Adenovirus-vectored T cell vaccine for hepacivirus shows reduced effectiveness against a CD8 T cell escape variant in rats

Protection of Novel Adenovirus Vectored Vaccine in Rats Against Wild-Type Hepacivirus and Variant Infections

BACKGROUND AND AIMS

Hepatitis C virus (HCV) vaccines are urgently needed to achieve WHO's goal for the elimination of viral hepatitis by 2030. The lack of suitable animal models for evaluating vaccine efficacy has greatly hindered the development of HCV vaccines. By using the rat model chronically infected with rodent hepacivirus from Rattus norvegicus (RHV-rn1), a hepacivirus homologously close to HCV as a surrogate model of HCV infection, we assessed the protective effectiveness of the RHV-rn1 vaccine Sad23L-RHVns.

METHODS

Sad23L-RHVns vaccine was constructed with the nonstructural proteins (NS) 3-5B genes of RHV-rn1. SD rats were immunised with Sad23L-RHVns by prime or prime-boost regimen via intramuscular injection, then challenged 4 weeks post vaccination by RHV-rn1. A part of the rats were rechallenged with a variant 15 weeks post the first challenge of RHV-rn1.

RESULTS

The specific T-cell responses to NS3-5B antigens were induced by prime immunisation, which were significantly enhanced by boost vaccination. The inoculated rats and controls were challenged by wild-type RHV-rn1, of all the primed and control rats having persistently high levels of viremia, whereas 7 of 9 (77.8%) boosted rats cleared RHV-rn1 infection. Interestingly, the resolver acquired immune protection against re-challenging with variant and showed significantly higher T-cell responses than the nonresolver in 25 weeks post rechallenge.

CONCLUSIONS

Sad23L-RHVns with prime-boost regimen protected 77.8% of rats against wild-type RHV-rn1 infection, and resolvers showed high levels and maintenance of T cell immunity against the variant. Our findings that maintenance of effective T cell immunity is required for RHV-rn1 resolution may provide insight to develop the HCV vaccine in humans.

Developing T Cell Epitope-Based Vaccines Against Infection: Challenging but Worthwhile

T cell epitope-based vaccines are designed to elicit long-lived pathogen-specific memory T cells that can quickly activate protective effector functions in response to subsequent infections. These vaccines have the potential to provide sustained protection against mutated variants, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which are increasingly capable of evading neutralizing antibodies. Recent advancements in epitope discovery, T cell receptor analysis, and bioinformatics have enabled the precise selection of epitopes and the sophisticated design of epitope-based vaccines. This review outlines the development process for T cell epitope-based vaccines. We summarize the current progress in T cell epitope discovery technologies, highlighting the advantages and disadvantages of each method. We also examine advancements in the design and optimization of epitope-based vaccines, particularly through bioinformatics tools. Additionally, we discuss the challenges of validating the accurate processing and presentation of individual epitopes and establishing suitable rodent models to evaluate vaccine immunogenicity and protective efficacy.

Phenotype and fate of liver-resident CD8 T cells during acute and chronic hepacivirus infection

Immune correlates of hepatitis C virus (HCV) clearance and control remain poorly defined due to the lack of an informative animal model. We recently described acute and chronic rodent HCV-like virus (RHV) infections in lab mice. Here, we developed MHC class I and class II tetramers to characterize the serial changes in RHV-specific CD8 and CD4 T cells during acute and chronic infection in C57BL/6J mice. RHV infection induced rapid expansion of T cells targeting viral structural and nonstructural proteins. After virus clearance, the virus-specific T cells transitioned from effectors to long-lived liver-resident memory T cells (TRM). The effector and memory CD8 and CD4 T cells primarily produced Th1 cytokines, IFN-γ, TNF-α, and IL-2, upon ex vivo antigen stimulation, and their phenotype and transcriptome differed significantly between the liver and spleen. Rapid clearance of RHV reinfection coincided with the proliferation of virus-specific CD8 TRM cells in the liver. Chronic RHV infection was associated with the exhaustion of CD8 T cells (Tex) and the development of severe liver diseases. Interestingly, the virus-specific CD8 Tex cells continued proliferation in the liver despite the persistent high-titer viremia and retained partial antiviral functions, as evident from their ability to degranulate and produce IFN-γ upon ex vivo antigen stimulation. Thus, RHV infection in mice provides a unique model to study the function and fate of liver-resident T cells during acute and chronic hepatotropic infection.

Mutational escape from cellular immunity in viral hepatitis: variations on a theme

Approx. 320 million individuals worldwide are chronically infected with hepatitis viruses, contributing to viral hepatitis being one of the 10 leading causes of death. Cellular adaptive immunity, namely CD4+ and CD8+ T cells, plays an important role in viral clearance and control. Two main mechanisms, however, may lead to failure of the virus-specific T-cell response: T-cell exhaustion and mutational viral escape. Viral escape has been studied in detail in hepatitis C virus (HCV) infection, where it is thought to affect approx. 50% of virus-specific CD8+ T-cell responses in persistent infection, to influence natural infection outcome and to contribute to failure of preventive vaccination strategies. In hepatitis B virus (HBV) as well as HBV/hepatitis D virus (HDV) co-infection, the impact of viral escape has been studied in detail only recently.