LISBON, Portugal—Celebrated U.S. cellist Yo-Yo Ma joined refugees from the Afghanistan National Institute of Music in the Portuguese capital Lisbon on Tuesday for a performance of Mozart’s Eine kleine Nachtmusik. Ma joined young Afghan and Portuguese musicians on a small stage at the National Conservatory, where the refugees who arrived last December are studying. “The best defense against anything is culture,” Ma told the Lisbon audience of dozens of people in a speech. “They risked their lives for something they believed in and you, in Lisbon, opened your hearts and risked … all kinds of things in order to do what is human,” he said. Portugal granted asylum to a 273-person group, including some 150 students, from the Afghanistan National Institute of Music as they fled Afghanistan in the wake of a Taliban takeover last August. Ma had a hand in helping them get out of Afghanistan. The Taliban seized …