Research on CECs

Circulating endothelial cells: A short introduction

Figure 1: Circulating endothelial cells: Mediators of detachment and protective factors
Figure 1: Circulating endothelial cells: Mediators of detachment and protective factors

Early on, circulating endothelial cells have been detected on the basis of cell morphology in smears of peripheral blood (1). The next important step was to establish immunocytochemistry of these cells. Using sickle cell anaemia as an example, elevated cell numbers were demonstrated in active disease (2). This approach, however, was still cumbersome and more elegant techniques were eagerly awaited. In this regard, immunomagnetic isolation was an important step forward (3, 4). This approach had already been used to detect rare cells, such as tumour cells, in peripheral blood. The technique seemed particularly appropriate because circulating endothelial cells are also rare in peripheral blood. Using this approach, circulating endothelial cells were demonstrated in patients with rickettsial infection (5) and intracellular rickettsial antigens were detected. Patients with acute coronary syndrome also had elevated cell numbers (6). Since then, circulating endothelial cells have been detected in a broad variety of vascular diseases (7). Little, if anything, is currently known about pathogenetic implications of these cells. Mechanisms of detachment are also unknown (8). Figure 1 highlights fields of uncertainty.

References:

  • Bouvier CA, Gaynor E, Cintron JR, Bernhardt B, Spaet T. Circulating endothelium as an indication of vascular injury. Thromb Diath Haemorrh 1970; 40:163.
  • Solovey A, Lin Y, Browne P, Choong S, Wayner E, Hebbel RP. Circulating activated endothelial cells in sickle cell anemia. N Engl J Med 1997; 337(22):1584-1590.
  • Hewett PW, Murray JC. Immunomagnetic purification of human microvessel endothelial cells using Dynabeads coated with monoclonal antibodies to PECAM-1. Eur J Cell Biol 1993; 62(2):451-454.
  • Dignat-George F, Sampol J. Circulating endothelial cells in vascular disorders: new insights into an old concept. Eur J Haematol 2000; 65(4):215-220.
  • George F, Brouqui P, Boffa MC, Mutin M, Drancourt M, Brisson C et al. Demonstration of Rickettsia conorii-induced endothelial injury in vivo by measuring circulating endothelial cells, thrombomodulin, and von Willebrand factor in patients with Mediterranean spotted fever. Blood 1993; 82(7):2109-2116.
  • Mutin M, Canavy I, Blann A, Bory M, Sampol J, Dignat-George F. Direct evidence of endothelial injury in acute myocardial infarction and unstable angina by demonstration of circulating endothelial cells. Blood 1999; 93(9):2951-2958.
  • Blann AD, Woywodt A, Bertolini F, Bull TM, Buyon JP, Clancy RM, Haubitz M, Hebbel RP, Lip GYH, Mancuso P, Sampol J, Solovey A, Dignat-George F. Circulating endothelial cells. Biomarker of Vascular Disease: A consensus statement. Thrombosis Haemostasis 2005 published online January 7
  • Woywodt A, Bahlmann F, de Groot K, Haller H, Haubitz M. Circulating endothelial cells: Life, death, and repair of the endothelial cell layer. Nephrology, Dialysis, Transplantation 2002; 17: 1728-1730

Circulating endothelial cells in ANCA-associated vasculitis

We have studied the vascular biology of ANCA-associated small-vessel vasculitis since 2000 (1). In our first study, we detected markedly elevated cell numbers in patients with active disease. We could demonstrate that cell numbers decline during the course of immunosuppressive treatment. Preliminary studies showed a necrotic phenotype in the vast majority of cells (2). In a subsequent study, we evaluated patients with relapse and granulomatous disease. Our results indicate that elevated counts of circulating endothelial cells discriminate between vasculitis and granulomatous inflammation (3).

References

  1. Haubitz M, Woywodt A. Circulating endothelial cells and vasculitis. Internal Medicine 2004; 48: 660-667
  2. Woywodt A, Streiber F, de Groot K, Regelsberger H, Haller H, Haubitz M. Circulating endothelial cells are markers for ANCA-associated small-vessel vasculitis. Lancet 2003; 361(9353); 206-10
  3. Woywodt A, Goldberg C, Kirsch T, de Groot K, Erdbruegger U, Haller H, Haubitz M. Circulating endothelial cells in relapse and limited granulomatous disease due to ANCA-associated vasculitis. Annals of the Rheumatic Diseases 2005 Sep 8; [Epub ahead of print]

Circulating endothelial cells in renal transplantation

Figure 2: Acute vascular rejection in a renal graft
Figure 2: Acute vascular rejection in a renal graft

In this setting, microvascular endothelial cells are important for several reasons. First, endothelial cells serve as a barrier between donor cells within the graft and circulating leukocytes of the recipient. Secondly, endothelial cells of the recipient are targets of drug toxicity and cardiovascular disease is a major cause of morbidity and mortality in these patients. Finally, endothelial cells may become the target of immune events in acute vascular rejection (figure 2). We first studied a group of renal transplant recipients and demonstrated markedly elevated cell numbers in vascular rejection. Surprisingly, all other renal transplant recipients had elevated cell numbers as well (1). We speculated that this finding reflects calcineurin inhibitor toxicity. We therefore studied renal transplant recipients who were not on calcineurine inhibitors and compared cell numbers with a group of matched renal transplant recipients who were receiving these drugs. We were able to demonstrate significantly lower cell numbers in patients without calcineurine inhibitors (2). These finding is in keeping with our hypothesis.

References

  1. Woywodt A, Schroeder M, Gwinner M, Mengel M, Jaeger M, Schwarz A, Haller H, Haubitz M. Elevated numbers of circulating endothelial cells in renal transplant recipients. Transplantation 76: 1-4 (2003)
  2. Woywodt A, Schroeder M, Mengel M, Schwarz A, Gwinner W, Haller H, Haubitz M. Circulating endothelial cells are a novel marker of cyclosporine-induced endothelial damage. Hypertension 41: 721.723 (2003)

Circulating endothelial cells in haematopoetic stem cell transplantation

Figure 3: Endothelial swelling in a small vessel after HSCT
Figure 3: Endothelial swelling in a small vessel after HSCT

Microvascular endothelial cells are crucial in this setting because a variety of complications occur here. Veno-occlusive disease of the liver, capillary leak syndrome and thrombotic microangiopathy come to mind (figure 3). Graft-versus-host disease has been demonstrated to be a disorder of microvascular endothelial cells. We were able to demonstrate markedly elevated circulating endothelial cells after conditioning, indicating severe endothelial damage. Interestingly, we noted a dose effect in that patients with reduced intensity conditioning had significantly lower cell numbers (1). Further studies must now show whether elevated cell numbers predict vascular complications (2).

References

  1. Woywodt A, Scheer J, Hambach L, Buchholz S, Ganser A, Haller H, Hertenstein B, Haubitz M. Circulating endothelial cells as markers of endothelial damage during hematopoietic stem-cell transplantation. Blood 2004 prepublished online January 8
  2. Woywodt A, Buchholz S, Haubitz M, Hertenstein B. Counting the cost: Markers of endothelial damage in haematopoietic stem-cell transplantation. Bone Marrow Transplantation 2004 published online Nov 1