PROTECTIVE IMMUNITY IN BALB C MICE AGAINST THE SIMIAN-VIRUS 40-INDUCED MKSA TUMOR RESULTING FROM INJECTION OF RECOMBINANT LARGE T-ANTIGEN -REQUIREMENT OF CD8(+) T-LYMPHOCYTES/

BALB/c mice are often considered ''low responders'' or even ''nonrespo nders'' with regard to cytolytic CD8(+) T lymphocytes and SV40 large T Ag (TAg). Large TAg and fragments thereof were produced by recombinan t technology and injected into BALB/c mice that were subsequently chal lenged by i.p. injection of syngeneic TAg-expressing mKSA tumor cells. Two portions of the TAg were found to induce protective immunity, one stretching from amino acid residues 1-272 and the other from amino ac id residues 683-708. In mice thus protected, the spleens were virtuall y free of cytotoxic T cells but CD8(+) T lymphocytes obtained from the peritoneal cavity during rejection of the mKSA cells were directly ly tic for TAg-expressing target cells. Depleting immune mice of CD4(+) o r CD8(+) T lymphocytes by treatment with mAb abolished their ability t o resist tumor development. We conclude that immunity against SV40 TAg -expressing tumor cells in BALB/c mice is dependent on both CD4(+) and CD8(+) T lymphocytes.