Abstract
Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are two humanotropic g-herpesviruses that infect a large part of the human population. They can both persist lifelong in human B cells and contribute to a number of B cell lymphoproliferative diseases, that mostly arise in immunocompromised individuals.
Primary effusion lymphoma (PEL) is associated with KSHV, but about 90% of tumors are also positive for EBV. The first part of this PhD thesis is a review that sums up the knowledge on EBV and KSHV in PEL and innate and adaptive immune responses that can control EBV and KSHV but are also counteracted by both viruses.
A recently established humanized mouse model of KSHV infection showed that KSHV can persist in EBV co-infected mice, and arising tumors share characteristics of PEL. The second part of this thesis utilized KSHV and EBV co-infection to investigate KSHV-specific adaptive immune responses in vivo. While EBV-directed immune responses are well understood, knowledge on KSHV-directed immune responses is limited to epidemiological and patient-based studies. We showed that cytotoxic CD8+ T cells expanded in KSHV coinfected animals, and KSHV-specific IgM antibodies with specificities similar to those observed in KSHV+ individuals were generated in these mice. Depletion of T cells increased both EBV and KSHV viral titers and tumor burden in KSHV co-infected animals. Additionally, T cells isolated from KSHV co-infected humanized animals could specifically kill KSHV and EBV dual infected B cell lines and were specific to KSHV ORF6.
The third part of this thesis utilized KSHV lytic gene mutant viruses deficient for complete KSHV lytic gene expression through a stop mutation in the replication and transcription activator (RTA) or the KSHV lytic gene K2 that encodes for viral IL-6 through gene deletion. We observed decreased tumor formation in animals co-infected with EBV and KSHV rta-stop mutant or KSHV delta K2 mutant compared to KSHV wildtype co-infection independent of infectivity or viral titers. In vitro generated B cell lines revealed that cells coinfected with EBV and KSHV rta-stop or KSHV delta K2 were deficient in cell growth, and viability of KSHV rta-stop co-infected cells was impaired. In vivo transfer of these cells revealed that expansion capacity of KSHV+ cells was increased in KSHV wildtype co-infected cells compared KSHV mutant virus co-infected cells, which revealed a role of KSHV lytic genes in cell survival and expansion.
Over all, humanized mice are a suitable platform to investigate basic functions of the immune system in human g-herpesvirus infections and enable studies on the role of individual KSHV genes through the use of KSHV mutant viruses in EBV co-infections. They support the investigation of immune responses, and thereby make the investigation of immune-based therapeutics and vaccine development targeting KSHV possible.
Rieble, Lisa