VITAMIN-D-3 TREATMENT OF TUMOR BEARERS CAN STIMULATE IMMUNE COMPETENCE AND REDUCE TUMOR-GROWTH WHEN TREATMENT COINCIDES WITH A HEIGHTENED PRESENCE OF NATURAL SUPPRESSOR CELLS

By secreting granulocyte-macrophage colony-stimulating factor (GM-CSF) , Lewis lung carcinoma tumors induce immune suppressive granulocyte-ma crophage progenitor cells. Treating mice having established tumors and high levels of suppressor activity with vitamin D-3 eliminated suppre ssor activity, increased anti-tumor immunity, induced an immune stimul atory cell population, and reduced tumor growth. When instead, the vit amin Dg treatment was initiated earlier, when implanted tumors first b ecame detectable and when natural suppressor activity was less promine nt, the treatment had no effect. Thus, vitamin D-3 treatment can stimu late the immune competence of tumor bearers when treatment is targeted to coincide with a heightened presence of GM-CSF-induced suppressor c ells.