To investigate the co-stimulatory role of CD277 in T-cell signaling, CD3 mAb versus CD3+CD277 mAb coated beads were used to stimulate CD4+ T cells and phosphoflow analysis was performed. CD4+ T cells were stimulated with mAb coated beads for various periods of time (Fig. 2). Induction of Akt and ERK-1/2 phosphorylation using CD3 mAb coated beads was detected specially at late time points such as 30 min (Fig. 2A and B). These TCR-induced phosphorylation events were enhanced when a combination of CD3 plus CD277 mAbs were used. Moreover, this CD277 co-stimulation revealed phosphorylation events as early as 2 min after stimulation

(Fig. 2B). These results show that CD277 stimulation is involved in the regulation of T-cell signaling induced by the TCR-CD3 complex. As the CD28 molecule is known to be a potent co-stimulator of TCR-induced signaling events in primary T cells 15, the role of CD277 was analyzed in the modulation check details of an optimal (CD3+CD28)-induced T-cell stimulation. Purified CD4+ T cells were stimulated with various concentrations of mAbs against CD277 (from 5 to 17 μg/mL) or isotype control IgG1, together with anti-CD3 plus anti-CD28 for different periods of time (2, 5, 10 and 30 min) (Fig. 2). The CD277 cross-linking strongly increases the phosphorylation of Akt and ERK-1/2 induced by CD3+CD28 stimulation (Fig. 3A and B). This effect was dose

and time dependent (Fig. 3B). Hence, we thus demonstrated that CD277 triggering potentialize the TCR signal as expected for a co-stimulatory signal and that it further enhanced the cosignals provided by CD28. Imatinib We next decided to investigate the functional consequences of the activation of these signaling pathways. To investigate the CD277 cosignaling effects on T-cell proliferation and cytokine production induced by CD3+CD28 co-stimulation, CD4+ T cells were stimulated with various concentrations of CD277 mAb (from 5 to 17 μg/mL), together with CD3 plus CD28 mAbs Molecular motor (Fig. 4). The amount of mAbs able to bind on the beads stays

equal along the stimulation conditions by adding IgG1 isotype control and anti-MHC class I (MHC I). The proliferation was evaluated by measuring the dilution of CFSE cytosolic dye in stimulated CD4+ T cells (Fig. 4A). The CD277 cross-linking on CD4+ T cells strongly activates CD4+ T-cell proliferation mediated by CD3 plus CD28 mAbs in a dose-dependent manner. Among the CD3+CD28 stimulated, only 60% of these cells are divided at day 5 (Fig. 4C). The CD277 mAb cross-linking strongly enhances CD4+ T-cell division already induced by CD3 plus CD28 mAbs in a dose-dependent manner, such as 90% of cells are divided (Fig. 4C). In parallel, our results also showed that the engagement of CD277 increased the proliferation (Fig. 4B) and the secretion of cytokines induced by CD3+CD28 stimulation in a dose-dependent manner (Fig. 4D).