Depression of cell-mediated immunity by tumour cell products: induction of resistance by immunotherapeutically active extracts of bovine ocular squamous cell carcinoma.

Tumours produce substances that inhibit the expression of cell-mediated immunity, in the form of delayed-type hypersensitivity in mice. Phenol-saline extracts of bovine ocular squamous cell carcinoma (BOSCC) which have immunotherapeutic activity in cattle were able to immunize mice against this depressive effect. Such immunization was effective against products of BOSCC, a spontaneous rat tumour, three of four human tumour cell lines and (in other experiments) mouse tumours. Phenol-saline extracts of mouse tumour cell lines were immunogenic (protective against depression of delayed-type hypersensitivity) in mice. Fractions of BOSCC phenol-saline extracts which were immunotherapeutically active in cattle were generally also protective in mice. The protective activity was lost after treatment with proteinase K, and was present in the supernatant after precipitation with 55% ammonium sulphate. It was not affected by treatment with RNase or DNase or by heating to 50 degrees C for 2 h. It was present in gel filtration fractions with an apparent molecular weight of 10,000-37,000 daltons. The immunogenic factor in mice and the immunotherapeutic factor in cattle may be related to each other.