Table 1.

Advantages and disadvantages of stem cells

Cells	Source	Advantages	Disadvantages
Neural stem cells	Primary tissues, (fetal, neonatal, and adult brain) or embryonic stem cells and induced pluripotent stem cells	(1) Easy to access;	(1) Strong immunogenicity;
		(2) No ethical issues;	(2) The mechanism of cell proliferation, differentiation, and migration is unclear
		(3) No histocompatibility.	.
Mesenchymal stem cells	Bone marrow, adipose tissue, and umbilical cord	(1) Widespread sources;	(1) Bone marrow mesenchymal stem cells-limited raw materials, poor proliferation, and traumatic;
		(2) Secrete multiple bioactive factors;	(2) No unified identification standard for umbilical cord blood mesenchymal stem cells, and the culture technology in vitro and differentiation are not yet mature.
		(3) Directional migration.
Embryonic stem cells	Early embryo	(1) Strong proliferation ability;	(1) Ethical issues;
		(2) Abundant sources;	(2) The allograft produces a great rejection reaction;
		(3) Can be passed on.	(3) Unrestrained differentiation;
			(4) Tumorigenicity.
Induced pluripotent stem cells	Gene recombination	(1) No ethical issues;	(1) Complex operation process;
		(2) No histocompatibility.	(2) Low reprogramming efficiency;
			(3) Mutation induction;
			(4) Tumorigenicity.

Each stem cell has a specific neurogenic potential and can achieve certain results, but there are still many problems to be solved before they can be used for clinical applications.