Hepatitis B virus and microRNAs: Complex interactions affecting hepatitis B virus replication and hepatitis B virus-associated diseases

Table 1 Cell-based model systems for the study of hepatitis B virus

Model system	Source	Characteristics
Cell lines
HepG2	Human hepatoblastoma[59]	Transformed cell line that is easy to grow and maintain. Serves as a model system for HBx-dependent HBV replication, although these cells cannot be directly infected by HBV
HepG2.2.15	HepG2 with two integrated head-to-tail dimers of HBV genome[62]	Stably replicates HBV and produces infectious virus; however, continuous passage since development has created a large separation from the parental HepG2 cells so that differences between HepG2 and HepG2.2.15 cells may not be HBV-specific
HepAD38	HepG2 stably expressing HBV pgRNA that is controlled by a tetracycline-responsive promoter[63]	Presence or absence of tetracycline (tet) allows cell line to act as its own baseline. HBV replication easily controlled, but only pgRNA expression is under tet-control, so some viral proteins maystill be made in the presence of tet
Huh7	Human hepatoma[60]	Transformed cell line that is easy to grow and maintain. Cells cannot be directly infected by HBV. For reasons that remain unknown, HBV replication in these cells is HBx-independent
PLC/PRF/5	Human hepatoma[185]	Transformed cell line that is easy to grow and maintain. These cells express HBsAg from integrated HBV DNA
HepaRG	Human hepatoma[186]	Transformed cell line, but differentiation can be induced to promote primary hepatocyte-like characteristics. After differentiation, these cells can be directly infected with HBV, although the infection efficiency is low. Acquisition of a differentiated, hepatocyte-like phenotype requires two-week maintenance in 2% DMSO prior to induction of differentiation; this process generates a mixed culture of hepatocytes and cholangiocytes
Primary cells
Cultured primary human hepatocytes	Hepatocyte isolation from liver tissue	Natural target of an HBV infection; however, quickly lose susceptibility to an HBV infection after isolation and culture. These cells can be difficult to acquire, difficult to maintain in culture, and begin to de-differentiate soon after isolation and plating. These cells can be difficult to transfect
Cultured primary mouse/rat hepatocytes	Perfused liver and isolation of hepatocytes	Primary cells that can be cultured to maintain a "normal" phenotype and serve as a surrogate model for studies in primary human hepatocytes. Support HBV replication although not direct HBV infection. Isolation requires access to animals and ability to reliably isolate high quality hepatocytes
Liver tissue samples	HCC and adjacent normal liver tissue; HBV and non-HBV liver tissue	Primary cells can give a more accurate profile of the liver RNA transcripts and expressed proteins than transformed cell lines. Disease versus normal tissue comparisons facilitate analysis of disease-mediated differences; however, it is often difficult to determine if differences are a cause or consequence of the disease. Requires access to patient samples that is often hampered by a finite supply and limited access such that these samples are often only used for primary screens or final confirmation
Peripheral blood mononuclear cells	Circulation	Easier to acquire than primary hepatocytes, but only support low levels of HBV infection and replication

HBV: Hepatitis B virus; HBx: Hepatitis B virus -X protein.