Human genomics of acute liver failure due to hepatitis B virus infection: An exome sequencing study in liver transplant recipients

Common mechanisms in pediatric acute liver failure

Acute liver failure (ALF) is a rare but potentially fatal disease in children. The etiology is multifactorial, including infection, autoimmune, and genetic disorders, as well as indeterminate hepatitis, which has a higher requirement for liver transplantation. Activation of the innate and adaptive immune systems leads to hepatocyte-specific injury which is mitigated by T regulatory cell activation. Recovery of the native liver depends on activation of apoptotic and regenerative pathways, including the integrated stress response (ISR; e.g., PERK), p53, and HNF4α. Loss-of-function mutations in these pathways cause recurrent ALF in response to non-hepatotropic viruses. Deeper understanding of these mechanisms will lead to improved diagnosis, management, and outcomes for pediatric ALF.

Human genetic basis of fulminant viral hepatitis

In rare cases, hepatitis A virus (HAV) and hepatitis B virus (HBV) can cause fulminant viral hepatitis (FVH), characterized by massive hepatocyte necrosis and an inflammatory infiltrate. Other viral etiologies of FVH are rarer. FVH is life-threatening, but the patients are typically otherwise healthy, and normally resistant to other microbes. Only a small minority of infected individuals develop FVH, and this is the key issue to be addressed for this disease. In mice, mouse hepatitis virus 3 (MHV3) infection is the main model for dissecting FVH pathogenesis. Susceptibility to MHV3 differs between genetic backgrounds, with high and low mortality in C57BL6 and A/J mice, respectively. FVH pathogenesis in mice is related to uncontrolled inflammation and fibrinogen deposition. In humans, FVH is typically sporadic, but rare familial forms also exist, suggesting that there may be causal monogenic inborn errors. A recent study reported a single-gene inborn error of human immunity underlying FVH. A patient with autosomal recessive complete IL-18BP deficiency was shown to have FVH following HAV infection. The mechanism probably involves enhanced IL-18- and IFN-γ-dependent killing of hepatocytes by NK and CD8 T cytotoxic cells. Proof-of-principle that FVH can be genetic is important clinically, for the affected patients and their families, and immunologically, for the study of immunity to viruses in the liver. Moreover, the FVH-causing IL18BP genotype suggests that excessive IL-18 immunity may be a general mechanism underlying FVH, perhaps through the enhancement of IFN-γ immunity.

The genetic variability of hepatitis B virus subgenotype F1b precore/core gene is related to the outcome of the acute infection

AIM

To assess the association of viral and host genetic variability with the outcome of acute infection with hepatitis B virus subgenotype F1b (HBV/F1b).

METHODS

The cohort consisted of 26 patients with acute HBV/F1b infection who exhibit different outcomes: spontaneous resolution (n = 10), progression to chronic hepatitis (n = 10) and acute liver failure (n = 6). HLA SNPs (rs3077, rs9277542, rs2856718 and rs7453920) were determined. The S gene and core promoter/precore/core region were direct sequenced, and this latter region was also ultra-deep sequenced. Mean number of mutations, mutation rate, Shannon entropy, positive selection sites and mutational patterns of quasispecies were compared between groups.

RESULTS

HLA SNPs were associated with spontaneous resolution or progression to chronic hepatitis, but not with the development of acute liver failure. The mean number of mutations in the S gene was similar among the three groups. Patients with spontaneous resolution had the lowest number of mutations, mutation rates and Shannon entropy values in the precore/core compared to the other two groups. Ten positive selection sites mapped on HLA-restricted epitopes were related to progression to chronic hepatitis and acute liver failure. Mutations T1753C, A1762T, G1764A, C1766T, T1768A G1896A, G2092T and T2107C were associated with acute liver failure and progression to chronic hepatitis.

CONCLUSION

Highly heterogeneous and complex HBV precore/core carrying specific point mutations, combined with the host HLA background, were associated with a worse clinical outcome of acute HBV/F1b infection.