| Embryonic stem cells (ES, ESC) | Blastocysts or immuno-surgically isolated inner cell mass (ICM) from blastocysts. | ES cells grow as tightly adherent multicellular colonies with a population doubling time of ~12 h, maintain a stable euploid karyotype even after extensive culture and manipulation, can differentiate into a variety of cell types in vitro, and can contribute to all cell types, including functional sperm and oocytes, when injected into a blastocyst (m). ES cells form relatively flat, compact colonies with a population doubling time of 35–40 h (h). |
| Embryonic germ cells (EG, EGC) | Primordial germ cells (PGCs) from embryos at E8.5–E12.5 (m). Gonadal tissues from 5–11 week post-fertilization embryo/fetus (h). | EG cells show essentially the same pluripotency as ES cells when injected into mouse blastocysts (m). The only known difference is the imprinting status of some genes (e.g., Igf2r): Imprinting is normally erased during germline development, and thus, the imprinting status of EG cells is different from that of ES cells. |
| Trophoblast stem cells (TS, TSC) | Trophectoderm of E3.5 blastocysts, extraembryonic ectoderm of E6.5 embryos, and chorionic ectoderm of E7.5 embryos. | TS cells can differentiate into trophoblast giant cells in vitro (m). TS can contribute exclusively to all trophoblast subtypes when injected into blastocysts (m). |
| Extraembryonic endoderm cells (XEN) | ICM from blastocysts | XEN cells can contribute only to the parietal endoderm lineage when injected into a blastocyst (m). |
| Embryonal carcinoma cells (EC) | Teratocarcinoma—a type of cancer that develops in the testes and ovaries | EC cells rarely show pluripotency in vitro, but they can contribute to nearly all cell types when injected into blastocysts (m). EC cells often have an aneuploid karyotype and other genome alterations (m, h). |
| Mesenchymal stem cells (MS, MSC) | Bone marrow, muscle, adipose tissue, peripheral blood, and umbilical cord blood (m, h) | MS cells can differentiate into mesenchymal cell types, including adipocytes, osteocytes, chondrocytes, and myocytes (m, h). |
| Multipotent adult stem cells (MAPC) | Bone marrow mononuclear cells (m, h); postnatal muscle and brain (m) | MAPCs are very rare cells that are present within MSC cultures from postnatal bone marrow (m, h). MAPCs can be cultured for >120 population doublings, can differentiate into all tissues in vivo when injected into a mouse blastocyst, and can differentiate into various cell lineages of mesodermal, ectodermal, and endodermal origin in vitro (m). |
| Spermatogonial stem cells (SS, SSC) | Newborn testis (m) | SS cells can reconstitute long-term spermatogenesis after transplantation into recipient testes and restore fertility (m). |
| Germline stem cells (GS, GSC) | Neonatal testis (m) | GS cells can differentiate into three germlayers in vitro and contribute to a variety of tissues, including germline, when injected into blastocysts (m). |
| Multipotent adult germline stem cells (maGSC) | Adult testis (m) | maGSC can differentiate into three germlayers in vitro and can contribute to a variety of tissues, including germline, when injected into blastocysts. |
| Neural stem cells (NS, NSC) | Fetal and adult brain (subventricular zone, ventricular zone, and hippocampus) | NS cells can be cultured as a heterogeneous cell population of monolayer or floating cell clusters called neurospheres. NS cells can differentiate into neuron and glia in vivo and in vitro. Recently, the culture of pure population of symmetrically dividing adherent NS cells became possible. |
| Unrestricted somatic stem cells (USSC) | Mononuclear fraction of cord blood (h) | USSCs can differentiate into a variety of cell types in vitro and can contribute a variety of cells types in in vivo transplantation experiments in rat, mouse, and sheep (h). USSCs are CD45– adherent cells and can be expanded to 1015 cells without losing pluripotency (h). |
| Epistem cells (EpiSC) | Early postimplantation epiblast (m) | EpiSCs can differentiate into three germlayers in vitro and form teratomas but cannot contribute to normal tissues when injected into blastocysts (m). EpiSCs (m) are shown to be more similar to ESC (h) than ESC (m). |
| Induced pluripotent stem cells (iPS, iPSC) | Variety of terminally differentiated cells and tissue stem cells (m, h) | ESC-like cells originally derived by introducing four transcription factors (Klf4, Pou5f1/Oct4, Sox2, and Myc) into mouse embryo fibroblasts by retroviral vectors (m). iPS cells are essentially indistinguishable from ES cells. A number of somatic cell types can be converted into iPS cells using different combinations of transcription factors and treatment with small molecules. |