embryonic stem cell
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Imagine catching a master builder at the exact moment before they have decided what to build — full of potential, trained in everything, committed to nothing yet. Embryonic stem cells are cells captured from a very early embryo, at a stage when the cells of the future body have not yet chosen their jobs. Grown in the lab, they keep that open-ended, undecided state.
Precisely, embryonic stem cells (ES cells) are pluripotent cells derived from the inner cell mass of a blastocyst — the cluster of cells inside a roughly five-day-old embryo that would normally go on to form the body. In culture, with the right conditions, they self-renew almost indefinitely while staying pluripotent, meaning they can be coaxed into any of the body's cell types. This makes them an extraordinary research tool and a starting point for regenerative medicine.
Embryonic stem cells are scientifically powerful but ethically and practically complex. Deriving them traditionally involves an early human embryo, which raises ethical debate, and transplanting ES-derived cells into a patient can trigger immune rejection because they are genetically foreign. These hurdles are a major reason induced pluripotent stem cells — which can be made from a patient's own adult cells — attracted such intense interest as an alternative.
The first human embryonic stem cell lines were established in 1998 from the inner cell mass of donated blastocysts; kept in the right culture conditions, descendants of those original cells are still dividing and pluripotent decades later.
ES cell lines: pluripotent cells from a blastocyst that self-renew for years in culture.
Embryonic stem cells are pluripotent, not totipotent — the whole embryo is taken at the blastocyst stage, and the ES cells themselves cannot rebuild the placenta or form a complete organism on their own.