Identification of HBV Surface Ag Variants in Patients with Hepatitis before and after Immunization

Abstract

Background: Chronic hepatitis B virus (HBV) infection represents a major global public health problem. Though there is an effective prophylactic vaccine, more than 370 million people round the globe are chronically infected with HBV. In spite of vaccination, as a therapeutic approach in chronic carriers, some patients are unable to induce an immune response. Such failure is often caused by emergence of mutations in immune epitope of the surface gene.

Materials and Methods: 19 consecutive chronic HBsAg carriers with chronic hepatitis and detectable level of serum HBV DNA were given 3 standard injections of the B vaccine at one month interval. Blood samples were collected from each patient before each dose of the vaccine. Nested-PCR was performed on each specimen using specific primers which amplified the S-Ag region. Direct sequencing and alignment of sequences with Iranian species and databases were used for detecting probable mutations.

Results: Direct sequencing revealed substitutions in these sequences which were silent and/or amino-acid-changing mutations outside the "a" determinant of surface genes. Most mutations were occurred in the 205-215 regions. The changes included 92 amino acids: 51 in the immune epitope (25 in the CTL epitopes, 21 in the Th cell epitopes and 5 amino acid in the B cell epitopes) and other changes were observed in other regions. The distribution of the mutations could be categorized in 3 groups: The mutation was increased in 3 samples after treatment, was decreased in 6 samples after treatment, and was not different with pretreatment in 7 samples.

Conclusion: Mutations occurred outside the "a" determinant. Mutations of the immune epitopes Th and CTL cell could be a type of escape immune response and are responsible for failure in response to immunotherapy.