Development of germline-targeting HCV E2 immunogens to drive neutralizing antibody evolution

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Chronic infection by the hepatitis C virus (HCV) is associated with severe liver disease including hepatocellular carcinoma and it has become one of the leading causes for liver transplantation. Recently licensed antiviral combination therapies reach cure rates greater than 95%. However, treatment is costly and does not protect from viral re-infection. Moreover, many patients are not diagnosed and unaware of their infection, and virus transmission remains high. Therefore, the development of a prophylactic HCV vaccine is an unmet medical need. Accumulating evidence underpins the importance of neutralizing antibodies for the clearance of HCV during natural infection. Notably, 20-30% of exposed individuals naturally clear the infection and neutralizing antibodies can be triggered by immunization, raising hopes that a prophylactic HCV vaccine can be developed. However, the induced antibody responses in serum are usually modest with regard to breadth and potency, although broadly neutralizing monoclonal human and murine antibodies (bnAbs) with high potency have been identified. Such bnAbs develop from the so-called inferred germline B cell receptor (iGL BCR) via somatic hypermutation of the antigen-binding regions in a long process that requires clonal selection and affinity maturation for an optimized fine-tuning of the antibody-antigen interaction. Sequence analysis of numerous bnAbs targeting HCV glycoproteins revealed that few somatic mutations are required for affinity maturation, indicating that the usage of so-called germline-targeting immunogens, i.e., engineered immunogens targeting a specific iGL BCR, could potentiate the induction of bnAbs. The goal of this project is therefore to provide the proof-of-concept that usage of such engineered germline-targeting immunogens results in an enhanced development of the respective bnAb and potentially an increased neutralization capacity of serum. We will develop recombinant HCV glycoproteins into germline-targeting immunogens that bind to iGL BCR with higher affinity and therefore have a higher capacity to stimulate the corresponding B cells. For this purpose we will use in parallel 1) a structure-based protein engineering strategy and 2) a library-based surface display strategy. We will investigate the immunogenicity of the resulting immunogens in a recently developed transgenic humanized mouse model that produces human antibodies (Erlanger mighty mouse antibody platform; EMMA). These mice will allow us to follow antibody maturation by single cell B cell sequencing and therefore assess the impact of individual immunogens on the development of bnAbs.Our results will contribute to a better understanding of the interplay between HCV and the human immune system as well as the manipulability of the latter by targeted stimulation of certain B cell populations. They will therefore pave the way for the development of a novel prophylactic and therapeutic vaccine to combat HCV infection.