Contribution of Recipient-Derived Cells in Allograft Neointima Formation and the Response to Stent Implantation

et al. (2008) Contribution of Recipient-Derived Cells in Allograft Neointima Formation and the Response to Stent Implantation. PLoS ONE 3(3): e1894. doi:10.1371/journal.pone.0001894 Contribution of Recipient-Derived Cells in Allograft Neointima Formation and the Response to Stent Implantation Xiaoli Ma 0 Benjamin Hibbert 0 Dawn White 0 Richard Seymour 0 Stewart C. Whitman 0 Edward R. O'Brien 0 Pieter Hendrik Reitsma, Leiden University Medical Center, Netherlands 0 Vascular Biology Laboratory, University of Ottawa Heart Institute , Ottawa, Ontario , Canada Allograft coronary disease is the dominant cause of increased risk of death after cardiac transplantation. While the percutaneous insertion of stents is the most efficacious revascularization strategy for allograft coronary disease there is a high incidence of stent renarrowing. We developed a novel rabbit model of sex-mismatched allograft vascular disease as well as the response to stent implantation. In situ hybridization for the Y-chromosome was employed to detect male cells in the neointima of stented allograft, and the population of recipient derived neointimal cells was measured by quantitative polymerase chain reaction and characterized by immunohistochemistry. To demonstrate the participation of circulatory derived cells in stent neointima formation we infused ex vivo labeled peripheral blood mononuclear cells into native rabbit carotid arteries immediately after stenting. Fourteen days after stenting the neointima area was 58% greater in the stented vs. non-stented allograft segments (p = 0.02). Male cells were detected in the neointima of stented female-to-male allografts. Recipient-derived cells constituted 72.165.7% and 81.564.2% of neointimal cell population in the non-stented and stented segments, respectively and the corresponding proliferation rates were only 2.760.5% and 2.360.2%. Some of the recipientderived neointimal cells were of endothelial lineage. The ex vivo tagged cells constituted 9.060.4% of the cells per high power field in the stent neointima 14 days after stenting. These experiments provide important quantitative data regarding the degree to which host-derived blood-borne cells contribute to neointima formation in allograft vasculopathy and the early response to stent implantation. - Funding: This work is supported by an operating grant to EOB (UOP #36383) that is jointly funded by the Canadian Institutes of Health Research (CIHR) and Medtronic. SCW is a New Investigator of the Heart and Stroke Foundation of Ontario and the recipient of the Great-West Life and London Life Research salary award. EOB holds a Research Chair that is jointly funded by the CIHR and Medtronic. Competing Interests: The authors have declared that no competing interests exist. The artery wall consists of three layers: the (inner) intima, the media and the (outer) adventitia. Non-diseased human coronary arteries normally have a modest layer of intimal thickening (or neointima, NI) that consists of an accumulation of smooth muscle cells (SMCs) and extracellular matrix[1]. Currently, it is believed that medial SMC proliferation and inward migration, as well as the transmigration and retention of blood borne inflammatory cells play key roles in transforming a benign NI into the obstructive lesions that are seen in atherosclerotic coronary artery disease (CAD), as well as allograft coronary disease (ACD) that occurs after heart transplantation[2,3]. Like garden variety CAD, ACD can ultimately lead to life threatening clinical sequelae, and the most common revascularization strategy for either of these entities involves the insertion of metallic scaffolding devices known as stents. While stent renarrowing due to recurrent NI formation (also know as in-stent restenosis or ISR) occurs in up to 5-30% of CAD lesions (depending on the stent and/or drug coating on the stent)[4,5], ISR is a more frequent and serious problem for ACD lesions[3,69]. For example, Simpson and colleagues report 6 and 12 month ISR rates of 41% and 53%; respectively, with 39% of stented patients dying or undergoing repeat cardiac transplantation within approximately 2 years of their first intervention[9]. The histopathology of ACD is characterized by inflammatory cell infiltrates with SMC accumulation and hence is more akin to ISR than the complex atherosclerotic lesions. Indeed, Jonas and colleagues recently demonstrated that angiographic progression of ACD and ISR lesions in allograft coronary arteries correlate and share histological features[3]. The pathogenesis of ACD is incompletely understood, and debate lingers over the relative importance of immune vs. nonimmune factors, as well as the origin of NI cells. Unfortunately, experimental studies involving a variety of animal models of transplantation have produced discordant results (see review by Hillebrands et al.[10]). Indeed, there is critical concern when highresolution confocal or deconvolution microscopy is not used to track cell lineage in allografts (see editorial by Hoofnagle et al.[11]). Regardless of these experimental studies, one cannot ignore observations from a handful of important human studies that suggest that host cells participate in allograft disease. For example, in 1971 Kennedy and Weissman[12] used anti-sera directed against donor and host HL-A antigens to suggest host cells were at least partially responsible for NI formation in a human cardiac allograft coronary artery. Together with at least five larger and more sophisticated studies of human transplantation, there is already irrefutable evidence that extracardiac cells engraft both non-diseased or diseased arteries of allografts[1317]. Hence, while there is information available about the involvement of host-derived cells in allograft NI formation, many questions remain. For example, the precise degree to which host cells populate the allograft NI has only been assessed semi-quantitatively by sampling a relatively small number of cells in just a handful of arteries. Certainly, a more comprehensive quantitative assessment of the degree to which blood borne host cells participate in NI formation is required before we can assign a level of significance to these cells in the pathogenesis of allograft vascular disease, and determine the need to develop therapeutic strategies to inhibit their participation. Therefore, the goals of the current study are to address the following questions using a rabbit model of allograft vasculopathy and the response to stent implantation: i) what is the origin of NI cells in allografts with or without stents? ii) to what (precise) degree do recipient cells contribute to the NI formation? and iii) what is the identity of the NI cells that populate the allograft NI? Model of Allograft Vascular Disease and Stent NI Formation New Zealand White (NZW) rabbits were used for these experiments because their carotid artery is similar in calibre to human coronary arteries and hence suitable (...truncated)