**3.5 Examples of clinical studies with adult stem cells**

As of today, FDA-approved cellular and gene therapy products are limited to the hematopoietic progenitor cells from CB for alloHSCT in patients with disorders affecting the hematopoietic systems, autologous chondrocytes on a porcine collagen membrane for repair of cartilage defects of the knee, allogeneic cultured keratinocytes and fibroblasts in the treatment of mucogingival conditions, and a few chimeric antigen receptor (CAR) autologous cellular immunotherapies (https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/ approved-cellular-and-gene-therapy-products).

In addition to the treatment of the disorders affecting hematopoietic system, CB alloHSCT has also been applied in clinical trials to treat nonmalignant diseases. More than 20 years ago, CB transplantation had been initiated in infants and children with Krabbe's disease [130, 131]. Krabbe's disease is an autosomal recessive disorder due to deficiency of the lysosomal enzyme galactocerebrosidase, leading to progressive neurologic deterioration and death in early childhood. These transplantation studies demonstrated that CB cells, both hematopoietic and non-hematopoietic in origin, could engraft in the patients' central nervous system, providing the missing enzyme and facilitating neural cell repair. Particularly, the young patients that underwent transplantation before the development of symptoms showed significant improvements in developmental skills, while the children who underwent transplantation after the onset of symptoms had minimal neurologic improvement [130, 131]. A long-term follow-up (median 9.5 years, range 4–15 years) study further demonstrated that the surviving patients who underwent early CB transplantation function at a much higher level than untreated children or children who were symptomatic at the time of alloHSCT [132]. Based on the observed efficacy of CB transplantation on improving neurological outcome, Cotten et al. conducted a pilot study on intravenous infusion of autologous CB in 184 pediatric patients who had their CB banked at birth and were subsequently diagnosed with acquired neurological disorders [133]. This investigation demonstrated the safety and feasibility of autologous CB infusion in these pediatric recipients. Subsequently, Cotten et al. also reported the safety and feasibility of autologous CB infusion in neonates diagnosed as hypoxic ischemic encephalopathy [134].

Over the last two decades, there have been an increasing number of clinical trials involving stem cell treatment for various degenerative diseases. For cardiovascular disease alone, there have been more than 200 clinical trials using various cell types including skeletal myoblasts, autologous bone marrow mononuclear cells (BMMNCs), CD133<sup>+</sup> bone marrow cells, endothelial progenitors, autologous CD34<sup>+</sup> cells, MSCs, cardiopoietic stem cells that were generated by

**113**

*Innovations in Human Stem Cell Research: A Holy Grail for Regenerative Medicine*

treating MSCs with a cocktail of trophic factors, allogeneic and autologous c-kit<sup>+</sup> cardiac stem cells isolated from biopsies obtained during coronary artery bypass grafting, and cardiosphere-derived cells generated from culture outgrowth of heart biopsies (reviewed in [135]). Most studies demonstrated that the tested cells were safe and the procedures were feasible. However, the efficacy of these cell therapies remains inconclusive. Early clinical trials, ranging from pilot to phase III double-blinded placebo-controlled studies, such as TOPCARE-AMI, BOOST, FNCELL, and REPAIR-AMI, demonstrated significant efficacy (evaluated-based on left ventricular ejection fraction, LVEF) of BMMNC treatment in patients with acute myocardial infarction. However, recent multicenter, double-blinded, and placebo-controlled studies, such as TIME, LateTIME, and SWISS AMI trials, found no improvements after BMMNC administration in LVEF and other parameters measured by cMRI. Even the same center, which reported significant improvement in heart function in the initial pilot trial and subsequent partly randomized and open-label study on autologous CD133<sup>+</sup> bone marrow cell infusion during coronary artery bypass graft surgery [136,

sion in a strictly double-blind, fully randomized, and placebo-controlled trial (CARDIO133, NCT00462774) [138]. It has also to be mentioned that a report on the initial results of a phase I, open-label, and randomized trial using autologous c-kit+ cardiac stem cells in patients with ischemic cardiomyopathy was recently retracted from the journal, due to lack of reliability on the production of cells

