A
steroid, 6-chloro-17-hydroxypregna-1,4,6-triene-3,20-doine (CHP) that exhibits selective activity in several models of cellular immunity including an apparent inhibitory action on the elicitation of
delayed hypersensitivity, was examined in a new, simple experimental model for assessing aspects of host-cell-mediated immunological competence. This model is based upon the capacity of the adult mouse to prevent the progressive growth of
tumors induced by the Moloney sarcoma virus. Two
steroids reported to have immunosuppressive activity in other assay systems, namely,
cortisol and
progesterone, were also studied. Control mice and those injected with CHP maintained their capacity to reject the
tumor. In contrast, significant numbers of mice receiving a single large injection of
cortisol or
progesterone succumbed to progressive
tumor growth under the experimental conditions used. The data indicate that CHP, while influencing selected parameters of cellular immunity, e.g., the elicitation of
delayed hypersensitivity, does not decrease the capacity of the host to mount a defense against the progressive growth of the Moloney virus-induced
sarcoma. The results indicate that CHP may be useful in modulating specific aspects of cellular immunity without altering others. In addition, the experimental model described provides a simple method of assessing the possible immunosuppressive effects of naturally occurring and synthetic agents on viral-induced
tumor growth.