Bluebird bio (BLUE) received an unsolicited, nonbinding buyout proposal from Ayrmid for

an upfront cash payment of $4.50 a share and a one-time contingent value right of $6.84 a share, payable on reaching a net sales milestone.

Bluebird had agreed to be acquired by funds managed by Carlyle (CG) and SK Capital Partners for $3 a share in cash and a one-time contingent value right of $6.84 a share payable upon achieving a net sales milestone.

Ayrmid didn't submit any proposal as part of the earlier review of alternatives, bluebird bio said Friday in a statement.

Bluebird bio said it "remains subject to the terms of the merger agreement" with Carlyle and SK Capital, and the board "has not changed its recommendation in support of the merger."

The board is reviewing the Ayrmid offer, which is "subject to certain conditions and further negotiations between the parties, including confirmatory diligence," blubird bio said.

The shares of bluebird bio jumped 9.1% in recent after-hours trading.

Price: 4.45, Change: +0.37, Percent Change: +9.07