Human osteosarcoma and mammary carcinoma cells were cultured separately in a medium supplemented with fetal calf serum, until they were confluent. The medium was then replaced by serum-free medium supplemented with heparin. Both cell cultures secreted collagenase, and this activity was inhibited by a cartilage-derived protein of low molecular weight. Since cartilage is rarely invaded by neoplasms, the presence of this inhibitor may play an important role in the regulation of tumor invasion.

established by infection of human cord blood lymphocytes with SI Raji virus, were maintained in RPMI 1640 medium supplemented with 8% fetal calf serum. The medium contained 100 units of penicillin and 50 Mg of streptomycin per ml.Superinfection of Raji and HLB Cells. Raji cells and HLB cells were superinfected with HR1 virus in minimal essential medium lacking phosphate with 2% fetal calf serum as reported previously (5).Test for Transforming Activity of SI Raji Virus. Human cord blood was collected into syringes rinsed with preservative-free heparin and dextran was added to a final concentration of 1%. After the blood stood at 370 for 1 hr, cell-rich plasma was collected and the mononuclear leukocytes were separated from plasma on Ficoll-Hypaque gradients (6). Isolated leukocyte populations were incubated overnight in a humidified CO2 incubator at the concentration of 1 X 106 cells per ml in RPMI 1640 medium supplemented with 20% fetal calf serum. Leukocytes were collected by centrifugation at 1000 rpm for 10 min and resuspended in supernatant fluid of superinfected Raji cells (48 hr after superinfection) that had been made cell free by filtration through a nitrocellulose membrane filter (0.45 um pore size). After 1 hr of adsorption with occasional shaking, infected cells were washed once and then maintained at 106 cells per ml at 370 in RPMI 1640 medium containing 20% fetal calf serum. Half the medium was replaced with fresh medium weekly.Calculation of EBV Genome Content. EBV-specific cRNA was prepared in vitro from EBV DNA by using Escherchia coli RNA polymerase. Alkaline-denatured DNA in 0.90 M NaCl/ 0.090 M sodium citrate was passed through nitrocellulose membrane filters and single-stranded DNA was fixed to it by baking at 80°under reduced pressure for 2 hr. cRNA (1.

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C-type RNA viruses of avian, feline and simian origin induce sarcomas in marmosets and a simian herpesvirus induces lymphomas and/or lymphocytic leukemias. Virus genome expression is usually repressed to various degrees in vivo, but becomes derepressed if the tumor cells are grown in vitro. The high susceptibility of marmosets to oncogenic viruses and the hematopoietic chimerism between offspring make them ideal animals for studying not only the oncogenic activity of animal tumor viruses and of potentially oncogenic materials but also the immune response to the viral-induced neoplastic diseases.

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