Studies on murine sarcoma virus; A morphological comparison of tumorigenesis by the harvey and moloney strains in mice, and the establishment of tumor cell lines

Anatomic lesions produced by the Moloney and Harvey strains of Murine Sarcoma Virus (MSV‐M and MSV‐H) in mice have been compared. Erythroblastic splenomegaly is a distinctive feature of disease produced by MSV‐H. Solid tumors induced by both viruses were quite similar in morphology, although some consistent differences were noted. The tumors appear to arise by massive recruitment of primitive mesenchymal cells rather than by clonal proliferation. The morphological features of these lesions would suggest that, although MSV‐M and MSV‐H are similar entities, they are not quite identical. Four transplant lines have been established from the mouse tumors; three MSV‐H and one MSV‐M. The MSV‐M line (CBA strain) was initiated with difficulty and did not release sarcoma virus. The MSV‐H lines (two CBA and one BALB/c) were easier to initiate and virus release was demonstrated both in vivo and in vitro. In addition to tumor growth at the site of implantation, the BALB/c line also produced splenic erythroblastosis. The MSV‐M and one of the MSV‐H CBA lines underwent a distinctive alteration during the course of in vivo passage in which the original spindle‐cell lesion evolved into an undifferentiated small‐cell tumor.