Correlation of fulminant hepatitis B and escape mutations in the 2nd loop of the HBsAg a-determinant

Most of the estimated 600,000 fatalities caused by Hepatitis B Virus (HBV) annually derive from sequelae of chronic infection. Chronification is strongly and inversely correlated with symptoms of hepatitis with cases leading to chronification usually not showing symptoms and cases with symptoms mostly leading to cure within 6 months. Key to this phenomenon is a strong immune response to viral components, which leads to elimination of infected hepatocytes and thereby causes clinical symptoms. Because of this, one of the most promising therapeutic approaches is to elicit a T-cell response against viral proteins by therapeutic vaccination of chronic Hepatitis B patients. To understand the factors triggering a solid T-cell response, we thoroughly analyzed cases of acute and chronic Hepatitis B presenting in our clinic. These included 13 chronic and 7 acute and symptomatic cases of which 2 had a fulminant course with highly impaired liver functions. Strikingly, similar mutations were observed in both virus strains causing fulminant hepatitis, each harboring a mutation depleting the HBeAg start codon as well as HBsAg escape mutations situated in the 2nd loop of the a-determinant (S143L; T140S + S143 M). Correlating to this, an intense CD8 T-cell response predominantly targeting HBsAg was measured via intra-cellular cytokine staining. Another HBsAg escape mutation (A128V) was found in a case of symptomatic but not fulminant Hepatitis B. No such mutants were detected in asymptomatic and chronic hepatitis B patients. This observation is supported by two recent reports of fulminant hepatitis caused by similar HBsAg escape mutants of the 2nd loop of the a-determinant (Schubert 2013, Magiorkinis 2013).

While the loss of HBeAg has been associated with fulminant hepatitis for a long time, HBsAg escape mutants have mostly been described in the context of chronic infections e.g. when negative HBsAg tests in occult infections prompted the molecular analysis of these strains (Weinberger, 2000) or after HBV variants escaped vaccine induced or passively administered anti-HBs antibodies (Protzer-Knolle, 1998). Since these settings involve escape mainly from antibodies, studies analyzing the antigenicity of HBsAg escape mutants focused on their reactivity to antibodies and largely neglected the role of the cellular response. The accumulation of these mutants in fulminant hepatitis observed by us and others in association with the strong CD8 response against HBsAg epitopes suggest a link and two possible explanations: (1) The observed mutations are being selected by escape from a strong T-cell response, or (2) the mutations observed are itself the cause of the strong T-cell response by increasing the antigenicity of HBsAg. To answer these questions, we are currently comparing the T-cell responses to wild type HBsAg and to mutant HBsAg harboring the described HBsAg escape mutations.