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/genes and their role in virus control and pathogenesis. His lab also helped elucidate 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. 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.