BASEL, Switzerland: Novartis has halted eight clinical trials of its experimental cell therapy rap-cel after three patients experienced severe, life-threatening immune reactions that led to their deaths.

The Swiss drugmaker said September 1 that the pause, which affects trials targeting autoimmune and neurological disorders, was implemented on August 24 after it was notified of the three cases.

The reaction occurs when the body's defense system overreacts and attacks its own organs. Novartis said this type of severe immune reaction is a known, potentially life-threatening risk of CAR T-cell therapy.

U.S. drugmaker Bristol Myers has also voluntarily paused studies of its rival CAR T-cell treatment, zola-cel, "out of an abundance of caution" while it reviews safety data.

Novartis said it is conducting a comprehensive review of the deaths and working with independent safety boards to determine what happened and find ways to identify dangerous side effects earlier.

The company is also sharing information with health authorities and will continue monitoring patients who have already received the treatment.

Two Novartis trials involving patients with lymphoma and leukemia have not been affected by the halt.

The eight trials that have been paused include studies of rap-cel for inflammatory diseases such as lupus, rheumatoid arthritis and vasculitis, as well as nerve- and muscle-weakening disorders including multiple sclerosis and myasthenia gravis.

Rap-cel is a type of CAR T-cell therapy, a relatively new treatment in which a patient's immune cells are removed, modified to recognize and destroy specific target cells, and then reinfused into the patient.

The process has been successful in treating blood cancers, and drugmakers have more recently been testing CAR T-cell therapies for autoimmune and other conditions.

Novartis shares were up 4% on Tuesday as investors focused on the late-stage success of the company's oral multiple sclerosis drug, remibrutinib.

The Wall Street Journal first reported the rap-cel trial halt.

A Bristol Myers spokesperson said its pause was introduced after patients experienced temporary, reversible inflammation. The company said the treatment's overall safety profile remains in line with other CAR T therapies.