Trials of staphylococcal protein A-treated plasma infusions in cancer therapy: clinical effects and implications for mode of action.

The data presented here indicate that patients with advanced cancer exhibit a modest but definite objective response rate to biweekly infusions of autologous plasma treated with purified, covalently bound staphylococcal protein A in a relatively nontoxic treatment program. The possibility that responses could be enhanced by alteration of treatment parameters, improved patient selection, and/or combined therapy remains to be explored. In vitro studies indicate that tumor cell killing can be produced in an ovarian cancer cell line using ascitic fluid of some ovarian cancer patients that has been treated with small amounts of protein A covalently linked to silica gel or agarose. This may be a suitable model system for exploration of possible humoral mechanisms of protein A-associated tumoricidal effects. The available literature indicates an antitumor effect of protein A-treated patient plasma in a variety of in vitro systems, as well as in animal and human tumors in vivo. Preliminary investigations of the mechanism of these effects are inconsistent and support the view that several different mechanisms of tumor cell killing may be operative in different settings.