The halt was implemented on August 24 after Novartis was notified of three cases of a severe, life-threatening immune reaction. Complications from the reaction, in which the body's defense system overreacts and attacks its own organs, led to the deaths, the Swiss drugmaker said.

Novartis is conducting "a comprehensive review of the observed safety events" and is working with independent safety boards to review what happened as well as to find ways to catch dangerous side effects earlier.

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Novartis said its two trials in patients with lymphoma and leukemia were not affected by the halt.

The drugmaker said that this type of severe immune reaction is a known, potentially life-threatening risk of CAR-T therapy. Novartis added that it is actively sharing information with health authorities and will continue to monitor patients who have already received the treatment.

The trials affected include those for inflammatory diseases such as lupus, rheumatoid arthritis, and vasculitis and nerve- and muscle-weakening disorders including multiple sclerosis and myasthenia gravis.

Rap-cel is a type of CAR-T therapy which modifies a patient's immune cells to recognise and destroy specific target cells. While traditionally used to treat blood cancers, drugmakers have been testing these therapies for autoimmune and other conditions.

Shares of the Swiss drugmaker were up 4 percent on Tuesday as investors focused on the late-stage success of its oral multiple sclerosis drug, remibrutinib. 

The Wall Street Journal first reported the halt. The newspaper said US drugmaker Bristol Myers had also paused similar trials of its CAR-T treatment in autoimmune disorders as a precautionary measure.

Bristol did not immediately respond to a Reuters request for comment outside of business hours. 

In July, Novartis reported that group sales exceeded expectations in the second quarter of 2026, on the back of a range of new products.

Novartis said in a statement that sales in the period from April to June rose by three percent to $14.4 billion (12.6 billion euros), compared with the second quarter of 2025.

That was slightly higher than the $14 billion forecast by analysts polled by Swiss agency AWP.

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The Basel-based group is facing the expiry of patents for a number of its drugs, including Entresto, a flagship treatment for heart failure.

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