Although there are a substantial number of clinical studies, it is difficult to compare results between trials. Sources of cell products, mode of cell delivery and cell dose, timing of administration, the age and complications of patients, and the choice of surrogate endpoint markers are all the variables for the efficacy of each

When it comes to a stem cell therapy, it is tempting to think of it as the cell replacement therapy, that is, the stem cells engraft and differentiate to replace the damaged cells in vivo. However, although a few studies demonstrated that MSCs

cardiomyocytes and also transdifferentiate in animal models [140, 141], most studies reveal no evidence of therapeutic cells to undergo real cell replacement

cardiomyocytes in experimental animals with infarction [142, 143]. Rather, paracrine effects, e.g., secretion of growth factors to enhance tissue preservation and/ or recruitment of endogenous repair, have been considered as the major mode of action of stem cells 137,138. Similar lack of differentiation has also been reported when neural stem cells or progenitors were transplanted in animal models [144]. It would be interesting to see whether administration of human ES or iPSC-derived mature cells, such as cardiomyocytes and neurons as mentioned in the first part of the chapter, would result in more effective outcomes in the recruited patients, as in preclinical studies, these fully differentiated cells appeared to be able to function-

For cellular therapies, there is a choice of using either autologous or allogeneic cells. The autologous cells have the advantage of circumventing immunogenicity; however, the cell dose could be limited per isolation and the quality may not be reliable. Moreover, as mentioned above, the function of tissue stem cells declines

cardiac stem cells and cardiosphere-derived cells do not become

bone marrow cell infu-

cells could fuse with

*DOI: http://dx.doi.org/10.5772/intechopen.88790*

137], later revealed no significant benefits of CD133<sup>+</sup>

**3.6 Lessons learned from clinical stem cell therapies**

could undergo tri-lineage differentiation and human CD34<sup>+</sup>

ally integrate in the recipient tissue [49, 50].

and integrity of the data [139].

clinical study.

in vivo. Even c-kit<sup>+</sup>

*Innovations in Human Stem Cell Research: A Holy Grail for Regenerative Medicine DOI: http://dx.doi.org/10.5772/intechopen.88790*

treating MSCs with a cocktail of trophic factors, allogeneic and autologous c-kit<sup>+</sup> cardiac stem cells isolated from biopsies obtained during coronary artery bypass grafting, and cardiosphere-derived cells generated from culture outgrowth of heart biopsies (reviewed in [135]). Most studies demonstrated that the tested cells were safe and the procedures were feasible. However, the efficacy of these cell therapies remains inconclusive. Early clinical trials, ranging from pilot to phase III double-blinded placebo-controlled studies, such as TOPCARE-AMI, BOOST, FNCELL, and REPAIR-AMI, demonstrated significant efficacy (evaluated-based on left ventricular ejection fraction, LVEF) of BMMNC treatment in patients with acute myocardial infarction. However, recent multicenter, double-blinded, and placebo-controlled studies, such as TIME, LateTIME, and SWISS AMI trials, found no improvements after BMMNC administration in LVEF and other parameters measured by cMRI. Even the same center, which reported significant improvement in heart function in the initial pilot trial and subsequent partly randomized and open-label study on autologous CD133<sup>+</sup> bone marrow cell infusion during coronary artery bypass graft surgery [136, 137], later revealed no significant benefits of CD133<sup>+</sup> bone marrow cell infusion in a strictly double-blind, fully randomized, and placebo-controlled trial (CARDIO133, NCT00462774) [138]. It has also to be mentioned that a report on the initial results of a phase I, open-label, and randomized trial using autologous c-kit+ cardiac stem cells in patients with ischemic cardiomyopathy was recently retracted from the journal, due to lack of reliability on the production of cells and integrity of the data [139].

