Coexpression of CD4 and CD8α on rat T-cells in whole blood:: a sensitive marker for monitoring T-cell immunosuppressive drugs

The aim of this study was to develop a new quantitative method for measuring in vitro the effects of T-cell immunosuppressive drugs by flow cytometry. Rat whole blood samples were stimulated with the T-cell mitogen succinylated concanavalin A in the presence or absence of different drugs. After 3 days, the expression of CD25 and CD8 alpha in mitogen-stimulated CD4(+) cells increased 10- to 20-fold as measured by flow cytometry. Drug efficacy and potency was calculated based on dose-response curves of the drug-mediated decrease in CD4(+)/CD8 alpha (+)/CD25(+) cells. The expression of CD8 alpha in mitogen-stimulated CD4(+) cells was blocked completely by calcineurin inhibitors (cyclosporine A and FK-506), and partially by rapamycin and SDZ-RAD. The IC50 (50% inhibitory concentration) values obtained were (mean +/- S.E.): 99.5 +/- 16.6 nM for cyclosporine A, 10.4 +/- 1.3 nM for FK-506, 1.8 +/- 0.7 nM for rapamycin, and 6.4 +/- 1.1 nM for SDZ-RAD. Our results show, for the first time, that CD8 alpha, used as an activation antigen, is a sensitive marker for monitoring T-cell immunosuppression. (C) 2001 Elsevier Science B.V. All rights reserved.