Lexeo Therapeutics Announces Merger Agreement to Acquire Mantle

What Happened

• On September 16, 2026 Lexeo Therapeutics, Inc. entered into an Agreement and Plan of Merger to acquire Mantle Therapeutics, with Lexeo’s wholly owned Merger Sub merging into Mantle and Mantle surviving as a wholly owned subsidiary of Lexeo. At the Effective Time each outstanding Mantle share (other than excluded shares) will convert into the right to receive an aggregate upfront purchase price of $5,300,000 in cash plus $3,000,000 in Lexeo common stock (unregistered, issued under Section 4(a)(2)/Reg D exemptions). Mantle restricted stock will vest and be cancelled for the same consideration; outstanding SAFEs and convertible notes will be cancelled or paid out per their terms.

Key Details

• Execution date: Merger Agreement signed September 16, 2026; public disclosure filed via Form 8-K on September 22, 2026.
• Upfront consideration: $5.3M cash + $3.0M in Lexeo common stock (total $8.3M upfront).
• Contingent consideration: one-time additional cash of $1.0M and up to $12.0M in milestone payments over 12 years (mix of cash and stock valued by a 30-day VWAP).
• Stockholder support: Key Mantle stockholders holding ~76.1% of outstanding Mantle capital stock (as-converted) and ~83.5% of preferred stock agreed to vote in favor of the merger.
• Closing conditions & timing: customary conditions apply (stockholder approval, accuracy of reps/warranties, no material adverse effect); either party may terminate if the merger is not consummated by November 16, 2026.

Why It Matters

• The transaction brings Mantle’s assets and programs into Lexeo in exchange for a modest upfront cash and equity package plus potential future milestone obligations. For investors, the immediate tangible impacts are (1) Lexeo will issue $3.0M of common stock (unregistered) which will affect share count/dilution, and (2) Lexeo may incur up to $13.0M in additional payments if contingent events occur.
• The merger is subject to shareholder approval and customary closing conditions; there is no guarantee any contingent payments will be made. Lexeo also disclosed a related press release, corporate presentation and a conference call/webcast on September 22, 2026.