Passive immunotherapy prevents expression of endogenous Moloney virus and amplification of proviral DNA in BALB/Mo mice.

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Abstract
BALB/Mo mice carrying the Moloney murine leukemia virus (M-MuLV) as an endogenous virus become viremic soon after birth and develop leukemia at a later age. M-MuLV-specific gene expression and an increase of virus-specific DNA copies in lymphatic target organs are characteristics of the preleukemic phase. Passive immunotherapy of newborn BALB/Mo mice with anti-gp70 glycoprotein or with antiM-MuLV serum prevented viremia and significantly delayed the subsequent development of leukemia. Molecular hybridization experiments showed that virus-specific genome transcription and virus-specific DNA amplification were completely suppressed by antiserum treatment. Thus, virus-specific RNA concentrations in target organs of immunized BALB/Mo mice of 6 mo. or older were as low as in normal BALB/c mice. This is an age at which untreated BALB/Mo mice have already developed malignant lymphoma. Antiserum treatment interferes with the early events of virus expression and thus prevents the subsequent steps leading to leukemia.