Hypervariable region diversity of hepatitis C virus and humoral response: comparison between patients with or without cirrhosis

Broadly cross-reactive mimotope of hypervariable region 1 of hepatitis C virus derived from DNA shuffling and screened by phage display library

The hypervariable region 1 (HVR1) is the target of neutralizing antibodies but with isolate specificity. The aim of this study was to obtain immunogenic mimotopes of HVR1, which can react broadly with different HVR1 antibodies and could be one of the candidate immunogens in an effective vaccine against HCV. Thirty-one HVR1 cDNA fragments were digested by DNase I into a pool of random fragments and reassembled by repeated cycles of annealing in the presence of DNA polymerase to their original size. The shuffled HVR1 was then inserted into the gene III phagemid vector pCANTAB-5E and displayed on the surface of the phage. Eight individual phages were selected after four rounds of biopanning against anti-HVR1. ELISA was carried out on immobilized purified phages, respectively, to detect their reactivity with a panel of sera. DNA sequences of the inserts were analyzed and compared with the consensus sequences defined by Puntoriero et al. [(1998) EMBO J 17:3521-3533]. The reactivity of the eight selected clones to the 30 sera were from 53.3 to 80%. Among these, phage 13 (ETYVSGGSAARNAYGLTSLFTVGPAQK, aa 384-410) reacted most broadly. None of the selected sequences encoded for peptides corresponded to known HVR1 from original viral isolates. The two high reactive phages had the similar amino acid sequences with the consensus, which might play a particular role in determining the frequency of reactivity. In conclusion, this study has used effectively DNA shuffling combined with phage display technology to identify broadly cross-reactive mimotopes recognized by human polyclonal antibodies. Mimotope 13 and 23 appeared to be most reactive immunologically and could be candidate immunogens. Efforts are now underway to identify their neutralizing antibodies by immunization of animals.

Production and characterization of monoclonal antibodies specific for a conserved epitope within hepatitis C virus hypervariable region 1

Frequent mutations in hypervariable region 1 (HVR1) of the main envelope protein of hepatitis C virus (HCV) is a major mechanism of persistence by escaping the host immune recognition. HVR1 contains an epitope eliciting neutralizing antibodies. This study was aimed to prepare broadly cross-reacting, high-affinity, monoclonal antibodies (MAb) to the HVR1 C terminus of HCV with potential therapeutic neutralizing capacity. A conserved amino residue group of glycine (G) at position 23 and glutamic acid (Q) at position 26 in HVR1 was confirmed as a key epitope against which two MAbs were selected and characterized. MAbs 2P24 and 15H4 were immunoglobulin G1 kappa chain [IgG1(kappa)], cross-reacted with 32 and 30 of 39 random C-terminal HVR1 peptides, respectively, and did not react with other HCV peptides. The V(H) of 2P24 and 15H4 heavy chains originated from Igh germ line v gene family 1 and 8, respectively. In contrast, the V(L) kappa sequences were highly homologous. The affinity (K(d)) of 2P24 and 15H4 (10(-9) or 10(-8) M with two immunizing peptides and 10(-8) M with two nonimmunizing HVR1 peptides) paralleled the reactivity obtained with peptide enzyme immunoassay. MAbs 2P24 and 15H4 captured 25 of 31 (81%) HCV in unselected patients' plasmas. These antibodies also blocked HCV binding to Molt-4 cells in a dose-dependent fashion. The data presented suggest that broadly cross-reactive MAbs to a conserved epitope within HCV HVR1 can be produced. Clinical application for passive immunization in HCV-related chronic liver disease and after liver transplantation is considered.

Evolutionary rate and genetic drift of hepatitis C virus are not correlated with the host immune response: studies of infected donor-recipient clusters

Six donor-recipient clusters of hepatitis C virus (HCV)-infected individuals were studied. For five clusters the period of infection of the donor could be estimated, and for all six clusters the time of infection of the recipients from the donor via blood transfusion was also precisely known. Detailed phylogenetic analyses were carried out to investigate the genomic evolution of the viral quasispecies within infected individuals in each cluster. The molecular clock analysis showed that HCV quasispecies within a patient are evolving at the same rate and that donors that have been infected for longer time tend to have a lower evolutionary rate. Phylogenetic analysis based on the split decomposition method revealed different evolutionary patterns in different donor-recipient clusters. Reactivity of antibody against the first hypervariable region (HVR1) of HCV in donor and recipient sera was evaluated and correlated to the calculated evolutionary rate. Results indicate that anti-HVR1 reactivity was related more to the overall level of humoral immune response of the host than to the HVR1 sequence itself, suggesting that the particular sequence of the HVR1 peptides is not the determinant of reactivity. Moreover, no correlation was found between the evolutionary rate or the heterogeneity of the viral quasispecies in the patients and the strength of the immune response to HVR1 epitopes. Rather, the results seem to imply that genetic drift is less dependent on immune pressure than on the rate of evolution and that the genetic drift of HCV is independent of the host immune pressure.