A NEW IMMUNE ESCAPE MUTANT OF HEPATITIS-B VIRUS WITH AN ASP TO ALA SUBSTITUTION IN AA144 OF THE ENVELOPE MAJOR PROTEIN

A new hepatitis B virus (HBV) mutant with an Asp to Ala substitution i n aa144 of the envelope major protein was identified from the blood sa mples of two persistently infected patients. They were born to HBsAg-p ositive carrier mothers. The patients had been immunized with HBV vacc ine after birth, under a standard schedule of 3 injections at 0, 1 and 6 months, but failed to be protected. The mutant was stable and was p resent in the blood samples collected at 1 and 4 years of age from pat ient 105. To study the antigenic differences, two expression plasmids, pExpW (wild type) and pExpM (mutant), were constructed, and HBsAgs we re expressed in COS-M6 cells. The binding activities of the HBsAg from pExpW and pExpM were compared with anti-a-epitope monoclonal antibody and with anti-HBs polyclonal antibody, respectively, by radioimmunoas say. The results showed that the binding activity of HBsAg of pExpM wa s distinctly lower than that of pExpW, and the HBV mutant with envelop e major protein(144Asp-->Ala) was shown to be a new immune escape vari ant.