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 in aa144 of the envelope major protein was identified from the blood samples of two persistently infected patients. They were born to HBsAg-positive carrier mothers. The patients had been immunized with HBV vaccine 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 present in the blood samples collected at 1 and 4 years of age from patient 105. To study the antigenic differences, two expression plasmids, pExpW (wild type) and pExpM (mutant), were constructed, and HBsAgs were 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 radioimmunoassay. The results showed that the binding activity of HBsAg of pExpM was distinctly lower than that of pExpW, and the HBV mutant with envelope major protein144Asp-->Ala was shown to be a new immune escape variant.