In a number of clinical circumstances it would be desirable to artificially conceal cellular antigenic determinants to permit survival of heterologous donor cells. A case in point is the problem encountered in transfusions of patients with rare blood types or chronically transfused patients who become allosensitized to minor blood group determinants. We have tested the possibility that chemical modification of the red blood cell (RBC) membrane might serve to occlude antigenic determinants, thereby minimizing transfusion reactions. To this end, we have covalently bound methoxy(polyethylene glycol) (mPEG) to the surface of mammalian RBC via cyanuric chloride coupling. Human RBC treated with this technique lose ABO blood group reactivity as assessed by solution-phase antisera agglutination. In accord with this, we also find a profound decrease in anti-blood group antibody binding. Furthermore, whereas human monocytes avidly phagocytose untreated sheep RBC, mPEG-derivatized sheep RBC are ineffectively phagocytosed. Surprisingly, human and mouse RBC appear unaffected by this covalent modification of the cell membrane. Thus, mPEG-treated RBC are morphologically normal, have normal osmotic fragility, and mPEG-derivatized murine RBC have normal in vivo survival, even following repeated infusions. Finally, in preliminary experiments, mPEG-modified sheep RBC intraperitoneally transfused into mice show significantly improved (up to 360-fold) survival when compared with untreated sheep RBC. We speculate that similar chemical camouf lage of intact cells may have significant clinical applications in both transfusion (e.g., allosensitization and autoimmune hemolytic disease) and transplantation (e.g., endothelial cells and pancreatic  cells) medicine.The transfusion of red blood cells (RBC) is the most common, and best tolerated, form of tissue transplantation. Indeed, in 1993, over 14 million units of blood were donated for transfusion in the United States alone (1). In most transfusions, simple blood typing (ABO͞Rh-D) is sufficient to identify appropriate donors. Occasionally, however, appropriate donors for patients with rare blood types cannot quickly be found; a situation that may become life-threatening. More often, problems are encountered in individuals who receive chronic transfusions, such as patients with sickle cell anemia and thalassemia. In such patients, alloimmunization against minor RBC antigens can make it nearly impossible to identify appropriate blood donors (2-4). Previous studies in which purified proteins were covalently modified with poly(ethylene glycol) (PEG) provided a possible solution to this problem. PEG-modified proteins have been shown to have increased in vivo survival and to be nonimmunogenic, even with repeated infusions (5, 6). We therefore explored the hypothesis that the covalent binding of PEG to intact RBC might mask RBC surface antigens and thereby permit the survival of heterologous or even xenogeneic RBC.To experimentally test this hypothesis, human, mouse, and sheep RBC were...
1. The effects of intracellular QX-314 on Ca2+ currents were examined in CA1 pyramidal cells acutely isolated from rat hippocampus. In neurons dialyzed with 10 mM QX-314 (bromide salt), the amplitude of the high-threshold Ca2+ current was on average 20% of that in control cells and the current-voltage relationships (I-Vs) were shifted in the positive voltage direction. 2. The positive shift in the I-Vs was due to the presence of intracellular Br-, because it was reproduced by 10 mM NaBr and was not present when the chloride salt of QX-314 was used. 3. Low-threshold (T-type) Ca2+ currents, at test voltages of -50 and -40 mV, were on average < 45% of control amplitude in cells containing 10 mM QX-314 (chloride salt) and < 10% of control amplitude in cells with 10 mM QX-314 (bromide salt). 4. In neurons dialyzed with 1 mM QX-314, high-threshold Ca2+ currents were still significantly different from control and Na+ currents were not completely blocked. 5. The proportions of high-threshold Ca2+ current blocked by omega-conotoxin GVIA, omega-agatoxin IVA, and nimodipine were similar in cells dialyzed with 10 mM QX-314 and control cells, indicating that the drug does not selectively inhibit any of the Ca2+ channel subtypes distinguished by these antagonists.
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