Sugantha Govindarajan

Viral and immunological determinants of hepatitis C virus clearance, persistence, and disease.

To define the early events that determine the outcome of acute hepatitis C virus (HCV) infection, we compared the course of viremia with the peripheral and intrahepatic T cell response and intrahepatic cytokine profile in six acutely infected chimpanzees. Three different outcomes were observed after peak viral titers were reached: sustained viral clearance, transient viral clearance followed by chronic infection, and chronic infection that persisted at initial peak titers. The results indicate that HCV spread outpaces the T cell response and that HCV rapidly induces but is not controlled by IFN-α/β; that viral clearance follows the entry and accumulation of HCV-specific IFN-γ-producing T cells in the liver; and that it may not require the destruction of infected cells.

Synthesis of a novel hepatitis C virus protein by ribosomal frameshift

Hepatitis C virus (HCV) is an important human pathogen that affects ∼100 million people worldwide. Its RNA genome codes for a polyprotein, which is cleaved by viral and cellular proteases to produce at least 10 mature viral protein products. We report here the discovery of a novel HCV protein synthesized by ribosomal frameshift. This protein, which we named the F protein, is synthesized from the initiation codon of the polyprotein sequence followed by ribosomal frameshift into the −2/+1 reading frame. This ribosomal frameshift requires only codons 8–14 of the core protein‐coding sequence, and the shift junction is located at or near codon 11. An F protein analog synthesized in vitro reacted with the sera of HCV patients but not with the sera of hepatitis B patients, indicating the expression of the F protein during natural HCV infection. This unexpected finding may open new avenues for the development of anti‐HCV drugs.

Mutations that permit efficient replication of hepatitis C virus RNA in Huh-7 cells prevent productive replication in chimpanzees

The development of a subgenomic replicon derived from the hepatitis C virus (HCV) strain Con1 enabled the study of viral RNA replication in Huh-7 cells. The level of replication of replicons, as well as full-length Con1 genomes, increased significantly by a combination of two adaptive mutations in NS3 (E1202G and T1280I) and a single mutation in NS5A (S2197P). However, these cell culture-adaptive mutations influenced in vivo infectivity. After intrahepatic transfection of chimpanzees, the wild-type Con1 genome was infectious and produced viral titers similar to those produced by other infectious HCV clones. Repeated independent transfections with RNA transcripts of a Con1 genome containing the three adaptive mutations failed to achieve active HCV infection. Furthermore, although a chimpanzee transfected with RNA transcripts of a Con1 genome with only the NS5A mutation became infected, this mutation was detected only in virus genomes recovered from serum at day 4; viruses recovered at day 7 had a reversion back to the original Con1 sequence. Our study demonstrates that mutations that are adaptive for replication of HCV in cell culture may be highly attenuating in vivo.

The p7 polypeptide of hepatitis C virus is critical for infectivity and contains functionally important genotype-specific sequences

The role of the hepatitis C virus (HCV) p7 protein in the virus life cycle is not known. Previous in vitro data indicated that this 63-aa polypeptide is located in the endoplasmic reticulum and has two transmembrane domains (TMDs) connected by a cytoplasmic loop; the amino- and carboxyl-terminal tails are oriented toward the endoplasmic reticulum lumen. Furthermore, recent in vitro studies suggested that HCV p7 could function as a virus-encoded ion channel. It might therefore be a relevant target for future drug development. We studied the role of HCV p7 in vivo. Because HCV does not replicate efficiently in cell culture, we mutagenized p7 of an infectious genotype 1a cDNA clone and tested RNA transcripts of each mutant for infectivity in chimpanzees by intrahepatic transfection. Appropriate processing of mutant polypeptides was confirmed by studies in transfected mammalian cells. Mutants with deletions of all or part of p7 and a mutant with substitutions of two conserved residues in the cytoplasmic loop were not viable. Thus, p7 is essential for infectivity of HCV. A chimera in which the p7 of the 1a clone was replaced with p7 from an infectious genotype 2a clone also was not viable. This finding suggests a genotype-specific interaction between p7 and other genomic regions. To define which portions of p7 played the most significant role for this interaction, we tested three chimeras with the 1a backbone in which only specific domains of p7 had the 2a sequence. A p7 chimera with 2a tails and TMDs and the 1a cytoplasmic loop was not viable. A mutant with 2a tails and cytoplasmic loop and 1a TMDs also was not viable. However, a p7 chimera with 2a TMDs and cytoplasmic loop and 1a tails was viable. The transfected chimpanzee became viremic at week 2, and recovered viruses had the chimeric sequence. These data indicate that the amino- and/or carboxyl-terminal intraluminal tails of p7 contain sequences with genotype-specific function.

