Author + information
- Stephanie L. Sellers, PhD,
- Geoffrey W. Payne, PhD,
- Michael A. Seidman, MD, PhD and
- Jonathon A. Leipsic, MD∗ ()
- ↵∗St. Paul's Hospital University of British Columbia, 1081 Burrard Street, Vancouver, British Columbia V6Z 1Y6, Canada
We thank Dr. Torii and colleagues for their interest in and comments on our recent work regarding the histologic analysis of explanted transcatheter heart valves (THVs) (1). In general, we would like to note that endothelial cell (EC) surface markers have historically been the focus of a great deal of debate because of their diversity and heterogeneous performance (2,3). Furthermore, in the emerging field of understanding cellular response to THVs, much remains to be learned, including further characterization of EC markers as we discuss in our manuscript and have continued to focus on in ongoing projects.
In addressing the specific concerns raised, we would like to highlight that in our manuscript we note the presence of CD31-positive endothelial-like cells and assessed a hyperplasia phenotype from cross-sections but did not comment on extent of coverage of the entire leaflet. This is an important limitation as noted in our discussion. We do believe our interpretation of CD31 staining as endothelial-like cells is supported by our data; the cells staining for CD31 in Figure 3 of our manuscript are nucleated and show distinct cell borders, although we cannot exclude that platelets are coating these cells. However, we have provided additional representative images (Figure 1) of staining from an Edwards Sapien model THV explanted after 14 days (a point at which we noted hyperplasia) that shows both membranous and cytoplasmic CD31 staining of nucleated cells, suggesting that the signal is not merely an artifact of surrounding platelets. This is in contrast to adjacent thrombus that shows diffuse CD31 staining but with only rare nuclei and no discrete cell borders. Furthermore, all cells, both in our original Figure 3 and here in Figure 1B, are negative for CD45, arguing strongly against them being leukocytes. This pattern of staining was consistent across all timepoints. Although we acknowledge that CD34 can also be used as marker of ECs, we believe it is important to discuss observations within the published data that this marker is not considered endothelial specific, as it has been shown to stain many vascular and hematopoietic cell types and many mesenchymal elements, as well as to fail to stain some types of ECs (3,4).
In closing, we thank Dr. Torii and colleagues for their insights and discussion and anticipate that they will share our appreciation of the complexity of endothelial biology and debate how best to study these cells in the setting of THV pathology. Moreover, we expect they also appreciate the challenges that are posed by the small overall sample size of THVs studied to date, which is a major limitation to the field. To help advance our collective knowledge, we propose that an in-depth analysis of endothelial and inflammatory cell markers in a larger number of THVs is an integral next step to move the field forward—an endeavor on which we would welcome collaboration with Dr. Torii and colleagues and any others in the field.
Please note: Supported by Edwards Lifesciences and unrestricted grants from the Silber and Belzberg Family Foundations. Dr. Leipsic is supported by a Canadian Research Chair in Advanced CardioPulmonary Imaging; and provides institutional corelab services to Edwards Lifesciences, Medtronic, Neovasc, Tendyne Holdings, and Abbott; and is a consultant to Circle CVI and HeartFlow. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Sellers S.L.,
- Turner C.T.,
- Sathananthan J.,
- et al.
- Rakocevic J.,
- Orlic D.,
- Mitrovic-Ajtic O.,
- et al.