In a rapid turnaround, biotech firm Juno Therapeutics has been given the green light to resume testing a promising cancer therapy that involves genetically engineering patients’ immune systems.

Last week, the U.S. Food and Drug Administration ordered Juno to halt its trial of the treatment after three patients died. The company said the deaths were not the result of the immune cells, which are modified outside the body before being injected back into a patient, but of a toxic reaction to a preconditioning drug used as part of the treatment. That compound, fludarabine, has been removed from the protocol.

Juno’s stock rebounded on the news, after it had plunged 30 percent last week when the trial was stopped. Whether the company will be able to beat competitors Kite Pharma and Novartis to market remains to be seen. Juno had been planning on seeking FDA approval in 2017.

Initial trials for Juno’s therapy, known as CAR-T, have produced remarkable results in patients with recurrent acute lymphoblastic leukemia—about eight in 10 patients saw their tumors disappear. But the treatment is risky, so the tests have been limited to patients facing long odds of survival.

(Read more: Endpoints, “Unexpected Deaths Put Promising Immunotherapy on Hold,” “Gene Therapy’s First Out-and-Out Cure Is Here,” “Biotech’s Coming Cancer Cure”)