Induction and regression of primary moloney sarcoma virus-induced tumors in mice.

A. FEFER, J. L. McCOY, AND J. P. GLYNNUnited States Public Health Corps; Drug Evaluation Branch, National Cancer Institute, N IH; and Microbiological Associates, Inc.,Bethesda, Maryland 20014SUMMARYNewborn BALB/c, C57BL/6, and (BALB/c X C57BL/6) Fi(CBF) mice were equally susceptible to tumor induction byMoloney sarcoma virus (MSV). A significant incidence of spontaneous regressions of primary tumors was observedâ€”aphenomenon unique to this tumor system. Of tumors induced in newbornBALB/c, C57BL/6, and CBF mice, 4/151, 20/43, and 12/49,respectively, regressed. Serum from mice whose primary tumorsregressed neutralized the oncogenicity of MSV. The three strainsof adult mice were equally susceptible to tumor induction byMSV. X-irradiation of adult mice with 350 R one day prior toMSV inoculation did not affect susceptibility to oncogenesis, butaffected the fate of the tumor. Whereas all tumors induced inunirradiated adult mice completely regressed, many tumors induced in X-irradiated mice grew progressively and killed thehosts. It is therefore suggested that in this tumor system, with itsremarkably short latency period to tumor formation, the immunologie competence of the host may not be a prime factor intumor induction, but may determine whether a primary tumor,once formed, will regress or kill the host. All the adult mice werebled 9, 21, and 50 days after MSV inoculation, and their seratested against Moloney lymphoma cells by the indirect fluorescent antibody test. No relationship between antibody productionand tumor regression was evident.INTRODUCTIONMoloney (16) recently noted the development of sarcomas innewborn mice inoculated with a potent Moloney leukemia viruspreparation. Cell-free extracts of the sarcomas induced tumorsat the site of inoculation in virtually all newborn mice and inweanling BALB/c mice. Pathologic studies (17) revealed thetumors to be rhabdomyosarcomas. By electron microscopy, Dai-ton (5) observed virus particles, morphologically indistinguishable from the murine leukemia viruses, budding from connectivetissue cells.Transplantable MSVMndueed tumors were difficult to obtainbecause they regressed in most normal histocompatible recipients.However, tumors transplanted into preirradiated mice usuallygrew progressively. The tumors were shown to be antigenic in1The following abbreviations are used :MSV, Moloney sarcomavirus; FMR, Friend, Moloney, and Rauscher viruses or lymphomacells; CBF, (BALB/c 9 X C57BL/6 rnmice was observed. To determine the role of the host's immunologie competence in this unique phenomenon, the inductionand regression of primary MSV-induced tumors was investigatedin three strains of newborn mice, and in normal and X-irradiatedadult mice.MATERIALS AND METHODSMiceMale and female BALB/c, C57BL/6, and CBF mice, 12-16weeks old, were used. All mice were obtained from the productioncolonies of Texas Inbred Mice and Batelle Memorial Institute.Pregnant females were observed daily. Mice used as "newborns"were always less than 72 hours old.VirusesAll experiments were performed with a single pool of MSV,Lot No. SV-216-RP No. 45, a one gram equivalent tumor extractfrom Moloney sarcomas of BALB/c origin (7). X-irradiation of MiceThis procedure was performed as previously described (7). The Indirect Fluorescent Antibody TestThe technic developed by MA¶ller(14), using suspensions ofviable cells, was employed; 0.05 ml of undiluted antiserum wasadded to a pellet containing 2 X IO6trypan blue-unstained cells.The suspension was incubated at 37Â°Cfor 20 minutes and washed4 times in Hank's Balanced Salt Solution. The resulting pelletwas incubated for 20 minutes at 37Â°Cwith 0.05 ml of fluorescein-conjugated goat-antimouse globulin (Hyland) diluted 1:5. After4 more washings, the cells were examined under the fluorescencemicroscope. Samples were read blind. Cells manifesting diffusefluorescence of the type that MA¶llerdemonstrated to be indica-1626 CANCER RESEARCH VOL. 27Downloaded from cancerres.aacrjournals. org on May 6, 2015. © 1967 American Association for Cancer Research.