Liver fibrosis progression is related to CD4 cell depletion in patients coinfected with hepatitis C virus and human immunodeficiency virus.

A total of 204 patients with liver biopsy-proven hepatitis C virus (HCV) infection, 84 with and 120 without human immunodeficiency virus (HIV) coinfection, were studied, to evaluate variables possibly associated with the stage of liver fibrosis. All patients were injection drugs users, with a mean age of 32 years and an estimated duration of HCV infection of 12 years. Twenty-four patients (11%) had many fibrous septa with (5%) or without (6%) cirrhosis, 56 (27%) had few fibrous septa, and 124 (60%) had no fibrous septa. In all patients, an association was found between CD4 cell counts <500 cells/mm(3)and the presence of many fibrous septa (odds ratio, 3.2; P=.037), independent of HIV infection and other factors. These results suggest that HIV infection-induced CD4 depletion is independently associated with the severity of liver fibrosis in chronic HCV infection.

Fulminant B Viral Hepatitis: Role of Delta Agent

The prevalence of delta-markers among 71 patients with fulminant B viral hepatitis was found to be 33.8%. The majority of the patients with delta-markers showed serologic evidence of simultaneous acute delta-infection and B viral infection. Only 5 of the 24 patients with serologic markers of acute delta-infection in this fulminant group were presumably infected chronically with hepatitis B virus as shown by the absence of immunoglobulin M antibody to hepatitis B core antigen. A study of serologic markers of acute delta-infection among 118 patients with nonfulminant acute B viral hepatitis, in contrast, revealed only 4.2% incidence. This significant difference in the prevalence of simultaneous acute B and delta viral infections between the fulminant and the nonfulminant acute hepatitis groups indicates a higher morbidity rate associated with simultaneous infection. When the fulminant group was divided into acute B viral infection without delta-markers (subgroup 1), simultaneous acute B and delta-infections (subgroup 2), and chronic asymptomatic B with acute delta-infections (subgroup 3), for comparison of survival data, the mortality rate was not significantly different in the first two groups when the patients were age matched.

Short-term prednisone therapy affects aminotransferase activity and hepatitis C virus RNA levels in chronic hepatitis C

BACKGROUND/AIMS The effects of corticosteroids on chronic hepatitis B have provided insight into the mechanism of liver cell injury caused by hepatitis B. In this study, this model was applied to investigate the effects of prednisone on alanine aminotransferase (ALT) and hepatitis C virus (HCV) RNA levels in chronic hepatitis C. METHODS Ten patients with chronic hepatitis C who had increased levels of ALT and HCV RNA detectable in serum were given a 7-week course of a tapering dose of prednisone. Quantitation of serum HCV RNA was determined by polymerase chain reaction (PCR) and by branched-chain DNA amplification. RESULTS ALT levels decreased in 8 of 10 patients during therapy. Mean ALT levels of all 10 patients decreased from 184 to 84 U/L (P = 0.002) and then rebounded in 7 of the 8 patients after discontinuation of prednisone. HCV RNA was detectable by the branched DNA technique in 9 of 10 patients. These values increased in all 9 patients during prednisone therapy. The mean serum HCV RNA levels increased from 40.9 before treatment to 414.3 Eq/mL x 10(5) during treatment (P = 0.043). Using PCR, HCV RNA titers increased one log-fold in 8 of 10 patients (geometric mean of 1:4420 to 1:23410). HCV RNA levels decreased to pretreatment values within a mean of 2.8 weeks (range, 1-5) after discontinuation of prednisone. CONCLUSIONS These responses in ALT and HCV RNA suggest the participation of an immune-mediated mechanism in the liver cell injury in chronic hepatitis C.

