Murine Mammary Tumor Virus Protein Vaccine: Induction of Antivirus Immunity andInhibition or Acceleration of Growth of Transplanted Mammary Tumors

BALB/c and DBAf mice were vaccinated with different doses of a protein fraction of the murine mammary tumor virus (MuMTV), enriched for the major glycoprotein gp52. Twenty days after vaccination, the mice were challenged with live tumor cells: BALB/c with an MuMTV-induced mammary tumor, DBAf with the MuMTV-positive leukemia L 1210. Alum and an interphase material isolated from Mycobacterium smegmatis (IPM) were used as an adjuvant; control animals were treated with the adjuvant alone. In BALB/c mice treated with 1 µg of the gp52-enriched protein fraction precipitated on alum, the onset of tumor growth was delayed 10 weeks; a dose of 10 µg had no clear effect, whereas 100 µg caused clear acceleration of tumor growth. Each of the vaccinated animals developed a tumor, as compared to 60% of the control group. In DBAf mice low doses of the vaccine accelerated tumor growth. In general, acceleration was stronger when a higher dose was used. Fifty µg of IPM and the gp52-enriched protein fraction in DBAf mice resulted in protection. In combination with 100 µg IPM, however, tumor growth was accelerated. Cellular reactivity to the virus was determined by means of the leukocyte adherence inhibition (LAI) assay. Serum was tested for the presence of factors that either block or enhance the LAI reaction and for the presence of antibodies with the membrane immunofluorescence test. Protection was observed when serum blocking factors were absent, even if cellular immune reactivity and antibody titer were low. When serum blocking factors were present, protection was observed only when it was combined with high antibody titers and strong cellular immunity.