Sixteen cultures of continuous human cell lines were tested for oncornaviruses. Six cultures spontaneously released theviruses into the culture fluid. Five cultures released the virusesafter treatment with 5-bromodeoxyuridine or mitomycin C. Five cultures were negative. The viruses belonged to the B and Ctypes of oncornaviruses. Possible origin of the viruses is discussed.
A virus has been isolated from a clone of continuous cell line that was derived from human cancer tissue (HEp‐2 cells). The clone of HEp‐2 cells retains human Karyotype and has no heterogeneous contamination. Injection of the cells and the virus into mice of C3H/Sn, C3H/H2P, BaLB/c lines and into newborn hamsters did not produce tumors in animals. Intracellular virus possesses morphological characteristics of oncornaviruses type A and B; extracellular virus has the properties of oncornaviruses type B. The virus bands at ϱ = 1.16 g/ml in sucrose density gradients, and the production of it is inhibited by actinomycin D. The virions contain reverse transcriptase, and the products of reaction are double‐stranded DNA and RNA:DNA hybrids. The virus is immunologically distinct from mouse mammary tumor virus. Possible human origin of the virus is discussed.
The oncornaviruses isolated from continuous human cell lines and the Mason-Pfizer virus share a common group-specific antigen that is revealed in the immunodiffusion test. They have no common antigens with the mouse mammary tumor virus.
SummaryEleven lines and sublines of larynx carcinoma (HEp-2), cervical cancer (IteLa) and dedifferentiated astrocytoma (DAPT) cells were examined and viruses were isolated from eight lines. Electronmicroscopic, biophysical and biochemical examinations of the viruses showed that they belong to the B-type oneornaviruses. The virions had a size of 100 to 150 nm, they banded at densities of 1.16 to 1.17 g/ ml in sucrose gradients and t~NA from the virions contained 60--70 S component. The reproduction of the viruses was inhibited by actinomycin D, and the virions possessed reverse transcriptase (gNA-dependent DNA polymerase) activity. The isolated viruses differed antigenically from mouse mammary tumor virus.
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