Abstract 403: Tracking the Migration of Porcine Mesenchymal Stem Cells with the MRI Contrast Agent Ferex in an AAA Model

Abstract

Introduction: Mesenchymal stem cells (MSC) are being investigated in porcine abdominal aortic aneurysm (PAAA) models for their repair potential. This study uses MSCs labeled with the MRI contrast agent Ferex to non-invasively evaluate MSC migration in-vivo. Methods: MSCs from 6 pigs were isolated from bone marrow via Ficoll Paque separation and expanded in culture. Using a Lentiviral vector, MSC from all 6 pigs were transfected with green florescent protein (GFP). MSCs from 4 of these pigs were also labeled with 200μg/ml Ferex using Poly-L-Lysine and then analyzed for Ferex uptake and viability. Preservation of the MSC phenotype was confirmed using flow cytometry by detecting positive CD90 and negative CD45 and CD117. Transmission electron microscopy established that Ferex localized to lysosomes. MSCs were then injected into the adventitia of the PAAA. In-vivo MRI was performed using multiple echo gradient echo sequences. Effective transverse relaxation times (T2* values) were calculated on a pixel-by-pixel basis as a function of time post cell transplantation. Results: Ferex labeled MSCs were visible post transplantation at 4, 11, 15 and 21 days using MRI. The MRI signal void (decreased T2* values) correlated with the presence of Ferex within the PAAA. This signal loss progressively expanded circumferentially at each study interval representing cellular movement. MSC migration and localization were confirmed with GFP visualization on fluorescence microscopy and immunohistochemistry. In-vivo MRI signals also correlate with iron deposition on Perl’s stain. Conclusion: Ferex can be used as an in-vivo tracking agent of MSCs in PAAA models.