Human cytomegalovirus (CMV) is one of the major causes of severe complications in immunocompromised patients, such as recipients of hematopoietic cells, solid organ transplantation, and HIV-infected individuals. CMV is also a major pathogen in congenital infection. It can cause life-threatening diseases and severe neurological sequelae in newborn infants. CMV phosphoprotein pp65 is thought to be a major antigen for CMV-specific cellular immunity.