Intra-lesional injection of immunostimulants in bilateral rat tumors.

Rats grafted with either two or six fragments of isogenic methylcholanthrene-induced transplantable fibrosarcomas were treated IT1 with living BCG or killed C. parvum or a mixture of both immunostimulants. Various tumor combination and therapeutic agent dosages were compared. When two fragments of the same tumor McFiFi2 (S) were grafted simultaneously, IT treatment of one of these with 2 mg of BCG induced cure of both in 50% of the animals, but IT injection of 2 X 10(9) C. parvum was completely without effect in this situation. The prognosis was however, improved when the dose of immunostimulant was increased. The best results were obtained when each individual tumor in rats with two or six simultaneous identical grafts were treated with a mixture of BCG and C. parvum. The combination of IT immunostimulant treatment and surgical excision of the treated lesion demonstrated a persistence of the curative effect on the remote untreated tumor. Double grafting with isologous non-identical tumors revealed the influence of tumor burden and of the specificity of anti-tumor action of the treatment. The distant specific regression obtained in this system implies a specific immunological mechanism mediated by effector cells and/or antibodies which can circulate, identify the target cell and destroy it. This is in accordance with morphological observations. The intimate contact between BCG and the growing structured tumor is necessary for the therapeutic phenomenon.