ADAMTS13 Improving the Cell Engraftment Efficacy in Mouse Model of Bone Marrow Transplantation

Abstract 1077

The adhesive protein von Willebrand factor (VWF) plays an essential role on physiologic hemostasis, mediating platelet aggregation under high shear stress conditions. However excessive functions of VWF could cause thrombotic occlusion of microvasculature such as arterial capillaries, where blood flow creates a typical high shear stress. The VWF-cleaving protease ADAMTS13 is therefore thought to down-regulate precisely the VWF function to maintain enriched microcirculation. In this context, we hypothesized that this ADAMTS13 role might contribute to better donor cell homing and engraftment in various cell therapy approaches, in which fluent blood flow could be critical in the microcirculation system. To test this hypothesis, we investigated the essential role of ADAMTS13 on the donor cell engraftment using bone marrow transplantation (BMT) model in Adamts13 −/− and wild-type mice. Irradiated recipient mice were received 2 × 10⁶ GFP positive cells from the sex-matched GFP donor mice. All of irradiated recipient mice without receiving BMT died within 21 days. Although there is no difference between Adamts13 −/− and wild-type mice in survival rate after 7days of BMT, Kaplan-Meier analysis revealed that the percent ratio of survival rate starts significantly declining after 14 days of BMT in the group of Adamts13 −/− mice. The successful cell engraftment in BMT was assessed by the number of GFP-positive neutrophils in peripheral blood at the several time points from BMT. As a result, the duration achieving the number of GFP-positive neutrophils over 500/μL was found to significantly delay in the Adamts13 −/− mice, as compared with the wild-type mice (20.2±3.8 days vs. 14.4±3.3 days). However, histological examination during the whole observation periods could not detect any typical thrombotic lesions of micro vessels developed in both wild-type and Adamts13 −/− mice. In addition, the delayed cell engraftment observed in the Adamts13 −/− mice became normalized by the bolus administration of recombinant ADAMTS13 (10 μg/mouse) at the day 0 of BMT. Bone marrow analysis at the day 1 of BMT revealed that the number of GFP-positive blood cells in bone marrow was significantly reduced in the Adamts13 −/− mice as compared with the wild-type mice, which could result in the delayed cell expansion at the day 7 and day14 of BMT in Adamts13 −/− mice. The single bolus injection of recombinant ADAMTS13 was found to fully correct the delayed cell expansion in bone marrow in the Adamts13 −/− mice. Our results indicate that the regulation of VWF-mediated thrombotic or inflammatory responses by ADAMTS13 could contribute to better microcirculation which could be critical for efficient donor cell homing and engraftment in BMT, suggesting a therapeutic potential of ADAMTS13 in cell therapy approaches.