Last week, federal health regulators in the United States suspended the clinical trial of an anticancer treatment developed by Juno Therapeutics following the deaths of three participants this year.

Now, after a modification to the leukemia treatment, the U.S. Food and Drug Administration (FDA) has allowed Juno to resume its study, but only without a specific chemotherapy drug.

What Caused The Deaths?

The company's experimental treatment known as JCAR015 is designed to treat adult patients with B cell acute lymphoblastic leukemia.

However, in May, one study participant passed away, while two more participants died in late June from swelling of the brain.

According to Seattle-based Juno Therapeutics, the problem did not stem from JCAR015, but from a chemotherapy drug called fludarabine, which is used during the pretreatment.

The company said last week that it will submit documents to the FDA including revisions in the trial protocol and patient consent forms.

Juno will resume its trials but without fludarabine and will instead use the chemotherapy drug cyclophosphamide, which was already part of JCAR015.

Promising But Unproven?

Juno's JCAR015 treatment, which uses a new approach called chimeric antigen receptor (CAR-T), is "promising, but still unproven," according to The New York Times. The treatment modifies a patient's immune system to target and attack cancer cells.

More specifically, the person's white blood cells are taken away from the body and changed to identify and kill cancer cells when returned.

Initial studies have shown that striking results in the treatment of lymphoma and leukemia, offering hope to patients, oncologists and investors.

However, JCAR015 has been found to induce severe side effects. This includes overreactions in the immune system and neurological toxicity such as intense swelling in the brain known as cerebral edema.

Competition And Stocks

Other pharmaceutical companies such as Kite Pharma Inc. and Pfizer Inc. are also pursuing the CAR-T treatment approach. CAR-T is part of a wider scientific trend in which the immune systems of patients are harnessed to fight cancer.

Meanwhile, in after-hours trading, the shares of Juno Pharmaceuticals increased 25.3 percent to $34.83. The company's stocks dropped Friday, July 8, after the FDA announced the suspension.

Juno was launched in 2013 in collaboration with scientists from the Fred Hutchinson Cancer Research, the Seattle Children's Research Institute and the Sloan Kettering Cancer Center.

In December 2014, Juno went public at $24 a share.

In 2015, the biotech company announced that it was partnering up with Celgene Corp. for a 10-year project focused on treatments for autoimmune diseases and cancer.

According to the Wall Street Journal, Celgene initially invested $1 billion in Juno, including a $150 million payment and an $849.8 million stock purchase.

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