A novel hepatitis B virus mutant with A-to-G at nt551 in the surface antigen gene.
OBJECTIVE
Hepatitis B surface antigen (HBsAg) mutant of hepatitis B virus (HBV) is one of the important factors that result in immune escape and cause failure of immunization. In this study we reported and characterized a novel HBV mutant with A-to-G at nt551 and intended to provide theoretical data for prevention of HBV infection in China.


METHODS
A methodology comprising polymerase chain reaction (PCR) amplifying, M13 bacteriophage cloning and nucleotide sequencing was used to analyze the sera of the pediatric patient who was hepatitis B (HB) immune failure. Expression plasmids containing the mutant S gene and a wild-type (adr) S gene were constructed respectively and the recombinant HBsAg were expressed in COS-7 cells under the regulation of SV40 early promoter. The recombinant proteins were investigated for their immunological reactivity with different monoclonal antibodies (mAb) against "a" determinant and vaccine-raised human neutralizing antibodies.


RESULTS
It was found that there was a new point mutation at nt551 of the HBV (adr) genome from A to G, leading to a substitution of methionine (Met) to valine (Val) at position 133 in the "a" determinant of HBsAg. Compared to the wild-type HBsAg, the binding activity of the mutant HBsAg to mAbs (A6, A11 and S17) and to vaccine-raised human anti-hepatitis B surface antibody (anti-HBs) decreased significantly.


CONCLUSIONS
According to the facts that the patient has been immunized with HB vaccine and that the serum is anti-HBs positive and HBsAg negative, and based on the nucleotide sequence analysis of the mutant HBV S gene and its alteration of antigenicity, the HBV is considered to be a new vaccine-induced immune escape mutant different from the known ones.
Chen
Hua-Biao
HB
Huadong Research Institute for Medical Biotechnics, Nanjing 210002, Jiangsu Province, China. chenhuabiao@hotmail.com
Fang
De-Xing
DX
Li
Fa-Qing
FQ
Jing
Hui-Ying
HY
Tan
Wei-Guo
WG
Li
Su-Qin
SQ
D000409:Alanine; D000595:Amino Acid Sequence / Q000235:genetics; D019943:Amino Acid Substitution; D001483:Base Sequence / Q000235:genetics; D002675:Child, Preschool; D005998:Glycine; D006514:Hepatitis B Surface Antigens / Q000235:genetics*; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D017354:Point Mutation / Q000235:genetics*
D006514:Hepatitis B Surface Antigens; D000409:Alanine; D005998:Glycine