Thousand Oaks-based Amgen lost an appeals court bid April 3 to obtain a patent related to “natural killer” cells in bone marrow in a ruling that could make it harder for biotechnology companies to obtain protection on DNA sequencing, according to Bloomberg News.

Amgen, the world’s largest biotechnology company, was appealing the U.S. Patent and Trademark Office’s rejection of an application for the sequencing of a protein linked to ways to fight tumors and viruses. On April 3, the appeals court upheld the agency’s decision.

Amgen fell 72 cents to $46.47 in Nasdaq Stock Market trading that day. Shares have dropped about 19 percent this year.

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