关于干细胞

Stem cells are undifferentiated, or “blank,” cells. This means they’re capable of developing into cells that serve numerous functions in different parts of the body. Most cells in the body are differentiated cells. These cells can only serve a specific purpose in a particular organ. For example, red blood cells are specifically designed to carry oxygen through the blood.

All humans start out as only one cell. This cell is called a zygote, or a fertilized egg. The zygote divides into two cells, then four cells, and so on. Eventually, the cells begin to differentiate, taking on a certain function in a part of the body. This process is called differentiation.

Stem cells are cells that haven’t differentiated yet. They have the ability to divide and make an indefinite number of copies of themselves. Other cells in the body can only replicate a limited number of times before they begin to break down. When a stem cell divides, it can either remain a stem cell or turn into a differentiated cell, such as a muscle cell or a red blood cell.

由于干细胞具有转变为其他各种细胞的能力，因此科学家认为它们对于治疗和理解疾病可以有用。根据梅奥诊所干细胞可以用来:

  • grow new cells in a laboratory to replace damaged organs or tissues
  • 纠正器官的部分无法正常工作
  • 细胞遗传缺陷的研究原因
  • research how diseases occur or why certain cells develop into cancer cells
  • test new drugs for safety and effectiveness

有几种类型的干细胞,可以used for different purposes.

Embryonic stem cells

Embryonic stem cells come from human embryos that are three to five days old. They are harvested during a process called in-vitro fertilization. This involves fertilizing an embryo in a laboratory instead of inside the female body. Embryonic stem cells are known as pluripotent stem cells. These cells can give rise to virtually any other type of cell in the body.

非胚胎（成人）干细胞

Adult stem cells have a misleading name, because they are also found in infants and children. These stem cells come from developed organs and tissues in the body. They’re used by the body to repair and replace damaged tissue in the same area in which they are found.

For example, hematopoietic stem cells are a type of adult stem cell found in bone marrow. They make new red blood cells, white blood cells, and other types of blood cells. Doctors have been performing stem cell transplants, also known as bone marrow transplants, for decades using hematopoietic stem cells in order to treat certain types of cancer.

Adult stem cells can’t differentiate into as many other types of cells as embryonic stem cells can.

Induced pluripotent stem cells (iPSCs)

Scientists have recently discovered how to turn adult stem cells into pluripotent stem cells. These new types of cells are called induced pluripotent stem cells (iPSCs). They can differentiate into all types of specialized cells in the body. This means they can potentially produce new cells for any organ or tissue. To create iPSCs, scientists genetically reprogram the adult stem cells so they behave like embryonic stem cells.

突破创造了一种“脱离分化”干细胞的方法。这可能使它们在理解疾病的发展方面更有用。科学家希望可以用某人的皮肤制成细胞来治疗疾病。这将有助于防止免疫系统拒绝器官移植。正在进行研究以找到安全生产IPSC的方法。

Cord blood stem cells and amniotic fluid stem cells

Cord blood stem cells are harvested from the umbilical cord after childbirth. They can be frozen in cell banks for use in the future. These cells have been successfully used to treat children with blood cancers, such as leukemia, and certain genetic blood disorders.

在羊水中也发现了干细胞。这是围绕母亲子宫内发育的婴儿的液体。但是，需要更多的研究来帮助了解羊水干细胞的潜在用途。

Adult stem cells don’t present any ethical problems. However, in recent years, there has been controversy surrounding the way human embryonic stem cells are obtained. During the process of harvesting embryotic stem cells, the embryo is destroyed. This raises ethical concerns for people who believe that the destruction of a fertilized embryo is morally wrong.

Opponents believe that an embryo is a living human being. They don’t think the fertilized eggs should be used for research. They argue that the embryo should have the same rights as every other human and that these rights should be protected.

