Novartis paused eight clinical trials of an experimental therapy targeting autoimmune and neurological disorders in late August, after three patients died.

The Swiss pharmaceutical company temporarily halted the studies after learning of three fatal cases of a severe immune response, a spokesman said. It wasn't immediately clear when the deaths occurred.

The experimental treatment, which Novartis calls rap-cel, is a so-called cell therapy called CAR-T. It works by removing a patient's own immune cells, engineering them in a lab to hunt down and kill malfunctioning cells and then infusing them back into the body. Novartis was testing rap-cel in lupus, multiple sclerosis and other autoimmune diseases.

The company is conducting "a comprehensive review of the observed safety events," said the spokesman, who described the fatal immune response as a known safety risk in CAR-T therapies.

Novartis said it is working with independent safety boards overseeing each paused study and sharing what it knows with regulators.

Studies of rap-cel in cancer patients are continuing.

Bristol Myers Squibb said that it had paused similar trials of its CAR-T treatment in autoimmune disorders as a precautionary measure. It wasn't immediately clear when the New Jersey-based pharma paused its studies of the treatment, called zola-cel.

The company decided to pause its program during regular study protocol after researchers identified "transient and reversible inflammatory events," according to a Bristol Myers spokesperson.

"We are focused on completing our evaluation and resuming enrollment as quickly as possible," the spokesperson said.

Both companies' therapies work in similar ways. Each targets the same protein, called CD19, found on the surface of certain immune cells, in hopes of destroying the faulty cells driving the disease and giving the immune system a fresh start.

CAR-T can be a complicated and costly process. The complication behind the Novartis deaths happens when the immune cells, once reinfused, overreact and set off a wave of inflammation that can damage organs. Doctors have seen it before in cancer patients who received CAR-T therapy.

Novartis and Bristol Myers each have similar one-time cell therapies on the market to treat cancer, each of which cost more than $500,000.