Alumis (ticker: $ALMS) and Acelyrin (ticker: $SLRN) have announced a definitive merger agreement in an all-stock transaction. The merger comes amid significant declines in both companies' stock prices following their initial public offerings (IPOs), with Acelyrin's shares down 88% from its IPO valuation of $540 million and Alumis down 65% from its IPO valuation of $250 million. Following the announcement, trading of both companies' shares was halted in after-hours trading. Additionally, Halper Sadeh LLC has initiated an investigation into whether the sale of Acelyrin is fair to its shareholders. The merger aims to strengthen their positions in the immune drug market, with plans to advance a psoriasis drug into late-stage clinical trials.