“Defective” mutations of hepatitis D viruses in chronic hepatitis D patients

Detection of hepatitis D virus RNA carrying large fragment deletions in patients with severe hepatitis B/D receiving oral antiviral therapy

A chronic lymphocytic leukemia patient had achieved complete virological suppression of hepatitis B virus (HBV) by oral antiviral therapy. Unexpectedly, fulminant hepatitis D virus (HDV) reactivation occurred, resulting in mortality. Cloning and sequence analysis identified a novel large fragment HDV deletion mutant containing only 69% of the standard genome. Reverse transcription-PCR assay revealed persistence of this mutant with variations of the wild-type-to-mutant ratios during the clinical course. Serum samples from 405 patients with chronic hepatitis B were then submitted for HDV RNA analysis. Of them, 20 (4.9%) were positive for HDV RNA and 5 HDV RNA large fragment deletions were identified in three patients, all under entecavir treatment. Two of them suffered from acute hepatitis exacerbations leading to liver failure while the third had repeated hepatitis flares. The peak bilirubin levels in these three patients were significantly higher than the others without large fragment deletions (P = 0.003). The deleted regions (527-702 bases) encompassed two ribozyme domains as well as part of the hepatitis D antigen (HDAg) reading frame. In conclusion, exacerbations of hepatitis D could occur, leading to fulminant hepatitis, even after complete virological suppression of HBV. Large fragment HDV RNA deletions were identified in some hepatitis D patients who were treated with entecavir but still experiencing severe hepatitis.

Ribozyme-independent replication of a defective hepatitis D virus RNA derived from hepatitis B/D patients receiving antiviral therapy

Novel hepatitis D virus (HDV) RNA mutants carrying large fragment deletions were identified in the serum samples of two hepatitis B/D patients receiving antiviral therapy. Sequence analysis revealed that the deleted regions encompassed both ribozyme domains. The mutant persisted in the serum samples for at least 2 and 10 months, respectively in the two patients, raising the question of whether such mutants could replicate in the absence of ribozyme domains. Thirty anti-HDV antibody-positive serum samples derived from 17 patients receiving antiviral therapy were submitted for RT-PCR detection of HDV RNA deletion mutants. Large fragment HDV RNA deletions were found in 4 patients. Of them, two had liver biopsy samples available. Northern blot analysis revealed high molecular weight HDV RNA replication intermediates, genomic and anti-genomic senses, in the liver tissues. Transfection of an in vitro transcribed HDV RNA deletion mutant (1.28 kb) into Huh7 and HepG2 cells also resulted in generation of high molecular weight HDV RNA species in the hepatoma cells (>6.5 kb) with secretion of a 6.5 kb HDV RNA species into the medium. In conclusion, we discovered novel large fragment deletion mutants of HDV RNA in hepatitis B/D patients receiving antiviral therapy. Such mutants did not contain ribozyme domains but could replicate in the liver cells to generate high molecular weight but not unit-length HDV RNA.

Hepatitis delta virus genetic variability: from genotypes I, II, III to eight major clades?

Hepatitis D virus (HDV) is a satellite of hepatitis B virus (HBV) for transmission and propagation, and infects nearly 20 million people worldwide. The HDV genome is composed of a compact circular single-stranded negative RNA genome with extensive intramolecular complementarity. Along with epidemiological, geographic distribution and pathological patterns, the variability of HDV has been limited to three genotypes and two subtypes that have been characterized to date. Recently, extensive phylogenetic reconstructions based on the delta antigen gene and full-length genome sequence data, have shown a wide and probably ancient radiation of African lineages, suggesting that the genetic variability of HDV is much more complex than previously thought. Indeed, sequences previously affiliated with genotype IIb should now be considered as belonging to clade 4 (HDV-4) and African HDV sequences segregate within four additional clades: HDV-5, HDV-6, HDV-7 and HDV-8. These results bring the geographic distribution of HDV closer to the genetic variability of its helper HBV.

Reciprocal interference between specific CJD and scrapie agents in neural cell cultures

Infection of mice with an attenuated Creutzfeldt-Jakob disease agent (SY-CJD) interferes with superinfection by a more virulent human-derived CJD agent (FU-CJD) and does not require pathological prion protein (PrPres). Using a rapid coculture system, we found that a neural cell line free of immune system cells similarly supported substantial CJD agent interference without PrPres. In addition, SY-CJD prevented superinfection by sheep-derived Chandler (Ch) and 22L scrapie agents. However, only 22L and not Ch prevented FU-CJD infection, even though both scrapie strains provoked abundant PrPres. This relationship between particular strains of sheep- and human-derived agents is likely to affect their prevalence and epidemic spread.

Evolution of hepatitis delta virus RNA genome following long-term replication in cell culture

Previous studies have defined a novel cell culture system in which a modified RNA genome of hepatitis delta virus (HDV) is able to maintain a low level of continuous replication for at least 1 year, using a separate and limited DNA-directed source of mRNA for the essential small delta protein. This mode of replication is analogous to that used by plant viroids. An examination was made of the nucleotide changes that accumulated on the HDV RNA during 1 year of replication. The length of the RNA genome was maintained, except for some single-nucleotide deletions and insertions. There was an abundance of single-nucleotide substitutions, with a 22-fold excess of these being base transitions rather than transversions. Of the detected transitions, at least 70% were consistent with being the consequences of posttranscriptional RNA editing by an adenosine deaminase acting on RNA. The remainder of the changes, including the single-nucleotide insertions and deletions, are likely to be the consequence of misincorporation during transcription. In addition, an intermolecular competition assay was used to show that the majority of the genomes present after 1 year of replication were essentially as competent in replication as the original single HDV RNA sequence that was used to initiate the genome replication. A model is provided to explain how, in this experimental system, the observed single-nucleotide changes were essentially neutral in terms of their effect on the ability of the HDV genome to carry out continued rounds of replication.