Why Do Viruses Cause Cancer? Highlights of the First Century Of
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PERSPECTIVES TIMELINE sarcomatous chest tumour that Rous suc- cessfully transplanted into other chickens that were related to the same brood8,9. By Why do viruses cause cancer? 1911, he had shown that the cancer could be transmitted through cell-free tumour Highlights of the first century of extracts and thus must be caused by a small transmissible agent, probably a virus. human tumour virology These experiments knowingly built on the pioneering work of two Danish scientists, Vilhelm Ellerman and Oluf Bang (FIG. 1), Patrick S. Moore and Yuan Chang who published similar results in 1908 on Abstract | The year 2011 marks the centenary of Francis Peyton Rous’s landmark the viral transmission of avian erythrob- 10 experiments on an avian cancer virus. Since then, seven human viruses have been lastosis . As cancers are not contagious, viral causes for chicken cancer were shortly found to cause 10–15% of human cancers worldwide. Viruses have been central to thereafter relegated to being scientific modern cancer research and provide profound insights into both infectious and curiosities11. Rous gave up his studies on non-infectious cancer causes. This diverse group of viruses reveals unexpected viral cancers 4 years later and little further connections between innate immunity, immune sensors and tumour suppressor progress was made in tumour virology signalling that control both viral infection and cancer. This Timeline article until the 1930s when mammalian tumour viruses began to be described12,13. Rous describes common features of human tumour viruses and discusses how new eventually returned to viral tumour biology technologies can be used to identify infectious causes of cancer. through his studies with Richard Shope on the cottontail rabbit papillomavirus in The burden of viral infections in cancer age-old cancer patterns on an international 1934. These studies led to investigations of is high but underappreciated by much scale3–5. In this Timeline article, we pro- the co-carcinogenic effects of coal tars on of the cancer research community. The vide an overview of the major milestones virus-induced tumours. Interest in viral International Agency for Research on in research on viruses and human cancer causes for cancer redoubled in the early Cancer estimates that one in five cancer (TIMELINE) and highlight common features 1950s following Ludwik Gross’s discovery cases worldwide are caused by infection, among the human cancer viruses (TABLE 1). of an acutely transforming murine retrovi- with most caused by viruses1,2. These Non-viral infectious causes for human rus (BOX 1) and a polyomavirus that caused cancers are particular public health prob- cancer are reviewed elsewhere6,7. murine tumours14. The culmination of this lems for the developing world, as well as first century of tumour virology would for under served and immunosuppressed Discovery of tumour viruses be celebrated with Nobel Prizes awarded populations in developed countries. Most On 1 October 1909, Francis Peyton Rous in 2008 for the discovery by Harald zur importantly, these cancers have readily began his famous cancer virus trans- Hausen of high-risk HPV strains that cause identifiable targets for diagnosis, preven- mission experiments at the Rockefeller cervical cancer and the discovery of HIV, tion and therapy. Vaccination programmes Institute, USA, on a 15-month-old an agent that does not initiate cancer but against two human tumour viruses, hepa- barred Plymouth Rock hen that had been indirectly ‘sets the stage’ for malignancy titis B virus (HBV) and human papilloma- brought to him by a farmer from Long through immuno suppression, by François virus (HPV), have already begun to alter Island, New York, USA. The chicken had a Barré-Sinoussi and Luc Montagnier. Timeline | Some major discoveries and events during the first century of tumour virology Initial descriptions Adenovirus Nobel Prizes of the AIDS Rous carries out and SV40 are Nobel Prize awarded Description of awarded to Discovery of epidemic and Experiments on virus Discovery of shown to to Rous reverse Temin, p53 AIDS-related virus transmission transmission murine induce transcription Baltimore associated cancers such as KS of rabbit experiments for leukaemia tumours in HBV described25,26 and and with SV40 T and non-Hodgkin’s myxomatosis14 avian sarcoma8,9 retrovirus198 rodents200,201 as cause of hepatitis retroviruses173,174 Dulbecco antigen182,183 lymphomas202 1898 1908 1909 1933 1936 1951 1953 1962 1964 1965 1966 1967 1970 1975 1976 1979 1980 1981 First demonstration Identification Description Discovery of Discovery of first EBV • Cellular origin of the Discovery of HTLV-I20 of cell-free of of mouse murine human tumour immortalization SRC oncogene transmission of papillomavirus mammary polyomavirus199 virus: EBV of primary described177 HBV linked to hepatocellular avian viral in rabbit tumour described in lymphocytes192 • Nobel Prize awarded carcinoma27 and HBV leukaemia10 papillomas196 virus197 Burkitt’s lymphoma to Blumberg vaccine approved: the first cell lines15 ‘anticancer’ vaccine EBV, Epstein–Barr virus; FDA, US Food and Drug Administration; HBV, hepatitis B virus; HPV, human papillomavirus; HTLV-I, human T-lymphotropic virus-I; KS, Kaposi’s sarcoma; KSHV, Kaposi’s sarcoma herpesvirus also known as human herpesvirus 8 (HHV8); VLP, virus-like particles. 