Project Summary An estimated 58 million people worldwide are infected with hepatitis C virus (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. Such efforts as funded by the parent proposal require a significant amount of protein production and the current equipment in use in support of protein production under this award is obsolete and no longer supported by the manufacturer. Moreover, the equipment has experienced several recent failures and diminished functionality. Therefore, the supplemental award will allow the team to maintain our current scientific momentum by ensuring the timely production of antigens for bioanalytical characterization, structural analysis, and immunological evaluation in animal models.