Key Highlights

● Lexeo completed its acquisition of Mantle Therapeutics on September 29, 2026 under a merger agreement signed on September 16, 2026.

● Upfront consideration is $5.3 million in cash, subject to adjustments, and $3.0 million in Lexeo common stock at closing.

● The agreement adds a one-time $1 million cash payment and up to $12 million in milestone payments over 12 years.

● Milestone payments may be made in cash or Lexeo common stock, valued using a 30-day trailing volume-weighted average price.

Lexeo Therapeutics, Inc. (NASDAQ:LXEO) told the U.S. Securities and Exchange Commission on September 29, 2026 that it has completed its acquisition of Mantle Therapeutics Inc. The deal closed the same day it was reported, under a merger agreement the parties signed on September 16, 2026. According to the Form 8-K, Lexeo is paying $5.3 million in cash, subject to certain adjustments, and $3.0 million in shares of its common stock at closing, with further payments that depend on future events.

How the Deal Is Structured

The merger agreement has four parties: Lexeo, Mantle, Magma Merger Sub Inc., a wholly owned subsidiary of Lexeo, and Shareholder Representative Services LLC, which acts for the former Mantle holders. Magma Merger Sub Inc. merged with Mantle, and Mantle became a wholly owned subsidiary of Lexeo when the merger took effect on September 29, 2026.

The upfront consideration is described per share of Mantle capital stock, with aggregate amounts of $5,300,000 in cash and $3,000,000 in Lexeo common stock. The filing says the cash portion is subject to certain adjustments but does not spell out how they are calculated. Restricted stock of Mantle vested in full immediately before closing and received the same consideration as other Mantle stock. Mantle's SAFEs, or simple agreements for future equity, were cancelled in exchange for the applicable liquidity-event consideration, and its convertible promissory notes were cancelled on payoff under the merger agreement.

Contingent Payments over 12 Years

Beyond the upfront amounts, the agreement provides two kinds of contingent consideration. The first is a one-time aggregate cash payment of $1 million, which depends on the achievement of certain events that the filing does not detail. The second is up to $12 million in aggregate milestone payments over a 12-year milestone term, tied to specified development and regulatory milestones relating to Mantle's product candidates.

Milestone payments may be made in cash or in Lexeo common stock. Where stock is used, its value is determined using a 30-day trailing volume-weighted average price. Lexeo also states that it makes no guarantee that any milestone will be achieved and has committed only to use commercially reasonable efforts in developing and commercializing the product candidates. The total potential consideration described in the filing is therefore larger than the upfront $8.3 million of cash and stock, but the milestone portion is payable only if the specified events occur.

What the Filing Covers and Leaves Out

The 8-K lists three items. Item 2.01 covers completion of an acquisition. Item 3.02 covers unregistered sales of equity securities, which applies because Lexeo is issuing common stock to Mantle holders; the filing states the shares are issued in reliance on the exemption in Section 4(a)(2) of the Securities Act of 1933 and, or, Regulation D, and have not been registered under the Securities Act or any state securities law. Item 9.01 lists exhibits, including the merger agreement and the cover page interactive data file.

Several details are not provided. The filing does not describe Mantle's business or product candidates, does not state how many Lexeo shares were issued or the price used to determine that number, does not mention any lock-up on the new shares, and does not describe any prior relationship between Lexeo and Mantle. Item 9.01 does not include financial statements of the acquired business or pro forma financial information. R. Nolan Townsend, Lexeo's Chief Executive Officer, signed the report on September 29, 2026.

Mantle Milestone Payments Over a 12-Year Term

The $5.3 million cash figure is described as subject to adjustment. The milestone term runs 12 years, and any milestone payments, in cash or stock, depend on the development and regulatory milestones set out in the merger agreement, which is filed as an exhibit to the 8-K.