另一方面，干细胞研究的支持者认为，胚胎还不是人类。他们指出，研究人员获得了捐赠夫妇的同意，他们的卵和精子被用来创建胚胎。支持者还认为，无论如何，在体外受精期间产生的受精卵都会被丢弃，因此可以更好地使用科学研究。

With the breakthrough discovery of iPSCs, there may be less of a need for human embryos in research. This may help ease the concerns of those who are against using embryos for medical research. However, if iPSCs have the potential to develop into a human embryo, researchers could theoretically create a clone of the donor. This presents another ethical issue to take into consideration. Many countries already have legislation in place that effectively bans human cloning.

In the United States, federal policy regarding stem cell research has evolved over time as different presidents have taken office. It’s important to note that no federal regulation has ever explicitly banned stem cell research in the United States. Rather, regulations have placed restrictions on public funding and use. However, certain states have placed bans on the creation or destruction of human embryos for medical research.

Stem cell policy under former President George W. Bush

2001年8月，前总统乔治·W·布什（George W. Bush）批准了一项法律，该法律将为胚胎干细胞的有限研究提供联邦资金。但是，这样的研究必须符合以下标准：

  • 收获过程包括破坏胚胎，于晚上9点之前开始。2001年8月9日。
  • 干细胞是从出于生殖目的而创建的胚胎中获得的，不再需要。
  • 获得了捐赠胚胎的知情同意，捐赠并不涉及经济奖励。

Stem cell policy under President Barack Obama

2009年3月，巴拉克·奥巴马（Barack Obama）总统撤销了前总统布什的声明，并发布了行政命令13505. The order removed the restrictions on federal funding for stem cell research. This allowed the National Institutes of Health (NIH) to begin funding research that uses embryonic stem cells. The NIH then published guidelines to establish the policy under which it would fund research. The guidelines were written to help make sure that all NIH-funded research on human stem cells is morally responsible and scientifically relevant.

全球大学，研究机构和医院正在进行干细胞研究。研究人员目前正在专注于寻找控制干细胞如何变成其他类型细胞的方法。

细胞分化的过程

A primary goal of research on embryonic stem cells is to learn how undifferentiated stem cells turn into differentiated stem cells that form specific tissues and organs. Researchers are also interested in figuring out how to control this process of differentiation.

多年来，科学家开发了操纵干细胞过程以创建特定细胞类型的方法。这个过程称为定向分化。最近studyalso discovered the first steps in how stem cells transform into brain cells and other types of cells. More research on this topic is ongoing.

Cell-based therapies

If researchers can find a reliable way to direct the differentiation of embryonic stem cells, they may be able to use the cells to treat certain diseases. For example, by directing the embryonic stem cells to turn into insulin-producing cells, they may be able to transplant the cells into people with type 1 diabetes.

可能用胚胎干细胞治疗的其他医疗状况包括：

  • traumatic spinal cord injury
  • stroke
  • severe burns
  • rheumatoid arthritis
  • heart disease
  • hearing loss
  • 视网膜疾病
  • 亨廷顿氏病
  • Parkinson’s disease

California’s Stem Cell Agency提供了目前在干细胞研究中正在进行的疾病计划和临床试验的详细列表。此类项目的示例包括：

  • injecting modified stem cells directly into the brain after a stroke
  • 使用干细胞在内耳中替换检测声音的内耳受损细胞，有助于恢复听力
  • altering the genes of stem cells to make them resistant to diseases, such as AIDS, and then inserting them into people with the disease
  • 培养干细胞以修复骨质疏松症患者的脆弱骨骼

Using stem cells to test new drugs

Researchers are also using differentiated stem cells to test the safety and effectiveness of new medications. Testing drugs on human stem cells eliminates the need to test them on animals.

Stem cell research has the potential to have a significant impact on human health. However, there is some controversy around the development, usage, and destruction of human embryos. Scientists may be able to ease these concerns by using a new method that can turn adult stem cells into pluripotent stem cells, which can change into any cell type. This would eliminate the need for embryonic stem cells in research. Such breakthroughs show that much progress has been made in stem cell research. Despite these advancements, there’s still a lot more to be done before scientists can create successful treatments through stem cell therapy.