Prevalence of endogenous type-C virus in normal hamster tissues and hamster tumors induced by chemical carcinogens, simian virus 40, and polyoma virus

Immortality of cell cultures derived from brains of mice and hamsters infected with Creutzfeldt-Jakob disease agent

Isolates from six patients with Creutzfeldt-Jakob disease (CJD) were injected into various strains of hamsters and mice, and the infective agent was propagated. Serially passaged cultures were established from these CJD agent-infected brains and from uninfected control brains. All healthy cultures (21 out of 21) from CJD agent-infected brains became immortal and/or transformed. In contrast only 3 out of 13 normal brain cultures became immortal, and the rest died out with serial propagation in vitro. The fact that permanent cell lines were readily derived from multiple rodent strains and all CJD isolates tested suggests that a transforming capability is an intrinsic property of CJD agents. This conclusion is supported by demonstrations of in vitro cell transformation by CJD infectious brain fractions. Although the molecular mechanism of transformation events associated with the CJD agent is not presently known, a provocative possibility is that the CJD agent has a direct effect on the host genome by mechanisms analogous to those known for slowly oncogenic retroviruses.

Hamster endogenous retrovirus (HaER) isolated from SV-40 induced tumor cells

A hamster cell line obtained from a secondary transplanted SV-40-induced tumor was found to spontaneously release type C virus particles. The particles possessed all biochemical features characteristic of retroviruses and induced syncytium formation in XC cells but were not oncogenic for hamsters. Nucleic acid hybridization assays demonstrated that the isolated virus was an endogenous retrovirus of hamster, lacking sequence homology with mouse and other animal species.

Characterization and distribution of nucleic acid sequences of a novel type C retrovirus isolated from neoplastic human T lymphocytes

A type C retrovirus (designated HTLV) recently isolated from a cell line derived from a lymph node and later from peripheral blood of a person with cutaneous T-cell lymphoma (mycosis fungoides) was characterized by nucleic acid hybridization experiments. HTLV [3H]cDNA hybridized 90% to its own 70S RNA with kinetics consistent with the genetic complexity of other retroviruses, but it did not hybridize substantially to RNA or proviral DNA from any animal retroviruses (types B, C, and D), including those from nonhuman primates. Conversely, [3H]cDNA from other retroviruses did not hybridize to RNA or DNA of the human T-cell line producing HTLV. HTLV proviral sequences were present (two to three copies per haploid genome) in DNA of these cells, and homologous sequences were present in the cell cytoplasmic RNA (0.3% viral sequences by weight). HTLV-related nucleic acid sequences were not found in DNA from various other human tissues. The results indicate that HTLV is a new class of type C virus that is not an endogenous (genetically transmitted) retrovirus in man.

C-type RNA virus from hamster cells transformed in vitro by 1-B-D-arabinofuranosylcytosine

Evidence of type-C RNA viral activity in fetal hamster cells transformed in vitro by 1-B-D-arabinofuranosylcytosine (ara-C) after at least one in vivo passage is described. The virus possesses properties typical of other type-C RNA viruses, such as: a) morphology as determined with the electron microscope, b) presence of 70S RNA, c) enhanced expression following treatment with halogenated pyrimidines, d) group specific antigens of hamster type, and e) a buoyant density of 1.15 g per cm3. However, the virus particles are deficient in RNA-dependent DNA polymerase activity under conditions that easily detect Rauscher Leukemia virus and will infect neither hamster, rat, mouse, human nor rabbit cells. The possible role of this virus in chemical carcinogenesis of cultured hamster fetal cells is discussed.

Characterization of cell lines derived from hamster tumors induced with the BK virus

Some of the properties of three continuous cell lines derived from BK virus-induced hamster tumors were examined. The cell lines had in vitro growth characteristics of transformed cells. Morphologically most of the cells were fibroblastic, but multinucleated giant cells were also common. Ultrastructurally all three cell lines displayed the usual features of cells grown in vitro. Marked variation in the nuclear size and shape as well as prominent nucleoli were characteristic to these cells. No viruses or virus-like particles were found. Virus isolation attempts by fusing the cells with Vero cells were negative, and no virion antigen was detected in these cells by immunofluorescence. T antigen similar to that of other papovaviruses was found in the cells. This antigen stained with sera from a number of hamsters carrying transplanted BK virus-induced tumors, and also with SV 40 T antisera. The antigen disappeared after 30 minutes at 56 degrees C. Cytogenetic analyses showed that the three cell lines were heteroploid with subtetraploid numbers of chromosomes. Chromosome abnormalities were also seen. All three cell lines induced sarcomatous tumors in adult hamsters after subcutaneous inoculation.

