Antibodies to an Interfering Epitope in Hepatitis C Virus E2 Can Mask Vaccine-Induced Neutralizing Activity

Kachko, Alla; Frey, Sharon E.; Sirota, Lev; Ray, Ranjit; Wells, Frances; Zubkova, Iryna; Zhang, Pei; Major, Marian E.

Hepatitis C virus (HCV) neutralization occurring at the E2 region 412–426 (EP-I) could be enhanced when antibodies directed specifically to the E2 region 434–446 (EP-II) were removed from serum samples of persistently infected patients and vaccinated chimpanzees, a phenomenon of so-called antibody interference. Here we show that this type of interference can be observed in individuals after immunization with recombinant E1E2 proteins. One hundred and twelve blinded serum samples from a Phase I, placebo-controlled, dose escalation trial using recombinant HCV E1E2 with MF59C.1 adjuvant in healthy HCV-negative adults were tested in ELISA for binding reactivity to peptides representing the E2 regions 412–426 (EP-I) and 434–446 (EP-II). All samples were subsequently tested for neutralizing activity using HCVcc 1a(H77)/2a chimera, HCVpp H77 and HCVpp HCV-1 after treatment to remove EP-II-specific antibodies or mock treatment with a control peptide. Among the 112 serum samples we found 22 double positive (EP-I and EP-II), 6 EP-II positive only, 14 EP-I positive only and 70 double negative. Depleting EP-II antibodies from double positive serum samples increased ID(50) neutralizing antibody titers (up to 4.9-fold) in up to 72% of samples (p≤0.0005) contrasting with ID(50) neutralization titer increases in 2 of 70 double negative samples (2.9%) (p>0.5). In addition, EP-I-specific antibody levels in serum samples showed a significant correlation with ID(50) neutralization titers when EP-II antibodies were removed (p<0.0003). CONCLUSION: These data show that antibodies to the region 434–446 are induced during immunization of individuals with recombinant E1E2 proteins and that these antibodies can mask effective neutralizing activity from EP-I-specific antibodies. Elicitation of EP-II-specific antibodies with interfering capacity should be avoided in producing an effective cross-neutralizing vaccine aimed at the HCV envelope proteins.