Combined transplantation of mesenchymal stem cells and endothelial progenitor cells for tissue engineering: a systematic review and meta-analysis
- Kunming Sun†1, 2,
- Zheng Zhou†3,
- Xinxin Ju1, 2,
- Yang Zhou1, 2,
- Jiaojiao Lan1, 2,
- Dongdong Chen1, 2,
- Hongzhi Chen1, 2,
- Manli Liu1, 2 and
- Lijuan Pang1, 2Email author
© The Author(s). 2016
Published: 10 October 2016
Combined cell implantation has been widely applied in tissue engineering in recent years. In this meta-analysis, we aimed to establish whether the combined transplantation of mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) promotes angiogenesis and tissue repair, compared with transplantation of a single cell type, following tissue injury or during tissue regeneration.
The electronic databases PubMed, EMBASE, MEDLINE, Chinese Biomedical Literature, and China National Knowledge Infrastructure were searched in this systematic review and meta-analysis. Eighteen controlled preclinical studies involving MSC and EPC transplantation in animal models of disease, or in coculture in vitro, were included in this review. The vessel density and other functional indexes, which were classified according to the organ source, were used to evaluate the efficiency of cotransplantation. Publication bias was assessed.
There was no obvious difference in angiogenesis following combined cell transplantation (EPCs and MSCs) and transplantation of EPCs alone; however, an improvement in the function of damaged organs was observed following cotransplantation. In addition, combined cell transplantation significantly promoted tissue recovery in cardiovascular disease, cerebrovascular disease, and during bone regeneration. Compared with combined transplantation (EPCs and MSCs) and transplantation of MSCs alone, cotransplantation significantly promoted angiogenesis and bone regeneration, as well as vessel revascularization and tissue repair in cerebrovascular disease; however, no obvious effects on cardiovascular disease were observed.
As an exploratory field in the discipline of tissue engineering, MSC and EPC cotransplantation offers advantages, although it is essential to assess the feasibility of this approach before clinical trials can be performed.
Following injury, the repair and regeneration of tissue requires the availability of a sufficient blood supply . Numerous studies have demonstrated that angiogenesis is an important mechanism underlying the repair and functional recovery of injured tissue . Therefore, it is necessary to develop approaches that promote angiogenesis and neovascularization, enabling the repair and regeneration of damaged tissue and dysfunctional cells. In recent years, several reports have described the application of cell-based therapies, involving the transplantation of a combination of cell types in regenerative medicine. Mesenchymal stem cells (MSCs) are a type of adult stem cells derived from the bone marrow with multidirectional differentiation potential, which differentiate into various cell types, according to their specific microenvironment, and also participate in the regeneration of blood vessels and damaged tissues . In contrast, endothelial progenitor cells (EPCs) are mononuclear cells that circulate in the blood and are derived from different tissues. They can also participate in vascular repair by migrating to distant vessels, differentiating into mature endothelial cells (ECs), and replacing old and injured ECs . It is expected that transplantation of a combination of both types of cells should compensate for the limitations of transplantation of either EPCs or MSCs alone, because the former are unable to differentiate into cardiocytes in vivo , whereas the latter preferentially differentiate into tissue cells but fail to elicit an improvement in tissue function owing to a lack of specificity . Accordingly, cell therapy using a combination of both cell types has been performed in various studies with the aim of achieving synergistic effects in terms of angiogenesis and tissue regeneration. The present systematic review and meta-analysis was conducted to assess the effectiveness of cotransplantation on the repair of damaged tissue and to provide novel insights into the potential utility of such therapies in regenerative medicine.
A systematic search of relevant articles was performed in accordance with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines . The following terms were used as keywords when searching the electronic databases PubMed, EMBASE, MEDLINE, Chinese Biomedical Literature (CBM), and China National Knowledge Infrastructure: (MSCs OR mesenchymal stem cells OR mesenchymal stromal cells) AND (EPCs or endothelial progenitor cells).