## **3.6 Lessons learned from clinical stem cell therapies**

Although there are a substantial number of clinical studies, it is difficult to compare results between trials. Sources of cell products, mode of cell delivery and cell dose, timing of administration, the age and complications of patients, and the choice of surrogate endpoint markers are all the variables for the efficacy of each clinical study.

When it comes to a stem cell therapy, it is tempting to think of it as the cell replacement therapy, that is, the stem cells engraft and differentiate to replace the damaged cells in vivo. However, although a few studies demonstrated that MSCs could undergo tri-lineage differentiation and human CD34<sup>+</sup> cells could fuse with cardiomyocytes and also transdifferentiate in animal models [140, 141], most studies reveal no evidence of therapeutic cells to undergo real cell replacement in vivo. Even c-kit<sup>+</sup> cardiac stem cells and cardiosphere-derived cells do not become cardiomyocytes in experimental animals with infarction [142, 143]. Rather, paracrine effects, e.g., secretion of growth factors to enhance tissue preservation and/ or recruitment of endogenous repair, have been considered as the major mode of action of stem cells 137,138. Similar lack of differentiation has also been reported when neural stem cells or progenitors were transplanted in animal models [144]. It would be interesting to see whether administration of human ES or iPSC-derived mature cells, such as cardiomyocytes and neurons as mentioned in the first part of the chapter, would result in more effective outcomes in the recruited patients, as in preclinical studies, these fully differentiated cells appeared to be able to functionally integrate in the recipient tissue [49, 50].

For cellular therapies, there is a choice of using either autologous or allogeneic cells. The autologous cells have the advantage of circumventing immunogenicity; however, the cell dose could be limited per isolation and the quality may not be reliable. Moreover, as mentioned above, the function of tissue stem cells declines

*Innovations in Cell Research and Therapy*

be of an issue in CB stem cells.

**3.5 Examples of clinical studies with adult stem cells**

approved-cellular-and-gene-therapy-products).

As will be mentioned below, CB hematopoietic progenitor cells are among the few stem cell products that are approved by the FDA. Over 40,000 CB transplantations have been performed worldwide in both adults and children for the treatment of around 80 different disorders [129]. The advantage of using CB and cord blood CB-derived stem cells compared to other adult stem cell sources is the fast availability and ease in collection without causing any discomfort or risk to the donors. Moreover, being early in development, CB stem cells have not been exposed to immunological challenge and are less likely to carry somatic mutations than other adult cells. Any age- or stress-related transcriptional remodeling that might have impacted the stem cell function of adult stem cells, as discussed above, would not

As of today, FDA-approved cellular and gene therapy products are limited to the hematopoietic progenitor cells from CB for alloHSCT in patients with disorders affecting the hematopoietic systems, autologous chondrocytes on a porcine collagen membrane for repair of cartilage defects of the knee, allogeneic cultured keratinocytes and fibroblasts in the treatment of mucogingival conditions, and a few chimeric antigen receptor (CAR) autologous cellular immunotherapies (https://www.fda.gov/vaccines-blood-biologics/cellular-gene-therapy-products/

In addition to the treatment of the disorders affecting hematopoietic system, CB alloHSCT has also been applied in clinical trials to treat nonmalignant diseases. More than 20 years ago, CB transplantation had been initiated in infants and children with Krabbe's disease [130, 131]. Krabbe's disease is an autosomal recessive disorder due to deficiency of the lysosomal enzyme galactocerebrosidase, leading to progressive neurologic deterioration and death in early childhood. These transplantation studies demonstrated that CB cells, both hematopoietic and non-hematopoietic in origin, could engraft in the patients' central nervous system, providing the missing enzyme and facilitating neural cell repair. Particularly, the young patients that underwent transplantation before the development of symptoms showed significant improvements in developmental skills, while the children who underwent transplantation after the onset of symptoms had minimal neurologic improvement [130, 131]. A long-term follow-up (median 9.5 years, range 4–15 years) study further demonstrated that the surviving patients who underwent early CB transplantation function at a much higher level than untreated children or children who were symptomatic at the time of alloHSCT [132]. Based on the observed efficacy of CB transplantation on improving neurological outcome, Cotten et al. conducted a pilot study on intravenous infusion of autologous CB in 184 pediatric patients who had their CB banked at birth and were subsequently diagnosed with acquired neurological disorders [133]. This investigation demonstrated the safety and feasibility of autologous CB infusion in these pediatric recipients. Subsequently, Cotten et al. also reported the safety and feasibility of autologous CB infusion in neonates diagnosed as hypoxic ischemic

