Three assays, one based on monoclonal antibodies and the
The dominant neutralizing epitopes of hepatitis B virus (HBV) are contained within the envelope proteins; hepatitis others on polyclonal antibodies, were employed to detect hepatitis B surface antigen (HBsAg)-reactive samples in both B surface antigen (HBsAg), the smallest of these proteins, is used in the current vaccine. The dominant epitope cluster vaccinated and unvaccinated populations in areas of the world where hepatitis B virus (HBV) is endemic. Any discordant in HBsAg is within the major hydrophilic region (MHR) and is termed the a determinant. It is widely regarded as being sera were tested by polymerase chain reaction (PCR) to confirm current infection, and sequence data were obtained from between amino acids 124 and 147 (Fig. 1); the evidence for this is based largely on peptide studies. 1,2 Most antibody to the DNA coding for the major hydrophilic region (MHR) of HBsAg of those samples positive for PCR. In all countries HBsAg (anti-HBs) in sera from vaccinees binds to amino acids 139-147. 3 The number of individual epitopes that are studied, samples that reacted in one HBsAg assay but not another were found. In the most extreme case, about 5% of neutralizing is unknown because of the lack of an animal model. Variation in this 9-amino acid region can affect bind-viremic sera in Papua New Guinea were nonreactive in the monoclonal HBsAg assay; 9 of the 13 PCR-positive samples ing of antibodies to other sites of HBsAg, namely around amino acid 122 4,5 and also variation at amino acid 120 5 or had novel or once-described variants, or a variant out of its usual genotype context. In South Africa, samples with se-insertions between amino acids 121 and 124 can affect binding to the area between amino acids 139-147. [6][7][8] Thus, the a quences of subtype ayw2 reacted poorly, particularly in the polyclonal assay. Two had novel variants. In Sardinia, anti-determinant is a conformational cluster of epitopes that extends at least to amino acid 120. Antibodies to this region body to hepatitis B core antigen (anti-HBc) was analyzed as a marker of infection. A significant proportion of anti-HBc-are used in diagnostic assays for HBsAg detection.
Commercial HBsAg assays have variable sensitivity, which positive, but monoclonal HBsAg-negative, vaccinees and unvaccinated persons were found to be PCR positive, as were potentially affects their diagnostic efficacy. How real a problem this is and whether variants of the S gene are associated some individuals without any markers of hepatitis B virus infection. Five more novel variants were found in these with this have not been comprehensively studied. Variants have been described in vaccinees, [9][10][11][12] in those receiving groups. There are implications for the design of HBsAg assays, which may have to be modified according to local sequence monoclonal 13 or polyclonal 14 immunotherapy, and in patients who react poorly, or not at all, in HBsAg assays. [5][6][7][8]15 variability. Not all discordant samples were explained by variants, indicating that assay sensitivity is fundamental to diag-Because some of these variants result in almost total abrogation of monoclonal, and occasionally of polyclonal, 16 anti-nostic efficacy. Overall, this study defined 16 novel variants and 2 new potential epitope clusters. (HEPATOLOGY 1997 body binding, they potentially pose a threat to the success of vaccination and to the supply of safe blood products. 26:1658-1666.)
Major questions facing policy makers are whether the vaccine formulation needs to be changed and, if so, how to do so. Fundamental to these questions is an understanding of the prevalence, variety, and antigenic importance of such muta-Abbreviations: HBV, hepatitis B virus; HBsAg, hepatitis B surface antigen; anti-HBs, tions in unvaccinated and vaccinated populations. There are antibody to HBsAg; MHR, major hydrophilic region; PCR, polymerase chain reaction; reports of polymerase chain reaction (PCR)-positive sera in mAbs, monoclonal antibodies; pAbs, polyclonal antisera; ELISA, enzyme-linked immuthe absence of HBsAg 17 ; these may be caused by infections nosorbent assay; pAb-ELISA, pAb-based highly sensitive ELISA; HCW, health care with envelope variants or strains with mutations in other workers; anti-HBc, antibody to hepatitis B core antigen; S/CO ratio, signal to cutoff ratio; HBeAg, hepatitis B e antigen.
regions of the genome, such as the X gene. 18,19 Such strains