Immunomodulatory effects of allogeneic blood transfusions: clinical manifestations and mechanisms.

Recognition that allogeneic transfusion associated immunomodulation can increase morbidity in allogeneically transfused individuals has become a major concern for those involved in transfusion medicine. However, whether allogeneic blood transfusions predispose recipients to increased risk for cancer recurrence or to bacterial infections is still unproven. In contrast, data from studies in experimental animal models suggest that allogeneic blood transfusion associated immunomodulation is an immunologically mediated biological effect which is associated primarily with the infusion of allogeneic leukocytes. Moreover, the available experimental animal data suggest that pre-storage leukoreduction, as opposed to post-storage leukodepletion, is effective in ameliorating this tumor growth-enhancing effect of allogeneic blood. While considerable data have accumulated in an attempt to unravel the mechanism of the immunomodulatory effect of allogeneic blood transfusions, the precise mechanism of this effect has not yet been elucidated.