UK-based speciality biopharmaceutical company Mereo BioPharma Group PLC has agreed to acquire U.S.-based drug maker OncoMed Pharmaceuticals Inc. in an all-stock transaction valued at $57.4 million.

Under the terms of the deal, Mereo will pay for around 23.7 million new ordinary shares at $24.19 per share to current OncoMed shareholders, who will also receive contingent value rights representing the right to receive future cash payments based on milestone achievements.

The acquisition is expected to complete in the first half of 2019. OncoMed generated a market capitalization of $42.9 million.

Following completion of the move, Moero shareholders will own 75 percent of the enlarged group, while OncoMed shareholders will own 25 percent.