Biotech ends donor immune cell therapy for arthritis after 2 trial deaths

A third company has now reported deaths in trials of cell therapies for autoimmune disease. Last week, Bristol Myers Squibb revealed that a patient had died 44 days after a dose of its engineered immune cell therapy, as Biohack reported in our previous article.¹ On October 27, 2026, Artiva Biotherapeutics said it will stop developing its own cell therapy, called AlloNK, after two people in its trial died, and will lay off most of its staff.¹ Unlike the earlier cases, Artiva says neither death was caused by its cells.¹

What happened

AlloNK is made from “natural killer” cells, a type of immune cell, taken from donated cord blood. The cells are not genetically changed.² In the trial they were given together with rituximab, an antibody drug sold as Rituxan for arthritis and several cancers.³ The trial was a mid-stage “basket” study, meaning one study testing the same treatment in several diseases at once: rheumatoid arthritis, Sjögren’s disease, inflammatory muscle diseases (myositis) and systemic sclerosis.³ Its registry record planned to enroll about 90 people, with safety as the main thing being measured.²

Artiva disclosed two deaths. In the first, a patient developed leukoencephalopathy, a damaging and potentially fatal brain condition.¹ Before getting the cells, patients received a planned course of two chemotherapy drugs, cyclophosphamide and fludarabine, meant to clear out some of their own immune cells first.³ “The investigator and an independent safety review assessed the event as likely related to fludarabine-associated neurotoxicity,” the company said.³

Artiva reported that death to the US Food and Drug Administration (FDA) and to the trial’s independent safety board. The FDA then asked the company to pause enrollment and dosing in the trial.³ Artiva also stopped its plans to begin a Phase 3 trial, the last big kind of test before a drug can be approved.³

The second patient “experienced sudden death” about two months after starting treatment.¹ The cause has not been determined. A trial researcher concluded that neither AlloNK nor “any other component” of the treatment was to blame.¹ This death was also reported to the FDA and the safety board.³

Why Artiva stopped, beyond the deaths

The company said the deaths were not its only reason. It also pointed to its risk-benefit assessment, the likelihood of future enrollment delays, and the treatment’s development and sales outlook.³ According to Artiva, the data “continued to demonstrate deep B cell depletion and clinical activity” in line with earlier results. B cells are the immune cells this approach aims to clear out.³ But it added that “longer-term follow-up did not reflect the level of durability of clinical response the Company believes is needed to support continued development.”³ In plain terms, the company judged that the benefit it saw did not last long enough.

Artiva plans to cut about 94% of its workforce.³ Based on its last quarterly filing, that would be roughly 98 of its 104 full-time employees.³ It has hired the bank Leerink Partners to review options that include a merger, a sale or licensing of its technology, or dissolving the company.³ It said it had about $319.1 million in cash and investments at the end of September, a preliminary and unaudited figure.³ Its shares fell 30.5% on the day of the announcement.³

A planned presentation of AlloNK data at the ACR Convergence 2026 rheumatology meeting, set for November 6 to 11 in Orlando, has been canceled, along with a November 9 investor webcast.³

What this does not show yet

Everything known so far comes from the company’s statement. None of the safety or benefit data has been published in a medical journal. The judgments about cause come from the trial’s own investigators and, for the first death, an independent safety review the company described.³ The cause of the second death is still unknown.³

The sources also do not say how many people in total received AlloNK in the trial, so it is not possible to tell how common such events were. And because the company says the first death was likely tied to fludarabine, not to the cells, the case says little about whether donor-made natural killer cells themselves carry this risk.

Artiva said it will publish details of the first case “given the widespread use of fludarabine-containing lymphodepletion regimens in cell therapy development.”³ Lymphodepletion is the step of clearing out some immune cells before a cell therapy is given. That publication should let outside doctors judge the link for themselves.

Who is behind it

Artiva sponsored and ran the trial.² The company is based in San Diego, where it also makes its cell products.³ It had changed direction before: it canceled plans to go public in 2022, then shifted to autoimmune diseases and listed its shares two years later.¹

Several investment firms cut their ratings on the stock, including Cantor Fitzgerald, TD Cowen, Needham, H.C. Wainwright and Wedbush.³ TD Cowen analyst Tyler Van Buren wrote that Artiva could sell or license its technology or merge, given its “sizable” cash, but that “regardless of the outcome, we do not expect meaningful appreciation” in the share price.¹

Artiva CEO Fred Aslan said:

We are deeply saddened by the deaths of two patients who participated in our clinical studies and extend our sincere condolences to their families.

That statement was released by the company.³

How it fits with the other cases

Cell therapies first made their name in blood cancers, and drugmakers have more recently been testing them in autoimmune and other conditions.⁴ In late August, Novartis paused eight trials of its therapy, rap-cel, in conditions including lupus, rheumatoid arthritis and multiple sclerosis after three patients died. It said the deaths followed a severe immune reaction in which the body’s defenses attack its own organs.⁴ Bristol Myers Squibb paused studies of its rival therapy, zola-cel, after what it called temporary, reversible inflammation, as covered in our earlier article.⁴ Then came the Bristol Myers death disclosed last week.¹

The products are not the same. The Novartis and Bristol Myers treatments are CAR-T therapies made from each patient’s own cells, which are removed, re-engineered and given back.¹ They were made using a fast manufacturing process that Wall Street analysts have flagged as a possible cause of the problems.¹ Other analysts have suggested that certain patient characteristics might raise the risk, and that other factors could also play a part.⁵ Artiva’s natural killer cells came from donors instead, and had been seen across the field as a potentially more convenient “off-the-shelf” option.¹

So far, the companies have put the deaths down to different causes: a severe immune reaction at Novartis, and fludarabine or an unknown cause at Artiva.⁴³ What links the three cases is the setting, not a shared cause.

What to watch next

• Artiva’s publication on the brain condition linked to fludarabine, which the company has promised.³
• The close-out of its trials. Artiva said it will work with the FDA, investigators and review boards on “an appropriate and orderly close-out,” including continued safety monitoring.³
• The strategic review. Artiva said it will not give updates until its board approves a course of action or the process ends.³ It said updated clinical data “may be presented at future scientific meetings depending on the outcome.”³
• The Novartis and Bristol Myers reviews, which could affect how patients are chosen, how cells are made and how people are monitored in other trials in this area.⁵