Trials testing an experimental medication have been urgently halted following the death of multiple participants.

Swiss drug manufacturer Novartis said Tuesday that it paused eight clinical trials of the cell therapy rap-cel after the deaths of three patients.

The halt began on August 24 after Novartis was notified of three cases of a rare but life-threatening allergic reaction called immune effector cell-associated hemophagocytic syndrome (IEC-HS), the company spokesperson said.

The reaction causes the body’s immune system to overreact and attack otherwise healthy organs, which led to ‘fatal outcomes,’ according to the spokesperson.

Novartis said it is conducting ‘a comprehensive review of the observed safety events’ and is working with safety boards to review what happened and how to catch dangerous side effects earlier.

Rap-cel is a form of CAR-T therapy, which modifies a patient’s immune cells so they can recognize and destroy targeted harmful cells. Novartis said the reaction is a known severe complication of CAR-T and that it is actively monitoring patients who have already received the treatment.

‘The temporary halt will allow for a more comprehensive review of the evolving clinical and safety data across the program,’ a Novartis spokesperson said.

The paused trials focused on inflammatory diseases such as lupus, rheumatoid arthritis and vasculitis, as well as nerve and muscle disorders including multiple sclerosis and myasthenia gravis. Studies testing the treatment on cancer are still ongoing.

New Jersey-based drug manufacturer Bristol Myers Squibb also voluntarily paused enrollment in autoimmune trials testing its own CAR-T treatment zolacabtagene autoleucel, or zola-cel, ‘out of an abundance of caution’ and to ‘review clinical data across our zola-cel program,’ according to a spokesperson email given to BioPharma Dive.

Bristol Myers Squibb said it has detected ‘transient and reversible inflammatory events’ during routine safety testing and that it aims to evaluate and resume testing ‘as quickly as possible.’

Phase 1 trial results published in February found one case of IEC-HS. The company said the drug’s safety profile ‘remains consistent with the known profile of CAR-T therapies.’

Read More: Trial for autoimmune disease treatment urgently halted after multiple participants die