We next analysed whether costimulation with sc CD86/anti-CD33 or sc CD80/anti-CD33 antibodies (used at 10 μg/ml from now on) could increase Ca2+ signals following focal stimulation by pre-loaded CHO cells. Analysing parental Jurkat T cells (Fig. 4a), E6-1 Jurkat T cells (Fig. 4b) or naïve, unstimulated primary CD3+ T cells (Fig. 4c), we could not observe any significant differences between stimulation with dscFv anti-CD33/anti-CD3 alone or in combination with sc CD80/anti-CD33 or sc CD86/anti-CD33. However, the differences with respect to the proliferation and the killing capacity between dscFv anti-CD33/anti-CD3

with or without costimulation (Figs 1, 2) were always analysed after 4 days. During this time, T cells had reached effector status. In a next step, we mimicked these conditions. To generate effector T cells without progestogen antagonist exposing them to dscFv anti-CD33/anti-CD3 before the actual Ca2+ imaging experiment, naïve T cells were stimulated either with PHA and IL-2 or with anti-CD3/anti-CD28-coated beads. We have previously shown that this protocol generates an almost pure effector T-cell population.23 We repeated the Ca2+ imaging experiments with these effector T cells and observed clear differences between stimulation with dscFv anti-CD33/anti-CD3 alone and stimulation with dscFv anti-CD33/anti-CD3 in combination with the costimulatory

molecules. Stimulation of the effector T cells with dscFv anti-CD33/anti-CD3 in combination with sc CD86/anti-CD33 induced larger Ca2+ signals than dscFv anti-CD33/anti-CD3 in combination with sc CD80/anti-CD33 or dscFv anti-CD33/anti-CD3 alone (Fig. 4d), which AZD5363 price matches with the proliferation and cytotoxicity data shown in Figs 1 and 2. Because CD28 and CTLA-4 are the main receptors for CD80 and CD86 on T cells, we analysed their expression. We did not detect significant CD28 expression

on parental Jurkat T cells, however, it was clearly expressed on E6-1 Jurkat T-cells Ponatinib (Fig. 4e,f). It was also modestly expressed on naïve T cells but up-regulated during T-cell maturation, following stimulation of naïve T cells with IL-2 and PHA or anti-CD3/anti-CD28-coated beads (Fig. 4g,h). There was no detectable CTLA-4 surface expression on both Jurkat T-cell lines (Fig. 4e,f ) and naïve T cells (Fig. 4g) but there was a clear up-regulation during T-cell maturation (Fig. 4h). CD28 is recruited to the immunological synapse (IS) even in the absence of CD80 or CD86 costimulation. However, its localization at the IS can be disrupted by CTLA-4, which needs ligand binding to be recruited to the IS.37 Costimulation should therefore influence effector T-cell signalling much more than signalling in naïve cells because only effector cells express CD28 and CTLA-4 at high levels. This is indeed the case as shown in Fig. 4(d,h). Interfering with the function of CD28 should cancel the difference between CD80 and CD86 costimulation in effector T cells.