Isolation of heavy chain only antibodies to support design of HCV vaccine

Hepatitis C virus (HCV) is a serious and growing public health problem despite recent developments in antiviral therapeutics. An effective cross-genotype vaccine is needed to achieve the global elimination of HCV. HCV E2 envelope (Env) glycoprotein is the main target for neutralizing antibodies (nAbs), aiding HCV clearance and protection. A molecular-level understanding of Ab neutralization responses against HCV is imperative for the rational design of cross-genotype vaccine antigens.

The failure of B cell-based vaccination trials to prime a broad immune response highlighted that further optimization of the current vaccine candidates or the development of alternative vaccination approaches is urgently needed to control the spread of HCV. To this aim, we selected an alternative approach using HCV-specific heavy chain only antibodies (HCAbs) to discover and characterize novel HCV Env neutralization epitopes. We immunized Llamas with E2 antigens and isolated a library of E2-specific HCAbs. The HCAbs were engineered to recombinant single-domain antigen-specific nanobodies (Nbs). Following this, we expressed and purified 53 Nbs, 24 of which succeeded in binding with a high affinity to E2 antigens. Some of the Nbs were able to bind to E1E2 antigens from different HCV isolates. Indeed, most of the subsequent Nbs were able to block the binding of E2 to the host cell receptor CD81, suggesting the capability of the Nbs to inhibit viral entry to the host cells. Our results will be used to advance the understanding of the neutralization response against HCV and promote the rational design of the HCV vaccine.