Naturally Occurring Antibodies That Recognize Linear Epitopes in the Amino Terminus of the Hepatitis C Virus E2 Protein Confer Noninterfering, Additive Neutralization

Abstract

Chronic hepatitis C virus (HCV) infection can persist even in the presence of a broadly neutralizing antibody response. Various mechanisms that underpin viral persistence have been proposed, and one of the most recently proposed mechanisms is the presence of interfering antibodies that negate neutralizing responses. Specifically, it has been proposed that antibodies targeting broadly neutralizing epitopes located within a region of E2 encompassing residues 412 to 423 can be inhibited by nonneutralizing antibodies binding to a less conserved region encompassing residues 434 to 446. To investigate this phenomenon, we characterized the neutralizing and inhibitory effects of human-derived affinity-purified immunoglobulin fractions and murine monoclonal antibodies and show that antibodies to both regions neutralize HCV pseudoparticle (HCVpp) and cell culture-infectious virus (HCVcc) infection albeit with different breadths and potencies. Epitope mapping revealed the presence of overlapping but distinct epitopes in both regions, which may explain the observed differences in neutralizing phenotypes. Crucially, we failed to demonstrate any inhibition between these two groups of antibodies, suggesting that interference by nonneutralizing antibodies, at least for the region encompassing residues 434 to 446, does not provide a mechanism for HCV persistence in chronically infected individuals. H epatitis C virus (HCV) has infected approximately 180 million people worldwide (2). Following infection, most people fail to clear the virus, and a chronic infection, often with serious sequelae, ensues (1, 38). HCV-related end-stage liver disease is the leading indication for liver transplantation, and reinfection of the grafted liver occurs rapidly (32). A systematic review of the research literature recently suggested that there is little, if any, benefit gained by the treatment of liver transplant recipients with standard antiviral regimens (24), and possible adverse effects associated with newly emerging direct-acting antivirals may limit their usefulness in this clinical setting. Antibodies are usually well tolerated, and the successful administration of anti-hepatitis B virus immunoglobulin (Ig) (HBIG) (50, 59) sets an important precedent for HCV. The administration of HCV-neutralizing antibodies during the anhepatic phase and following transplantation could likewise prevent the reinfection of the grafted liver; the reduced incidence of HCV in individuals receiving HBIG containing anti-HCV antibodies (20) supports this notion. However, to date, the therapeutic administration of serum immunoglobulin or monoclonal antibodies targeting HCV has been disappointing (10, 51), indicating that further studies of the polyclonal response are needed, if we are to harness the opportunity that antibody therapy offers.There is also an urgent need for the development of safe and effective HCV vaccines to prevent infection. Significant progress has been made toward T-cell-based vaccines (22), but these vaccines will not be sufficient to elici...

Cooperativity in Virus Neutralization by Human Monoclonal Antibodies to Two Adjacent Regions Located at the Amino Terminus of Hepatitis C Virus E2 Glycoprotein

“…The low frequency of responses to aa 412 to 423 was also observed on a population basis, in which 13 of 88 (15%) serum samples from seropositive blood donors were identified in our studies. This percentage is higher than previously reported percentages of 2 to 3% (29,50), likely because of differences in the populations of HCV-infected individuals and their stages of HCV infection. Earlier studies were of individuals infected with HCV of diverse genotypes (29,50), while our study was mostly of individuals infected with HCV of genotypes 1 and 2 (55).…”

“…Serum samples from HCV-infected blood donors were tested for reactivity to a synthetic peptide composed of a genotype 1a H77C sequence, aa 410 to 425, to identify individuals having antibodies against aa 412 to 423 on the HCV E2. Thirteen of 88 (15%) serum samples reacted to this peptide as measured by ELISA, which is a percentage that was significantly higher than those previously reported (2 to 3%) (29,50). The peripheral B cells from a donor infected with HCV genotype 2b who had a high serum antibody binding titer to aa 410 to 425 and Ͼ1:10,000 neutralizing titer against genotype 2a JFH1 HCVcc were employed to construct a yeast display scFv antibody library, as described previously (33).…”

“…The structural presentation of aa 412 to 423 could be influenced by other regions of the E2 glycoprotein in spite of sequence conservation. Other studies employing human polyclonal antibodies to aa 412 to 423 have revealed variable reactivity between genotypes 1a and 2a in HCVcc isolates (29).…”

“…More importantly, the presence of epitope II-specific antibodies interfered with the neutralization activity of epitope Ispecific antibodies. However, conflicting studies that employed similar approaches of isolating polyclonal antibodies to synthetic peptides encompassing aa 412 to 423 and aa 434 to 446 also have been reported (29). Eluted polyclonal antibodies from both peptides neutralized HCV, and when combined, they showed additive neutralizing activities.…”

Structural Basis for Penetration of the Glycan Shield of Hepatitis C Virus E2 Glycoprotein by a Broadly Neutralizing Human Antibody

“…Antigenic domain E is composed of overlapping linear epitopes located within amino acids 412-423 (QLINTNG-SWHIN) of E2 (E2 412-423 ) (20,21). This region is involved in HCV binding to the CD81 entry receptor (22,23), which likely explains why it is so highly conserved among Ͼ5,500 E2 sequences in the GenBank TM database.…”