Shares of Juno Therapeutics (JUNO) crashed in post-market trading Thursday after the company said the FDA put a hold on its trial of immuno-oncology candidate JCAR015 in acute lymphoblastic leukemia following several patient deaths.

TRIAL HALT: The FDA notified Juno it put a clinical hold on the Phase 2 trial of JCAR015 in ALL after three patient deaths. The fatalities occurred after the addition of chemotherapy drug fludarabine to the pre-condition regimen, the company noted. Transitioning from the setback, Juno proposed to the FDA to continue the trial with only cyclophosphamide -- another chemotherapy product -- in the pre-condition regimen, with the agency then requesting a full plan from the company related to that proposal which Juno said it will submit this week. The news does not affect its other CAR-T candidates, including JCAR017, the company noted.

MANAGEMENT COMMENTARY: Speaking during a subsequent conference call, Juno executives said the halt would "likely impact" its previous target of getting JCAR015 approved as early as 2017. The company took care to note that it remains encouraged about the potential for JCAR015 to treat ALL, and explained: "I think it's fair to say at this point that it isn't necessarily fludarabine that's the problem. It's the preconditioning regimen plus JCAR015 at this dose. Fludarabine, in some ways, acts like a dose amplifier. It could be that this is an increase in exposure associated with the amplifying effect of fludarabine. That's one of the things that is high on our list of things to understand."

BARCLAYS NEUTRAL ON CAR-T PRIOR TO JUNO NEWS: On Wednesday, Barclays analyst Jonathan Eckard initiated coverage of Juno and fellow CAR-T developer Kite Pharma (KITE) with Equal Weight ratings, saying near-term hurdles give him caution. The analyst said the utility and value of cellular immunotherapy "will ultimately expand beyond the current target oncology settings," though potential regulatory and commercial headwinds for these early products keep him on the sidelines for now. Though all FDA biologic approvals are complex, CAR-T products "could face even greater hurdles" given the difficulty and cost of manufacturing drugs tailored to individual patients, Eckard argued. That said, the analyst noted that Juno's $1B-plus cash position and collaboration with Celgene (CELG) "provide significant runway to weather any bumps," while Kite's lack of a partner could transition from a headwind today to a strategic benefit in the future.

PRICE ACTION: Shares of Juno crashed 27.5% to $29.60 in after-hours trading. The news pulled down several competitors testing their own CAR-T therapies, with Kite dropping 8.3%, Novartis (NVS) inching down 0.08%, Lion Bio (LBIO) slumping 8%, and bluebird bio (BLUE) falling 5.4%. ZIOPHARM (ZIOP) and Celgene, meanwhile, are down a respective 3.8% and 1.4%.