Modification of the anti-tumour immune response by suppressor gene products of lymphoid cells.

Immunization of mice with BALB/c spleen cells leads to the production of effector lymphocytes which are cytostatic in in vitro assays to tumours of the same haplotype or carrying cross-reacting antigens. Immunization with B10.D2, a strain H-2 identical with BALB/c, does not generate cytostatic effector cells, nor does immunization with the F1 hybrids between B10.D2 and BALB/c. Analysis of the progeny of backcrosses of the F1 hybrids to BALB/c gave evidence that the suppressive effect of B10.D2 immunization is controlled by a single gene. Spleen cells from mice immunized with BALB/c or B10.D2 cultured in vitro with the corresponding stimulator cells yielded soluble factors in the supernatants that were respectively capable of amplifying or suppressing the in vitro cytostatic effect. Such experiments revealed that the inhibition of cytostasis caused by immunization with B10.D2 is not at the sensitization but at the effector phase of the assay. Possible mechanisms of action of this suppressor gene are discussed.