Deep Sequencing Reveals The Characteristics Of HBV S Region In Vertical Transmission And The Influence Of Mutations On Vaccination Failure

Objective: To investigate the characteristics of hepatitis B virus(HBV)S region genes in vertical transmission and the influence of S region mutations on the vaccination failure.Methods: A total of 9 mother-child pairs with chronic hepatitis B virus were recruited to this study,and all the children had completely received vaccine.All patients' liver function remained normal during the course of the disease.First,extract HBV DNA from the serum,and the HBV S region gene was amplified by PCR.And the S region gene was purified and fragmented into small fragments of 250-500 bp.Then,add Barcode primer to the fragments of each sample,purify the fragments with gel extraction.Finally,the samples were sequenced by deep sequencing,and analyze the sequencing data using bioinformatics methods.Results: The analysis of the sequencing data showed that all mother-child pairs are genotype B and genotype C mixed infection.The dominant genotype of 7 pairs was genotype B,and 2 pairs were genotype C.The dominant genotype of mothers was the same as that of children.The dominant genotypes did not change during vertical transmission.Phylogenetic tree analysis showed that consistency of consensus sequences between mother and child was higher than 98.5%.By comparing the average Shannon entropy of the same amino acid sites,we found that the diversity of most amino acid sites had small difference between mothers and children,and the trend of diversity is basically consistent between mothers and children.The mutations shared by mothers and children made up a high proportion of children`s mutations and the rate were 83.13±8.45%.Furthermore,many mutations that can cause amino acids change were found distributed through hepatitis B virus S region gene.Especially in the major hydrophilic region(MHR)containing the "a" determinant.Among them,C137 S or C139 Y that had an important influence on the structure of a-determinant were observed in all mother-child pairs.Conclusion: All the results indicated that the mutations of mothers and children were remarkably consistent and HBV S gene was highly conserved in vertical transmission.It also showed that immune escape mutations were pre-existing in the mothers.HBV with immune escape mutations was transmitted to children through vertical transmission,and resulted in the vaccination failure.