Biotechnosium...

Tissue engineering is the use of a combination of cells within an artificially-created support system (e.g. an artificial pancreas or a bioartificial liver. The term treatments">regenerative medicine is often used synonymously with tissue engineering, although those involved in regenerative medicine place more emphasis on the use of stem cells to produce tissues.

In 2003, the NSF published a report entitled "The Emergence of Tissue Engineering as a Research Field" [1], which gives a thorough description of the history of this field.

Micromass cultures of C3H-10T1/2 cells at varied oxygen tensions stained with A commonly applied definition of tissue engineering, as stated by Langer and Vacanti, is "an interdisciplinaryfield that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve function or a whole organ". ^{Tissue engineering has also been defined as "understanding the principles of tissue growth, and applying this to produce functional replacement tissue for clinical use."citation needed]}

^{Powerful developments in the multidisciplinary field of tissue engineering have yielded a novel set of tissue replacement parts and implementation strategies. Scientific advances in biomaterials, stem cells, growth and differentiation factors, and biomimetic environments have created unique opportunities to fabricate tissues in the laboratory from combinations of engineered extracellular matrices ("scaffolds"), cells, and biologically active molecules. Among the major challenges now facing tissue engineering is the need for more complex functionality, as well as both functional and biomechanical stability in laboratory-grown tissues destined for transplantation. The continued success of tissue engineering, and the eventual development of true human replacement parts, will grow from the convergence of engineering and basic research advances in tissue, matrix, growth factor, stem cell, and developmental biology, as well as materials science and bioinformatics.}

The term cloning is used by scientists to describe many different processes that involve making duplicates of biological material. In most cases, isolated genes or cells are duplicated for scientific study, and no new animal results. The experiment that led to the cloning of Dolly the sheep in 1997 was different: It used a cloning technique called somatic cell nuclear transfer and resulted in an animal that was a genetic twin -- although delayed in time -- of an adult sheep. This technique can also be used to produce an embryo from which cells called embryonic stem (ES) cells could be extracted to use in research into potential therapies for a wide variety of diseases.

Thus, in the past five years, much of the scientific and ethical debate about somatic cell nuclear transfer has focused on its two potential applications: 1) for reproductive purposes, i.e., to produce a child, or 2) for producing a source of ES cells for research.

Cloning for Reproductive Purposes

The technique of transferring a nucleus from a somatic cell into an egg that produced Dolly was an extension of experiments that had been ongoing for over 40 years. In the simplest terms, the technique used to produce Dolly the sheep - somatic cell nuclear transplantation cloning - involves removing the nucleus of an egg and replacing it with the diploid nucleus of a somatic cell. Unlike sexual reproduction, during which a new organism is formed when the genetic material of the egg and sperm fuse, in nuclear transplantation cloning there is a single genetic "parent." This technique also differs from previous cloning techniques because it does not involve an existing embryo. Dolly is different because she is not genetically unique; when born she was genetically identical to an existing six-year-old ewe. Although the birth of Dolly was lauded as a success, in fact, the procedure has not been perfected and it is not yet clear whether Dolly will remain healthy or whether she is already experiencing subtle problems that might lead to serious diseases. Thus, the prospect of applying this technique in humans is troubling for scientific and safety reasons in addition to a variety of ethical reasons related to our ideas about the natural ordering of family and successive generations.

Scientific Uncertainties

Several important concerns remain about the science and safety of nuclear transfer cloning using adult cells as the source of nuclei. To date, five mammalian species -- sheep, cattle, pigs, goats, and mice -- have been used extensively in reproductive cloning studies. Data from these experiments illustrate the problems involved. Typically, very few cloning attempts are successful. Many cloned animals die in utero, even at late stages or soon after birth, and those that survive frequently exhibit severe birth defects. In addition, female animals carrying cloned fetuses may face serious risks, including death from cloning-related complications.

An additional concern focuses on whether cellular aging will affect the ability of somatic cell nuclei to program normal development. As somatic cells divide they progressively age, and there is normally a defined number of cell divisions that can occur before senescence. Thus, the health effects for the resulting liveborn, having been created with an "aged" nucleus, are unknown. Recently it was reported that Dolly has arthritis, although it is not yet clear whether the five-and-a-half-year-old sheep is suffering from the condition as a result of the cloning process. And, scientists in Tokyo have shown that cloned mice die significantly earlier than those that are naturally conceived, raising an additional concern that the mutations that accumulate in somatic cells might affect nuclear transfer efficiency and lead to cancer and other diseases in offspring. Researchers working with clones of a Holstein cow say genetic programming errors may explain why so many cloned animals die, either as fetuses or newborns.

Ethical Concerns

The announcement of Dolly sparked widespread speculation about a human child being created using somatic cell nuclear transfer. Much of the perceived fear that greeted this announcement centered on the misperception that a child or many children could be produced who would be identical to an already existing person. This fear is based on the idea of "genetic determinism" -- that genes alone determine all aspects of an individual -- and reflects the belief that a person's genes bear a simple relationship to the physical and psychological traits that compose that individual. Although genes play an essential role in the formation of physical and behavioral characteristics, each individual is, in fact, the result of a complex interaction between his or her genes and the environment within which he or she develops. Nonetheless, many of the concerns about cloning have focused on issues related to "playing God," interfering with the natural order of life, and somehow robbing a future individual of the right to a unique identity.

Policy and Regulation

Several groups have concluded that reproductive cloning of human beings creates ethical and scientific risks that society should not tolerate. In 1997, the National Bioethics Advisory Commission recommended that it was morally unacceptable to attempt to create a child using somatic cell nuclear transfer cloning and suggested that a moratorium be imposed until safety of this technique could be assessed. The commission also cautioned against preempting the use of cloning technology for purposes unrelated to producing a liveborn child.