Over the last two decades, there have been an increasing number of clinical trials involving stem cell treatment for various degenerative diseases. For cardiovascular disease alone, there have been more than 200 clinical trials using various cell types including skeletal myoblasts, autologous bone marrow mono-

bone marrow cells, endothelial progenitors,

cells, MSCs, cardiopoietic stem cells that were generated by

**112**

encephalopathy [134].

autologous CD34<sup>+</sup>

nuclear cells (BMMNCs), CD133<sup>+</sup>

with age. It was also reported that BMMNCs isolated from patients with chronic ischemic heart disease have a significantly reduced migratory and colonyforming activity in vitro and a reduced neovascularization capacity in vivo, as compared to healthy controls [145]. Therefore, for the patients that are elderly and suffer from pathological insults, they may not benefit from treatment using their own cells. For allogeneic cells, the cell dose is less of an issue than autologous cells. As off-the-shelf products, they are presumably validated for safety and efficacy before being applied to patients. However, generation of cell lots with consistent potency and comparability has been recognized as a significant issue for clinical translation. Recently, two independent investigations reported that clinical-grade human neural stem cell product (HuCNS-SC; proprietary of StemCells, Inc.), in contrast to the research-grade NSCs provided by the same company, failed to demonstrate the efficacy in animal models of spinal cord injury and Alzheimer's disease, respectively [144, 146]. However, despite being informed of the negative impact of stem cell engraftment on functional outcome in the animal model, the company initiated a clinical trial testing this product in patients with cervical spinal cord injury (NCT02163876) in December 2014 and subsequently reported a small improvement in motor strength in 4/5 subjects in the 6-month interim report. However, the clinical trial was terminated in May 2016, due to a lack of significant improvements and the lack of a trend for improvements over time [146]. In this study, there were no details on how the clinical- and research-grade products were made differently that might contribute to the disparity on the efficacy of animal studies. HuCNS-SC was derived from donated fetal brain tissue based on fluorescence-activated cell sorting of CD133<sup>+</sup> cells and expanded as neurospheres. It is possible that the clinical- and research-grade products were from different donors with varying genetic background and/or developmental stage. It is also possible that the scale-up production of the cell products under good manufacturing practice (GMP) unfavorably changed the therapeutic function of the cells. Nevertheless, the lack of efficacy of the cell product in the animal model was consistent with the failure of the clinical trial. It has to be noted that in vivo preclinical testing of the final clinical product is not required by the FDA, because "human-derived cellular therapy products intended for clinical administration in animals may not be informative" [147]. As a result, stem cell products are increasingly entering clinical studies for various disease conditions without prior efficacy studies in animal models, outpacing our understanding on their potential mechanisms of action. Although it is true that not all the animal models recapitulate spectrum of human diseases and it is difficult to extrapolate the results from the animal study to human, the lesson learned from the failures of clinical studies including HuCNS-SC is the importance of robust and reliable potency assays to characterize the cells and to ensure the consistency between different manufacturing lots before applying to patients. Recently, the International Society of Stem Cell Research (ISSCR) released updated guidelines on stem cell research and clinical translation, recommending that the cells entering clinical trials are based on sound scientific rationales with robust manufacturing and animal efficacy data, in addition to a safety package to support clinical trials [148].
