In vitro isolation and characterization of the GA strain of feline sarcoma virus

Exploring the link between viruses and cancer in companion animals: a comprehensive and comparative analysis

Currently, it is estimated that 15% of human neoplasms globally are caused by infectious agents, with new evidence emerging continuously. Multiple agents have been implicated in various forms of neoplasia, with viruses as the most frequent. In recent years, investigation on viral mechanisms underlying tumoral transformation in cancer development and progression are in the spotlight, both in human and veterinary oncology. Oncogenic viruses in veterinary medicine are of primary importance not only as original pathogens of pets, but also in the view of pets as models of human malignancies. Hence, this work will provide an overview of the main oncogenic viruses of companion animals, with brief notes of comparative medicine.

Characteristics of three strains of feline fibrosarcoma virus grown in cat and marmoset monkey cells

Two strains of feline fibrosarcoma virus (ST-FeSV and GA-FeSV) were found to induce tumors in cats and marmosets, and to transform feline and marmoset cells in vitro after primary inoculation. A third strain (SM-FeSV) failed to induce tumors or transform marmoset cells after primary inoculation; however, when SM-FeSV-injected marmoset cultures were passed 26 times in vitro, the cell cultures released infectious virus which transformed marmoset fibroblasts but still failed to induce tumors in marmosets. ST-FeSV induced mainly round-cell type transformation (r foci), GA-FeSV induced predominantly mixed round-fusiform cell type transformation (fr foci), and SM-FeSV induced r and fr type foci with a higher proportion of fusiform cells in the fr foci than seen with GA-FeSV. Transforming virus was obtained from r or mixed r/fr foci of ST-FeSV but not from fr foci; heat treatment changed the virus from producing almost exclusively r type foci to inducing an increased number of fr foci. Passage of FeSV in cat cells yielded viruses with a higher ratio of infectivity for feline vs marmoset cells, while passage of FeSV in marmoset cells yielded virus with a relatively higher infectivity ratio for marmoset cells; the three strains differed in the degree of change in the infectivity ratio. Despite the alteration of host range of SM-FeSV propagated in marmoset fibroblasts, the virus retained feline P-30 antigen by CF and FA assays. Neutralization tests did not indicate but also did not exclude an alteration of the surface antigens of ST-FeSV or SM-FeSV propagated in marmoset fibroblasts. The alteration of the relative infectivity of FeSV during passage in marmoset cells may be due to: (1) the selection of a variant present in the original heterogenous uncloned population; (2) mutation; or (3) recombination with some marmoset genetic material, possibly an as yet unidentified endogenous marmoset virus.

Specificity of the DNA product of RNA-dependent DNA polymerase in type C viruses. II. Quantitative analysis

A number of mammalian Type C viruses were analyzed for relatedness by the technique of DNA.RNA hybridization. Viral DNAs were prepared in single-stranded form from complexes with 70S viral RNA formed during endogenous polymerase reactions. Extent of hybridization was assayed with the single-strand nuclease (S-1) from Aspergillus oryzae. Results obtained indicated a high degree of viral specificity, with significant cross-reactions being observed only with viruses obtained from within a species, as in the case of mouse and cat viruses, or in the special case of woolly monkey-gibbon comparisons. Comparisons of RD-114 virus, recently determined to be of feline origin, and conventional feline Type C viruses (FeLV), revealed minimal relatedness, especially when feline virus was grown on human cells, thus indicating the possibility of coexistence of greatly disparate Type C viruses within one species. A rat-specific virus, recovered from tumors induced by murine sarcoma virus, was found to contain genetic material common to both the original mouse virus and viruses indigenous to the rat, even though only rat-specific proteins have been detected during infection by this virus.

Isolation of RD-114-like oncornavirus from a cat cell line

A clone of cells derived from a continuous line of cat cells (CCC) spontaneously produced an RNA C-type virus (CCC virus) which did not have the group-specific antigen of the standard strains of feline leukemia viruses but did have that of the RD-114 virus. Single-hit infection of a virus yielding CCC cell with only the feline leukemia virus pseudotype of murine sarcoma virus [MSV(FeLV)] resulted in the release of a pseudotype of MSV coated with the CCC virus envelope. Host range, transmission of virus, helper functions, interference properties, and specific neutralization showed that the CCC and the RD-114 isolates as well as their respective MSV pseudotypes are closely similar if not identical. Parental, virus-negative cells frozen before the existence of RD-114 were chemically induced to yield CCC-like virus de novo. Infection of susceptible human cells with the chemically induced virus resulted in interference with the CCC virus pseudotype of MSV but not with the FeLV pseudotype of MSV.