A global burden
More than 5 per cent of all cancers worldwide are caused by persistent infection with this virus. Infection by the human papilloma virus is the most common sexually transmitted agent, afflicting 50-80 per cent of the population. Of the more than 100 HPV types known, about 40 infect the genital tract, and 15 of these put women at high risk for cervical cancer. In addition, HPV is found in some vulval, penile, oral and other cancers. Human papilloma virus can be detected in 99.7 per cent of women with histologically confirmed cervical cancer, affecting some 500,000 women per year.
Against the prevailing view during the 1970s, Harald zur Hausen postulated a role for human papilloma virus (HPV) in cervical cancer. He assumed that the tumour cells, if they contained an oncogenic virus, should harbour viral DNA integrated into their genomes. The HPV genes promoting cell proliferation should therefore be detectable by specifically searching tumour cells for such viral DNA. Harald zur Hausen found novel HPV-DNA in cervix cancer biopsies, and thus discovered the new, tumourigenic HPV16 type in 1983. In 1984, he cloned HPV16 and 18 from patients with cervical cancer. The HPV types 16 and 18 were consistently found in about 70% of cervical cancer biopsies throughout the world.
Harald zur Hausen demonstrated novel properties of HPV that have led to an understanding of mechanisms for papilloma virus-induced carcinogenesis and the predisposing factors for viral persistence and cellular transformation. He made HPV16 and 18 available to the scientific community. Vaccines were ultimately developed that provide ≥95 per cent protection from infection by the high risk HPV16 and 18 types. The vaccines may also reduce the need for surgery and the global burden of cervical cancer.
The discovery of HIV
Following medical reports of a novel immunodeficiency syndrome in 1981, the search for a causative agent was on. Françoise Barré-Sinoussi and Luc Montagnier isolated and cultured lymph node cells from patients that had swollen lymph nodes characteristic of the early stage of acquired immune deficiency. They detected activity of the retroviral enzyme reverse transcriptase, a direct sign of retrovirus replication. They also found retroviral particles budding from the infected cells. Isolated virus infected and killed lymphocytes from both diseased and healthy donors, and reacted with antibodies from infected patients. In contrast to previously characterized human oncogenic retroviruses, the novel retrovirus they had discovered, now known as human immunodeficiency virus (HIV), did not induce uncontrolled cell growth. Instead, the virus required cell activation for replication and mediated cell fusion of T lymphocytes. This partly explained how HIV impairs the immune system since the T cells are essential for immune defence. By 1984, Barré-Sinoussi and Montagnier had obtained several isolates of the novel human retrovirus, which they identified as a lentivirus, from sexually infected individuals, haemophiliacs, mother to infant transmissions and transfused patients. The significance of their achievements should be viewed in the context of a global ubiquitous epidemic affecting close to one per cent of the population.
Soon after the discovery of the virus, several groups contributed to the definitive demonstration of HIV as the cause of acquired human immunodeficiency syndrome (AIDS). Barré-Sinoussi and Montagnier's discovery made rapid cloning of the HIV-1 genome possible. This has allowed identification of important details in its replication cycle and how the virus interacts with its host. Furthermore, it led to development of methods to diagnose infected patients and to screen blood products, which has limited the spread of the pandemic. The unprecedented development of several classes of new antiviral drugs is also a result of knowledge of the details of the viral replication cycle. The combination of prevention and treatment has substantially decreased spread of the disease and dramatically increased life expectancy among treated patients. The cloning of HIV enabled studies of its origin and evolution. The virus was probably passed to humans from chimpanzees in West Africa early in the 20th century, but it is still unclear why the epidemic spread so dramatically from 1970 and onwards.
Identification of virus−host interactions has provided information on how HIV evades the host’s immune system by impairing lymphocyte function, by constantly changing and by hiding its genome in the host lymphocyte DNA, making its eradication in the infected host difficult even after long-term antiviral treatment. Extensive knowledge about these unique viral host interactions has, however, generated results that can provide ideas for future vaccine development as well as for therapeutic approaches targeting viral latency.
HIV has generated a novel pandemic. Never before has science and medicine been so quick to discover, identify the origin and provide treatment for a new disease entity. Successful anti-retroviral therapy results in life expectancies for persons with HIV infection now reaching levels similar to those of uninfected people.