SUMMARY The overall goals of this U01 application are two-fold. First, to investigate two potential KSHV targets, one structural and one non-structural, to determine if these two targets are capable of protecting vaccinated animals from infection. And, the second, to compare two vaccine strategies to stimulate immune responses to the KSHV antigens. The first approach utilizes mRNA-lipid nanoparticles (mRNA-LNPs) vaccines, the widely used vaccine strategy that has proven capable of inducing protective immunity against SARS-CoV2. The second approach employs a novel vaccine strategy that targets CD180, a toll-like receptor (TLR) expressed on antigen presenting cells (APCs) that can stimulate robust immune responses to conjugated antigens, even in the context of immune suppression. To accomplish these goals, we will utilize the rhesus macaque rhadinovirus (RRV)/rhesus macaque (RM) model of KSHV-like infection to evaluate the KSHV targets and compare the immune responses induced by the mRNA-LNPs and targeted CD180 vaccine platform. The innovation and strengths of this application are several and include the collaboration formed amongst the principal investigator, and co-investigators from the biotechnology sector (Abacus Bioscience), whose company's focus is on a novel targeted CD180 vaccine platform (anti-CD180) capable of inducing robust immune responses to conjugated antigens in rodents and nonhuman primates (NHPs), and academic co-investigator, whose expertise is on the characterization of primate antibody-mediated function. Importantly, data presented in the preliminary studies section supports this application as 1) CD180 is expressed on multiple B cell lineages, dendritic cells and monocytes, similar to that shown in humans. 2) fusion of an antigen to agonist anti-CD180 antibody (aCD180) provides the simultaneous antigen delivery and activation of the APC, resulting in a potent antigen-specific IgG production and expansion of activated antigen-specific T cells in immunocompetent and immune suppressed animals. 3) we have successfully expressed two recombinant aCD180-KSHV antigen complexes (aCD180-K8.1 ectodomain and aCD180-KSHV vIL6) to evaluate in vitro and in vivo. 4) we have established an oral challenge model for RRV infection, that results in virus infection. 5) we have created the necessary chimeric KSHV/RRV recombinants pseudotyped with KSHV glycoprotein K8.1 or a recombinant RRV encoding KSHV vIL-6 in place of RRV vIL-6. These chimeric RRV recombinants can infect and establish latent infections in RM, identical to wild-type RRV. Thus, the overall goals are to compare state-of-the-art mRNA-LNPs to the novel anti-CD180 platform to stimulate an anti-K8.1 and anti-vIL6 immune responses in immune competent and SIV-infected RM prior to oral RRV challenge/infection. The overall hypothesis is immunization targeting KSHV proteins will develop cell and humoral immune responses against viral antigens. This direct head-to-head comparison serves as a...