Donor leukocytes (WBC) (WBC)

Donor leukocytes, also known as passenger white blood cells, are residual immune cells found in red blood cell (RBC) concentrates after blood collection (FDA, 2022). These cells are not the intended therapeutic agent and are often considered contaminants that can cause significant adverse effects in transfusion recipients (StatPearls, 2023). They are the primary cause of febrile non-hemolytic transfusion reactions (FNHTR) due to the release of pyrogenic cytokines and can lead to HLA alloimmunization, which complicates future blood component matching and organ transplantation (AABB, 2021). Most severely, viable donor T-lymphocytes can proliferate and attack the tissues of an immunocompromised recipient, resulting in transfusion-associated graft-versus-host disease (TA-GVHD), a condition with a mortality rate exceeding 90% (PubMed, 2019). To prevent these complications, blood products are typically "leukoreduced" through specialized filtration or "irradiated" to cross-link DNA and prevent cellular division (NIH, 2020).

Other names

White blood cellsPassenger leukocytesResidual leukocytes

Leukoreduction filters remove cells via size-exclusion and adherence, while irradiation and pathogen reduction technologies (PRT) like amotosalen or riboflavin induce DNA cross-linking or damage to prevent T-cell proliferation (FDA, 2022; StatPearls, 2023).