Abstract.-DNA isolated from skin epitheliomas containing papovavirus induced lymphomas within four to eight weeks in 40 to 50 per cent of newborn Syrian hamsters injected. This DNA effect was eliminated by DNase but not by RNase and was not induced by DNA preparations of transplanted epitheliomas or the induced lymphomas. Lymphomas were similarly induced by cellfree filtrates from certain human tumors such as gastric carcinomas and ovarian tumors. Little or no lymphoma effects were observed following injections with filtrates derived from normal human or animal tissues or human blood. The lymphomas induced by DNA and human tumors were transmissible by cell-free filtrates to newborn Syrian hamsters; however, successful serial passage, like the primary lymphomas induced by the DNA preparations, depended upon the use of a newborn hamster from a special breeding colony of hamsters.Introduction.-In previous publications, we reported both the spontaneous incidence of multiple skin epitheliomas (papillomas) containing large numbers of papovaviruses in Syrian hamsters1 and an associated induction of leukemias, predominantly lymphomas.2 The latter originated in almost every case in the liver of Syrian hamsters which as newborns had been treated with cell-free filtrates from the hamster skin tumors. The hamster lymphomas, which were separately transmissible by cell-free extract, contained a virus with the morphology of the C-type murine leukemia virus; interestingly, the papovavirus present in skin tumors could not be detected in the lymphomas by electron microscopic examination. Herewith, we report additional results concerning especially the induction of hamster lymphomas by DNA from spontaneous skin epitheliomas containing papovavirus. In addition, experiments are briefly described in which the lymphomas also appeared in significant numbers after subcutaneous inoculation of hamsters with filtrates derived from certain human tumors.Materials and Methods.-DNA was isolated from tissues of primary skin epitheliomas containing papovavirus. The tissue was either freshly excised or frozen at -80'C. The

No abstract

The protein pattern of a type-D retrovirus (PMFV) isolated from and propagated in human cell lines has been investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Staining with Coomassie blue and labeling with 14C-leucine/14C-lysine revealed five viral polypeptides with molecular weights of 10,000, 12,000, 15,000, 25,000, and 68,000. The 68,000 D-protein was shown to be a glycoprotein by incorporation of 3H-glucosamine and the 15,000 D-protein was identified as a phosphoprotein. By comparing PMFV with the closely related Mason-Pfizer monkey virus (MPMV) in co-electrophoresis experiments no clear difference was detected in viral 14C-leucine/14C-lysine profiles. The viruses differ, however, with respect to their glycoprotein patterns. A glycoprotein corresponding to the gp20 of MPMV has not been detected in PMFV irrespective of the cell line used for propagation of viruses.

IN an earlier communication we reported on multiple epithelial skin tumours in Syrian hamsters in which a Papova virus has been detected with great regularity, in large quantities, and in characteristic histological distribution, as evidenced by electron microscopic observation (Graffi et al., 1967). In experiments designed to transmit this disease by means of subcellular extracts from these tumours to other animals we surprisingly obtained in Syrian hamsters and, in certain circumstances, also in rats, leukoses and reticuloses. It is these that are the subject of the present report. MATERIALS AND METHODSSubcellular tumour extracts were prepared as follows: tissue from skin tumours of hamsters ( Fig. 1 and 2) was vigorously homogenized in a glass homogenizer in phosphate-buffered saline (PBS) solution and the homogenate was diluted 1: 5 to 1: 10 and centrifuged. One group of animals was treated with the supernatant of the homogenate obtained after centrifugation at 3000 r.p.m. for 20 minutes. In most experiments, however, the material injected was subjected to centrifugation at 4000 to 6000 r.p.m. twice or three times, followed by filtration through G4 glass filters twice. In some cases the filtrate was diluted 1: 1 with 0 * 25 M saccharose solution and centrifuged at 100,000 g for 40 to 60 minutes and the sediment was administered to the animals after suspension in PBS solution. By the same series of procedures, cell-free G4 filtrates were obtained from hamster leukoses induced by the injection of papilloma-derived material and from cell transplants of such leukoses. All manipulations were carried out in the cold (2°C.) as quickly as possible. The extracts were administered to (1) newborn Syrian hamsters of our own random-bred hamster colony that has a low spontaneous incidence of the type of skin tumour in question (maximum 5 per cent) and a low incidence of leukaemias mainly lymphomas (Horn and Siewert, 1968) arising in the mesenteric lymph nodes (about 3 per cent); (2) newborn Syrian hamsters of another hamster colony in which neither of the two types of tumour occur spontaneously; (3) newborn rats of a Wistar strain that has a spontaneous leukaemia incidence of about 0 5 per cent. The filtrate was in most cases injected subcutaneously, but occasionally intraperitoneally, in doses of 0 * 2 to 0 * 3 ml. per newborn hamster, or 0 -4 to 0 * 5 ml. per newborn rat.The electron microscopic investigation was performed with ultra-thin sections from tumours and from leukaemic infiltrates in liver, lymph nodes, spleen, kidney, etc. Material was fixed in glutaraldehyde and osmic acid and embedded in Epon. Uranyl and lead acetate were used to make contrast preparations.

No abstract