Circulating endothelial progenitor cell numbers are not associated with donor organ age or allograft vasculopathy in cardiac transplant recipients

Circulating Progenitor Cells Are Associated With Plaque Progression And Long-Term Outcomes In Heart Transplant Patients

AIMS

Circulating progenitor cells (CPCs) play a role in vascular repair and plaque stability, while osteocalcin (OC) expressing CPCs have been linked to unstable plaque and adverse cardiovascular outcomes. However, their role in cardiac allograft vasculopathy (CAV) has not been elucidated. This cohort study aimed to investigate the contribution of CPCs on CAV progression and cardiovascular events after heart transplantation.

METHODS AND RESULTS

A total of 80 heart transplant patients (mean age 55 ± 14 years, 72% male) undergoing annual intravascular ultrasound (IVUS) had fresh CPCs marked by CD34, CD133, and OC counted in peripheral blood using flow cytometry, on the same day as baseline IVUS. CAV progression was assessed by IVUS as the change (Δ) in plaque volume divided by segment length (PV/SL), adjusted for the time between IVUS measurements (median 3.0, interquartile range (IQR) [2.8, 3.1] years), and was defined as ΔPV/SL that is above the median ΔPV/SL of study population. Major adverse cardiac events (MACE) was defined as any incident of revascularization, myocardial infarction, heart failure admission, re-transplantation, stroke and death. Patients with higher CD34+CD133+ CPCs had a decreased risk of CAV progression (odds ratio 0.58, 95% confidence interval [CI] [0.37, 0.92], p = 0.01) and MACE (hazard ratio [HR] 0.79, 95% CI [0.66, 0.99], p = 0.05) during a median (IQR) follow up of 8.0 years (7.2, 8.3). Contrarily, higher OC+ cell counts were associated with an increased risk of MACE (HR 1.26, 95% CI [1.03, 1.57], p = 0.02).

CONCLUSIONS

Lower levels of CD34+CD133+ CPCs are associated with plaque progression and adverse long-term outcomes in patients who underwent allograft heart transplantation. In contrast, higher circulating OC+ levels are associated with adverse long term outcomes. Thus, CPCs might play a role in amelioration of transplant vasculopathy, while OC expression by these cells might play a role in progression.

TRANSLATIONAL PERSPECTIVE

The results of the current study suggest lower levels of circulating CD34+CD133+ cell levels are associated with cardiac allograft vasculopathy progression and future adverse cardiovascular events, while higher OC+ cell levels are associated with a greater risk of future cardiovascular events. Further studies confirming our findings might elucidate the role of circulating progenitor cells in the pathophysiology of CAV. Moreover, our findings might support the use of circulating progenitors as biomarkers, as well as the notion of cell therapy as potential treatment option for CAV, a disease with severe burden and limited treatment options.

The hematopoietic stem cell number in the peripheral blood of pediatric recipients correlates with the outcome after living donor liver transplantation

It has been proposed that circulating HSCs play a role in graft survival after liver transplantation. The aim was to analyze the relationship between the number of HSCs before and after LDLT and liver function, immune biomarkers, and clinical outcomes in pediatric patients. We studied 15 pairs of adult healthy liver donors and pediatric recipients with ESLD. The CD34/CD45+ cell number was measured in the blood via flow cytometry, and plasma levels of immune biomarkers - via ELISA. CD34/CD45+ cell number in the recipients decreased within the first week after LDLT. The cell number before LDLT was negatively correlated with the plasma levels of CRP and the development of graft dysfunction in the early post-transplant period. After LDLT, the CD34/CD45+ cell number was positively correlated with the pretransplant plasma level of sCD40L, a T-cell activation marker. In adult liver donors, the cell number did not change within the first week after liver resection and was lower than in pediatric recipients. The results suggest that in pediatric recipients, the HSC number may be associated with graft function and could be regarded as a potential predictor of the clinical outcome after LDLT.

Endothelial dysfunction and cardiac allograft vasculopathy

Cardiac allograft vasculopathy remains a major challenge to long-term survival after heart transplantation. Endothelial injury and dysfunction, as a result of multifactorial immunologic and nonimmunologic insults in the donor and the recipient, are prevalent early after transplant and may be precursors to overt cardiac allograft vasculopathy. Current strategies for managing cardiac allograft vasculopathy, however, rely on the identification and treatment of established disease. Improved understanding of mechanisms leading to endothelial dysfunction in heart transplant recipients may provide the foundation for the development of sensitive screening techniques and preventive therapies.

