Correspondence

Tumor Angiogenesis

N Engl J Med 2008; 359:763-764August 14, 2008

Article

To the Editor:

In the review of tumor angiogenesis by Kerbel (May 8 issue),1 endothelial progenitors are described as negative for CD45, positive for vascular endothelial growth factor receptor 2 (VEGFR-2), and positive for CD133, and the review by Bertolini et al.2 is cited as the source for this definition. This assertion is incorrect; in the article by Bertolini et al., endothelial progenitors are actually defined as CD45dimCD34+VEGFR-2+CD133+ cells.

Flow cytometric analyses that we performed on blood from normal subjects showed that, among CD34+ cells, a discrete population of CD45dimCD133+VEGFR-2+ cells could be discerned. Back-gating on VEGFR-2+CD133+ cells showed that all these cells expressed CD34. CD34+CD45− cells were virtually absent, with the exception of possible debris or endothelial-cell microparticles, as demonstrated by their forward and orthogonal light-scatter properties (Figure 1Figure 1Analysis of Peripheral-Blood Mononuclear Cells Stained with CD45-PE-Cy7, CD34-PE, and VEGFR-2-APC.). Our results confirm Bertolini and colleagues' definition of endothelial progenitors as CD45dimCD34+VEGFR-2+CD133+.

Gianpaolo Zerbini, M.D., Ph.D.
San Raffaele Scientific Institute, 20132 Milan, Italy
g.zerbini@hsr.it

Mara Lorenzi, M.D.
Harvard Medical School, Boston, MA 02115

Alessio Palini, M.S.C.
San Raffaele Scientific Institute, 20132 Milan, Italy

2 References

1. 1

   Kerbel RS. Tumor angiogenesis. N Engl J Med 2008;358:2039-2049
   Full Text | Web of Science | Medline

2. 2

   Bertolini F, Shaked Y, Mancuso P, Kerbel RS. The multifaceted circulating endothelial cell in cancer: towards marker and target identification. Nat Rev Cancer 2006;6:835-845
   CrossRef | Medline

Author/Editor Response

Zerbini and colleagues are correct about the discrepancy in referring to endothelial progenitor cells as “CD45−”1 versus “CD45dim.”2 It is not uncommon for some investigators to use these terms interchangeably, as I have, and to sometimes describe these cells as CD45− (e.g., in a report by Alvarez et al.3) and sometimes as CD45dim (e.g., in a report by Duda et al.4). However, partly on the basis of data in the figure presented by Zerbini and colleagues, the point is made that these cells are phenotypically distinct, thus calling for a more precise definition when referring to endothelial progenitor cells. I agree. Whether endothelial progenitor cells are CD45dim in all cases cannot be said with certainty at present, which highlights the problem of an accepted standard definition of endothelial progenitor cells based especially on expression of cell-surface markers but also on functional criteria. An international consensus workshop is needed to make recommendations regarding such a standard definition, given the importance of endothelial progenitor cells in cancer and cardiovascular disease. It is also reassuring that the data of Bertolini and colleagues2 showing that human endothelial progenitor cells have a CD45dimCD34+VEGFR-2+CD133+ phenotype were confirmed.

Robert S. Kerbel, Ph.D.
Odette Cancer Centre, Toronto, ON M4N 3M5, Canada
robert.kerbel@sri.utoronto.ca

4 References

1. 1

   Kerbel RS. Tumor angiogenesis. N Engl J Med 2008;358:2039-2049
   Full Text | Web of Science | Medline

2. 2

   Bertolini F, Shaked Y, Mancuso P, Kerbel RS. The multifaceted circulating endothelial cell in cancer: towards marker and target identification. Nat Rev Cancer 2006;6:835-845
   CrossRef | Medline

3. 3

   Alvarez DF, Huang L, King JA, ElZarrad MK, Yoder MC, Stevens T. Lung microvascular endothelium is enriched with progenitor cells that exhibit vasculogenic capacity. Am J Physiol Lung Cell Mol Physiol 2008;294:L419-L430
   CrossRef | Web of Science | Medline

4. 4

   Duda DG, Cohen KS, Scadden DT, Jain RK. A protocol for phenotypic detection and enumeration of circulating endothelial cells and circulating progenitor cells in human blood. Nat Protoc 2007;2:805-810
   CrossRef | Web of Science | Medline

Citing Articles (3)

Citing Articles

1. 1

   Gianpaolo Zerbini, Annalisa Colucci, Anna Maestroni, Elisabetta Miserocchi, Francesco Bandello, Giulio Modorati. (2012) Increased stromal cell-derived factor-1 concentration levels in aqueous from patients with uveal melanoma. Melanoma Research 22:1, 98-99
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2. 2

   Chia-Chi Chien, Ivan M. Kempson, Cheng Liang Wang, H.H. Chen, Yeukuang Hwu, N.Y. Chen, T.K. Lee, Cyril Petibois, Kelvin K.-C. Tsai, Ming-Sheng Liu, Kwang-Yu Chang, C.S. Yang, G. Margaritondo. (2011) Complete microscale profiling of tumor microangiogenesis. Biotechnology Advances
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3. 3

   Myka L. Estes, Julie A. Mund, David A. Ingram, Jamie Case. 2010. Identification of Endothelial Cells and Progenitor Cell Subsets in Human Peripheral Blood. .
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