What's Causing Juno Therapeutics Shares to Tumble 11.9% Today

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What happened

After the company presented data on its chimeric antigen receptor T-cell therapy (CAR-T), JCAR017, at the annual American Society of Hematology conference over the weekend, Juno Therapeutics (NASDAQ: JUNO) shares are losing 11.9% of their value at 2 p.m. EST Monday.

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So what

Juno Therapeutics reported arguably best-in-class safety for JCAR017 in non-Hodgkin lymphoma at the conference, but investors appear disappointed that response rates weren't higher.

To be clear, JCAR017's efficacy has been solid, and the latest data show that it still matches up well against Novartis (NYSE: NVS) and Gilead Sciences (NASDAQ: GILD) CAR-Ts, Kymriah and Yescarta, respectively. All three of these gene therapies re-engineer a patient's T-cells so that they can better find and destroy cancer cells  -- and in trials, all three therapies have delivered impressive response rates at the three-month and six-month marks.

In JCAR017's case, the overall response rate in patients receiving the dose level that's being studied in the company's ongoing pivotal study was 74% at three months. The complete response rate for these patients was 68% at three months and 50% at six months.

Overall, 80% of patients receiving any dose of JCAR017 in the study who were in a complete response at three months stayed in complete response at six months. Also, 92% of patients in response at six months were still in response at the cutoff date for the data presentation.

It's bad science to compare these findings with findings from Novartis and Gilead Sciences' separate trials, but in my opinion, JCAR017 stands its ground with its competitors based on those figures.

Where JCAR017 really shined was in its safety, though. Across the entire study, only one of 91 patients experienced severe cytokine release syndrome (CRS), a potentially life-threatening condition that's been common in CAR-T studies. Additionally, only 12% experienced severe neurotoxicity, another common adverse event that's been witnessed at higher rates in studies evaluating Yescarta and Kymriah.

Now what

If the response rates had separated significantly from the rates reported by Gilead Sciences and Novartis, then it would have been a slam-dunk presentation. Nevertheless, the trial appears to be a success, and if results are confirmed in the company's ongoing pivotal trial, then Juno Therapeutics could end up with the best-in-class CAR-T on the market because of its safety advantages. Data from JCAR017's pivotal trial are expected in 2018.

Initially, CAR-Ts are being evaluated in relapsing or refractory patients for whom there are limited treatment options, but over time, studies could prove that they're effective earlier in treatment, too. If so, then the ability to deliver high-rate response suggests they'll be standard care -- and given their six-figure price tags, that represents a multibillion-dollar market opportunity to Juno Therapeutics and its competitors.

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Todd Campbell owns shares of Gilead Sciences. His clients may have positions in the companies mentioned. The Motley Fool owns shares of and recommends Gilead Sciences. The Motley Fool recommends Juno Therapeutics. The Motley Fool has a disclosure policy.