The eligibility criteria for including articles in this systematic review and meta-analysis were as follows: (1) all studies included were controlled comparison studies involving stem/progenitor cells and coimplantation in animals in vivo or coculturing of cells isolated from animals in vitro; (2) all studies included had at least two groups, an experimental group (EPCs and MSCs, coimplantation/coculture) and/or a control group (MSCs or EPCs alone); and (3) English or Chinese published papers and theses were included.
The exclusion criteria for including articles in this systematic review and meta-analysis were reviews and articles that: (1) were duplicated previously; (2) had insufficient statistical data; or (3) had a lack of control groups.
Using vessel density as the main parameter presented publication bias.
All studies were read and all data were extracted independently by two reviewers (KMS and ZZ). Disagreements were resolved by a third reviewer (LJP). Data were extracted following a standard format: the first author’s name, year of publication, animal species, numbers in the intervention and control groups, cell numbers in both groups, cell-injection time after generating the animal model, measurement time for the indices, and other parameters measured in the studies that were also included in this meta-analysis. In addition to vessel density, left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), the rate of increase in the maximum left ventricular pressure (+dp/dt), and the rate of decrease in the maximum left ventricular pressure (−dp/dt) were chosen as functional indices for evaluating the effect on left ventricular function via echocardiography . The activity of alkaline phosphatase (ALP) in cells was used as an early marker of osteogenic differentiation . Brain-derived neurotrophic factor (BDNF) exerts protective effects against ischemia and hypoxia-induced brain injury . All parameters were dependent on their organ sources to estimate the efficacy of cell therapies [9, 10].
All data were analyzed by presenting pooled relative risks and 95 % confidence intervals using Review Manager Version 5.3. Because heterogeneity was reported in terms of vessel density, LVSP, LVEDP, +dp/dt, and –dp/dt, a random-effects model was used, and heterogeneity was evaluated using the I 2 statistic. In the absence of sufficient data for pooling, the results of individual studies are presented descriptively. Sensitivity analysis could not be performed because the data were complex. We extracted key parameters that may affect end therapy, such as the animal species used, the type and number of injected cells, the time of cell injection after modeling, and the time of measurement following the injection of cells. Small-study effects were explored using funnel plots.
Search results and study characteristics
The main parameter: vessel density
Femoral head necrosis and bone regeneration
Characteristics of the included studies
First author, year
Number of animals used for intervention, EPC + MSC
Number of animals used for controls, EPC/MSC
Number of cells used for intervention, EPC + MSC
Number of cells used as controls, EPC/MSC
Time of cell therapy after making the model
Time point of index measure
Index of measure
Suuronen, 2007 
5 × 105 + 5 × 105
1 × 106/1 × 106
1. LVEF, FS
2. Infarct area
3. Infarct length
4. Heart rate
5. Arteriole density
Derval, 2008 
5 × 105 + 5 × 106
5 × 105/5 × 106
1. Capillary density
2. Scar thickness
3. Infarct size
4. Heart rate
Zhang, 2008 
1 × 106 + 1 × 106
2 × 106/2 × 106
1. Cardiac function and hemodynamics (ejection fraction, FS, LVEDD, LVEDP, +dp/dt, –dp/dt)
2. Capillary density and regional myocardial blood flow
3. Myocardial fibrosis
4. Angiogenic growth factor protein and mRNA expression
Yi, 2010 
0.5 ml + 0.5 ml
1 ml/1 ml
1. Hemodynamics (LVSP, LVEDP, +dp/dt, –dp/dt)
2. Infarct size
3. Capillary density
Xiaolin, 2010 
2 × 106 + 0.5 × 107 × 3
2 × 106
7 days, 14 days
Yuhui, 2010 
5 × 106 + 5 × 106
5 × 106/5 × 106
Cardiac function (LVSP, LVEDP, +dp/dt, –dp/dt)
Zigdon-Giladi, 2015 
5 × 105 + 5 × 105
4 weeks and 12 weeks
1. Blood vessel density
2. Vertical bone height
Zigdon-Giladi, 2014 
5 × 105 + 5 × 105
1. Bone volume fraction (BV/TV)
2. Tissue mineral density (TMD)
Shaolong, 2014 
14 days and 28 days
1. Vessel density
Xian, 2013 
3 days, 7 days, and 14 days
1. ALP activity
2. The OC expression
3. Cell proliferation activity
Li, 2013 
24 h, 3 days, 7 days, and 14 days
1. ALP activity
2. Mineralized nodule
3. Gene expression of key osteogenic markers
4. Matrigel 2D assay
Seebach, 2012 
5 × 105
5 × 105/5 × 105