The influence of MuLV and SV40 viruses on senescence in mouse fibroblasts in vitro

Mouse cells productively infected with Moloney leukaemia virus (MuLV) underwent senescence in a manner similar to control cells, although they recovered more readily as an established line. Rapidly growing cell lines were also obtained following simian virus 40 (SV40) infection of senescent cells. However, superinfection of senescent MuLV-producing cells by SV40 led to slower growing cells with a reduced output of infectious MuLV.

The endogenous origin and transmission of RNA viral genomes that code for cancer

In certain experimental animals, type-C virus genomes are universally prevalent. They are mostly but not exclusively transmitted genetically and produce tumors naturally as well as when transmitted experimentally. The spontaneous virus and tumor expressions are regulated and modified by genetic factors; and virus-specific virogenes used as vaccines prior to high-level natural expressions can suppress natural expressions of the virogenes. Application of this significant information to the prevention of cancer in mice now seems quite feasible; however its application to the control of human cancer is still dependent on the isolation of specific human type-C virus(es).

I. In vitrol transformation of rat embryo cells: correlations with the known tumorigenic activities of chemicals in rodents

Susceptibility to chemically induced transformation changed as a rat embryo cell culture was passaged. For the first 35 to 60 passages, the cultures were diploid and resistant to transformation by chemical carcinogens. However, cultures infected with a murine leukemia virus were transformed by chemicals. For the next 60 passages, the cultures were heteroploid, but retained contact inhibition and were not tumorigenic. Even without addition of heterotypic viruses, these heteroploid cultures could be transformed by chemicals, but the endogenous rat C-type virus could be demonstrated in the transformed cultures. At higher passages, the rates of spontaneous transformation gradually increased so that the cultures could not be used for transformation studies. Chemically induced transformation of the stable heteroploid cell line (F1706) was manifested by an easy to read focal alteration. Initial observations based on these foci were confirmed by inoculating the morphologically altered cells into isogeneic newborn rats. A number of carcinogenic and noncarcinogenic chemical analogues were tested for their ability to transform F1706 cultures. The compounds tested included 4 azo dyes, 12 polycyclic hydrocarbons, 12 aromatic amines, and 7 miscellaneous compounds. Based on the known activities of the same chemicals in rodents, certain active compounds failed to induce transformation in any test, and others induced transformation in only some tests, but these in vitro tests, if used as a screening assay, would have been correct in 82% of all individual tests, and over-all, would have correctly predicated the carcinogenic activity of 33 of the 35 agents tested.

Behavior of three types of ribovirus-like particles in segregating hamster times mouse somatic hybrids

An electron microscopic study of somatic hybrids resulting from a cross between hamster melanoma cells harboring R-type particles and mouse fibroblasts harboring intracisternal A-type and (mostly) immature C-type particles was performed. The major findings are: (a) hybrid cells that retain a large fraction of both hamster and mouse chromosomes produce all three types of particles; (b) the loss of mouse chromosomes is followed by that of intracisternal A- and C-type particles; (c) the continued production of A- and C-type particles is dependent on the retention of different mouse chromosomes; (d) the mixed intracellular population of R- and A-particles comprises a small number of complex structures in which the two types of virions are enclosed within a common envelope.

Radioimmunoassay for the major structural protein of hamster type C viruses

A radioimmunoassay for the major, group-specific antigen (p30) of hamster type C viruses was developed. The test detected approximately 5 ng of viral protein per ml and was highly specific for hamster viruses when used with homologous antibody. Comparison of three hamster viruses, two being mouse-hamster pseudotypes, in homologous and heterologous intraspecies assays, showed no evidence of type specificity for these proteins. The pseudotype viruses showed no evidence of mouse virus p30 antigenic determinants. An interspecies antigen assay employing (125)I-labeled hamster p30 and anti-feline p30 was completely inhibited by cat (feline leukemia virus), hamster, and rat viruses, to a slightly lesser degree by mouse viruses, and only poorly by RD 114 and Gibbon ape viruses. The Mason-Pfizer virus did not inhibit this assay. Hamster p30 was detected by radioimmunoassay in individual embryos from two LSH hamsters and in several adult tissues, excluding muscle at levels below that required for detection in complement-fixation tests.