3e). At all the doses tested, there was no significant difference in IL-2 production by T cells activated by SD-4+/+ versus SD-4−/− SCH772984 molecular weight DC. Altogether, SD-4 deletion had no impact on T-cell responses in the absence of accessory signals delivered by DC, but it augmented the DC-induced response (enhanced co-stimulatory signals resulting from lack of the inhibitory function

of DC-HIL/SD-4 between APC and T cells). Since SD-4−/− T cells were hyper-reactive to allo-antigen in the mixed lymphocyte reaction (Fig. 3a), we examined their effect on acute GVHD (Fig. 4). BALB/c mice were γ-irradiated at a sub-lethal dose and then infused with T-cell-depleted allogeneic BM cells (from C57BL/6 mice) with or without CD3+ T cells isolated from KO or WT mice. Body weight was noted weekly and survival was noted daily through to day 100. All mice lost about 30% of initial body weight within a week after BM transplantation,

but recovered some weight during the 2nd week. Thereafter, differentially treated mice displayed disparate Tyrosine Kinase Inhibitor Library outcomes (Fig. 4a). Mice that received BM cells alone completely recovered their weight 3 weeks post-BM transplantation and survived for at least 100 days. Mice that received BM cells plus SD-4+/+ T cells partially recovered their weight, with 50% dying by day 32, and the rest survived for at least 100 days (Fig. 4b). By contrast, mice that received BM cells plus SD-4−/− T cells lost weight progressively (up to 40%) due to severe diarrhoea, with 50% dying by day 14, and all dead by day 32. We also examined proliferation of infused T cells in recipients, by measuring the number of donor-derived T cells (H-2Kb+) in spleen and liver of mice at day 5 post-BM transplantation (Fig. 4c,d). In spleen (Fig. 4c), there was twofold to threefold greater CD4+ and CD8+ SD-4−/− T cells than SD-4+/+ T cells, and also more CD69+ (activated) cells than in recipients of SD-4+/+ T cells. Similar results were observed in liver, which is another major target of acute GVHD (Fig. 4d).[1] These results indicate that infusion of T cells devoid

of SD-4 worsens morbidity and mortality of acute GVHD, most likely through hyper-reactivity to allo-antigen. Because donor-derived Treg cells are known to play a pivotal Glycogen branching enzyme role in preventing GVHD induced by co-injection of BM cells and T cells isolated from C57BL/6 mice into total body γ-irradiated BALB/c mice,[24] we studied the influence of SD-4 deletion on the T-cell-suppressive activity of Treg. We examined expression of SD-4 on conventional CD4+ Foxp3− T cells (Tconv) versus CD4+ Foxp3+ Treg cells (Fig. 5). The Tconv and Treg cells freshly isolated from naive WT mice represented 90% and 10%, respectively, and neither expressed SD-4. In contrast, PD-1 was expressed by a minuscule fraction of Tconv cells (4·6%) and by some Treg cells (22% of Foxp3+ cells) (Fig. 5a). The Tconv and Treg cells were activated by culture for 2 days with immobilized anti-CD3/CD28 antibody.