FDA's review of Helix's IND application took forty-three days. Under the agency's accelerated pathway for rare disease treatments, the application was assessed by a team of four reviewers in the Office of Tissues and Advanced Therapies. None of them requested the raw pathology slides or necropsy reports from the macaque study. According to three former FDA officials with experience reviewing gene therapy applications, who spoke on condition of anonymity because they were not authorised to discuss internal processes, the agency relies heavily on sponsor-submitted summaries for preclinical data, particularly when the application involves a rare disease with no approved therapies.

'The presumption is that companies are acting in good faith,' one former reviewer said. 'You're looking at thousands of pages. You can't re-run every experiment. If the summary says the deaths were unrelated, and there's no obvious red flag in the tables, it can pass.' The FDA approved Helix's IND on July 16, 2024, authorising a Phase I trial in up to twelve patients with advanced Duchenne muscular dystrophy. The trial opened for enrollment at four sites in September 2024.

The First Patient

Daniel Ortega was nineteen years old when he enrolled in the HLX-217 trial at the University of California, San Francisco, in October 2024. Born with Duchenne muscular dystrophy, he had lost the ability to walk at fourteen and required ventilator support at night. His mother, Carmen Ortega, told The Editorial that the trial represented 'the only hope we had left.' She said the consent form mentioned liver monitoring but characterised the risks as 'mild to moderate.' It made no reference to the macaque deaths.

Daniel received his first infusion on October 22, 2024. Within ten days, his liver enzymes began to rise. By November 3, his alanine aminotransferase level—a marker of liver damage—had reached 847 units per liter, more than twenty times the upper limit of normal. On November 7, he was admitted to UCSF Medical Center with acute liver failure. He died on November 19, 2024. According to his medical records, reviewed by The Editorial with the family's consent, the cause of death was listed as 'fulminant hepatic necrosis, etiology under investigation.'

Two more patients—both in their twenties, both enrolled at separate trial sites—died of liver failure in January and March 2025. The trial was placed on clinical hold by the FDA on March 28, 2025. In its formal notice, the agency cited 'serious adverse events requiring further investigation.' It did not acknowledge that similar events had occurred in the company's preclinical studies.

How the System Failed

The regulatory framework governing gene therapy trials was designed in the aftermath of the 1999 death of Jesse Gelsinger, an eighteen-year-old who died during a gene therapy experiment at the University of Pennsylvania. In response, the FDA established stricter preclinical testing requirements and mandatory reporting of serious adverse events. But enforcement depends on the accuracy of company disclosures. 'The system assumes transparency,' said Dr. Leigh Turner, a bioethicist at the University of California, Irvine, who has studied gene therapy regulation. 'When a company deliberately omits data, the entire structure collapses.'

Documents reviewed by The Editorial show that Helix Biotherapeutics was under financial pressure when it submitted its IND application. The company had raised $127 million in venture funding between 2021 and 2023, but internal projections indicated it would exhaust its cash reserves by mid-2025 without additional investment. In an email dated May 2024, Helix's chief executive officer, Dr. Michael Brennan, wrote to the board of directors: 'We need the IND approval to close Series C. Any delay is existential.' Dr. Brennan did not respond to repeated requests for comment.

The FDA's own records reveal gaps in oversight. A 2023 report by the Office of Inspector General found that the FDA's Office of Tissues and Advanced Therapies had a backlog of more than two hundred IND applications and that reviewers spent an average of thirty-two hours assessing each submission—less than half the time recommended in the agency's internal guidelines. The report noted that 'staff shortages and increasing application volume have strained the office's capacity to conduct thorough reviews.'

The Company's Response

Helix Biotherapeutics issued a statement on March 29, 2025, one day after the FDA's clinical hold. The statement described the patient deaths as 'tragic outcomes' and said the company was 'cooperating fully with regulatory authorities.' It made no mention of the preclinical data. In a follow-up press release on April 15, 2025, the company announced it had 'voluntarily paused all development activities for HLX-217' and was conducting an internal review. Dr. Rajesh Kumar, the principal investigator who had authored the March 2024 memo warning of liver toxicity, resigned from the company in May 2025. He declined to comment for this article.

On January 12, 2026, the Department of Justice opened a criminal investigation into Helix Biotherapeutics for alleged violations of federal drug safety laws. According to a person familiar with the investigation, who spoke on condition of anonymity because the matter is ongoing, federal prosecutors are examining whether company executives knowingly submitted false information to the FDA. The company has not been charged. Helix's legal counsel, Arnold & Porter, said in a statement: 'Helix Biotherapeutics denies any wrongdoing and will vigorously defend itself against any allegations.'

The Families Left Behind

Carmen Ortega has joined the families of the two other deceased patients in filing a wrongful death lawsuit against Helix Biotherapeutics. Filed in federal court in San Francisco on February 3, 2026, the complaint alleges that the company 'knowingly concealed material safety information' and that the patients 'were subjected to a therapy that had already proven lethal in animal models.' The case is pending.

'They told us this was cutting-edge science,' Ortega told The Editorial in a phone interview in March 2026. 'They told us it was safe. They never told us monkeys had died the same way my son did.' She said she has reviewed the internal documents provided by the anonymous scientist. 'I want people to know what happened. I want them to know Daniel's name. And I want to know who decided his life was worth less than their funding round.'

What Happens Next

The FDA declined to comment on the specifics of the Helix case, citing the ongoing DOJ investigation. In a written statement, an agency spokesperson said: 'The FDA is committed to ensuring the safety of clinical trial participants and takes any allegation of data misrepresentation with the utmost seriousness. We are reviewing our processes to identify areas for improvement.'

In Congress, the case has prompted calls for stricter oversight of gene therapy trials. On March 24, 2026, Representative Anna Eshoo, a Democrat from California who chairs the House Energy and Commerce Subcommittee on Health, introduced the Clinical Trial Transparency Act, which would require companies to submit raw preclinical data to the FDA and impose criminal penalties for knowingly falsifying safety reports. 'This is not an isolated incident,' Eshoo said in a statement. 'It is a symptom of a regulatory system that has not kept pace with the explosion of experimental therapies.'

For now, the scientist who handed over the USB drive remains anonymous. She still works in the biotech industry, at a different company. 'I knew what would happen if I came forward publicly,' she said in a follow-up message in March. 'But I also knew what would happen if I didn't. Three families are grieving because people like me stayed silent for too long. I couldn't be one of them anymore.'

The broader implications extend beyond one company or one trial. As of March 2026, there are more than four hundred active gene therapy trials in the United States, according to ClinicalTrials.gov. Most are sponsored by small biotech firms operating under the same regulatory framework that failed to catch Helix's omissions. 'The promise of CRISPR and gene editing is real,' said Dr. Jennifer Doudna, a Nobel laureate and pioneer of CRISPR technology, in an interview with The Editorial. 'But so are the risks. We have to be honest about what we know and what we don't. The moment we stop being honest, people die.'