Anti-tumor potential of retinoic acid: stimulation of immune mediated effectors

Data are presented on the effects of retinoic acid (RA) treatment on the in vivo growth of tumors in two mouse strains. Inhibition of tumor growth as a result of systemic RA injection was observed in three out of seven tumor models. Using adult thymectomized, lethally irradiated and fetal liver (A x TFL) reconstituted mice, we found that inhibition of tumor growth is not due to direct toxic effects of RA but rather appears to be the result of stimulation of thymus-dependent immune-mediated effectors to suppress tumor growth. Results suggest that only strongly immunogenic tumors are sensitive to in vivo retinoid inhibition.