Regulation of the Immune Response to Tumor Antigens

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Abstract
Immunosuppressor (IS) cells were found to be generated in tumor-bearing animals (TBA) within 24 hr after inoculation of tumor cells of the methylcholanthrene-induced Sarcoma 1509a and appeared to persist in the hosts as long as the tumor was progressing. However, IS cells disappeared with 5 days after extirpation of the tumor. Increasing doses of thymus cells of TBA increased the degree of suppression of tumor rejection in immune syngeneic animals. Ten million thymus cells of TBA were capable of suppressing significantly the tumor rejection. The IS cells were detected in the thymuses, spleens, and draining lymph nodes, as well as in bone marrow of TBA, but could not be detected in the peripheral circulating blood. Since immunosuppressive activity of bone marrow cells from TBA was entirely abolished by the in vitro treatment of the cells with anti-θ serum and complement, the observed immunosuppression appears to be mediated by the T cell population. Hydrocortisone treatment of TBA did not abolish the suppressive activity of the thymus or spleen cells of the treated TBA, thus suggesting that IS cells were cortisoneresistant. The suppressive activity was found to be associated with cells of lowest density on centrifugation through a discontinuous density gradient of Ficoll. The results of this study, taken together with those presented in the preceding article, suggest that IS cells belong to a T cell subpopulation (immunosuppressor T cells). The relationships between immunosuppressor T cells and other T cell subpopulations, i.e., cytotoxic (effector) or helper (amplifier) T cells, remain to be elucidated in further experiments.

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