The intellectual property attorney who went head-to-head with the embattled blood-testing startup Theranos Inc. over trade secrets is back in Big Law.

John Fuisz and his boutique co-owner Jennifer Chen have joined Vinson & Elkins in Washington, D.C., as partners, the firm announced Monday. Fuisz worked at McDermott Will & Emery until 2010, when he started his own D.C. firm. It combined with Chen’s firm and took the name Fuisz Chen last year.