這張照片是受精後5~6天的人類細胞，稱為胚囊。剝開囊胚取出的內部細胞圖（圖中紅色突出部份），可用來製造胚胎幹細胞。
【摘譯自：Jan. 22, 2007 新聞週刊
http://www.msnbc.msn.com/id/16609288/site/newsweek/ 】
文：VIVIEN
科學家在治癒疾病與遏制生命中找到了另一條新的出路
目前幹細胞的研究主要分為兩大主軸，一是由成人身上取得研究組織，一是取自胚胎，而後者在取得檢體的過程中則有可能對胚胎造成傷害而引起很大的爭議。
但令人感到欣慰的事也許科學家已找到了第三條路同時巧妙的避開道德的爭論，也就是從懷孕婦女的羊膜液中取得幹細胞檢體。
幹細胞那裡來?
羊膜細胞(Amniotic Cells)
由羊膜穿刺術取得採樣，同時也可在寶寶出生之後的胎盤取得檢體。
利與弊：羊膜細胞具有多功能性(pluripotent)，即可發展成多樣的細胞類型，而且可容易的在實驗是中培養。另一方面在取得的過程中也讓科學家巧妙的迴避道德的爭議，但羊膜穿刺術對於媽媽與小孩確實存在著風險。
這張照片是科學家為培育胚胎幹細胞株，從囊胚取出內細胞團（這些囊胚通常是體外人工受精剩下的胚胎），將它們放在含有餵養細胞（feeder cell）的培養皿中，胚胎細胞會很快黏附在餵養細胞上。在幾天內，來自內細胞團的細胞會分裂出新細胞，並形成群體（上圖）。不過這些細胞要正式稱為胚胎幹細胞，還需符合兩個條件：它們要表現出幹細胞特有的標記；它們可進行數次細胞分裂或分盤培養，證明它們為穩定或永生的細胞株。
胚胎幹細胞(embryonic stem cell)
從早期的胚胎中單獨萃取出來幹細胞，才是所謂的胚胎幹細胞（embryonic stem cell）。人類的胚胎幹細胞是從生成時期未滿一週的受精卵中產生的。在正常狀況下，它們會形成較晚期胚胎中，最後再衍生出身體內所有不同的組織。由於胚胎幹細胞保有製造體內任何類型細胞的潛在能力，因此它們是也是多能性的（pluripotent）。目前胚胎幹細胞取得多源自捐贈與實驗是培育的。
利與弊：最主要的爭議來自道德問題，在取得胚胎幹細胞的同時也等於遏止了胚胎的生命，但胚胎幹細胞同時也具有多能性與快速繁殖的特性。
成年體細胞(adult cells)
取自成人體內的幹細胞，稱為成體幹細胞。主要的功能在維持與修復組織。但不易取得。成體幹細胞不涉及倫理問題，研究比較便利，然而其分化能力有限。
利與弊：通常只存在於人體需要修復的組織與器官中且其功能有限，譬如造血幹細胞通常只發展成血液細胞，相對限制了幹細胞研究。
未來的希望
科學家希望未來幹細胞研究能替代人類受損的細胞並長出健康的新細胞，但在這個部分的研究目前多被用在美容與老化的應用上，將來科學家們殷切的期望能應用在治療帕金森氏症（Parkinson’s disease）、阿茲海默症（Alzheimer’s disease）以及與心臟有關的疾病等。雖然解答在目前看起來仍遙遙無期但仍替病患帶了一線曙光。
Escaping a Moral Mess
Scientists may have found a way out of the quandary over whether to destroy embryos or cure people.
By MARY CARMICHAEL
Stem-cell research is divided into two major camps: one focused on cells from adults, the other on the controversial technique that destroys embryos. Now there may be a third way- a new category of stem cells that are readily available, perhaps ethically trouble-free and possibly as powerful and as flexible in function as their embryonic counterparts: amniotic-fluid stem dells, found in both the placenta and the liquid that surrounds growing fetuses.
Where Stem Cells Come From
Amniotic Cell
Source: Amniotic-fluid stem cells are collected by amniocentesis, in which some of the fluid surrounding the fetus is drawn out though a hollow needle inserted into the uterus. The cells can also be taken from the placenta or from tissues shed after birth.
PROS and CONS: Amniotic cells are hardy and pluripotent (they can grow into a variety of cell types), and reproduce quickly in the lab. Additionally, the way they’re collected may allow scientists to sidestep ethics debates. But amniocentesis carries a slight risk for the mother and child.
Embryonic Cells
Source: Typically gathered from the inner cell mass of a 4-to-5-day-old embryo (still a microscopic ball of cells at that stage), the embryonic cells are taken only from embryos that were fertilized in a lab and donated for research.
PROS and CONS: There major drawback involves ethics: removing embryonic stem cells destroys the embryo. Otherwise, the cells are pluripotent and multiply rapidly.
Adult Cells
Source: In an adult’s body, stem cells work to maintain and repair the tissues in which they’re found, such as the brain, liver, bone marrow, skeletal muscle and blood vessels. But the cells are relatively rare, and collecting the large numbers needed for research can be difficult.
PROS and CONS: Adult stem cells are often able to grow only into their tissues of origin, making them less versatile.
Hopes for The Future
Scientists are currently exploring the way in which stem cell can be used to replace damaged ells with healthy ones, But among the most promising areas of research is how stem cells may be used to rejuvenate tissues in patients with degenerative diseases such as Parkinson’s . Though a remedy remains far off, stem-cell research offers some hope and insight into how a cure might work.
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