Here's​ ​Why Cellectis SA Fell as Much as 31.6% Today

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What​ ​happened

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Shares of biopharma Cellectis (NASDAQ: CLLS) fell nearly 32% today after the company announced that the U.S. Food and Drug Administration had placed a clinical hold on its second leading product candidate, UCART123. The regulatory hold affects two ongoing phase 1 trials aimed at treating acute myeloid leukemia (AML) and blastic plasmacytoid dendritic cell neoplasm (BPDCN).

Today's news comes just days after Gilead Sciences reinvigorated the immunotherapy space by acquiring Kite Pharma in a blockbuster deal; for investors, it brings back unpleasant memories of Juno Therapeutics' clinical hold in summer 2016. The company is also developing chimeric antigen receptor T cell (CAR-T) immunotherapies for oncology indications.

As​ ​of​ ​1:27 p.m.​ ​EDT,​ ​the​ ​stock​ ​had​ ​settled​ ​to​ ​a​ ​20.1%​ ​loss.

So​ ​what

Cellectis provided a good level of detail about its preliminary knowledge of the event -- a patient death in the BPDCN trial -- that triggered the clinical hold. It will now work with the FDA in an attempt to resume the trials and alter the protocols to increase patient safety.

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While an unfortunate development for patients and investors, the news doesn't appear to be having much of an effect on the rest of the CAR-T space. That's refreshing, considering the major corrections that were catalyzed last summer by the Juno Therapeutics clinical hold.

However, bluebird bio (NASDAQ: BLUE) shares are also down today on the news from Cellectis. Most likely that's because both Cellectis and Bluebird rely on the same gene-editing technology (TALEN) for altering their therapeutic CAR-T cocktails. Whether or not it had anything to do with the patient death, or potential off-target effects, remains to be seen.

Now​ ​what

This is certainly a blow to Cellectis investors, but there's nothing they can do except wait. It's seems likely that the FDA will allow the trials to resume with modifications and further investigation, but that doesn't guarantee they'll be continued by management. Uncertainty is never kind to a stock.

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Maxx Chatsko has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends GILD. The Motley Fool recommends JUNO. The Motley Fool has a disclosure policy.