Abstract
A reliable source of positive control material is needed for immunoperoxidase or immunofluorescent terminal deoxynucleotidyl transferase (TdT) assays. The cell line RPMI 8402 was obtained from a patient with acute lymphoblastic leukemia and is positive for nuclear TdT. The kinetics of TdT expression in a series of cultured RPMI 8402 cells and the effect of cryopreservation on TdT expression were evaluated. The highest percentage of TdT + cells was detected on days 5–8 of RPMI 8402 cell cultures. TdT positivity was preserved for more than 3 years in cells stored in suspension at −70°C, and at least 76 days on slide preparations when fixed with methanol prior to freezing. We conclude that when RPMI 8402 cells with maximum TdT positivity are stored at −70°C, aliquots can be used as a constant source of positive control material thereby eliminating the necessity and expense of a continuing culture system.
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