Glycoprotein K8.1 is Critical for Liver and Bone Marrow Tropism of Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) in the Marmoset Infection Model

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a human tumor virus with significant disease burden, particularly in Sub-Saharan Africa, where Kaposi’s sarcoma is prevalent. KSHV disproportionately affects immunocompromised individuals and men who have sex with men. A suitable animal model is critical for the development of a preventive vaccine, as it must replicate viral spread and immune interactions. The common marmoset ( Callithrix jacchus ) had previously been established as conducive to KSHV infection with non-BAC-derived virus via the intravenous (i.v.) route. We used this animal model to establish the ability to infect marmosets with bacterial artificial chromosome (BAC)-derived KSHV and to establish the role of individual glycoproteins (GPs) in the colonization of specific host tissues. We infected three groups of four animals each with BAC16-derived KSHV wild type (wt), KSHV gH ^ASAELAAN , or KSHVΔK8.1. KSHV gH ^ASAELAAN contains mutations in gH that interfere with binding to the EphA2 receptor, which normally forms a high-affinity complex with gH/gL, whereas KSHVΔK8.1 does not express GP K8.1. The KSHV gH ^ASAELAAN mutant was used at a relatively higher concentration to overcome its intrinsic defect and to allow for analysis of tissue tropism. While seroconversion to the KSHV LANA antigen was variable, all animals exhibited clearly detectable viral DNA load in many tissues. Highest loads were detected in spleen, liver, heart and bone marrow. Viral DNA loads in these four tissues did not significantly differ between groups infected with KSHV wt or with the gH ^ASAELAAN mutant. However, KSHVΔK8.1-infected animals exhibited significantly lower levels of viral DNA in liver and bone marrow, but not in spleen or heart. Analysis of immune cells demonstrated significant activation of CD4 ⁺ and CD8 ⁺ T-cells in KSHV wt-infected animals. In wt and gH ^ASAELAAN -infected animals, different B cell subpopulations were found to expand after infection, which implies that the gH/gL glycoprotein complex may shape the host response to KSHV in unexpected ways. In summary, our findings demonstrate that neither the interaction with Eph family receptors nor GP K8.1 is essential for infection via the i.v. route but K8.1 plays a critical role for KSHV tissue tropism in vivo.