Immune Evasion Mechanisms of KSHV Complement and Fc-Receptor Proteins

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PROJECT ABSTRACT Kaposi sarcoma-associated herpesvirus (KSHV) is the causal agent of Kaposi sarcoma, a cancer that appears as tumors on the skin or mucosal surfaces, and two types of B-cell lymphomas, multicentric Castleman disease and primary effusion lymphoma. As there are no vaccines or therapeutic treatments to successfully prevent or eradicate KSHV, in part due to its ability to evade its host’s immune defenses, it remains a significant public health burden. Although B-cell lymphomas are rare, more than 44,000 new cases of Kaposi sarcoma are reported globally each year. Thus, there is a critical need to elucidate the mechanisms by which KSHV escapes the human immune system. Herpesviruses, including KSHV, co-evolved with their hosts over millions of years, hijacking host regulatory factors to camouflage themselves and evade a wide range of host defense measures. Notably, like other herpesviruses, KSHV has acquired a complement control protein (KCP) found to modulate the host complement-mediated immune defense. Unfortunately, studies of KCP in a biologically relevant setting have been hindered by the absence of a system to produce KCP-null KSHV and test the effects of KCP– complement interactions on virus-infected cells. To address these deficiencies, we generated recombinant KSHV (rKSHV) lacking KCP (rKSHVΔKCP) using newly established KSHV bacterial artificial chromosome (BAC) technology, as well as novel anti-KCP antibodies to characterize the mutant virus. During the mentored (K99) phase, I will use these resources to characterize the role of KCP in evading complement control and infection. In addition to KCP, KSHV encodes a glycoprotein, K1, that has acquired immunoglobulin structure domains with fragment crystallizable receptor (FcR) functions. Similar domains in other herpesviruses have been shown to act as distractor receptors for host antiviral antibodies that typically bind FcRs present on immune cells; however, the role of K1 in Fc-mediated immune evasion by KSHV has not been examined. Therefore, toward the end of the K99 phase, I propose to generate and characterize anti-K1 antibodies and characterize our recently generated stable rKSHVΔK1 producer cell lines. These resources will be utilized in the independent (R00) phase to characterize the Fc-type interactions and binding capabilities of K1. I will also study the mechanism by which K1 interferes with host FcR activation using a novel reporter assay. Finally, I will evaluate the efficacy of anti-K1 antibodies in blocking Fc-mediated immune evasion. Thus, the studies proposed herein will provide a better understanding of the role of KCP and K1 in host immune evasion. This work will greatly enhance the development of effective strategies to prevent and control KSHV infection and pathogenesis. Furthermore, the research and training proposed for the K99 phase will provide experience and knowledge in viral genomics/proteomics, immunobiology, and viral oncology, as well as a significant body of publishable data and preliminary data for many future studies, which will provide a solid foundation upon which to build my independent research career.