The late-stage biopharma said the plan will issue one right for each share of common stock as of the close of business on March 24. The rights will initially trade with its common stock, and will become exercisable only if any person acquires 10% or more of Acelyrin's outstanding common stock.

Acelyrin (NASDAQ:SLRN) announced Thursday a decision to adopt a limited-duration stockholder rights plan, also known as a poison pill, after Tang Capital Partners rapidly accumulated 8.8% of the company stock following an unsolicited acquisition offer.