The BZLF1 homolog of an Epstein-Barr-related γ-herpesvirus is a frequent target of the CTL response in persistently infected rhesus macaques

Although CD8⁺ T lymphocytes targeting lytic infection proteins dominate the immune response to acute and persistent EBV infection, their role in immune control of EBV replication is not known. Rhesus lymphocryptovirus (rhLCV) is a γ-herpesvirus closely related to EBV, which establishes persistent infection in rhesus macaques. In this study, we investigated cellular immune responses to the rhLCV BZLF1 (rhBZLF1) homolog in a cohort of rhLCV-seropositive rhesus macaques. rhBZLF1-specific IFN-γ ELISPOT responses ranging between 56 and 3070 spot-forming cells/10⁶ PBMC were detected in 36 of 57 (63%) rhesus macaques and were largely mediated by CD8⁺ T lymphocytes. The prevalence and magnitude of ELISPOT responses were greater in adult (5-15 years of age) rather than juvenile macaques (<5 years of age), suggesting that rhBZLF1-specific CTL increase over time following early primary infection. A highly immunogenic region in the carboxyl terminus of the rhBZLF1 protein containing overlapping CTL epitopes restricted by Mamu-A*01 and other as yet unidentified MHC class I alleles was identified. The presence of a robust CD8⁺ T lymphocyte response targeting this lytic infection protein in both rhesus macaques and humans suggests that these CTL may be important for immune control of EBV-related γ-herpesvirus infection. These data underscore the utility of the rhLCV-macaque model for studies of EBV pathogenesis.