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Cao Cancer Evo-Dev

is generally believed to be one of the major causes (or whose rare alleles are significantly associated
of chronic HBV infection in adulthood. Of the infants with decreased risks of chronic HBV infection) include
born to hepatitis B surface antigen (HBsAg)-positive rs3138053 (affecting NFKBIA), rs2856718, rs7453920,
mothers globally, 42.1% who did not receive HBV and rs9275319 (affecting HLA-DQ), and rs9277378,
passive-active immunoprophylaxis and 2.9% of infants rs2395309, rs2301220, and rs9277341 (affecting
who received the immunoprophylaxis acquired HBV HLA-DP) [12] . The polymorphic genotypes that are
infection perinatally. The perinatal infection occurred in significantly association with increased risks of chronic
84.2% and 8.7% of infants born to hepatitis B e-antigen progression of HBV infection as well as immune
(HBeAg)-positive mothers who did not and did receive selection of the end-stage liver diseases-associated
immunoprophylaxis, respectively. The infection rates HBV mutations are more frequent in the Han Chinese
were 6.7% and 0.4% for infants born to HBeAg- than in European populations. These data indicate that
negative-carrier mothers, respectively. Moreover, the the Han Chinese are inherently more apt to progressing
chronicity rates of HBV infection acquired perinatally into chronic infection once exposed to HBV infection
were 28.2% in infants born to HBeAg-negative mothers than European, whereas European tend to recover from
and 64.5% in infants born to HBeAg-positive mothers [12] . HBV infection spontaneously [12] . This might be one of
This is possible due to the fact that the immaturity of the reasons why chronic HBV infection and the HBV-
immune system in infants make it unable to recognize induced end-stage liver diseases are more frequent
HBV as an external antigen, thus establishing chronic in Chinese than in European populations. The HLA-
HBV infection although the immune response can be II genetic polymorphisms may predispose immune
aroused thereafter. Clearly, perinatal HBV infection is an imbalance upon HBV infection, impair immune function
important but not the predominant cause of chronic HBV for HBV clearance, and maintain chronic HBV infection
infection in adulthood. Chronic transformation of acute and hepatic inflammation, and thus facilitating the
hepatitis B caused by horizontal transmission among progression of CHB into liver cirrhosis and HCC.
adolescents and adults contributes to the remaining
proportion of chronic HBV infection. Approximately “Dead-end” evolution of HBV
8.5% of acute hepatitis B in adults in Shanghai, China, During HBV-induced hepatocarcinogenesis, both of
develops into chronic HBV infection 6 months after acute hepatic cells and the viruses experience the process
infection [13] . In mainland China where genotypes B (B2) of evolution. Viral evolution serves as a valuable
and C (C2 and C1) are endemic, HBV subgenotype B2 clue to investigate the mechanism underlying HBV-
is more apt to causing acute infection because of higher induced hepatocarcinogenesis. HBV belongs to
viral load in the virus-providing chronic carriers whereas the Hepadnaviridae family found in both mammals
HBV subgenotype C2 is more apt to causing chronic (orthohepadnaviruses) and birds (avihepadnaviruses)
transformation following an acute course [13,14] . HBV C2 is and is highly conserved in their host species during
more likely to develop liver cirrhosis and HCC than does the long-term evolutionary process. Although primate
HBV B2, the two major HBV subgenotypes endemic in hepadnaviruses are indigenous to their hosts,
China, possibly because of the stickiness nature of HBV hepadnaviruses isolated from apes are grouped as
subgenotype C2 [15-17] . The third most important cause HBV genotypes in phylogenetic analyses. With only
of chronic HBV infection and active inflammation is 5% divergence from the chimpanzee viral isolates,
the genetic predispositions of some key immune and the isolates from gorilla are categorized in the HBV
proinflammatory molecules. Genome-wide association genotypes. Avihepdnaviruses are the most distant
study in the eastern Asian populations have shown that relatives of HBV with a nucleic acid homology of only
a total of 11 single nucleotide polymorphisms (SNPs) 40%. Compared to avihepdnaviruses, Woodchuck
in genetic loci including HLA-DPA1 and HLA-DPB1, hepatitis virus and ground squirrel hepatitis virus as
some SNPs in genetic loci including HLA-DQ and -DR, mammalian hepadnaviruses are more closely related to
and a locus near HLA-Care significantly associated HBV and differ by only 17%. Genetic evolution analysis
with CHB [18-22] . Interestingly, these SNPs in the loci indicates that HBV and orthohepadnaviruses from non-
encoding human leukocyte antigen-class II (HLA-II) are human primates are phylogenetically clustered in the
also significantly associated with vaccine response as same evolutionary branch [28] . These evidences indicate
well as the risks of acute-on-chronic liver failure, HBV- that members of Hepadnaviridae family are highly
related liver cirrhosis, and HBV-associated HCC [23-27] . conserved in their evolutionary history. However, HBV
Interestingly, different human races have different allelic experiences a relative rapid evolution in their genome
frequencies of SNPs that affect the expression of HLA- since chronic HBV infection is established in a subset of
DP, HLA-DQ, and the inhibitory component of NF-κB infected populations.
complex IκBa gene NFKBIA. These genetic loci whose
dominant alleles are significantly association with Previous researches by our group identified the
increased risks of chronic progression of HBV infection wild-type HBV sequences (so-called the standard
Hepatoma Research ¦ Volume 3 ¦ October 27, 2017 243