Similarly, in 2001 the National Academy of Sciences issued a report stating that the United States should ban human reproductive cloning aimed at creating a child because experience with reproductive cloning in animals suggests that the process would be dangerous for the woman, the fetus, and the newborn, and would likely fail. The report recommended that the proposed ban on human cloning should be reviewed within five years, but that it should be reconsidered "only if a new scientific review indicates that the procedures are likely to be safe and effective, and if a broad national dialogue on societal, religious and ethical issues suggests that reconsideration is warranted." The panel concluded that the scientific and medical considerations that justify a ban on human reproductive cloning at this time do not apply to nuclear transplantation to produce stem cells. Several other scientific and medical groups also have stated their opposition to the use of cloning for the purpose of producing a child.

Cloning for the Isolation of Human ES Cells

The cloning debate was reopened with a new twist late in 1998, when two scientific reports were published regarding the successful isolation of human stem cells. Stem cells are unique and essential cells found in animals that are capable of continually reproducing themselves and renewing tissue throughout an individual organism's life. ES cells are the most versatile of all stem cells because they are less differentiated, or committed, to a particular function than adult stem cells. These cells have offered hope of new cures to debilitating and even fatal illness. Recent studies in mice and other animals have shown that ES cells can reduce symptoms of Parkinson's disease in mouse models, and work in other animal models and disease areas seems promising.

In the 1998 reports, ES cells were derived from in vitro embryos six to seven days old destined to be discarded by couples undergoing infertility treatments, and embryonic germ (EG) cells were obtained from cadaveric fetal tissue following elective abortion. A third report, appearing in the New York Times, claimed that a Massachusetts biotechnology company had fused a human cell with an enucleated cow egg, creating a hybrid clone that failed to progress beyond an early stage of development. This announcement served as a reminder that ES cells also could be derived from embryos created through somatic cell nuclear transfer, or cloning. In fact, several scientists believed that deriving ES cells in this manner is the most promising approach to developing treatments because the condition of in vitro fertilization (IVF) embryos stored over time is questionable and this type of cloning could overcome graft-host responses if resulting therapies were developed from the recipient's own DNA.

Ethical Concerns

For those who believe that the embryo has the moral status of a person from the moment of conception, research or any other activity that would destroy it is wrong. For those who believe the human embryo deserves some measure of respect, but disagree that the respect due should equal that given to a fully formed human, it could be considered immoral not to use embryos that would otherwise be destroyed to develop potential cures for disease affecting millions of people. An additional concern related to public policy is whether federal funds should be used for research that some Americans find unethical.

Policy and Regulation

Since 1996, Congress has prohibited researchers from using federal funds for human embryo research. In 1999, DHHS announced that it intended to fund research on human ES cells derived from embryos remaining after infertility treatments. This decision was based on an interpretation "that human embryonic stem cells are not a human embryo within the statutory definition" because "the cells do not have the capacity to develop into a human being even if transferred to the uterus, thus their destruction in the course of research would not constitute the destruction of an embryo." DHHS did not intend to fund research using stem cells derived from embryos created through cloning, although such efforts would be legal in the private sector.

In July 2001, the House of Representatives voted 265 to 162 to make any human cloning a criminal offense, including cloning to create an embryo for derivation of stem cells rather than to produce a child. In August 2002, President Bush, contending with a DHHS decision made during the Clinton administration, stated in a prime-time television address that federal support would be provided for research using a limited number of stem cell colonies already in existence (derived from leftover IVF embryos). Current bills before Congress would ban all forms of cloning outright, prohibit cloning for reproductive purposes, and impose a moratorium on cloning to derive stem cells for research, or prohibit cloning for reproductive purposes while allowing cloning for therapeutic purposes to go forward. As of late June, the Senate has taken no action. President Bush's Bioethics Council is expected to recommend the prohibition of reproductive cloning and a moratorium on therapeutic cloning later this summer.

Scientists have created nearly a dozen new lines of human embryonic stem (ES) cells that for the first time carry the genetic signature of diseased or injured patients. The breakthrough represents a dramatic increase in the efficiency of creating such lines and may eventually pave the way for treating conditions such as spinal cord injury with stem cell transplants.

Eggs-perts. Through practice with cow eggs (above) and other means, Korean researchers have increased their efficiency at cloning human embryos to create stem cells (inset). CREDIT: Lee Jin-man/AP; (inset) Hwang et al.

Last year, a group led by veterinarian Woo Suk Hwang and gynecologist Shin Yong Moon at Seoul National University reported the first derivation of ES cells from human nuclear transfer Science --a process that involves replacing an oocyte's nucleus with one from a different cell, and then chemically kick-starting development of the egg. But those efforts yielded just one cell line from more than 200 tries.

Hwang cautions that his team remains years away from transplanting the cells into people. "We have to be over-convinced" that the cells are safe, he says. However, the cell line derived from the diabetes patient should be of great interest to scientists.

"The possibility of being able to study disease in a culture dish is very exciting," says Douglas Melton, who has recently received permission from a university ethics committee to derive ES cells from diabetes patients in his laboratory at Harvard. "For the first time, we will have a chance to study the root causes of the disease."

The new results may also influence the ongoing political debate over whether research with human embryonic stem cells, cloned or not, is ethically justified. "Some people will hate it, others will love it," says Rudolf Jaenisch of the Massachusetts Institute of Technology. "But it puts the discussion on a very firm footing now. People will have to rethink the argument that it's not efficient."