Organ and stem cell transplants are proven and frequently used methods in modern clinical practice. However, even when performed regularly in specialized centers, some patients still experience a number of serious complications afterwards. Among other things, infections with fungi and viruses can jeopardize therapeutic success. For example, coinfection with cytomegalovirus, which belongs to the family of Herpes viruses, and the fungus Aspergillus fumigatus can be critical. This combination of pathogens poses a serious medical threat in organ and stem cell transplantation.