1. Area of neovascularization
2. VEGF release
Huiping, 2011 
1 × 105 + 1 × 105
1 × 105/1 × 105
1. ALP activity
2. Cell proliferation activity
Fedorovich, 2010 
1 × 105 + 1 × 105
–/2 × 105
2 weeks, 6 weeks
1. In-vitro analysis of 2D/3D network formation on Matrigel and osteogenic differentiation
2. In-vivo vascularization and bone formation
Usami, 2009 
5 × 106 + 1 × 107
5 × 106/1 × 107
7 days, 14 days
1. ALP activity
2. Soft X-ray
3. Implant capillary scoring
Zigen, 2013 
2 × 106 + 2 × 106
–/2 × 106
1. Cerebral infarction volume
3. Neurological score
Yao, 2014 
2 × 106 + 2 × 106
2 × 106/2 × 106
1. Cerebral infarction volume
3. Neurological score
Fenfang, 2014 
2 × 106 + 2 × 106
2 × 106/2 × 106
1. The expression of Bcl-2 and Bax
2. The Neurological Score
Cell-based therapy has been widely applied in bioengineering, as well as to facilitate tissue repair and regeneration. Neovascularization represents an important process involved in tissue regeneration , because a sufficient blood supply is required to ensure the availability of nutrients during tissue repair. The promotion of neovascularization during tissue repair is therefore the focus of intense effort in the field of regenerative medicine.
EPCs which reside in the bone marrow, adult peripheral blood, and human umbilical cord blood differentiate into mature ECs that not only participate in angiogenesis during embryonic development, but also play an important role in microvascular neovascularization and vascular endothelial repair following differentiation . MSCs, which represent important members of the stem cell family, possess the ability to self-renew, differentiate, and participate in angiogenesis . Numerous clinical trials have confirmed that MSCs may be used in the treatment of diseases such as chronic heart infarction, acute myocardial infarction, and hematological malignancies . MSCs and EPCs, which promote vascularization and tissue repair via different pathways, have both been used as seed cells for tissue engineering [26, 27]. Most previous studies have utilized single-cell transplantation, which suffers from several limitations. For several studies, it was reported that strategies involving the combined transplantation of multiple cell types are more effective than single-cell transplantation . This meta-analysis was conducted to access the efficacy of combined cell transplantation therapy in promoting angiogenesis and tissue repair.
Results showed that there was no difference in angiogenesis between the EPC and MSC cotransplantation group and the EPC single-transplantation group; the heterogeneity of the data was 88 %. This heterogeneity resulted from various factors, such as differences in the organization source, injection dose, and measurement time (Table 1). Because of the small amount of available data, we were unable to perform sensitivity analysis. Our findings indicated that the transplantation of EPCs alone achieved the same effect on angiogenesis as combined transplantation; however, MSCs were able to induce differentiation into EPCs under specific conditions . Several studies have reported that inducing the differentiation of EPCs into other cell types is no easier than inducing the differentiation of MSCs [12, 13, 28]. Numerous studies have demonstrated that these cells are capable of differentiating into ECs, thereby contributing to the formation of vascular networks [2, 10–15, 21]. These findings confirmed that EPCs may be utilized to achieve a significant enhancement in angiogenesis and revascularization. EPCs are considered capable of ensuring the availability of sufficient blood supply, thereby ensuring a source of nutrients during tissue repair. However, the present results showed that cell therapies using a combination of MSCs and EPCs may be applied to achieve improved tissue regeneration and repair, relative to the transplantation of either cell type alone. The results revealed that the combined transplantation of MSCs and EPCs achieved an improvement in cardiac function in cardiac diseases, in ALP activity and bone volume in damaged bone tissue, and in cerebral function in cerebrovascular diseases by increasing BDNF and reducing neurologic impairment. However, these results may be affected by the injection dose or organ source, and can also be associated with the injured tissue needing more new vessels to repair, the extent of tissue damage, or the ability of the tissue to regenerate. Our findings confirmed that combination therapy using both MSCs or EPCs is more effective than therapy using MSCs or EPCs alone, under some conditions. MSCs