B型肝炎病毒基因體變異在慢性B型肝炎急性發作的角色探討: 一前瞻性全長基因體研究(II)
Date Issued
2004
Date
2004
Author(s)
劉俊人
DOI
922314B002132
Abstract
The onset of acute exacerbation (AE) during the course of chronic hepatitis B is likely related
to the break of balance between virus and host immune responses. Whether such a break of immune
tolerance is triggered major by the changes of host immune status or by an alteration of HBV
hepatitis B virus (HBV) genome still remains controversial. To address this issue, a prospective
study from silent (asymptomatic) stage to acute exacerbation and a full-length sequencing strategy
are needed.
Although the underlying mechanism remains unknown, clinical observations and animal
studies clearly show that an upsurge of viral load always precedes or sometimes coincides with AE
in chronic hepatitis B. Thereby, a key to the understanding of these AEs seems to unravel the origin
and identity of such a viral surge. To clarify these issues, in the first year, we have already
collected the clinical and serological data from 14 patients who developed acute exacerbation of
chronic hepatitis B spontaneously, after discontinuing lamivudine treatment, or during interferon
treatment. We first regularly monitored the serum ALT levels and HBV DNA levels during the
development of acute exacerbation. Our results consistently showed that serum viral load resurged
before the maximal hepatitis activity in 13 (93%). We then performed full-length HBV genome
sequencing from the serum samples obtained at 4 points: at enrollment, at the peak of serum viral
load, at the peak of serum ALT level, and after acute exacerbation. We found that the viral genome
at virologic peak remained almost identical to that at baseline in 12 (86%) of them. On the contrary,
the viral genomes obtained after the development of hepatitis exacerbation are different from the
corresponding one at baseline in 7 (50%).
Our preliminary results suggested that the development of hepatitis B exacerbation was not
related to the changes of HBV genome. Nevertheless, from a viral evolution point of view, we need
to consider the origin of the HBV strains at baseline. Some viral strains may exist and remain
inactive in the host for a long time before reactivation, as is the case of chemotherapy-induced AE.
The other baseline viral strains, especially those from repeated spontaneous AE, may just represent
survivors from previous episode of AE. These HBV survivors may either be new viral variants
selected out from host immune surveillance in previous exacerbation, or they may remain the same
strain as prior to preceding AE and again trigger the current episode of exacerbation.
Our previous results suggested that the development of hepatitis B exacerbation was not
related to the changes of HBV genome. Nevertheless, from a viral evolution point of view, we need
to consider the origin of the HBV strains at baseline. Some viral strains may exist and remain
inactive in the host for a long time before reactivation, as is the case of chemotherapy-induced AE.
The other baseline viral strains, especially those from repeated spontaneous AE, may just represent
survivors from previous episode of AE. These HBV survivors may either be new viral variants
selected out from host immune surveillance in previous exacerbation, or they may remain the same
strain as prior to preceding AE and again trigger the current episode of exacerbation. (Liu et al,
Gastroenterology 2003)
AE of chronic hepatitis B is usually preceded by re-emergence or increase of HBV in the
serum. To investigate their origin, in the second year, we compared the identity of the serum viral
genome to that in the liver and in previous AE by full-length sequencing. The full-length viral
genome and extent of quasispecies were obtained from serum and liver biopsy specimens at the
same time from 9 subjects with hepatitis B exacerbation (group I). Composition of viral quasispecies was compared by the genetic diversity and the average number of nucleotide
substitutions within and between different viral sources. Another two patients with repeated AEs
(group II) were also enrolled and their serial serum ALT, HBV DNA levels and full-length
sequences were determined. In all group I patients, serum viral genome was identical to that in the
liver. The genetic diversity and the average number of nucleotide difference were also comparable
between serum and liver tissue. In two group II patients, viral variant emerged after previous AE
was not identical to that caused subsequent AE. Dominant viral strains for serial AEs in a single
patient did not show a sequential evolution, but presented as a horizontal selection of a minor
population from the original viral pool. The findings suggested that serum viral strain reflects the
intrahepatic one in AE. Random reactivation of the original HBV pool, other than a sequential
evolution of one strain, also contributes to the onset of repeated AE. (Liu et al, Hepatology 2004)
In the third year, the above full-length genomic sequencing and comparison work will be
continued. In addition, the serial serum cytokines including Th1 and Th2 cytokines immediately
before the onset of hepatitis B exacerbation will be determined to see if certain antiviral host factors
become defective before AE. Furthermore, since all serum and intrahepatic HBVs originate from
the covalently closed circular DNA (cccDNA) within the nucleus of the infected hepatocyte. HBV
have also been shown to replicate actively within the peripheral blood mononuclear cells (PBMC).
We will further clarify the compare the nucleotide sequences and genetic complexity among serum
viral genome, viral genome in the PBMC, intra-hepatic one and the cccDNA.
We expect providing evidence to clarify whether alteration of viral genome or changes in host
cytokine profiles is related to the trigger of AE. In longitudinal follow-up, we can further clarify the
impact of viral variations on AE and the biologic behavior of the emerged viral variants. Finally, we
will elucidate the representation of the serum HBV genome to that in the liver, in intrahepatic
cccDNA level, or within the PBMC.
Subjects
Acute exacerbation
hepatitis B virus
variant
viral load
full-length
genome
prospective
SDGs
Publisher
臺北市：國立臺灣大學醫學院內科
Type
report
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