The U.S. Food and Drug Administration placed a clinical hold on Iovance Biotherapeutics’ trial of its experimental cell therapy in lung cancer after a grade 5 adverse event – signifying a fatality – was reported. The patient death is potentially related to a pre-conditioning regimen in which the patient receives a short course of chemotherapy to kill immune cells before being infused with Iovance’s therapy, the company said in a statement released December 27th

The therapy, known as LN-145 TIL, is one of the California biotech’s tumor-infiltrating lymphocyte therapies being assessed in a phase 2 trial for patients who have progressed on chemotherapy and anti-PD-1 therapy for advanced non-small cell lung cancer (NSCLC). It uses white blood cells from a patient’s tumor, modifies them and puts them back into the patient to help the immune system destroy cancer cells.

The company will pause enrollment in the trial during the hold, while more than 100 patients with lung cancer who have already received the investigational treatment will continue to be monitored.

Early analysis of data from 23 patients found a 26.1% objective response rate – or one complete and five partial responses – plus a disease control rate of 82.6%. An updated analysis in November showed additional ongoing responses and a response duration greater than six months for 71% of confirmed responders, according to Iovance.

The FDA’s hold has no impact on any other trials conducted by the company, including the company’s lead asset, lifileucel, which is currently under review for the treatment of advanced melanoma.