Immunogenicity of a rat leukaemia of spontaneous origin (SAL).

The SAL rat leukaemia, which resembles acute myeloblastic leukaemia, appeared initially to be non-immunogenic since resistance to an i.p. challenge with as few as 100 cells could not be obtained using stimulation of the RES or by immunization with SAL cells exposed to x-rays, nitrogen mustard, iodoacetate or glutaraldehyde. However, immunization with SAL cells exposed to low doses of mitomycin-C slowed the growth of the challenge inoculum. Cells treated with high doses of mitomycin-C did not immunize. The results are interpreted in terms of rapid shedding of a tumour-specific antigen from the membrane of SAL cells.