**3.1. Clinical trials in cardiac disease**

have been implicated in the aging frailty syndrome, which is characterized by decreased strength, endurance, physiologic function, and reserve capacity in multiple organ systems [122, 123]. Moreover, aging, renal failure, C-reactive protein (CRP) levels, and other adverse health parameters have been shown to correlate significantly with poor angiogenic potency of bone marrow stem cells [105, 124]. These studies suggest that the therapeutic potential of autologous MSCs obtained from patients may be limited, whereas more robust repair and regeneration would occur by using allogeneic MSCs from young, healthy donors. Indeed, two clinical trials in patients with ischemic and dilated cardiomyopathy, respectively, compared autologous to allogeneic MSCs and found that although both provided benefits in cardiac structural endpoints, the allogeneic MSCs provided greater cardiovascular functional benefits [5, 7, 81]. On the other hand, a study on the impact of recipient age on the efficacy of MSC therapy found that older (>60 years of age) patients responded just as effectively as younger (<60 years of age) patients when administered either autologous or allogeneic MSC therapy for chronic ischemic cardiomyopathy [125]. This finding is highly significant since the majority of the population with cardiovascular disease requiring cell-based therapy is aged.

152 Stromal Cells - Structure, Function, and Therapeutic Implications

Although the evidence is conflicting [126–130], clinical trials of MSC therapy usually exclude patients with a history of cancer due to concerns regarding the MSCs' potential for carcinogenesis. It remains unclear whether MSCs have the potential to undergo spontaneous malignant transformation and/or whether they interact with surrounding tumor stromal elements [129–131]. Spontaneous malignant transformation of human bone marrow-derived MSCs has been shown in vitro during long-term cultures [127]. These MSCs underwent faster proliferation, failed to undergo complete differentiation, and exhibited altered morphology and phenotype. Moreover, when these altered MSCs were administered to immunodeficient mice rapid-growing tumors throughout the lung tissue were found. On the other hand, in a separate study [128], human bone marrow-derived MSCs were grown in culture and assessed at different time points for expression of various tumor-related proteins until they reached senescence or passage 25. A progressive decrease in proliferative capacity with shortened telomeres was observed in most cultured MSCs until they reached senescence. In addition, the MSCs did not express telomerase activity or telomerase reverse transcriptase transcripts, and no chromosomal abnormalities or alternative lengthening of telomeres were observed, supporting the safety of in vitro MSC expansion, and therapeutic use. Despite these encouraging findings, the functional, phenotypic, and genetic characterization of culture-expanded MSCs merits further careful study [129, 131, 132]. In addition, recent findings indicate that various direct (e.g., cell fusion) and indirect (e.g., exosome or vesicle-mediated) interactions between MSCs and cancer cells can produce functional interference and/or mutual acquisition of new cellular properties [130]. These functional and phenotypic cellular alterations can lead to changes in metastatic behavior and induce new cancer stem cell development. On the other hand, exosomes and

vesicle-mediated mechanisms may be a promising therapeutic tool against cancer.

Sex differences exist in many disease states as well as with respect to the role of MSCs in organ repair and regeneration after injury. There is evidence that female MSCs exhibit decreased apoptosis, interleukin-6, and tumor necrosis factor and increased endothelial growth factor and vascular endothelial growth factor expression compared to male donor MSCs [133].

**2.7. Sex differences in MSCs**

Multiple clinical trials suggest that MSCs can ameliorate left ventricular remodeling and improve cardiac function in patients with acute and chronic ischemic cardiomyopathy [7, 9, 11, 72, 84, 115, 116, 137–141]. The Transendocardial mesenchymal stem cells and mononuclear bone marrow cells for ischemic cardiomyopathy (TAC-HFT) trial demonstrated reverse remodeling and improved regional contractility of the scar as well as improved functional capacity and quality of life over 1 year in patients with chronic ischemic cardiomyopathy treated with transendocardial injection of autologous bone marrow-derived MSCs versus bone marrow mononuclear cells or placebo [9, 142]. The mesenchymal stromal cells in chronic ischemic Heart Failure (MSC-HF) trial showed that intramyocardial injection of autologous bone marrow-derived MSCs in patients with severe ischemic cardiomyopathy improved ventricular function and myocardial mass [140]. The same group showed that intramyocardial delivery of autologous MSCs into patients with coronary heart disease and refractory angina provided a sustained effect (3-year follow-up) in improving exercise capacity and ventricular function, and reducing hospitalization rates and revascularizations [143]. As mentioned previously, the CHART-1 study also demonstrated the anti-remodeling properties of cardiopoietic MSCs at the 1-year follow-up [72]. Encouraging results from preclinical studies with combination therapy [28, 79] have led to the initiation of the CONCERT-HF (NCT02501811) trial by the Cardiovascular Cell Therapy Research Network (CCTRN) in an effort to examine the effects of the transendocardial delivery of a combination of autologous bone marrowderived MSCs and cardiac progenitor cells into patients with ischemic cardiomyopathy.