878 | DECEMBER 2010 | VOLUME 10 www.nature.com/reviews/cancer © 2010 Macmillan Publishers Limited. All rights reserved PERSPECTIVES Table 1 | The human cancer viruses Virus Genome Notable cancers Year first Refs described Epstein–Barr virus (EBV; also Double-stranded DNA herpesvirus Most Burkitt’s lymphoma and nasopharyngeal 1964 15 known as human herpesvirus 4 carcinoma, most lymphoproliferative disorders, (HHV4)) some Hodgkin’s disease, some non-Hodgkin’s lymphoma and some gastrointestinal lymphoma Hepatitis B virus (HBV) Single-stranded and Some hepatocellular carcinoma 1965 25 double-stranded DNA hepadenovirus Human T-lymphotropic virus-I Positive-strand, single-stranded RNA Adult T cell leukaemia 1980 20 (HTLV-I) retrovirus High-risk human papillomaviruses Double-stranded DNA Most cervical cancer and penile cancers and some 1983–1984 29, (HPV) 16 and HPV 18 (some other papillomavirus other anogenital and head and neck cancers 30 α-HPV types are also carcinogens) Hepatitis C virus (HCV) Positive-strand, single-stranded Some hepatocellular carcinoma and some 1989 31 RNA flavivirus lymphomas Kaposi’s sarcoma herpesvirus Double-stranded DNA herpesvirus Kaposi’s sarcoma, primary effusion lymphoma and 1994 33 (KSHV; also known as human some multicentric Castleman’s disease herpesvirus 8 (HHV8)) Merkel cell polyomavirus (MCV) Double-stranded DNA polyomavirus Most Merkel cell carcinoma 2008 34 Human cancer viruses form virions in tumours (discussed below). Six more cancer viruses have been discov- The first human tumour virus, Epstein–Barr The discovery of EBV also sparked conten- ered, in addition to EBV (TABLE 1), which are virus (EBV; also known as human herpes- tion among cancer biologists because of the now widely accepted as causes for invasive virus 4 (HHV4)), was not described until difficulty in reconciling the near ubiquitous human tumours. Additional candidates 53 years after Rous’s initial experiments. infection of adults with EBV and the fact that are continuously proposed but their roles Anthony Epstein, Bert Achong and Yvonne EBV-associated cancers are uncommon16. in human cancer remain controversial and Barr used electron microscopy in 1964 to Furthermore, although Burkitt’s lymphoma unclear. This list is small but we can still identify EBV particles in cell lines from tumours from African and New Guinean draw at least one startling conclusion from it: African patients with Burkitt’s lymphoma15. patients are almost always positive for EBV, human cancer viruses do not fall into a sin- The unusual geographic distribution of sporadic Burkitt’s lymphomas in developed gle viral class. Much of the past century was Burkitt’s lymphoma had suggested a novel countries frequently lack EBV but retain devoted to the search for simple human can- environmental cause, such as a viral infection, signature MYC–IgH or MYC–IgL transloca- cer retroviruses similar to the Rous sarcoma which was confirmed by these early viro- tions17. This would require a rethinking of virus (BOX 1), but the only retroviruses asso- logical studies. This spurred other electron disease causality, as EBV does not follow ciated with human cancer are the complex microscopy-based searches for human cancer the Galilean principles of causality 18, which retroviruses: human T-lymphotropic virus-I viruses that largely turned out to be fruitless, require that a virus must be both necessary (HTLV-I) and HIV-1 and HIV-2. HIV does as cancer viruses generally do not replicate to and sufficient to be the cause of cancer (BOX 2). not directly cause cancer but it is frequently included as a cancer-causing agent by virtue of its induction of immunodeficiency, which promotes the development of cancers caused by other viruses2. • Discovery of Nobel Prizes A second surprise is that human cancer high-risk HPV types • Discovery and cloning FDA approved awarded to viruses span the entire range of virology and in cervical cancer29,30 of Hepatitis C virus31 HPV VLP-based Zur Hausen, • Initial descriptions of • Nobel Prizes awarded to Discovery of preventive Barré-Sinoussi include complex exogenous retroviruses HIV203 Bishop and Varmus KSHV in KS33 vaccine and Montagnier (such as HTLV-I), positive-stranded