Statistical significance of neutralization was determined via one-way analysis of variance (ANOVA) with Bonferroni correction. We used a phage-display library isolated from an alpaca immunized with HCV E2 to identify four nanobodies specifically recognizing E2 (Supporting Fig. 1). The nanobodies were expressed in Escherichia coli and antigen specificity was demonstrated via pull-down and immunofluorescence assay (Supporting Fig. 2). All four nanobodies were assessed for their ability to inhibit HCVpp and HCVcc infection. Determination of autologous neutralization of Vadimezan concentration HCVpp bearing glycoproteins of the immunogen HCV isolate UKN2B2.8 revealed that D03 neutralized virus
infection in a dose-dependent manner (>95% at 20 μg mL), while C09 possessed some neutralizing activity, and B11 and D04 had no effect on HCVpp infectivity (Supporting Fig. 3D). Subsequent analysis using selleck screening library JFH-1 HCVcc revealed that D03 had the strongest neutralizing effect, whereas C09 had a minor inhibitory effect (Fig. 1A). B11 and D04 did not show any neutralizing activity. Taken together, these data demonstrate that D03 neutralizes the infectivity of HCVpp and HCVcc expressing glycoproteins of HCV genotype 2. To assess the breadth of neutralizing activity, all four nanobodies were screened at a single concentration for their inhibitory effect on entry of pseudoparticles bearing a well-characterized and
diverse panel of HCV glycoproteins
that exhibited different sensitivities to serum neutralizing antibodies.[23] Only D03 possessed significant cross-neutralizing activity; C09 only neutralized HCVpp pseudotyped with genotype 2 glycoproteins (Fig. 1A). A more detailed analysis of the cross-reactive neutralization profile of D03 using a panel of HCVpp representing all six major HCV genotypes revealed that D03 neutralized across all genotypes, exhibiting 上海皓元 50% inhibitory concentrations that ranged between 1 and 10 μg/mL for most isolates. Some isolates, such as UKN2A1.2 (genotype 2a) and UKN2B1.1 (genotype 2b), were more easily neutralized by D03 than by monoclonal antibody (mAb) 1:7 (used as positive control[24]). However, other strains such as UKN3A13.6 (genotype 3a) and UKN5.15.7 (genotype 5) were more refractory to neutralization by D03 and required significantly more nanobody to achieve 50% inhibition. These results indicated that the epitope recognized by D03 is conserved across genetically diverse isolates, but presentation of the epitope at the virion surface may differ between strains. To gain insight into the conformation of its potential antigen-binding determinants, we crystallized D03 and determined its crystal structure to 1.8 Å resolution; details and statistics of the data collection, processing, and refinement are given in Supporting Table 1. As expected, the nanobody displayed an immunoglobulin fold (Fig. 2A).