Autologous adipose tissue-derived MSCs are also undergoing investigation in the cardiovascular field. The adipose-derived stromal cells for treatment of patients with chronic ischemic heart disease (MyStromalCell) trial was a phase II, first-in-man, single-center, double-blind, randomized, and placebo-controlled study of intramyocardial injections of autologous adipose-derived MSCs in patients with chronic ischemic heart disease and refractory angina but preserved ejection fraction [111, 112]. The MSCs were obtained from abdominal adipose tissue,

The transendocardial stem cell injection delivery effects on neomyogenesis study (TRIDENT) trial compared the safety and efficacy of two doses (20 million and 100 million) of allogeneic bone marrow-derived human MSCs delivered transendocardially in patients with ischemic cardiomyopathy [116]. Although both cell doses reduced scar size, only the 100 million doses increased LVEF, highlighting the crucial role of cell dose in the responses to cell therapy. In

neic bone marrow-derived MPCs (25, 75, and 150 million cells) delivered transendocardially in patients with ischemic and non-ischemic heart failure, no differences were observed in LVEF at 12 months of follow-up, although the 150 million MPC group had a significant reduction in left ventricular end-systolic and end-diastolic volumes, a measure of reverse remodeling, at 6 months and a non-significant decrease of both ventricular volumes at 12 months [56]. These and other ongoing studies determining the optimal dose and delivery are essential to advance the field, decipher mechanism(s) of action, and enhance planning of pivotal Phase III trials [148–152]. A recent trial assessed the safety and preliminary efficacy of intravenously administered, allogeneic, ischemia-tolerant MSCs in patients with non-ischemic cardiomyopathy [153]. Ischemia-tolerant MSCs are grown under chronic hypoxic conditions and have been shown to better migrate toward wound healing-related cytokines and cytokines found in ischemic tissues and express higher levels of hypoxia-inducible factor-1 [154]. These studies suggested that ischemia-tolerant MSCs may be therapeutically more effective than MSCs grown under normoxic conditions. An increase in LVEF and reductions in end-systolic and end-diastolic volumes were observed at three months of follow up in the treated group but was not significantly different from the placebo group. Functional capacity and health status were significantly improved in the MSC treated group compared to placebo. MSCs derived from umbilical cord (UC-MSCs) have also been tested in patients with heart failure. The randomized clinical trial of intravenous infusion umbilical cord mesenchymal stem cells on cardiopathy (RIMECARD) trial is a randomized, double-blind, placebo-controlled trial that evaluated the safety and efficacy of UC-MSCs administered intravenously in patients with heart failure of ischemic or non-ischemic origin [141]. Infusion of allogeneic UC-MSCs was safe, with no development of alloantigen directed antibodies post-infusion, and effective in improving LVEF, functional status, and quality of life. Intramyocardial delivery of UC-MSCs in patients with heart failure has also been shown to produce improvements in LVEF and end-systolic volume in patients with severe heart failure [155]. Ongoing clinical trials are assessing the safety and efficacy of allogeneic MSC therapy in patients with acute myocardial infarction, chronic ischemic and non-ischemic cardiomyopathy, and left ventricular assist devices. These studies will continue to pave the way for the development of allogeneic cell-based regenerative therapies for structural and functional disorders of the myocardium. The results from cardiovascular stem cell clinical trials are so far promising, with recent trials highlighting the vast therapeutic potential of allogeneic over autologous stem cells. However, many challenges remain, such as addressing long-term safety, serial stem cell injections, and optimal cell type, dose, and delivery route [148–152].

Endothelial dysfunction is characterized by impaired endothelial vasodilation, a proinflammatory and prothrombotic state, and impaired bioactivity of EPCs and contributes to the

enriched), alloge-

155

Mesenchymal Stromal Cells as a Therapeutic Intervention

http://dx.doi.org/10.5772/intechopen.78586

phase 2 dose-escalation study investigating immunoselected (Stro-1/Stro-3+

**3.2. Vascular disease**

**Figure 6.** Effects Of mesenchymal stem cell therapy in heart disease.

culture-expanded in vitro and stimulated with vascular endothelial growth factor-A (VEGF-A) (165) the week before treatment. The six month follow-up results demonstrated safety, and although a significant increase in exercise capacity was observed in the patients treated with the MSCs but not with placebo, there was no statistically significant difference between the MSC and placebo treatment groups.

