Vaccine Design

Gustaf Ahlén, Lars Frelin

Sunil Thomas

The hepatitis C virus (HCV) is a major cause of severe liver disease worldwide. It is estimated that around 130-170 million individuals are chronic carriers of the infection and they are over time at an increased risk of developing severe liver disease. HCV is often referred to as a silent epidemic because the majority of infected individuals do not develop any symptoms. Hence, many individuals are diagnosed at a late stage and thus in need of immediate treatment. Today we have very effective direct-acting antivirals (DAAs), which cure more than 90-95 % of all treated patients. However, this treatment is associated with high-costs and the use is limited to the patients with most advanced liver disease in high-income countries. Notably, a majority of the chronic HCV carriers live in resource-poor countries and do not have access to the new effective DAAs. We therefore need to develop alternative treatments for chronic HCV infection such as therapeutic vaccines. The idea with therapeutic vaccines is to reactivate the infected patient's own immune system. It is well known that patients with chronic HCV infection have dysfunctional immune responses to the virus. Hence, the vaccine should activate HCV-specific T cells that will home to the liver and eradicate the HCV infected hepatocytes. Importantly, one should also consider the combination of a therapeutic vaccine and DAAs as a treatment strategy to equip the resolving patients with post-cure HCV-specific immune responses. This would provide patients with a better protection against reinfection. Numerous genetic vaccine candidates for HCV have been developed and tested in clinical trials with limited effects on viral load and in general inefficient activation of HCV-specific immune responses. In this chapter we describe the rational of developing highly immunogenic vaccines for HCV. Different strategies to improve vaccine immunogenicity and methods to evaluate vaccine efficacy are described. Detailed description of vaccine delivery by intramuscular immunization in combination with in vivo electroporation/electrotransfer (EP/ET) is covered, as well as immunological analysis of primed immune responses by determination of interferon-γ (IFN-γ) production by ELISpot assay and direct ex vivo quantification of HCV NS3/4A-specific CD8+ T cells by pentamer staining. To analyze the in vivo functionality of primed NS3/4A-specific T cells we utilized the in vivo bioluminescence imaging technology. In conclusion, this chapter describes a method to design HCV vaccines and also a protocol to assess their efficacy.