Circulating apoptotic endothelial cells and apoptotic endothelial microparticles independently predict the presence of cardiac allograft vasculopathy

OBJECTIVES

Maintenance of endothelial homeostasis may prevent the development of cardiac allograft vasculopathy (CAV). This study investigated whether biomarkers related to endothelial injury and endothelial repair discriminate between CAV-negative and CAV-positive heart transplant recipients.

BACKGROUND

CAV is the most important determinant of cardiac allograft survival and a major cause of death after heart transplantation.

METHODS

Fifty-two patients undergoing coronary angiography between 5 and 15 years after heart transplantation were recruited in this study. Flow cytometry was applied to quantify endothelial progenitor cells (EPCs), circulating endothelial cells (CECs), and endothelial microparticles. Cell culture was used for quantification of circulating EPC number and hematopoietic progenitor cell number and for analysis of EPC function.

RESULTS

The EPC number and function did not differ between CAV-negative and CAV-positive patients. In univariable models, age, creatinine, steroid dose, granulocyte colony-forming units, apoptotic CECs, and apoptotic endothelial microparticles discriminated between CAV-positive and CAV-negative patients. The logistic regression model containing apoptotic CECs and apoptotic endothelial microparticles as independent predictors provided high discrimination between CAV-positive and CAV-negative patients (C-statistic 0.812; 95% confidence interval: 0.692 to 0.932). In a logistic regression model with age and creatinine as covariates, apoptotic CECs (p = 0.0112) and apoptotic endothelial microparticles (p = 0.0141) were independent predictors (C-statistic 0.855; 95% confidence interval: 0.756 to 0.953). These 2 biomarkers remained independent predictors when steroid dose was introduced in the model.

CONCLUSIONS

The high discriminative ability of apoptotic CECs and apoptotic endothelial microparticles is a solid foundation for the development of clinical prediction models of CAV.

Endothelial progenitor cells in cardiovascular disease and chronic inflammation: from biomarker to therapeutic agent

The discovery of endothelial progenitor cells in the 1990s challenged the paradigm of angiogenesis by showing that cells derived from hematopoietic stem cells are capable of forming new blood vessels even in the absence of a pre-existing vessel network, a process termed vasculogenesis. Since then, the majority of studies in the field have found a strong association between circulating endothelial progenitor cells and cardiovascular risk. Several studies have also reported that inflammation influences the mobilization and differentiation of endothelial progenitor cells. In this review, we discuss the emerging role of endothelial progenitor cells as biomarkers of cardiovascular disease as well as the interplay between inflammation and endothelial progenitor cell biology. We will also review the challenges in the field of endothelial progenitor cell-based therapy.

Association of CD14+ monocyte-derived progenitor cells with cardiac allograft vasculopathy

OBJECTIVE

The pathogenesis of cardiac allograft vasculopathy after heart transplant remains controversial. Histologically, cardiac allograft vasculopathy is characterized by intimal hyperplasia of the coronary arteries induced by infiltrating cells. The origin of these infiltrating cells in cardiac allograft vasculopathy is unclear. Endothelial progenitor cells are reportedly involved in cardiac allograft vasculopathy; however, the role of CD14(+) monocyte-derived progenitor cells in cardiac allograft vasculopathy pathogenesis remains unknown.

METHODS

Monocyte-derived progenitor cells were isolated from blood mononuclear cell fractions obtained from 25 patients with cardiac allograft vasculopathy and 25 patients without cardiac allograft vasculopathy.

RESULTS

Both patients with cardiac allograft vasculopathy and those without cardiac allograft vasculopathy had CD45(+), CD34(+), CD14(+), CD141(-), CD31(-) monocyte-derived progenitor cells that differentiated into mesenchymal lineages. Monocyte-derived progenitor cells formed significantly higher numbers of colonies in patients with cardiac allograft vasculopathy than in those without cardiac allograft vasculopathy; this correlated with posttransplant follow-up time. Importantly, monocyte-derived progenitor cells from patients with cardiac allograft vasculopathy expressed significantly more α smooth muscle actin and proliferated at a higher rate than did monocyte-derived progenitor cells of patients without cardiac allograft vasculopathy. In vitro experiments suggested a paracrine control mechanism in proliferation of monocyte-derived progenitor cells in cardiac allograft vasculopathy.

CONCLUSIONS

These results indicate that monocyte-derived progenitor cells are associated with cardiac allograft vasculopathy, have the ability to transdifferentiate into smooth muscle cells, and thus may contribute to intimal hyperplasia of coronary arteries in cardiac allograft vasculopathy. Targeting monocyte-derived progenitor cell recruitment could be beneficial in cardiac allograft vasculopathy treatment.

