H. zur Hausen

Characterization of a foamy virus isolated fromCercopithecus aethiops lymphoblastoid cells

A virus derived from cells of a lymphoblastoid line originating from the lymph node of a healthy African green monkey was characterized as a typical member of the foamy virus subgroup of retroviridae by its morphological, physicochemical, biological and biochemical properties (reverse transcriptase actvity). Besides the usual host range of foamy viruses, the isolated strain revealed a remarkable T-lymphotropism, distinguishing it from the prototypes of foamy viruses previously isolated from African green monkeys. Two foamy virus infections are demonstrated in human contacts of the African green monkey colony, with the animal harbouring the isolate.

Characterization of an EBV-like virus from African green monkey lymphoblasts

Abstract A lymphoblastoid cell line (AGM-2206) has been established from the peripheral blood of an African green monkey. Approximately 1% of these cells showed fluorescence for EBV capsid antigens (VCA), when examined with human EBV-VCA-positive sera by indirect immunofluorescence. Titration of human and monkey sera on AGM-2206 and P3HR-1 cells revealed a partial cross-reactivity between capsid antigens of the AGM virus and human EBV. In addition, cross-reactivity within the EA complex is suggested by reactivity of about 20% of monkey sera with human EBV-EA. Neither human nor monkey sera reacted with an EBNA-like antigen in AGM lymphoblasts. Cleavage patterns of AGM-EBV DNA with Eco RI and Hin dIII restriction endonucleases showed differences when compared to human EBV DNA isolated from B 95-8, P3HR-1, and QIMR-WIL cells. Hybridization of labeled EBV DNA from B 95-8 cells to fragments of AGM-EBV DNA blotted onto nitrocellulose filters resulted in some hybridization to a number of AGM-EBV DNA bands.

Partial characterization of the proteins of human papilloma viruses (HPV) 1-3.

The protein compositions of full and empty particles of human papilloma viruses 1, 2, and 3 were compared by SDS-gel electrophoresis. The protein patterns revealed a considerable variation in the relative concentrations of three major proteins (VP2, 3, and 4) in individual preparations. In some cases, heavy and light full particles prepared from the same wart showed a similar variability in the concentrations of VP2, 3, and 4. The different protein patterns were interpreted as resulting from conversion of VP2 into VP3 and 4. The molecular relationship of these three proteins was confirmed by BrCN cleavage which led to corresponding oligopeptides. Electron micrographs of empty particles revealed that the only detectable protein components VP3 and 4 are present in typical capsomeres.

Establishment of spontaneously outgrowing lymphoblastoid cell lines with Cyclosporin A

To establish spontaneously outgrowing EBV (Epstein-Barr virus) transformed lymphoid cell lines from healthy EBV-seropositive adults different culture conditions were investigated. The effect of T-cell depletion was compared with that of adding Cyclosporin A (CSA) to unseparated mononuclear blood cells, either at the onset of cultivation or after 3 weeks. The highest frequency of spontaneous outgrowth of EBV-transformed cells was obtained in unseparated cultures when the addition of CSA was delayed. The presence of unimpaired T cells at the onset of the culture period appeared to have a favourable effect on the spontaneous outgrowth of EBV-carrying lymphoblastoid cell lines.

Viruses in Human Tumors

Table 1 lists the possible interactions of viruses in oncogenesis and emphasizes the role of human pathogenic viruses. The majority of tumor viruses known today insert their genetic material into the host cell nucleus, where it persists. The expression of at least one viral function appears to be a prerequisite for the maintenance of the transformed state.

Papovaviruses and human tumors.

