Assessment of neutralizing activity of anti-hepatitis B surface antibodies from vaccinees and hepatitis B immunoglobulin preparation against various hepatitis B virus strains

Abstract

Hepatitis B (HB) vaccine is highly effective in preventing hepatitis B virus (HBV) infections, in particular mother-to-child transmission of HBV (MTCT). Nevertheless, perinatal HBV infections still occur despite adequate passive and/or active immunization of newborns. A hypothesis to explain this residual transmission is that anti-hepatitis B surface (anti-HBs) antibodies produced after vaccination or in hepatitis B immunoglobulin (HBIG) have insufficient and/or inefficient neutralizing activity. That neutralization activity cannot be measured with the ELISA tests that are commonly used to measure anti-HBs antibodies levels. An anti-HBs antibodies level of ≥10 mIU/mL is usually considered as conferring protective immunity against HBV infection; however, this antibody level does not provide information on the level or extent of neutralizing activity. Therefore, this study aimed 1) to assess the relationship between the titer of anti-HBs antibodies expressed in mIU/mL in vaccinees and in HBIG preparations, and their neutralizing activity using an in vitro infection model, 2) to investigate the breadth of neutralizing activity of anti-HBs antibodies with regard to HBV diversity and emerging variants. Samples used in this study were collected from 4 sources: i) individuals who received a plasma-derived HB vaccine, ii) who received recombinant vaccines, iii) who recovered from natural HBV infection, and iv) HBIG preparation. Anti-HBs antibody titers were measured using a commercial ELISA kit (Monolisa™ Anti-HBs PLUS, Bio-Rad, France) and results were expressed as mIU/mL. Neutralizing activity was determined using the hepatitis delta virus (HDV) in vitro infection assay as a practical surrogate to an HBV infection assay. HDV were constructed to express HBsAg of various genotypes/subtypes or immune escape variants. The neutralization activity was expressed as IC50 in μg of IgG/ml. Correlation between anti-HBs levels and neutralizing activity was analyzed using Spearman's rank correlation coefficient. Median neutralizing activity of anti-HBs antibodies against a variety of surface antigen of HBV (HBsAg) was compared using Mann-Whitney U test. The titer of anti-HBs antibodies elicited by plasma-derived vaccine showed the strongest correlation with neutralizing activity at r = 0.849 while antibodies elicited by recombinant vaccines and after recovery from infection showed a lower correlation at r = 0.785 and r = 0.447, respectively. Furthermore, antibodies obtained from the recovered group neutralized more significantly HBV serotype ayw, rather than serotype adw (p < 0.01). A significant reduction of neutralizing activity against immune escape HBV variants (D144A and G145R), as compared to wild type strain, was observed in all groups. This study would imply that, beside antibody titer measurement, functionality of these anti-HBs antibodies should be assessed especially with regard to HBV diversity. This information will contribute in the development of therapeutic and to the optimization of immunoprophylaxis strategies for prevention of HBV infection.