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SAFEİBLOODİSUBSTITUTESİCOMING
By Sean Henahan, Access Excellence  WASHINGTON, D.C., (May 13,
1997)- Safe blood substitutes may soon be available, thanks
to two recent developments, one involving antigen camouflage and the other
involving a stripped down form of hemoglobin.
Speaking at the annual meeting of the Pediatric Academic Societies, researchers reported the creation of a new process for camouflaging the surface of red blood cells that, in effect, creating a universal blood type. "It is our belief that this procedure for antigen camouflage may have significant potential in transfusion and transplant medicine, as well as in veterinary medicine," said Mark Scott, Ph.D., associate professor of pathology and laboratory medicine. The process involves coating the red blood cell with a biocompatible polymer called polyethylene glycol (PEG). The PEG molecules form permanent covalent bonds on the cell's surface. This coating effectively hides the antigenic molecules on the surface of the red blood cells such that the foreign cells are not recognized by the blood recipient's antibodies. For example, a person who has type A blood will naturally have antibodies that attach to the antigens on the surface of type B blood cells and destroy the foreign blood. "The attachment of PEG to the surface of type B blood camouflages the surface of the cell so the antigens can no longer be recognized and thus prevents the destruction of the antigenically foreign red blood cells," Dr. Scott said. A number of diseases, including thalassemia, that require repeated blood transfusions are often complicated by the development of antibodies to "minor" red cell antigens. This "allosensitization" can render these patients almost impossible to transfuse. It can be a life-threatening situation. In vitro, the PEG-modified red cells appear not to trigger allosensitization and may also be useful in clinical situations where allosensitization has already occurred. The investigators have tested the process in vitro with human, mouse, rat and sheep red blood cells, and in vivo with mice cells. When they transfused one type of PEG-modified red blood cells into mice that had a different blood type, the treated foreign red cells were not rejected. The modified cells, while antigenically "silent," remained structurally and functionally normal and had normal in vivo survival. Interestingly, the researchers were also able to transfuse sheep blood cells into mice and prolong the survival of these "very foreign" red cells up to 360 times that seen with untreated sheep cells from five minutes to 30 hours. In addition to allowing blood transfusions between individuals with different blood groups, the techniques may also be useful in tissue and organ transplantation to prevent rejection, Dr. Scott said. Studies with a number of other cell types modified by this technology have shown substantial promise at preventing tissue rejection. In a separate development, Belgian researchers announced positive results with a different approach to blood substitution. The researchers have been evaluating a new oxygen carrying product called DCLHb (Diaspirin Crosslinked Hemoglobin). More than 700 patients have been enrolled in DCLHb clinical trials in 15 indications to date. In a meeting with European regulatory scientists, Maurice Lamy, M.D., professor of anesthesia and intensive-care medicine, University of Liege, Belgium presented data from a heart surgery study involving 209 patients. Of the patients who received DCLHb, nearly 40 percent did not require blood after one day of follow-up. After seven days, one out of five patients treated with DCLHb were able to safely avoid the administration of blood, even though they did not receive the product after the first day. All patients in the study's control group received one or more units of blood. "Before this study, we hypothesized that DCLHb would improve oxygen delivery to tissues throughout the body and serve as an alternative to blood post-bypass," said Dr. Lamy. "We're quite encouraged with the results. Morbidity and mortality were the same for treatment and control groups which is a good indication of safety, a good indication of safety. Clinical results at 24 hours are particularly compelling. Since all oxygen-carrying solutions last only a short time in circulation, we were impressed to see that 39 percent of treated patients were able to avoid a transfusion the first day, and one out of five patients were able to avoid the administration of blood through the seven-day study period." Patients in the study suffered from severe cardiovascular disease and averaged 65 years of age. While blood transfusions are the standard of care for blood loss in bypass patients, the administration of a transfusion may result in complications in this group of severely ill patients. A readily accessible and safe alternative to blood would give physicians an alternative as they manage the recovery of bypass patients. Each year, more than 240,000 cardiac-bypass surgeries are performed in Europe; more than 500,000 cardiac- bypass surgeries are performed each year in the United States. DCLHb is made from human hemoglobin-- the iron-containing protein found in red blood cells that transports oxygen throughout the body. The product undergoes viral-inactivation process during its manufacture. The product may provide several potential advantages compared to blood. Unlike blood, it does not require typing or cross-matching, allowing medical personnel to administer it immediately to the critically ill and injured. It also can be stored for much longer periods of time than blood. "DCLHb is a very, very significant advance,'' blood-substitute authority Dr. Bob Winslow of the University of California at San Diego told the media. "It's very impressive. It's going to mean a tremendous advance in health care worldwide. The big winners are going to be the less developed countries that don't have good blood bank systems.''
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