Toll-like receptor 4 mediates synergism between alcohol and HCV in hepatic oncogenesis involving stem cell marker Nanog

Alcohol synergistically enhances the progression of liver disease and the risk for liver cancer caused by hepatitis C virus (HCV). However, the molecular mechanism of this synergy remains unclear. Here, we provide the first evidence that Toll-like receptor 4 (TLR4) is induced by hepatocyte-specific transgenic (Tg) expression of the HCV nonstructural protein NS5A, and this induction mediates synergistic liver damage and tumor formation by alcohol-induced endotoxemia. We also identify Nanog, the stem/progenitor cell marker, as a novel downstream gene up-regulated by TLR4 activation and the presence of CD133/Nanog-positive cells in liver tumors of alcohol-fed NS5A Tg mice. Transplantation of p53-deficient hepatic progenitor cells transduced with TLR4 results in liver tumor development in mice following repetitive LPS injection, but concomitant transduction of Nanog short-hairpin RNA abrogates this outcome. Taken together, our study demonstrates a TLR4-dependent mechanism of synergistic liver disease by HCV and alcohol and an obligatory role for Nanog, a TLR4 downstream gene, in HCV-induced liver oncogenesis enhanced by alcohol.

Epidemiology of Hepatocellular Carcinoma

Although rare in Canada and the United States, hepatocellular carcinoma (HCC) ranks as the eighth most common cancer in the world. High-risk regions are East and Southeast Asia, and sub-Saharan Africa. Independent of race and geography, rates in men are at least two to three times those in women; this sex ratio is more pronounced in high-risk regions. Rates of HCC in the United States have increased by 70% over the past two decades. Registry data in Canada and Western Europe show similar trends. In contrast, the incidence of HCC in Singapore and Shanghai, China, both high-risk regions, has declined steadily over the past two decades. Among white and black Americans, there is an inverse relationship between social class status and HCC incidence. Chronic infection by the hepatitis B virus (HBV) is by far the most important risk factor for HCC in humans. It is estimated that 80% of HCC worldwide is etiologically associated with HBV. In the United States, although the infection rate in the general population is low, HBV is estimated to account for one in four cases of HCC among non-Asians. Chronic infection by the hepatitis C virus is another important risk factor for HCC in the United States; however, this virus is believed to play a relatively minor role in the development of HCC in Africa and Asia. Dietary aflatoxin exposure is an important codeterminant of HCC risk in Africa and parts of Asia. In Canada and the United States, excessive alcohol intake, cigarette smoking and oral contraceptive use in women also are risk factors for HCC.

NK Cells Cause Liver Injury and Facilitate the Induction of T Cell-Mediated Immunity to a Viral Liver Infection

NK cells are a relatively rare cell population in peripheral lymphoid organs but are abundant in the liver, raising questions as to their function in immune responses to infections of this organ. To investigate this, cell-mediated immunity to viral liver infection induced by a type 5, replication-defective, adenovirus was examined. It is shown that NK cells in the absence of T cells cause hepatocyte apoptosis in virus-infected livers associated with an increase in liver enzymes in the serum. Concomitantly, NK cells induce production of IFN-γ, inhibitable by their elimination before infection. NK cells are shown to be necessary for optimal priming of virus-specific T cells, assessed by delayed-type hypersensitivity response and CTL activity, consistent with their ability to secrete IFN-γ. The conclusion is drawn that NK cells mediate two important functions in the liver: they induce cell death in the infected organ and concomitantly stimulate the induction of T cell-mediated immunity by release of IFN-γ.