Given their self-renewing and pluripotent capabilities, human embryonic stem cells (hESCs) are well poised as a cellular source for tissue regeneration therapy. However, the host immune response against transplanted hESCs is not well characterized. In fact, controversy remains as to whether hESCs have immune-privileged properties. To address this issue, we used in vivo bioluminescent imaging to track the fate of transplanted hESCs stably transduced with a double-fusion reporter gene consisting of firefly luciferase and enhanced GFP. We show that survival after transplant is significantly limited in immunocompetent as opposed to immunodeficient mice. Repeated transplantation of hESCs into immunocompetent hosts results in accelerated hESC death, suggesting an adaptive donor-specific immune response. Our data demonstrate that transplanted hESCs trigger robust cellular and humoral immune responses, resulting in intragraft infiltration of inflammatory cells and subsequent hESC rejection. Moreover, we have found CD4 ؉ T cells to be an important modulator of hESC immunemediated rejection. Finally, we show that immunosuppressive drug regimens can mitigate the anti-hESC immune response and that a regimen of combined tacrolimus and sirolimus therapies significantly prolongs survival of hESCs for up to 28 days. Taken together, these data suggest that hESCs are immunogenic, trigger both cellular and humoral-mediated pathways, and, as a result, are rapidly rejected in xenogeneic hosts. This process can be mitigated by a combined immunosuppressive regimen as assessed by molecular imaging approaches. molecular imaging ͉ immunological response ͉ immunosuppression

Background-Neutrophils and monocytes are centrally linked to vascular inflammatory disease, and leukocyte-derived myeloperoxidase (MPO) has emerged as an important mechanistic participant in impaired vasomotor function. MPO binds to and transcytoses endothelial cells in a glycosaminoglycan-dependent manner, and MPO binding to the vessel wall is a prerequisite for MPO-dependent oxidation of endothelium-derived nitric oxide (NO) and impairment of endothelial function in animal models. In the present study, we investigated whether heparin mobilizes MPO from vascular compartments in humans and defined whether this translates into increased vascular NO bioavailability and function. Methods and Results-Plasma MPO levels before and after heparin administration were assessed by ELISA in 109 patients undergoing coronary angiography. Whereas baseline plasma MPO levels did not differ between patients with or without angiographically detectable coronary artery disease (CAD), the increase in MPO plasma content on bolus heparin administration was higher in patients with CAD (Pϭ0.01). Heparin treatment also improved endothelial NO bioavailability, as evidenced by flow-mediated dilation (PϽ0.01) and by acetylcholine-induced changes in forearm blood flow (PϽ0.01). The extent of heparin-induced MPO release was correlated with improvement in endothelial function (rϭ0.69, PϽ0.01). Moreover, and consistent with this tenet, ex vivo heparin treatment of extracellular matrix proteins, cultured endothelial cells, and saphenous vein graft specimens from CAD patients decreased MPO burden. Conclusions-Mobilization of vessel-associated MPO may represent an important mechanism by which heparins exert antiinflammatory effects and increase vascular NO bioavailability. These data add to the growing body of evidence for a causal role of MPO in compromised vascular

Highlights Clinical performance of five different commercially available automated SARS-CoV-2 antibody tests. No overlap of “false” positive samples between different serology assays was observed. The ability to rule out acute SARS-CoV-2 infection at hospital admission with serology is limited.