The Swedish study included funding from Biogen Idec, Merck Serono, and Umea University.

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Bernstein, said the Merck-Serono pairing seemed to make sense for investors in both companies.

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Zymogenetics and Merck-Serono had stopped one study of a lupus treatment that was in some ways similar to Benlysta because of an infection risk.

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"Together with Serono, Merck will be a world-class biotechnology company and a major player in the global pharmaceutical market, " he said.

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For another, Merck has a strong sales force in Europe, whereas Serono has a sales presence in the U.S. The combination could be more efficient at pitching drugs to doctors and health bureaucracies.

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In March, Damstadt, Germany-based Merck set out on its own hostile bid for German neighbor Schering, bypassing Serono's "For Sale" sign.

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