Repression of productive viral replication by KSHV LANA correlates with reduced adaptive immune activation: potential...

Adaptive immune responses to primary Kaposi sarcoma-associated herpesvirus (KSHV) infection are poorly defined. To develop better small-animal models for understanding KSHV pathogenesis and immunity, we previously generated a chimeric virus in which the KSHV latency-associated nuclear antigen (kLANA), a conserved multifunctional protein critical for viral latency, was exchanged for the LANA homolog in murine gammaherpesvirus 68 (MHV68). Despite supporting comparable levels of latent infection between wild-type (WT) and KLKI MHV68, kLANA directly repressed MHV68 lytic replication and reactivation. We therefore hypothesized that suppression of lytic replication by kLANA dampens adaptive immune responses. To test this, mice were infected with equivalent doses of either WT or KLKI MHV68, and adaptive immune responses were evaluated over time. Compared to the WT virus, polyclonal B and T cell activation was starkly reduced following KLKI MHV68 infection, which correlated with reduced virus-specific humoral immunity and effector CD4⁺ and CD8⁺ T cell activation. Immune activation phenotypes were independent of the inoculating dose, as a high-dose infection with KLKI MHV68 still resulted in comparatively reduced adaptive immune activation. In contrast, infection of Ifnar1^-/- mice, which support enhanced KLKI MHV68 lytic replication, led to potent adaptive cellular and humoral immune activation by both WT and KLKI viruses, suggesting that a lytic replication threshold must be passed for viral antigen-driven adaptive immune engagement. Collectively, these data support the hypothesis that kLANA-mediated suppression of lytic replication limits polyclonal lymphocyte activation and facilitates adaptive immune evasion by holding viral replication below an antigenic activation threshold.IMPORTANCEKSHV is a gammaherpesvirus that establishes lifelong, chronic infections in humans and increases the risk of virus-associated cancers. Currently, there is little information on how primary KSHV infection influences adaptive immune development in healthy individuals. Rodent models, such as murine gammaherpesvirus 68 (MHV68), provide a valuable laboratory system for studying gammaherpesvirus pathogenesis in vivo. In this study, we report that infection with a previously characterized chimeric KSHV-MHV68 virus expressing KSHV LANA represses lytic viral replication and elicits weak adaptive immune responses following primary infection, despite efficient latency establishment. By enhancing KLKI MHV68 replication in vivo, we restore adaptive immune activation, providing evidence that a viral replication threshold must be eclipsed for potent adaptive immune engagement. We propose that KSHV, through LANA, evades detection by repressing lytic viral replication to remain "below the radar" of adaptive immune defenses during host colonization.