Drug developer Tanox ( TNOX) said its shareholders approved its acquisition by biotech giant Genentech ( DNA). Under the terms of the deal, Tanox stockholders will receive $20 a share in cash for each of their shares. The decision was made by a majority vote at a special meeting of stockholders Monday. About 34.2 million shares were voted in favor of the merger, representing roughly 75.5% of Tanox's total shares and 99.9% of the shares voted at the meeting. The transaction should close in the first quarter of this year, subject to customary closing conditions. Shares of Tanox closed 4 cents higher at $19.81 Friday.