A major drawback in the use of platelet transfusions is the development of platelet refractoriness that is usually caused by alloimmunization provoked by leukocytes present in the blood products. We evaluated the development of alloimmunization both by serological demonstration of HLA antibodies and by clinical demonstration of platelet refractoriness in 50 multitransfused children who exclusively received filtered, leukocyte-free blood products. The basic diagnoses included acute leukemia, pediatric solid tumors, and severe aplastic anemia. We also present a reference group of 10 similarly multitransfused children, who either deliberately or inadvertently had received nonfiltered blood products on some occasions. In the study group of 50 children, none developed platelet refractoriness. The median corrected increment was 11.1 times 109/1 at the time of initial diagnosis, and 10.4 at the time of the study 8 months later (median). None had detectable HLA antibodies in serum. In contrast, in the reference group 3/10 had HLA antibodies in serum, and 1/10 was clearly refractory to random pooled platelets. We conclude that systematic use of leukocyte-free blood components effectively prevents alloimmunization in heavily transfused children with cancer. Leukocyte depletion to the level of < 1 times 106 of contaminating leukocytes per unit is sufficient and seems to prevent alloimmunization totally.
