The Nobel Prize in Medicine 2020 for the Discovery of Hepatitis C Virus: Transforming Hepatology

Editorial

October 5, 2020 marks a major landmark in the field of hepatology: our colleagues Harvey J. Alter, MD (National Institutes of Health, Bethesda, US), Michael Houghton, PhD (University of Alberta, Edmonton, Canada) and Charles M. Rice, PhD (Rockefeller University, New York, US) received the Nobel Prize in Medicine for the discovery of hepatitis C virus (1, 2). This award recognizes a breakthrough which not only transformed virology, immunology and the understanding of liver disease biology but also revolutionized clinical care of millions of patients by enabling the implementation of diagnostic tests, improving the safety of blood products and finally the development of a treatment which can efficiently cure HCV infection and prevent liver cancer in the large majority of patients.

The history of this breakthrough is remarkable by a combination of different approaches in clinical and epidemiological research, molecular biology and virology as reflected by the complementary profile the three laureates: a physician scientist, a molecular biologist and a virologist whose combined work made the key contributions for the discovery of a long-sought virus causing liver disease and cancer (1).

Following the discoveries of hepatitis A and B viruses in the sixties and seventies, Harvey J. Alter at the Department of Blood Transfusion at the US National Institutes of Health in Bethesda, Maryland was studying the occurrence of hepatitis in blood transfusions recipients. Using blood tests for the newly-discovered hepatitis A and B viruses, Alter and his colleagues showed that the hepatitis observed in a large number of patients post transfusion was neither due to hepatitis A nor B virus infection (3, 4). Aiming to investigate whether the “non-A, non-B” hepatitis was caused by another virus, Alter and his colleagues then showed that blood from these patients could transmit the disease to chimpanzees, the only susceptible host besides humans (1, 5). Alter’s studies had defined a new, distinct form of chronic viral hepatitis (1) laying the ground for the subsequent discovery of the viral genome by Michael Houghton.

Following a decade-long failure of efforts to isolate the virus applying classical virus discovery methods such as visualization of viral particles, Michael Houghton, working at that time at Chiron Corporation in Emeryville, California, applied a different approach which is used to clone genes in molecular and cell biology. In tedious work of more than five years, Houghton and his Chiron colleagues Qui-Lim Choo PhD and George Kuo PhD, generated cDNA libraries from nucleic acids isolated from livers and plasmas of infected chimpanzees, provided by collaborator Daniel Bradley (then of the Centers of Disease Control and Prevention (CDC), Atlanta), and transferred them to bacteria using a highly efficient lambda bacteriophage cloning system. Assuming that some of these cDNAs would be derived from the unknown virus and that antibodies against the virus would be present in patients with blood-borne hepatitis, Houghton and his colleagues then used an expression cloning approach to uncover the viral genome by screening for viral cDNA fragments encoding viral proteins binding to patient-derived antibodies. The discovery of one positive clone called 5-1-1 finally enabled the identification of a novel RNA virus, which was then termed hepatitis C virus (HCV) (6). Proteins could be translated from the RNA molecule itself indicating that the virus had a positive strand RNA genome which was later classified as a distinct member of the Flaviviridae family. The presence of antibodies against viral proteins in well characterized patients and chimpanzees with non-A, non-B hepatitis unraveled HCV as the missing agent (7).

Following the discovery of the viral genome and its proteins by Michael Houghton and his team, it remained to be determined whether the virus by itself would be sufficient to cause liver disease. Charles M. Rice, a virologist at that time working at Washington University in St. Louis, Missouri, discovered a previously uncharacterized region in the 3’ non-translated end of the HCV genome (8) along with another RNA virus group in Japan headed by Kunitada Shimotohno (9). Assuming that this highly conserved region would be important for virus replication, Rice, Alexander Kolykhalov and their team generated HCV RNAs that included this region as well as consensus sequence for the rest of the genome to eliminate possible deleterious mistakes. Thereto, the Rice team used Alter’s well characterized HCV H77 isolate to make their library of cDNA clones. The consensus sequence was derived by sequencing multiple cDNA clones and painstakingly reconstructed using convenient restriction enzymes. Using this genetic engineering approach, the scientists then identified a full-length clone which resulted in a productive viral infection and liver disease in chimpanzees (10). This study confirmed that HCV alone could cause viral hepatitis and liver disease (1). A similar observation using a different clone was then made shortly afterwards by another team at the National Institutes of Health which corroborated the findings of Rice and his colleagues (11).

