A25 Impact of polymorphism in the hepatitis B surface gene on human leukocyte antigen (HLA) class II

There is still no cure for chronic hepatitis B virus infection (CHBV), a major cause of liver cancers and related malignancies. Elucidating the role of CD4+ T-helper cells in activating immunological responses that clear antigenic peptides during primary HBV infection holds a potential strategy for developing potent vaccines. Since the strength of CD4+ T cell responses is dictated by binding of viral epitopes to class-II human leukocyte antigens (HLAs), we hypothesize that the quality of immunological responses in CHBV patients is influenced by host genetics and HBV genotypes. Here, ninety-two non-recombinant complete HBV surface-gene proteins (PreS1/S) from Botswana were sequenced (genotype A 44(47.8%); D 48(52.2%)) and 15-mer binding epitopes restricted to nine HLA-class II molecules (DRB5/1) were mapped in silico. The HLAs used have high population coverage in Botswana. The total predicted epitopes per HLA were 94-(genotype A) and 105-(genotype D) for PreS1, 42 (A and D) for PreS2, and 105 (A and D) for S. Epitope densities (binding peptides to total epitopes) were 3 per cent and 6 per cent (PreS1A&D), 4 per cent and 2 per cent (PreS2A&D), and 23 per cent and 22 per cent (S1A&D). SA&D proteins had most polytopes: CPGYRWMCLRRFII66-81, PGYRWMCLRRFIIF67-82, GYRWMCLRRFIIFL68-83, and YRWMCLRRFIIFLF69-84 binding to 5 (55.6%) HLAs (DRB1*0101/0701/1101/1501 and DRB5*0101) used. HLA-DRB*0101 bound the most epitopes, and the least were bound by HLA-DRB*0302/0701/0401 for both genotypes. PreS1D polytope: PAFRANTANPDWDFN32-46 binds to DRB1*0101/0401/1302 and PreS2 polytopes: TAFHQALQDPRVRG6-19 and AFHQALQDPRVRGL7-20 bind to DRB1*010/1501 alleles. Non-synonymous mutations impair peptide-HLA binding when assessed as combinations of > 2. The least active HLAs may be associated with CHBV and vice-versa for HBV clearance, thus the algorithm may be used to predict HBV prognosis for different haplotypes. The results favor the use of epitopes from S protein as broad genotype vaccine. This study highlights the need to explore further the mechanisms of PreS1 and its effect on the immune system.