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This dissertation, Distinct vaccine-induced antibody responses and bispecific neutralizing immunoadhesins against SIV/HIV infection by Jia, Guo, 郭佳, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Our research laboratory has recently reported that mucosal priming with a replicating modified vaccinia Tiantan virus (MVTTgpe)-based vaccine elicits durable protection against pathogenic SIVmac239 infection in rhesus monkeys. However, the protective role of vaccine-elicited antibody responses remains poorly understood. Here, a novel yeast surface displayed (YSD) antigen library was established to quantitatively map the antigenic determinants presented by MVTTgpe-based and control vaccines as well as by SIVmac239 infection. The YSD-library allows the mapping of linear and some conformational epitopes as a major technical innovation, as validated by testing SIV-specific mAbs KK65, KK8 and VM-18S. While eight antigenic domains are characterized covering the entire SIVmac239 gp160, the MVTTgpe/Ad5gpe regimen uniquely induces antibody responses against a distinct major antigenic determinant (MAD) in V2 region as compared with the Ad5gpe/Ad5gpe vaccination and SIV infection. This MAD is associated with a higher titer of anti-V2 antibody responses, which inversely correlates with peak viral load. Unexpectedly, the MVTTgpe/Ad5gpe vaccine- challenge. The results showed that instead of recalling B cell memory response to V2, viral infection presents a distinct set of antigenic determinants with anti-V1V2 antibodies primarily directed to V1 region. Moreover, the anti-V1V2 antibody responses disappear in two infected macaques after they enter the stage of simian AIDS. SIVmac239 infection, therefore, can modulate vaccine-elicited B cell immunity by diminishing anti-V2 antibody memory responses in rhesus monkeys. These findings implicated that vaccine efforts with focus on V2 region would require periodic vaccinations to maintain a long-lasting high level of antibody responses for protection. In the absence of an effective vaccine for eliciting HIV-1-specific broadly neutralizing antibodies (bNAbs), passive immunization with bNAbs or Ab-like agents (e.g. immunoadhesin) becomes an attractive alternative for HIV-1 prevention. In this study, we aimed to design, optimize and produce secretory immunoadhesins (IAs) based on gene engineering of existing HIV-1 specific bNAbs for potency and production improvements. IAs are chimeric, antibody-like molecules that combine the functional domain of bNAb with immunoglobulin constant domains, including the hinge and Fc regions. We found that the modified secretory IAs not only preserved the neutralization activity of the parental bNAbs, but also had enhanced expression and smaller molecular size that is suitable for antibody gene-based in vivo delivery. Furthermore, we defined the synergistic effects of five IAs against HIV-1 infection and subsequently engineered two types of bi-specific IAs by combining the functional domains of Hu5A8, a humanized anti-CD4 antibody, and the bNAb PGT128. Significantly, one of the bi-specific IA, namely Bi-IA-Mono, neutralized 100% of the 33 viruses tested, including the transmitted/founder viruses and viruses resistant to both parental IAs. The remarkably enhanced neutralization activity of Bi-IA-Mono, either in potency and breadth, indicated the great potential of modified bi-specific IA to provide complete or nearly complete protection against major HIV-1 subtypes. Overall, our results demonstrated that the engineering of IA and bi-specific IA is an attractive way to improve anti-HIV-1 properties

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