Leukocyte reduction filters: A source of peripheral blood leukocytes for research and drug production

Sir, In blood banks, leukocyte reduction filters (LRFs) are used to remove leukocytes from blood products in order to prevent adverse transfusion reactions. A donated blood bag (450 mL) contains 1.6 × 109 to 4 × 109 leukocytes. Therefore, a valid source to obtain blood cells for research applications is the use of LRFs that retain >99% of the leukocytes. Recovery of cells from filters has been previously described.[123] Moreover, extracting antimicrobial peptides such as defensins from neutrophils trapped in leukofilters have been reported.[4] These studies show the importance of access to human cells in a large number and using them for future therapeutic applications. The present study is our experience in isolation of cells retained by the leukofilters in the Iranian Blood Transfusion Organization. We use Leukoflex LST-1 (Maco Pharma) to prepare leukoreduced products. After informed consent, blood was collected from healthy donors. Blood bags with a half-life of <24 h were filtered at 22°C by gravity flow and were then separated from the donation bag. The cells were extracted from inverted filters by backflushing with a 70-mL syringe filled with phosphate-buffered saline (PBS), pH 7.4, without MgCl2 and CaCl2, containing 5-mM ethylenediaminetetraacetic acid (EDTA) and 2.5% sucrose. The PBS solution was homogenized with the filter content and then collected in a sterile T-75 tissue culture flask. The wash fluid was then aliquoted to 50-ml tubes, and the buffy coat layer from each tube was combined into one tube. The cells were washed twice by low-speed centrifugation (300 ×g for 10 min) in PBS 1X in order to remove remained red blood cells. Cell count was done by an automatic hematology analyzer. The viability was assessed by trypan blue, and over 90% of the cells were viable. Approximately 4.4 × 108 leukocytes (mononuclear cells + granulocytes) were obtained from each filter using 70 ml of PBS (range = 2.7–6.9 × 108 leukocytes, n = 5). In a study by Wegehaupt et al.,[3] recovery of leukocytes from Terumo LR Express filter was evaluated. The median recovery of leukocytes was 356 × 106 cells (range = 200–549 × 106 cells, n = 10). In another study by Izquierdo et al.,[5] 8 × 108 leukocytes (range = 3.5–14×108 cells, n = 15) were recovered from WBF3 filters (Pall Medical) using 60 ml of PBS containing 2-mM EDTA. It should be noted that the number of cells obtained from different LRFs depends on the PBS volume used to backflushing. Therefore, there is a slight difference in the number of cells eluted. In conclusion, our experience showed LST-1 filters, as unusable products offer an abundant source of human cells for research and possible clinical purposes. One of the advantages of cell isolation from LRF is simplicity. These filters obtain from volunteer blood donors after informed consent, phlebotomy, and investigation for viral infections. Therefore, all these procedures are eliminated, and the cells are readily provided to research with no cost. The obtained cells can be a valuable replacement for the traditional sources of research cellular products. Financial support and sponsorship This study was financially supported by the Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran Conflicts of interest There are no conflicts of interest. Acknowledgment The authors acknowledge the Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran.