Project Summary
An estimated 71 million people worldwide are infected with HCV and are at heightened risk for severe liver
disease, including fibrosis, cirrhosis, and hepatocellular carcinoma. Although effective directly-acting antiviral
treatment is available, only an HCV vaccine will help prevent infection, associated pathologies, and effectively
reduce global disease burden. Cumulative evidence has shown that both B and T cell immunity contribute to the
control of acute HCV infection. A major challenge is the high variability across the genome especially in the
envelope E1E2 glycoproteins, the natural target of protective antibodies. An E1E2-based immunogen will need
to elicit broadly neutralizing antibodies (bnAbs) to multiple epitopes to overcome the high antigenic diversity of
HCV isolates and be of sufficient titers to achieve protective immunity. Our approach is supported by our recent
data that a secreted form of E1E2 (sE1E2) maintains its native-like properties and can elicit broader neutralizing
antibody responses than the membrane-bound form of E1E2 and secreted E2. Also, we have shown that
presentation of sE1E2 as multivalent virus-mimicking polymer assemblies (VMPAs) that include HCV core
protein can elicit cellular immune responses to sE1E2 and core antigens with potential immunopotentiating
activity for B and T cell responses. Accordingly, our central hypothesis is that rational structure-guided design of
E1E2 and co-formulation with conserved HCV T cell antigens as a VMPA vaccine will lead to optimal presentation
of conserved bnAb epitopes and elicit long-lasting B and T cell mediated immunity. Towards this end, we propose
the following Specific Aims: Aim 1, Rational E1E2 antigen design. We will advance our structure-guided E1E2
design to increase the immunogenicity of bnAb epitopes, and stabilize the native-like sE1E2 complex using
synthetic scaffolds. Aim 2, Structural characterization of HCV envelope complexes. We will structurally
characterize the E1E2 heterodimer complexed with key bnAbs, and new structures will be used for further E1E2
optimization. Aim 3, Formulation and characterization of virus-mimicking polymer assemblies. We plan to further
develop supramolecular assemblies of E1E2 for multimeric presentation of E1E2 and T cell antigens. Aim 4,
Immunological evaluation of B and T cell responses in animal models. Immunological assessment of our vaccine
candidates will be performed in mice, guinea pigs, and macaques. These studies will include an examination of
the specificity of neutralizing antibody responses as well as systemic and tissue resident memory T cells. Aim 5,
Vaccine efficacy in challenge model systems. Protection studies will utilize the only two available challenge
models. The first, an immunocompetent humanized mouse model to test the protective efficacy of our lead
vaccine candidates. The second, a human-mouse liver chimeric model that can be infected with antigenically
diverse clinical HCV isolates to demonstrate serum antibodies from vaccinated macaques passively transferred
to the chimeric mice will be protective. The overall program will lead to a rationally designed vaccine candidate
to induce broadly neutralizing antibodies and long-term memory T cell responses to prevent HCV infection.