Protein A-independent tumoricidal responses in dogs after extracorporeal perfusion of plasma over Staphylococcus aureus.

Protein A-positive or -negative Staphylococcus aureus preparations were used in an extracorporeal system to treat dogs with spontaneously occurring cancers. Tumor regression was seen in 4 of 7 dogs treated by reinfusion of plasma that had been incubated with protein A-positive S. aureus Cowan I strain (SAC). Therapy was associated with fever, liver enzyme abnormalities, and hypocomplementemia. Tumor response and toxicity could be diminished by more extensive washing of the SAC preparation. Tumor regression was also seen in 2 of 2 animals treated with protein A-negative S. aureus Wood strain 46. In addition, tumors regressed in 3 of 4 dogs treated with infusions of protein A-free saline extracts from S. aureus. These results suggest that the release of a non-protein A bacterial product contributes to tumor regression following incubation of plasma with S. aureus.