[U.S. Democratic presidential candidate Bernie Sanders addresses supporters at his campaign rally in Washington Square Park in the Greenwich Village neighborhood of New York City, April 13, 2016. REUTERS/Brendan McDermid]Thomson Reuters VATICAN CITY (Reuters) - Pope Francis met U.S. presidential candidate Bernie Sanders on Saturday morning before leaving for a visit to the Greek island of Lesbos, a participant at the meeting said. Columbia University Professor Jeffrey Sachs told Reuters that the meeting took place in the Vatican guesthouse where the pope lives and where Sanders had spent the night after addressing a Vatican conference on social justice. The Vatican said before the conference that a meeting had not been planned. Sachs said Sanders, who was accompanied by his wife, and the pope spoke for about five minutes. Sachs, his wife and a Vatican official were also in the room, Sachs said. (Reporting by Philip Pullella; Editing by Louise Ireland)