Immune Evaders: Hepatitis B Virus Surface Mutants Circulating in Pakistani Population

Abstract

Hepatitis B virus (HBV) cache the major etiological agent of chronic hepatitis infections. Pakistan alone stands as one of the world’s highest load of chronic hepatitis and mortality due to liver disease, cirrhosis and hepatocellular carcinoma. A large number of genomic variations have been reported in HBV over the past two decades and these induce a specific change in virus biology. The variants involved in host immune system evasion (S-mutants) dramatically modify the virus-host interactions when present and are a serious challenge to healthcare personnel. Hepatitis B virus surface antigen (HBsAg) contains a vastly conformational epitope cluster in major hydrophilic region (MHR) extending from amino acid 99-169 of Surface protein and antibodies produced by natural infection or by administration of vaccine confer cross-protective immunity against this hydrophilic region. However, aa substitution, insertion or deletion in MHR if present may lead to the modification of conformational epitope and altered immunogenicity of HBsAg thus making HBsAg undetectable (occult infections), or induces immune escape variants to evade virus clearance (escape mutants). To investigate this, a prospective study was conducted in 100 HBV infected patients identified randomly in different tertiary care hospitals of Islamabad, which lead to the characterization of sequence variations in HBsAg. A total of 13 TA-Cloned sequences of surface ORF were analyzed and the mutants circulating in virus evasion region include observed replacements in both humoral and/or cellular [major histocompatibility complex class I (MHC-I) and MHC-II] HBV mutated epitopes, such as Q 30K, T45S, T46P, L49R, S55P, T68I, I86T, Y100C, S114T, Abstract xviii T115I, T118V, P120T, R122K, P127T, P127S, A128V, G130N, T131N Y134V Y134F S143T I152V G159A F161Y A168T, A168V, F170S, V 180A, V194A, M198V, S207N. A 3D model of small surface protein and HBIg was developed using computational tools and these were docked to identify important residues involved in immune evasion. The insilico analysis confirms the presence of virus evaders circulating in Pakistani population. Novel treatment options have to be employed to treat accumulated viral mutations as seen in the case of Hepatitis B virus Surface mutants in Pakistan. These may include a modified vaccine (incorporating the Pakistani strain of HBV) for mutant strain along with an enhancement of B and T cell immune responses e.g. a multiepitope vaccine, and an HBIG directed against a mutated cluster of alpha determinant to treat such patients. There is a dire need that pathologists, pharmaceutical and the healthcare industry augment their awareness of HBV mutants and how these mutants may alter existing diagnostic and treatment options in the context of Pakistan.