Hepatitis C Virus: 30 Years After Its Discovery

This is a free sample of content from Hepatitis C Virus. Click here for more information on how to buy the book. Hepatitis C Virus: 30 Years after Its Discovery Michael Houghton Li Ka Shing Applied Virology Institute, Department of Medical Microbiology & Immunology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta T6G 2E1, Canada Correspondence: [email protected] Evidence for the existence of another hepatitis-causing pathogen, other than the known hepatitis A and B viruses, emerged in the mid-1970s. A frustrating search of 15 years was ended by the identification of the hepatitis C virus in 1989 using a recombinant DNA im- munoscreening method. This discovery quickly led to blood tests that eliminated posttrans- fusion hepatitis C and could show the partial efficacy of type 1 interferon-based therapies. Subsequent knowledge of the viral replication cycle then led to the development of effective direct-acting antivirals targeting its serine protease, polymerase, and nonstructural protein 5A that resulted in the approval of orally available drug combinations that can cure patients within a few months with few side effects. Meanwhile, vaccine strategies have been shown to be feasible, and they are still required to effectively control this global epidemic. ith the advent of the discoveries of the ic condition that could slowly lead to chronic Whepatitis B virus (HBV) in the 1960s by hepatitis and liver cirrhosis, which in turn could Baruch Blumberg and colleagues (Bayer et al. lead to end-stage liver disease and hepatocellular 1968) and the hepatitis A virus (HAV) in the carcinoma (Alter 1980). This knowledge ush- early 1970s by Feinstone et al. (1973), it became ered in an intense effort to discover the etiolog- evident, surprisingly, that most transfusion-as- ical agent(s) that, after a long delay, led to the sociated hepatitis cases were caused by neither of identification of the hepatitis C virus (HCV) in these viral infections (Prince et al. 1974; Fein- 1989. stone et al. 1975), thus heralding the era of non- A, non-B hepatitis (NANBH). In those days of large multiunit blood transfusions and the use of HCV DISCOVERY paid blood donors, rather than the use of volun- The basic challenges in identifying HCV were its teer blood today, the incidence of posttransfu- much lower titer relative to HAV and HBV; the sion NANBH (ptNANBH) could be as high as lack of a defined, specific antibody or antigen, 5%–10% (Hollinger et al. 1980). Initially per- which was key to the discovery of HBV (Bayer ceived as a minor disease because of the lack of et al. 1968); the lack of a defined viral morphol- significant morbidity during the acute phase of ogy evident in the electron microscope, as in the infection, it gradually became apparent that this discovery of HAV (Feinstone et al. 1973); and form of hepatitis frequently persisted as a chron- the lack of an in vitro system for propagating Copyright © 2020 Cold Spring Harbor Laboratory Press; all rights reserved Cite this article as Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a037069 1 © 2020 by Cold Spring Harbor Laboratory Press. All rights reserved. This is a free sample of content from Hepatitis C Virus. Click here for more information on how to buy the book. M. Houghton virus, which was instrumental in the discovery al approaches. The main contributors in my lab- of HIV (Barré-Sinoussi et al. 1983). Our work oratory in this time-consuming and frustrating also predated the routine use of the powerful work were Qui-Lim Choo, Amy Weiner, and polymerase chain reaction (PCR) nucleic acid Kangsheng Wang with invaluable support and amplification technology. guidance from Lacy Overby, who had previously Starting in 1982, my laboratory at the Chiron pioneered the introduction of HAV and HBV Corporation used blood samples from patients diagnostics while at Abbott Laboratories. diagnosed with NANBH, as well as liver tissue In late 1985 and early 1986, in addition to obtained from autopsies of NANBH patients continuing with most of the above approaches, provided by Tatsuo Miyamura from the Japa- we also started a new approach involving im- nese National Institutes of Health (NIH). Quick- munoscreening cDNA libraries made from ly realizing that the quality of nucleic acid NANBH-infected chimpanzee livers and plasma extracted from autopsied liver tissue was poor, using NANBH patient sera as a presumptive we sought a collaboration with Dan Bradley of source of virus-specific antibodies. Although the Centers for Disease Control and Prevention this approach did not always work even when (CDC) who was using the chimpanzee model using very well defined antibodies and despite for NANBH (Bradley et al. 1979) and who could the known chronicity of NANBH suggesting a provide fresh samples of blood and liver biopsies poor immune response, I decided to try what yielding intact nucleic acid. Much