An important issue in this new field is whether MSCs can be used as an allograft [5, 7, 89], avoiding the need for bone marrow aspiration of patients and tissue culture delays prior to treatment. Furthermore, the function of autologous MSCs may be impaired in patients with comorbidities and/or advanced age [101–104]. A meta-analysis of 82 preclinical studies [144] demonstrated that allogeneic therapy is safe and at least as effective as autologous MSC therapy, suggesting that allogeneic MSCs are characteristically immunomodulatory, as discussed above.

The therapeutic benefit of allogeneic MSCs versus placebo delivered intravenously has been investigated in patients after acute MI [11, 145, 146]. Not only did these results show the safety of allogeneic MSC delivery to humans, but also moreover, echocardiography demonstrated a 6% increase in ejection fraction at 3 months for patients treated with MSCs. Moreover, the percutaneous stem cell injection delivery effects on neo-myogenesis (POSEIDON) trial compared allogeneic vs. autologous MSCs delivered by transendocardial stem cell injection in patients with chronic ischemic cardiomyopathy and showed that both MSC types are safe and clinically effective [7, 147]. Similarly, the percutaneous stem cell injection delivery effects on neo-myogenesis – dilated cardiomyopathy (POSEIDON-DCM) trial demonstrated safety and efficacy of transendocardial autologous vs. allogeneic MSC therapy in patients with nonischemic, dilated cardiomyopathy, with a cardiac function efficacy preference toward allogeneic MSCs [5].

The transendocardial stem cell injection delivery effects on neomyogenesis study (TRIDENT) trial compared the safety and efficacy of two doses (20 million and 100 million) of allogeneic bone marrow-derived human MSCs delivered transendocardially in patients with ischemic cardiomyopathy [116]. Although both cell doses reduced scar size, only the 100 million doses increased LVEF, highlighting the crucial role of cell dose in the responses to cell therapy. In phase 2 dose-escalation study investigating immunoselected (Stro-1/Stro-3+ enriched), allogeneic bone marrow-derived MPCs (25, 75, and 150 million cells) delivered transendocardially in patients with ischemic and non-ischemic heart failure, no differences were observed in LVEF at 12 months of follow-up, although the 150 million MPC group had a significant reduction in left ventricular end-systolic and end-diastolic volumes, a measure of reverse remodeling, at 6 months and a non-significant decrease of both ventricular volumes at 12 months [56]. These and other ongoing studies determining the optimal dose and delivery are essential to advance the field, decipher mechanism(s) of action, and enhance planning of pivotal Phase III trials [148–152].

A recent trial assessed the safety and preliminary efficacy of intravenously administered, allogeneic, ischemia-tolerant MSCs in patients with non-ischemic cardiomyopathy [153]. Ischemia-tolerant MSCs are grown under chronic hypoxic conditions and have been shown to better migrate toward wound healing-related cytokines and cytokines found in ischemic tissues and express higher levels of hypoxia-inducible factor-1 [154]. These studies suggested that ischemia-tolerant MSCs may be therapeutically more effective than MSCs grown under normoxic conditions. An increase in LVEF and reductions in end-systolic and end-diastolic volumes were observed at three months of follow up in the treated group but was not significantly different from the placebo group. Functional capacity and health status were significantly improved in the MSC treated group compared to placebo.

MSCs derived from umbilical cord (UC-MSCs) have also been tested in patients with heart failure. The randomized clinical trial of intravenous infusion umbilical cord mesenchymal stem cells on cardiopathy (RIMECARD) trial is a randomized, double-blind, placebo-controlled trial that evaluated the safety and efficacy of UC-MSCs administered intravenously in patients with heart failure of ischemic or non-ischemic origin [141]. Infusion of allogeneic UC-MSCs was safe, with no development of alloantigen directed antibodies post-infusion, and effective in improving LVEF, functional status, and quality of life. Intramyocardial delivery of UC-MSCs in patients with heart failure has also been shown to produce improvements in LVEF and end-systolic volume in patients with severe heart failure [155].

Ongoing clinical trials are assessing the safety and efficacy of allogeneic MSC therapy in patients with acute myocardial infarction, chronic ischemic and non-ischemic cardiomyopathy, and left ventricular assist devices. These studies will continue to pave the way for the development of allogeneic cell-based regenerative therapies for structural and functional disorders of the myocardium. The results from cardiovascular stem cell clinical trials are so far promising, with recent trials highlighting the vast therapeutic potential of allogeneic over autologous stem cells. However, many challenges remain, such as addressing long-term safety, serial stem cell injections, and optimal cell type, dose, and delivery route [148–152].
