A team of Latham & Watkins attorneys has invalidated patents that threatened Janssen Biotech Inc.’s lucrative Darzalex blood cancer biologic drug. And they did it by using a lot of patentee MorphoSys AG’s own expert testimony.

U.S. District Judge Leonard Stark of Delaware ruled Friday that MorphoSys’ three patents on an antibody that binds to a protein known as CD38 are invalid for lack of enablement. The patents describe too many potential antibodies—potentially a quintillion, or 10 to the 19th power, according to Janssen. Although MorphoSys disputed that number, it conceded it could be in the billions, and Stark concluded that narrowing them down to the effective cancer killers would require undue experimentation.