In vitro activity: The inhibitory effect of S1P is revered by various concentrations of FTY720, with IC50 effect of 173 nM. In addition, FTY720 (10 nM) alone exerts no effect on the expression of co-stimulatory molecules. FTY720 reverses the increased expression of HLA-I induced by S1P for both the percentages of cells and the MFI, upon comparing the effect of S1P to the effect of combining S1P with FTY720. Medium and high-dose FTY720-P also enhances the levels of TGF-β1. TGF-β1 and Foxp3 mRNA expression are upregulated in the high-dose FTY720-P group. The proliferation of effector T cells is suppressed significantly in the medium and high-dose FTY720-P group at a Treg/Teff cell ratio of 1:1. At a ratio of 1:1, the proliferation of effector T cells is also suppressed in the high-dose FTY720 group.

Kinase Assay: The monocyte-derived immature dendritic cells (iDCs) are pretreated with various concentrations of S1P for various periods of time prior to their incubation with NK cells. Four hours incubation of autologous or allogeneic iDCs with 0.2-20 μM of S1P significantly protectes these cells from NK cell lysis. The IC50 values of S1P are calculated at 160 nM for autologous iDCs, and 34 nM for allogeneic iDCs.

Cell Assay: Immature DCs are left intact or are incubated with 2 μM S1P, 10 nM FTY720, 10 nM SEW2871 or the combinations of S1P with these drugs for 4 hours. As a control 1 μg/mL LPS is used. The cells are washed and incubated in a 96-well plate (v-bottom, 2 × 105 cells per well), washed again and resuspended in PBS buffer containing 0.1% sodium azide. They are labeled with 1 μg/mL FITC-conjugated mouse anti-human CD80, 1 μg/mL FITC-conjugated mouse anti-human CD83, 1 μg/mL FITC-conjugated mouse anti-human CD86, 1 μg/mL FITC-conjugated mouse anti-human HLA-class I, 1 μg/mL FITC-conjugated mouse anti-human HLA-DR, 1 μg/mL FITC-conjugated mouse anti-human HLA-E, or 1 μg/mL FITC-conjugated mouse IgG as a control. The cells are washed twice, and examined in the flow cytometer. Markers are set according to the isotype control FITC-conjugated mouse IgG. To stain NK cells with antibodies for various NK cell activating receptors, they are either left untreated or incubated with 2 μM S1P for 4 hours, washed and stained with 1 μg/mL PE-conjugated mouse anti-human NKp30 (CD337), 1 μg/mL PE-conjugated mouse anti-human NKp44 (CD336), 1 μg/mL PE-conjugated mouse anti-human NKG2D (CD314), or as a control 1 μg/mL PE-conjugated mouse IgG1, for 45 min at 4 °C. NK cells are also stained with 1 μg/mL FITC-conjugated anti-killer inhibitory receptor (KIR)/CD158 antibody which recognizes KIR2DL2, KIR2DL3, KIR2DS2 and KIR2DS4, and as a control with FITC-conjugated mouse IgG. The cells are washed twice, and examined in the flow cytometer. Markers are set according to the isotype control PE-conjugated or FITC-conjugated mouse IgG.