Cardiac allograft vasculopathy: current knowledge and future direction

Cardiac allograft vasculopathy (CAV) is a unique form of coronary artery disease affecting heart transplant recipients. Although prognosis of heart transplant recipients has improved over time, CAV remains a significant cause of mortality beyond the first year of cardiac transplantation. Many traditional and non-traditional risk factors for the development of CAV have been described. Traditional risk factors include dyslipidemia, diabetes and hypertension. Non-traditional risk factors include cytomegalovirus infection, HLA mismatch, antibody-mediated rejection, and mode of donor brain death. There is a complex interplay between immunological and non-immunological factors ultimately leading to endothelial injury and exaggerated repair response. Pathologically, CAV manifests as fibroelastic proliferation of intima and luminal stenosis. Early diagnosis is paramount as heart transplant recipients are frequently asymptomatic owing to cardiac denervation related to the transplant surgery. Intravascular ultrasound (IVUS) offers many advantages over conventional angiography and is an excellent predictor of prognosis in heart transplant recipients. Many non-invasive diagnostic tests including dobutamine stress echocardiography, CT angiography, and MRI are available; though, none has replaced angiography. This review discusses the risk factors, pathogenesis, and diagnosis of CAV and highlights some current concepts and recent developments in this field.

Levels of circulating CXCR4-positive cells are decreased and negatively correlated with risk factors in cardiac transplant recipients

The association between levels of circulating endothelial progenitor cells (EPCs) and heart transplant recipients (HTX) with cardiac allograft vasculopathy (CAV) is under debate. The chemokine receptor CXCR4 plays an important role in the mobilization of progenitor cells and is implicated in pathological conditions, including cardiovascular disease. This study aims to evaluate the association between EPCs and CXCR4-positive cells in HTX patients. Peripheral blood mononuclear cells (PBMCs) from 34 HTX patients and 25 control participants were analyzed by flow cytometry for CXCR4-positive cells and EPCs. Endothelial progenitor cells were defined by the expression of a range of hematopoietic and endothelial lineage markers in different combinations. The ability to form endothelial cell colonies in vitro was also assessed by colony-forming unit (CFU) assay. Phenotypic analysis of EPCs by flow cytometry revealed similar levels in HTX patients compared to controls. In addition, no difference was observed between levels of EPCs or CFU number in patients with and without CAV. By contrast, CFU assay revealed a reduced number of CFUs in HTX patients compared to controls (3.3% ± 0.95 and 13.3% ± 4.5%, respectively, P = 0.014). Likewise, levels of CXCR4-positive cells were significantly reduced (15.9 ± 1.4 in patients vs 24.8 ± 3.3% in controls, P < 0.01), negatively correlated with Framingham risk score (rho = -0.4, P = 0.02) and the number of risk factors (rho = -0.3, P = 0.049). Levels of CXCR4-positive cells were also correlated with CFU number (r = 0.65, P = 0.0005). These findings further develop our understanding of the role of EPCs and endothelial CFUs in cardiovascular disease, in addition to highlighting the potential importance of CXCR4 in heart transplantation.

CD34+CD140b+ cells and circulating CXCL12 correlate with the angiographically assessed severity of cardiac allograft vasculopathy

AIMS

We sought to determine whether circulating vascular progenitor cells, such as endothelial progenitor cells (EPCs) or smooth muscle progenitor cells (SPCs), were associated with the severity of cardiac allograft vasculopathy (CAV).

METHODS AND RESULTS

CD34(+)CD140b(+) SPCs and CD34(+)KDR(+) EPCs were measured in the peripheral circulation of 187 adult heart transplant recipients by flow cytometry. Cardiac allograft vasculopathy was quantified by angiography using a CAV-specific scoring system. Cardiac allograft vasculopathy was present in 84 patients (44.7%) and was classified as mild in 59 and severe in 25 cases. Circulating SPCs were more frequently detectable in CAV patients than in patients without CAV. The number of CD34(+)CD140b(+) cells showed a stepwise increase in patients with moderate and severe CAV. Smooth muscle progenitor cell counts were higher in patients with coronary stent implant compared with unstented patients with CAV. In contrast, peripheral CD34(+)KDR(+) EPC counts were not changed in CAV patients. Plasma CXCL12 levels correlated with the degree of CAV and SPC counts. None of the different immunosuppressive drug regimes was related to the SPC count or the CXCL12 levels. A multivariate regression analysis revealed that the SPC count was independently associated with the presence of CAV.

CONCLUSION

Circulating SPCs, but not EPCs, and plasma CXCL12 concentrations are elevated in CAV patients, indicating that they play prominent roles in transplant arteriosclerosis.