XENOTRANSPLANTATION II

L. Burdorf¹, T. Zhang², E. Rybak¹, I.I. Salles³, K. Broos³, E. Welty¹, C.J. Avon¹, A. Laaris¹, X. Cheng¹, D. Ayares⁴, H. Deckmyn³, R.N. Pierson iii⁵, A.M. Azimzadeh^5
1Department Of Surgery, University of Maryland, Baltimore/UNITED STATES OF AMERICA, ²Surgery, University of Maryland, Baltimore/MD/UNITED STATES OF AMERICA, ³Laboratory For Thrombosis Research, Irc, KU Leuven Campus Kortrijk, Kortrijk/BELGIUM, ⁴, Revivicor Inc, Blacksburg/UNITED STATES OF AMERICA, ⁵Surgery, University of Maryland, Baltimore/UNITED STATES OF AMERICA

Body: Introduction: Injury to GalTKO pig lungs usually occurs during perfusion with human blood, and is associated with immediate activation and sequestration of circulating platelets. In vitro data has shown that human GPIb platelet receptor can be activated by pig von Willebrand factor (VWF) through a non-physiologic, shear-stress independent mechanism, and that an anti-human GPIb antibody Fab can prevent this interaction. Here we evaluate whether targeting the GPIb-VWF axis using anti-GPIb Fab prevents platelet sequestration during a xenogeneic lung perfusion.
Methods: GalTKO.hMCP (n=4), GalTKO.hDAF and GalTKO.hCD39 (n=1 each) transgeneic pig lungs were perfused with heparinized fresh human blood until failure or elective termination at 4 hours. In 6 paired experiments (a contralateral lung was perfused under otherwise identical conditions), anti-GPIb Fab (6B4, 10mg/L blood) was administered as a single dose to the circulating blood before the perfusion was started. Historical GalTKO.hMCP (n=22) perfused with untreated human blood were also used as context for analysis.
Results: Addition of anti-GPIb Fab dramatically reduced platelet sequestration at 5’, 15’ and 30’ (% remaining of initial platelets at 30’: 92±36 vs. 45±25 without treatment, p=0.0013). Platelet activation (assessed by CD62P expression on CD41+ platelets) was significantly decreased at 5’ (ΔCD62P: anti-GPIb 0.3±0.8% vs. untreated 4.7±2%, p=0.0036) and 15’ (anti-GPIb 0.5±1.3% vs. untreated 3.7±3.3%, p=0.048), and remained low (n=3) or reduced (n=3) until lung failure or elective experimental termination at 4 hours (anti-GPIb 6.2±5.3% vs. untreated 17.2±8.2%, p=0.011). Moreover, platelet aggregates were decreased at early time-points (<30 minutes) in 4 of 6 experiments, although later sequestration and aggregation occurred to a variable degree. Anti-GPIb treatment had no effect on median survival time (225’ in both groups). Pulmonary vascular resistance, neutrophil sequestration, and thrombin formation (assessed as F1+2 fragments) were not consistently altered by the addition of anti-GPIb Fab.
Conclusion: Human platelet sequestration and activation by a GalTKO.hCD46 xenogeneic pig lung is mediated in part by the GPIb-VWF interaction, and is significantly attenuated by the administration of an anti-GPIb Fab. Future studies will evaluate whether more efficient GPIb inhibition (increased anti-GPIb Fab dosing, VWF depletion in the “donor” lung), blockade of additional platelet receptors (GPIIbIIIa, ADP), or coagulation cascade inhibition (Factor X or thrombin inhibition) can prevent residual platelet and coagulation cascade sequestration, and promote improved lung protection.

Disclosure: All authors have declared no conflicts of interest.