Biological activity and separation of a leukaemogenic virus from murine sarcoma virus‐harvey (MSV‐H)

Twelve different preparations of Murine Sarcoma Virus‐Harvey (MSV‐H) had leukaemogenic activity when tested in BALB/c and C3H/Bi mice or Sprague‐Dawley rats, some of which ultimately developed generalized lymphocytic leukaemia instead of reacting rapidly and characteristically with sarcoma formation and/or erythroblastic splenomegaly. Inactivation of MSV‐H by ether treatment, reducing its titre by dilution, and using the intramuscular route of injection, all biased towards leukaemogenesis. The leukaemogenic component could be separated by vertical transmission from three MSV‐H‐infected female mice, which themselves showed only sarcomas and/or splenic erythroblastosis, to as many as six successive generations of their untreated offspring. Presence of a leukaemogenic virus, probably MLV, was confirmed by serial passage of plasma filtrates from leukaemic animals, including leukaemic progeny, in newborn mice and rats. Lymphocytic leukaemia developed exclusively in these recipients and in those given a plasma concentrate. Moreover, pre‐treatment with the leukaemogenic virus enhanced the oncogenicity of MSV‐H in 8‐ and 14‐day‐old mice, as judged by an increased incidence of sarcomas. Pathological changes in the kidneys of the leukaemic mice are also described, which probably represent an immune deposit lesion related to the deposition of circulating complexes of viral antigen and anti‐viral antibody on the basement membranes of the glomerular capillaries.