Augmentation of specific tumor immunity against a syngeneic SV40-induced sarcoma in mice by retinoic acid.

The effects of retinoic acid, a vitamin A derivative, which has been shown to have immune adjuvant properties, were studied in vivo in a syngeneic tumor system by the use of the tumor-cell neutralization assay. The effector activity of spleen cells of BALB/c mice immune against a syngeneic SV40-induced sarcoma, mKSA, was specifically augmented by low doses of retinoic acid, whereas high doses had a suppressive effect. In addition, the time required for generation of the effector activity was shortened and the immune activity lasted longer in the retinoic acid-treated mice. With the use of cell-depletion techniques it was demonstrated that thymus-derived lymphocytes were affected by retinoic acid.