The influence of FK-506 and low-concentration ciclosporin on human lymphocyte activation antigen expression and blastogenesis: a flow cytometric analysis.

The influence of FK-506 and ciclosporin (CsA), either alone or in combination, on PHA- and alloantigen-induced human blood lymphocyte transformation was investigated. The concentrations of FK-506 and CsA required to cause 50% inhibition of mitogen-induced thymidine incorporation were 1.0 and 200 ng/ml respectively. Evidence of synergistic inhibition of DNA synthesis was obtained when doses of each drug below these concentrations were combined (FK-506, less than or equal to 0.5 ng/ml; CsA less than or equal to 50 ng/ml). In contrast, FK-506 and CsA failed to inhibit PHA-induced increases in cell size and granularity determined by flow cytometric analysis at 1 and 3 days of culture. Moreover, no significant changes in the expression of the interleukin 2 receptor (IL-2R; CD25), transferrin receptor (TR; CD71) or HLA-DR were observed in terms of percentage positive lymphocytes or mean cell surface membrane fluorescence intensity. In primary mixed lymphocyte cultures, 50% inhibition of thymidine incorporation was obtained with FK-506 and CsA concentrations of approximately 0.25 and 25 ng/ml respectively. Evidence of synergy was obtained when lower doses of each drug were combined (FK-506, less than or equal to 0.1 ng/ml; CsA less than or equal to 2 ng/ml). On their own, these concentrations of CsA were ineffective. In contrast to corresponding PHA-stimulated cells, FK-506-treated alloactivated lymphocytes exhibited reductions in IL-2R, TR and HLA-DR antigen expression, which in the cases of IL-2R and TR were further reduced by combination of FK-506 with low-concentration CsA. These data provide further evidence of the potential of combined low-dosage FK-506 and CsA for the control of human T-cell activation and proliferation in response to allostimulation.