Assessment of Immunobiological Effects Induced by Chemicals, Drugs or Food Additives. II. Studies with Cyclophosphamide

ABSTRACT To demonstrate the sensitivity of the assay systems and approach described in the preceding manuscript, studies have been undertaken in BALB/c mice exposed to non-lethal doses of the biological alkylating agent and immunosuppressant drug cyclophosphamide. The assays selected were the i125 isotopic footpad assay for measuring the delayed-type hypersensitivity response to the antigen keyhole limpet hemocyanin (KLH); Cunningham's plaque-forming cell procedure for cells producing IgM antibodies to sheep erythrocytes; the microculture lymphocyte proliferation assay with mitogens; and tumor susceptibility assays for measuring decreased resistance of non-immune mice to low concentrations of syngeneic transplantable tumor cells. Non-lethal doses of cyclophosphamide given either 2 or 7 days prior to KLH challenge in immune mice was shown to eliminate the delayed cutaneous response in these animals as measured by the Isotopic Footpad Assay suggesting a depletion of specific antigen memory cells. Drug treatment also rendered animals more susceptible to small doses of tumor cells when given prior to tumor challenge. This increased tumor susceptibility was evident by an increased proportion of tumor takes, increased mean tumor volumes, as well as a decrease in the mean latency time to tumor detection. Doses of CY as low as 14 mg/kg appear to modulate immunosurveillance to allow outgrowth of low numbers of tumor cells that are eliminated in normal mice. Further, it was shown that administration of CY had dramatic and reproducible depressive effects on the in vitro parameters of immuno-competence evaluated. The lymphoproliferative responses to general T- and B-cell mitogens of animals treated with CY were