Cells derived from tissue at the blastocyst stage are embryonic stem cells, totipotent but less than 100 cells to begin cell cultures. At 5-6 weeks of human development, the tissue is embryonic fetal and produces embryonic germ which are pluripotent cells and have more cells to begin cell culture (>1000). Organ specific cells are derived from 9-16 weeks of human fetal development and these cells have progenitor capacity which is that they cannot easily de-differentiate when the whole population is taken into account and there is a high number of cells (>106) for culture establishment. Adult stem cells can be found within all tissue types (from 9 weeks of gestation on) and these mesenchymal stem cells can be pluripotent. However, only 1 stem cell is found in every 104-105 cells in total specific tissue. Common tissues used in cell therapies to create cell lines in cell culture systems are bone marrow, adipose, placenta, amniotic fluid, retina, cornea and skin. Both positive (blue box) and negative (red box) factors are given for each specific cell type.
