4.2 MSCs
Until now, the only legal clinical stem-cell therapy was hematopoietic stem-cell therapy for childhood leukemia. Other therapies remain controversial because they are often related to abortion politics and human cloning. However, the research field of stem-cell therapy is constantly expanding, and scientists now have applied stem cells in neurodegeneration, brain and spinal cord injury, frailty syndrome, pancreatic beta cells, orthopedics, and other uses(Gazdic et al., 2018; Golpanian et al., 2017; R. Li et al., 2018; Lyon, 2018; Memon & Abdelalim, 2020). The significant difference between EPCs and MSCs is that a lower immunogenicity is associated with MSCs. However, if low immunogenicity leads to lengthy transplantation time and excessive allogeneic cells in the circulation of patients, this may lead to graft-versus-host disease (GVHD), which is the most severe side effect of stem cell therapy(Malard & Mohty, 2014).
Ethical issues continue to cause problems with allografts because embryonic stem cells are derived from human embryos, but this process will kill the embryo. A key issue is the voluntary actions of donors, and therefore, the choice of donation must be later than the choice of abortion, so as to avoid involuntary activities caused by monetary temptation or other factors. In addition to ethical issues, there are also many criticisms of the experimental procedures. Some critics report that only five basic trials seem to be used in 48 reports, and many trials contradict each other. Therefore, research into clinical stem cell therapy requires further development and stricter standards to limit disordered behavior and prevent damage to the reputation of scientists and the field of stem cell therapy(Heo, Choi, Kim, & Kim, 2016). He identity of patients after allogeneic stem cell transplantation is another inevitable problem. Because allogeneic stem cells can differentiate into allogeneic mature cells, the identity of patients still needs to be further discussed and confirmed. It is advantageous that the new technology of inducing pluripotent stem cells avoids this ethical tissue, and another benefit is that it provides even more convenient access as compared to autologous stem cells(Y. Y. Shi, R. P. Nacamuli, A. Salim, & M. T. Longaker, 2005).