Why Aduro Biotech's Clinical Hold Made Investors So Nervous

Aduro Biotech Inc.'s stock plummeted as much as 22 percent in premarket trading Monday, after a patient in a trial of the Berkeley company's trial of a pancreatic cancer treatment was found to have an infection from Listeria.

Why is that significant? Aduro's treatment, called CRS-207, reengineers Listeria — deleting genes that activate the bacteria's infection — to deliver its immune system-boosting treatment. If the bacteria, which is involved in food poisoning, pops up in patients, that means something went wrong somewhere along the way.

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