Ex vivo perfusion of plasma over protein A columns in human mammary adenocarcinoma. Evidence for a protein A leaking by radioimmunoassay

Abstract

A solid phase radioimmunoassay (RIA) has been developed for detection of protein A in human serum or plasma using plates coated with specific goat anti-protein A IgG and affinity-purified anti-protein A F (ab')2 fragments labelled with 125Iodine as a tracer. This RIA detected 25 ng of protein A per ml of serum or plasma. The 'intra-plate' coefficient of variation (CV) was 4.26%, whereas the 'inter-plate' CV was 5.86%, even in the presence of aggregated IgG. The presence of protein A was searched for by this RIA in samples collected during ex vivo perfusion of the plasma of patients suffering from a metastatic mammary adenocarcinoma either over columns of 'native' protein A (seven patients; group A) or over columns of protein A in which the Fc-binding capacity was destroyed (five patients; group B). A protein A leaking occurred with the same incidence (about 20% of the sessions) in both groups. However, major acute side effects (hypotension, chills, mild fever, etc.) and necrolytic responses were seen only in some patients from group A. In these cases, the incidence of side effects, but not of tumoricidal responses, increased with the protein A serum concentrations reached 1 h after the end of the sessions (25-150 ng ml-1). The data suggest that the therapeutic efficacy of ex vivo protein A immunoadsorption in breast cancer is related to the Fc-binding capacity of the columns rather than to a leakage of 'native' protein A into the blood stream.

Ex vivo perfusion of plasma over protein A columns in human mammary adenocarcinoma. Role of the Fc‐binding capacity of protein A in the side effects and the tumoricidal response

“…The 'leaking effect' hypothesis represents an attractive area for further research. Recent experiments have indeed confirmed the existence of a protein A leaking during perfusion of plasma over protein A columns [14]. Endotoxin might be also infused during plasma perfusion since the protein A-silica columns might contain nanogram quantities of endotoxin, as inactivated cyanogen-bromide Sepharose [26].…”

“…After this treatment the binding of heated protein A to IgG-coated microtitre plates was completely abolished as monitored by a competitive inhibition solid phase radioimmunoassay (RIA) using '251-labelled protein A [13]. However, this material still retained its capacities to react with goat antibodies to protein A, as demonstrated by RIA [14], and to stimulate B cells, as shown by Chen et al [lo]. Both native and denatured protein A preparations were covalently linked by carbodiimide to crystalline silica according to the method of Weetall [15].…”