The discovery of HCV opened a new research field, transformed the understanding of liver disease biology and resulted in a curative treatment now saving millions of lives by preventing advanced liver disease and cancer. Additionally, the discovery of the virus and its subsequent basic, translational and clinical research by many outstanding teams and investigators has resulted in the development of clinical diagnostic tools that have changed the safety of blood products and enabled screening for HCV infection – a key unmet medical need to prevent and treat liver disease.

The next scientific milestone following the discovery of the virus was the establishment of robust cell culture systems to unravel viral replication, virus-host interactions and pathogenesis. The establishment of replicons by Ralf Bartenschlager and Volker Lohmann (12) enabled efficient screening and/or testing of several classes of direct-acting antivirals (DAAs) targeting the viral proteins required for replication and protein processing. These comprise inhibitors of NS3/4 protease (PI), NS5A, and both nucleos(t)ide (NI) and non-nucleoside (NNI) NS5B polymerase inhibitors, all of which are now used safely as standard-of-care in the clinic (13). The subsequent identification of a unique viral isolate that efficiently infected a human hepatoma cell line, by Takaji Wakita and colleagues, finally enabled studies of the full viral life cycle (14). The following work of many outstanding virologists, chemists, immunologists, cell biologists, computational analysts and clinicians has enabled tremendous progress in understanding the molecular virology, immunology, pathogenesis, epidemiology and clinical disease of HCV infection.

Which are the next challenges laying ahead? According to estimates of the World Health Organization (WHO) around 71 million people worldwide are still chronically infected with hepatitis C. Despite the introduction of DAAs, in many areas of the world, chronic hepatitis C is still a major cause of death due to liver cirrhosis and cancer. Only a minority of infected patients is aware of the disease. Can HCV infection be eradicated on a global level? Unfortunately, several challenges remain (15): First, on a global level many patients do to not have access to DAAs, e. g. due to high costs or logistic issues. Second, reinfection remains possible even following successful viral cure - a key challenge e. g. in IV drug abusers. Third, in the absence of effective screening programs chronic HCV infection is frequently diagnosed at a late stage when cirrhosis or HCC are already present (as in high income countries) or is not diagnosed at all (as in low and middle income countries)(15). Fourth, while DAAs have shown to significantly and markedly improve the outcome of HCV-induced liver disease, the risk to develop HCC is not entirely eliminated in advanced liver disease (16).

The establishment of access to affordable treatment world-wide, effective HCV screening programs, and ultimately the development of a preventive vaccine are required to eradicate HCV infection on a global scale (15). Furthermore, effective strategies to prevent HCC in patients with cured HCV infection in advanced fibrosis are needed to eliminate the remaining risk of virus-induced liver disease.

I would like to finish this editorial with a personal note: as a physician scientist, I had and am having the privilege to work with the three laureates for more than two decades. In addition to their transforming world-class science, our field has also learned to appreciate their human qualities: this includes the wonderful humor and entertaining skills of Harvey Alter, the vision for the future and enthusiasm of Mike Houghton and the brilliant intellect combined with humbleness of Charlie Rice. It is not only exciting but also a great pleasure to interact and learn from them.

In summary, the hepatology community as well as their patients are very grateful for the work of the laureates and the Nobel committee for making finally the long-awaited choice. Collectively, the history of HCV’s discovery and antiviral drug development is one of the most striking examples of the impact of advances in biomedical research on disease outcome (15). Finally, the timing of the award may have been well chosen by the committee: the example of HCV discovery with the subsequent development of curative therapies may also serve as an encouragement to rapidly develop efficient antiviral treatment strategies for the control of SARS-CoV-2, the causative agent of COVID-19, which is also an RNA virus like HCV.