AbstractFicoll‐separated and monocyte‐depleted mononuclear cells isolated from normal leukapheresis products were cryopreserved. These cells were incubated with or without 1,000 U/ml of recombinant interleukin‐2 (rIL‐2) for 4 days, and their lymphokine‐activated killer (LAK) and natural killer (NK) activities were measured. IL‐2 activation induced a significant increase in the expression of the CD25 antigen. There was no change in CD2, CD3, CD4, CD8, CD16, CD56 and CD57 cell marker expression. Cryopreservation did not induce any change in the membrane antigen expression and in the lymphocyte subsets. The NK activity was well preserved and the decrease of LAK activity of IL‐2‐activated cells after cryopreservation was not significant. In contrast, cells activated before cryopreservation had a significantly lower cytotoxic activity and the number of cells expressing the IL‐2 receptor was also significantly reduced. However, the decrease of CD56 expression was not significant. CD25 expression seemed to be proportional to the LAK activity of the cells. This study demonstrated that cryopreserved lymphocytes, after 4 days of culture with rIL‐2, could be as active and could express the CD25 and CD56 cell surface markers in the same manner
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