Virus-like Particles in Chemically Induced Sarcomas in High- and Low-Leukemia Strains of Mice1

Well-differentiated fibrosarcomas and anaplastic sarcomas developed in the s.c. tissues of four low-leukemia strains of mice (BALB/cf/Ki, Af/Ki, C3H/KÌand C3Hf/Ki) as well as two high-leukemia strains (AKR/Ki and C58/KÌ) following a single injection of benzpyrene (0.004 mg/g body weight) as young adults. The incidence of sarcomas was significantly less in both high-leukemia strains than that in all four low-leukemia strains. Abundant type C murine leukemia virus particles were found in primary and transplanted sarcomas of AKR and C58 origin as well as in normal tissue of either tumor-bearing or nontumor-bearing mice. Type C virus particles were seen less frequently in primary and transplanted sarcomas arising in BALB/cf, C3Hf, and C3H mice. No virus-like particles were seen in either primary or transplanted sarcomas or normal tissues obtained from Af mice. Intracisternal type A virus particles were also seen in both primary and transplanted tumor tissue as well as normal tissue of AKR and C58 mice but not in the tumor or normal tissue of the other four strains. Type B mammary tumor virus particles were not seen in any sarcomas developing in any strain of mouse. Cell-free extracts of Af transplanted sarcomas in which no virus-like particles could be seen by electron microscopy proved to have biological activity when injected into newborn mice of the BALB/cf/Ki, C3Hf/Ki, C57BL/KÌ,and Af/Ki strains. This activity was characterized by an increased inci dence of the tumors, which occur in low to moderate inci dence in these strains. No sarcomas were seen in any of the injection-treated mice of any strain. Cell-free extracts of transplanted AKR sarcomas with abundant type C virus particles had no oncogenic effects when injected into newborn BALB/cf mice. Whereas an extract of the 1st transplant generation of C58 sarcomas with abundant virus particles was negative when injected into newborn BALB/cf mice, an extract from the 8th transplant generation of sarcomas was associated with an increase in lung tumors in the same strain of mice. These results indicate the complexity of the interactions between host genetic factors and the different murine onco genic viruses found in chemically induced sarcomas. A rela tionship between the virus-like particles found in these sar comas and their etiology was not established.