Bluebird bio (BLUE), Carlyle (CG) and SK Capital Partners said Wednesday they have amended their Bluebird acquisition agreement to give shareholders a new cash option of $5 a share.

Under the revised terms, shareholders can now choose either $5 a share in cash or keep the original structure of $3 a share in cash plus a $6.84 per share contingent value right, or CVR, tied to future net sales, the companies said. Shares tendered without a selection will receive the original offer with the CVR, they said.

According to the joint statement, Bluebird's board has approved the revised deal and urged shareholders to tender their shares, adding that the inability to reach majority support could lead to default on loan agreements and leave shareholders with no recovery in a possible bankruptcy.

The tender deadline has been extended to May 29, the companies said, adding that as of May 13, about 2.3 million shares had been tendered.

Bluebird shares were up more than 50% in early trading, while Carlyle's stock was 0.4% higher.