Treatment of canine transmissible venereal tumor by intravenous administration of protein A.

To determine if protein A can induce tumoricidal effects, transmissible venereal tumor-bearing dogs were treated by intravenous protein A administration. Each dog in the experimental group was treated twice a week with protein A, 100 micrograms/kg body weight, for a total of 10 treatments. Control dogs were treated with a 0.9% sodium chloride solution. No decrease in tumor volume attributable to protein A treatment was observed. However, transient healing of ulcerated tumors was observed in two dogs in the protein A-treated group but not in any in the control group. Following the first inoculation of protein A, a significant transient increase in polymorphonuclear cells and a significant transient decrease in lymphocyte and monocyte counts was detected, with a return of the counts to pretreatment levels by 24 h after the last protein A treatment. Intravenous protein A administration also failed to induce tumor regression in a guinea pig and a murine tumor model. These results suggest that the antitumor effects observed in protein A immunoadsorption studies have not been induced by leakage of protein A into the circulation.