Effect of combination treatment with cyclophosphamide and nonspecific passive immunization on a transplantable tumor in WKA rats.

Combination of cyclophosphamide (CY) and passive immunization with lymphoid cells sensitized to allogeneic tumor was studied in the treatment of a methylcholanthrene-induced transplantable fibrosarcoma in WKA rats. For determination of the most effective timing of combination treatment, rats given an injection of CY on Day 3 received passive transfer of the sensitized lymphoid cells on Day 0, 1, 2, 3, 4, or 6. A remarkable therapeutic effect was observed only when the passive transfer was combined on Day 4 with CY on Day 3. Rats inoculated with tumor succumbed in all cases without any treatment. After i.v. injection of CY on Day 3, 2 of 28 rats were cured (7.1%). Passive immunization with the sensitized lymphoid cells on Day 4 resulted in no therapeutic effect. After combination of CY on Day 3 and transfer of nonsensitized normal lymphoid cells on Day 4, 2 of 15 rats survived (13.3%). However, combination of CY and passive transfer of the nonspecifically sensitized lymphoid cells resulted in 23 survivors of 29 rats (79.3%).