Stipan Jonjić is a Croatian immunologist known for his fundamental work in viral immunology and pathogenesis, specifically related to cytomegalovirus infections. His research has focused on how immune cells, such as T cells and natural killer (NK) cells, respond to cytomegalovirus, using mouse cytomegalovirus as a model. His lab was among the first to show the importance of CD4 and CD8 T cells in controlling virus spread and preventing reactivation. Among his principal achievements is the characterization of viral immunoevasion strategies and their role in regulating immune responses. Jonjić also helped demonstrate how NK cells recognize infected cells and the viral evasion of immune detection, including the "missing-self" activation pathway of NK cells. He became the first Croatian scientist to win a European Research Council (ERC) Advanced Grant in 2012. He is a member of the Croatian Academy of Science and Arts, the German National Academy of Science (Leopoldina), and the European Academy of Microbiology.