Plasmapheresis as immunotherapeutic modality in the treatment of the canine venereal tumor.

Plasmapheresis was evaluated as a treatment modality for the transmissible venereal tumor (TVT) of the dog. The TVT is a unique tumor because of its capability for transplantation as a homograft between untreated randomly bred dogs and is characterized by the presence of dog leukocyte antigen (DLA) determinants on its tumor cells and reactivity in the mixed leukocyte tumor cell culture (MLTC). In the progressing phase, high titers of blocking antibodies measurable in the MLTC were noted. The purpose of this study was to evaluate the influence of plasmapheresis on the growth of established TVT and to correlate tumor response with the removal of blocking factors. Six pairs of DLA-identical dogs were used as experimental and control animals. Plasmapheresis was performed by discontinuous centrifugation using the Hemonetics model 30. An average of 1100 +/- 120 ml of plasma was exchanged on consecutive days during the third week after tumor injection. Consistently lower growth rates were observed in 2 experimental dogs, but there was no early rejection. Sera taken at day 14 of tumor growth contained significant blocking activity in all 12 dogs. Sera obtained post-plasmapheresis showed a decrease of blocking activity in all 6 experimental dogs, P less than 0.001. The TVT appears to be a suitable model for preclinical studies of plasmapheresis alone and in combination with other modalities.