A Hepatitis B Virus Variant with an Ile to Ser Mutation at aa126 of HBsAg.

For the detection of HBV variants in patients vaccinated with HBV vaccine but failed to be protected, 16 children patients were studied by using the polymerase chain reaction (PCR) to amplify the HBV S gene fragment. To increase the sensitivity, a nested PCR method was used. These 10 HBV S gene fragments amplified from patients were cloned into M13mp18 phage vector and then sequenced respectively. One of them, No.19, was found to have a point mutation within a determinant coding region (nt524-nt595) of the HBsAg. There was a G at nt 531 instead of T, leading to a change of Ile to Ser at aa126 of the major HBsAg. As aa126 is located in the first loop of the two-looped conformational structure of the determinant, and the Ile to Ser at aa 126 is a drastic change, it is suggested that the antigenicity of the HBsAg might be altered and the immune failure in patient No.19 was probably related to the mutation.