Kezar Life Sciences said it has paused a trial of its experimental drug for lupus to review safety data after four patients died in the mid-stage study.

The San Francisco-based company said it had informed the FDA and European regulators of the decision to pause enrollment and dosing in the trial. An independent study committee recommended the pause after reviewing safety data, following the deaths of patients enrolled in trials in the Philippines and Argentina.

Review of the data by the committee found three of the fatalities showed a common pattern of symptoms and the deaths happened close to the time of dosing, while a non-fatal adverse event showed a similar proximity to dosing.

To date, 84 patients have been enrolled in the mid-stage trial, according to Kezar. The company said it has not observed any instances of death or serious infections in prior clinical studies of zetomipzomib.

Another mid-stage trial testing zetomipzomib in patients with autoimmune hepatitis remains active with no serious adverse events observed to date, the drug developer said.