of our work hitherto I and many others had considered a was focused on using recombinant DNA meth- very risky approach (indeed, many illustrious ods to identify a cloned cDNA derived from a members of our science advisory board recom- viral mRNA or genome present in NANBH tis- mended against this approach). George Kuo in sue that was absent from control tissue using the neighboring laboratory to mine working on highly radioactive hybridization probes made Factor 8 characterization was an ardent enthusi- from each tissue (+/− hybridization probes). Al- ast of this approach and he was largely responsi- though this was successful at identifying many ble for stimulating me to try it. Dan Bradley was interesting genes clearly modulated by NANBH also a supporter of this strategy and was already infection, no viral clones could be identified after providing chimpanzee samples to another group several years of effort. This led us to request (and using this approach in a separate and indepen- cofund) the CDC to determine the infectious dent collaboration. titer of chimpanzee samples in an effort to pro- Initially, I prepared cDNA libraries from duce samples equivalent to that of the NIH’s poly(A)+ mRNA from four NANBH-infected patient H plasma determined in ∼1980 to have chimpanzee livers in the lambda gt11 phage. a chimpanzee infectious titer of 106.5 per mL The latter had been developed at Stanford to (CID50/mL) (Feinstone et al. 1981). This led to enable high-throughput cDNA immunoscreen- Dan eventually supplying us with chimpanzee ing (Young and Davis 1983). George optimized plasma of ∼106 CID/mL as well as liver tissue the detection methods using I125-radiolabeled samples from such animals. Unfortunately, we antihuman Ig and Qui-Lim carefully screened were still unable to identify viral clones with many millions of clones, but none of the posi- these samples using +/− hybridization probe tives could be proven to be of viral origin. Next, I methods or using hybridization probes derived made a random-primed gt11 cDNA library ex- from the known HBV, HDV, picornaviral, toga- tracted from NANBH-infected chimpanzee viral, and flaviviral genomes. In addition, many plasma based in part on Dan’s proposal that other attempts using these materials to produce the NANBH agent could possibly be flavi- or viral-specific monoclonal antibodies, to identify toga-like, and toga-like agents as classified at a large viral genome by silver staining of electro- that time were known not to possess poly(A)+ phoresis gels, to identify a viral reverse transcrip- tails. Again, however, no viral clones could be tase activity, and to produce a virus-propagation identified from Qui-Lim’s screening. In making cell culture system all failed along with addition- another cDNA library from NANBH-infected 2 Cite this article as Cold Spring Harb Perspect Med doi: 10.1101/cshperspect.a037069 © 2020 by Cold Spring Harbor Laboratory Press. All rights reserved. This is a free sample of content from Hepatitis C Virus. Click here for more information on how to buy the book. Hepatitis C Virus: 30 Years after Discovery chimpanzee plasma derived from both extracted chimpanzee livers but not in control liver RNA and DNA (not knowing what the elusive samples. viral genome comprised), I encountered severe 5. Blood recipients from the Kansas City problems with the aqueous nucleic extract form- blood bank undergoing acute posttransfu- ing a viscous gelatinous layer. Almost on the sion NANBH seroconverted to anti-5-1-1 point of discarding this extract, I persisted in antibody; making the cDNA library with little expectation of success and Qui-Lim screened it with his 6. Chimpanzees experimentally infected with usual exceptional care, this time using serum NANBH by Dan seroconverted to anti-5-1- derived from a chronically infected NANBH pa- 1 antibody, whereas his animals infected with tient. This patient displayed an unusually high HAV or HBV did not. serum alanine aminotransferase level indica- 7. The deciphered partial nucleotide sequence tive of unusually severe chronic NANBH. We of the large RNA molecule encoding clone thought that perhaps this patient may have 5-1-1 was very distantly related to the higher levels of circulating viral antibodies. flaviviruses. Previously, we had mainly used serum from con- valescent humans and chimpanzees (we now At this point in late 1987, Qui-Lim, George, know that chronic HCV patients have higher and myself considered that we had identified the levels of anti-HCV antibodies than individuals causative agent of blood-borne NANBH (Fig. 1), who have spontaneously resolved their acute in- called it the hepatitis C virus (HCV), and filed fections). the first of many patent applications. The work Qui-Lim found five positive clones. Intrigu- was officially published in early 1989 (Choo ingly, a couple were derived from the small et al.

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