Papovaviruses contain the two subgroups “polyomaviruses” and “papillomaviruses” (reviewed in [20]). Members of both subgroups are clearly oncogenic, most notably the papillomaviruses, which induce papillomas within their natural hosts (see review [24]). Viruses of both subgroups can be distinguished morphologically, biochemically, and biologically. The polyomaviruses are nonenveloped, eicosaedral particles of 40 nm containing a circular double-stranded DNA molecule of about 3.3 × 106 daltons. The papillomaviruses show similar structural features. They are, however, larger in size (50–55 nm) and contain a DNA molecule of about 5.0 × 106 daltons. The structural organization of the genome is totally different in both groups: In polyomaviruses, transcription of early and late genes occurs in opposite polarity involving both strands. Papillomavirus DNA has only one transcribed strand with a long stretch of base pairs separating early and late transcripts. Polyomaviruses thus far appear to be oncogenic under experimental conditions only, mainly after injection into newborn animals. Papillomaviruses, in contrast, are the causative agents of papillomas and contribute, under certain conditions, to malignant conversion.

The virus-cell gene balance model of cancerogenesis.

In recent years it became increasingly clear that infection of the human host by a number of viruses results in a probably life-long persistence of these agents within specific cells (reviewed e.g. zur Hausen, 1977a). Reactivation of persisting genomes is a well-known phenomenon in individuals infected by herpes group viruses (herpes simplex virus, varicella zoster virus) where neural cells have been identified as site of virus persistence. Infection with Epstein-Barr virus, the causative agent of infectious mononucleosis, leads to viral genome persistence in certain B-lymphocytes. They can be isolated and are readily propagated in tissue culture even years or decades after primary infection (reviewed by zur Hausen, 1975). Transmission of cytomegalovirus infections by blood transfusions has been frequently recorded, even from donors who acquired the virus several years earlier.

Viruses as Tumor Initiators and Tumor Promoters

The role of specific viral genes in the induction of malignant tumors is well established in viral infections by papovaviruses and adenoviruses (e.g. review by zur Hausen 1980). In these infections viral DNA may integrate into the host cell genome, and continuous expression of a viral function is a prerequisite for the maintenance of the transformed state.

Biochemical Detection of the Virus Genome

The possible involvement of a virus in the etiology of Burkitt’s lymphoma (BL), as originally suggested by Burkitt (1962), gained substance by the demonstration of herpes-like particles in cells of lymphoblastoid lines derived from this tumor (Epstein et al., 1964). The development of serologic tests by Henle and Henle (1966) and their application to large groups of patients and controls revealed the presence of antibodies to Epstein-Barr virus (EBV) antigens in all populations tested (Henle et al., 1969, 1970 a, 1973 a, b). These tests resulted in the discovery of the etiologic role of EBV in infectious mononucleosis (IM) (Henle et al., 1968) and demonstrated clearly the prevalence of antibodies in certain groups of tumor patients. Besides BL (Henle et al., 1969) other tumors were found to be correlated with high antibody titers against EBV antigens: this was notably the case in nasopharyngeal carcinoma (NPC) (Henle et al., 1970 a) and less pronounced (although still significant) in patients with Hodgkin’s disease (Levine et al., 1970; Hesse et al., 1973), chronic lymphatic leukemia, lymphocytic lymphoma (Johansson et al., 1971), and occasionally also in other diseases (Evans, 1971; Papageorgiu, 1973).

Biological Significance of Human Papillomavirus Early Gene Expression in Human Cervical Carcinoma Cells

For about 150 years infectious agents have been implicated as etiological factors for cervical cancer in women (Rigoni-Stern 1842; zur Hausen 1977b). A venereal transmission of these agents has been proposed since sexual promiscuity, early onset of sexual activity, and poor hygienic conditions emerged as potential risk factors. Genital infection with the herpes simplex virus (HSV) type 2 was suspected as a potential risk factor. Patients suffering from invasive cervical carcinoma were in a significantly higher percentage found to be HSV-seropositive than the respective control groups (Rawls et al. 1977; Melnick and Adam 1978). However, the virus itself or its genetic material has not regularly been found in cancer biopsy specimens (zur Hausen 1982) and a prospective study recently performed by Vonka and colleagues could not confirm HSV 2 infection as a potential risk factor for subsequent development of cervical cancer (Vonka et al. 1984).