Effect of cyclophosphamide on tumour growth and cell-mediated immunity in sheep with ovine squamous cell carcinoma.

Cyclophosphamide (CY) is shown to associate with partial or complete regression of ovine squamous cell carcinoma (OSCC), the rate of regression varying directly with CY dosage and inversely with maturity of tumour at the start of therapy. CY treatment given coincidental with injection of tumour extracts (TA) completely neutralised the tumour enhancement effects regularly associated with TA injections, and caused tumour regression comparable to that seen in sheep treated with CY alone. In discussion of the results, which incorporate parallel studies on cell-mediated responses, it is suggested that immunosuppression during tumour growth is due to formation of B suppressor lymphocytes and that CY treatment of OSCC may exert beneficial effects through its immunosuppressive action on such lymphocytes as much as its direct cytotoxic action on tumour cells.