(Reuters) -INmune Bio ( INMB ) said on Monday its experimental Alzheimer's drug failed to improve cognitive functions in patients with early stages of the mind-robbing disease in a mid-stage study, sending its shares plunging nearly 63% in premarket trading.

The drug, XPro, is designed to target and inhibit inflammatory signals associated with a type of protein called tumor necrosis factor without suppressing the immune system.

The study enrolled 208 patients with mild Alzheimer's disease (AD), or mild cognitive impairment, an early sign of the disease, who were randomly chosen to receive a weekly subcutaneous injection of XPro or a placebo for 24 weeks.

The drug was safe and well-tolerated, the company said, with injection site reactions the most common adverse event.

(Reporting by Mariam Sunny and Siddhi Mahatole in Bengaluru; Editing by Alan Barona and Sriraj Kalluvila)