Rihanna is lending her voice to support DKMS, the largest bone marrow donor center in the world with more than two million registered donors, in their bid for a $250,000 grant from Pepsi's Refresh Project. Check out the trend-setting, globetrotting singer's PSA to learn more about why she's getting behind this cause. To date, 19,000 DKMS donors have helped save lives by donating their bone marrow, but they need more donors if they're going to continue to make more life-saving matches. Want to get involved? Vote for DKMS by April 30 (you can vote daily!), and they could win Pepsi's challenge.