Novel immunoassay for the detection of hepatitis B surface 'escape' mutants and its application in liver transplant recipients

Hepatitis B virus (HBV) strains with mutations in the surface gene are responsible for the failure of prophylaxis with hepatitis B immunoglobulin (HBIG) in a proportion of patients transplanted for HBsAg positive cirrhosis. So far, the emergence and evolution of these 'surface antibody escape' mutants have been studied by DNA sequencing. In this study the use of an immunoassay is described for diagnosis and characterisation of HBV recurrence after liver transplantation (OLT), based on a monoclonal antibody able to recognise both wild-type and mutant HBsAg. Pre- and post-transplant samples from 22 patients transplanted for HBsAg positive cirrhosis were studied: Group A: 12 patients who reinfected the graft despite receiving HBIG; Group B: 6 patients with no HBV recurrence with continuous HBIG; Group C: 4 patients with HBV recurrence without prophylaxis. By running the new assay in parallel with an immunoassay that is susceptible to HBsAg mutants, 4 of 12 cases were identified in Group A with HBV recurrence due to surface antibody escape mutants, whereas in 8 patients this was due to the wild-type HBV. The results from the immunoassays were confirmed in all cases by HBV DNA sequencing. The surface gene mutations in the 4 patients affected codons 144 and 145 and in one of these 4 patients HBV strains with mutations in both codons were detected before and after transplantation. The epitope recognised by the new monoclonal antibody that reacts with both wild-type and mutant HBsAg seems to remain stable in the HBIG-induced HBV mutants. This serological approach allows rapid and cost-effective screening for HBsAg escape mutants in the liver transplant setting and may be helpful in the selection of appropriate prophylaxis.