are capable of differentiating into various cell types, thereby providing a source of cells for the repair of damaged tissues; therefore, combination therapy involving the transplantation of these cells achieves improved tissue repair. However, compared with the transplantation of MSCs alone, the effect of combined transplantation on left ventricular function was not clear; the + dp/dt or –dp/dt value represented a significant difference, but no difference was observed in LVSP and LVEDP. We speculate that this heterogeneity may be attributed to the varying injection times of EPCs and MSCs reported in the studies: one study reported that EPCs were injected for 3 days (0.5 × 107 EPCs/day) at 7 days post MSC injection . In other studies, both cell types were injected at the same time. These findings suggested that EPCs play a more important role in the early stages of vascularization than MSCs and that MSCs promote EPC proliferation and provide a stable microenvironment for these cells. The observed heterogeneity may also be attributed the reduced capacity of the myocardium to regenerate, or variations in factors such as instrument sensitivity.
To our knowledge, the present meta-analysis is the first to evaluate the effectiveness of combined cell-transplantation therapy. Because this form of cell therapy has not been widely applied in clinical trials to date, most of the included studies reported the efficacy of combination cell therapies from animal studies. Our results are expected to guide preclinical and clinical trials in investigating the efficacy of combination cell therapies. Further investigation is required to determine the optimal cotransplantation dose, therapeutic method, and time of treatment.
Our meta-analysis has several limitations. Since the data were complex and insufficient, we could not assess the heterogeneity or perform sensitivity analyses of studies related to vessel density. However, the main factors that may affect the end evaluation are listed and divided into various groups (Table 1) or presented descriptively.
Interest in combination cell therapy should increase in the future after better efficacy is achieved. In this study, we collected, read, and analyzed a large amount of articles to investigate the efficacy of combination cell therapy using statistical methods. Unfortunately, we could not perform further research and statistical analysis due to the small number of data, although we could still conclude that EPCs played an important role in vascular regeneration when compared with combined transplantation, which was associated with EPC characteristics such as differentiation into vascular ECs and composing the vascular wall. Combined transplantation could promote robust tissue regeneration. The underlying mechanism of stem/progenitor cell therapy in tissue repair is presently unclear. MSCs/EPCs can secrete several nutritional factors to promote the repair of tissue functions after entering into tissues, so as to continuously improve tissue functions and promote the regeneration of surrounding nerves. In addition, MSCs/EPCs may activate or promote the homing of other cells to damaged tissues during the regeneration of tissue cells [29, 30]. Recent research has only superficially investigated their regenerative abilities in tissues, and detailed analysis of the effects of the number of injected cells, injection mode, and other parameters has not been performed. Further research into these issues needs to be conducted before cell-based therapy can be safely and effectively applied in a clinical setting.
This work was supported by the National Natural Science Foundation of China (No. 81560053, No. 81160018); the Corps Doctor Foundation (No. 2014BB018); the Shihezi University Outstanding Youth Science and Technology Talent Cultivation Plan (No. 2013ZRKXJQ05); the One Thousand Youth Talents Plan (No. 2014); and the Pairing Program of Shihezi University with Eminent Scholar in Elite University (No. SDJDZ201508).
Availability of data and materials
The authors confirm that all data generated or analyzed during this study are available.
KMS and ZZ are co-first authors. KMS and LJP conceived and designed the experiments. KMS and ZZ performed the experiments. KMS, ZZ, HZC, DDC, and MLL analyzed the data. XXJ, YZ, and JJL contributed reagents/materials/analysis tools. KMS and ZZ wrote the paper. All authors read and approved the manuscript.
The authors declare that they have no competing interests.
Consent for publication
Ethics approval and consent to participate
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