Drug-induced tolerance to allografts in mice. I. Difference between tumor and skin grafts.

When AKR mice were primed with viable C57BL/6(B6) spleen cells and treated with cyclophosphamide 1-3 days later, a profound tolerance to B6 tumor allografts was induced. The tolerant state was maintained completely for as long as 8 weeks. Although tumor allografts grew progressively even when inoculated after complete rejection of skin grafts, B6 skin grafts were rejected by tolerant mice. In mice tolerant of B6 tumors, production of cytotoxic antibody and cytotoxic activity was reduced profoundly, but the delayed-type hypersensitivity level decreased only slightly. We therefore presume that the decrease in cytotoxic activity may allow progressive growth of tumor allografts, but the maintenance of delayed-type hypersensitivity or a low level of cytotoxicity, or both, precludes acceptance of skin allografts.