Acelyrin (SLRN) said Thursday it has adopted a stockholder rights plan in response to Tang Capital Partners' accumulation of an 8.8% stake in the company.

Under the plan, each shareholder will receive one right per common share held as of March 24. The rights will activate if any shareholder acquires 10% or more of the company's common stock. Upon activation, shareholders excluding the acquiring party can buy additional shares at the exercise price, additional shares of common stock having a then-current market value of twice such exercise price, the company said.

The rights plan, which also has customary flip-over and exchange features, is effective immediately and set to expire on March 12, 2026

Shares were over 3% higher in recent premarket activity.