Cloning, in its broadest sense, refers to the process of creating a genetically identical copy of an organism, cell, or even a piece of DNA. This occurs naturally in various forms, from bacteria to identical twins. When discussing human cloning, the focus shifts to specific laboratory techniques designed to produce a genetic duplicate of an existing human or human cells.
Understanding Somatic Cell Nuclear Transfer
The foundational technique for human cloning is called Somatic Cell Nuclear Transfer (SCNT). This process involves transferring the nucleus, which contains the genetic material, from a somatic cell into an enucleated egg cell. A somatic cell is any cell from the body other than a reproductive cell, such as a skin cell or a muscle cell, and contains a full set of chromosomes.
The first step in SCNT involves obtaining a somatic cell from the individual to be cloned. Simultaneously, an unfertilized egg cell is prepared by removing its nucleus, a process known as enucleation. This leaves an egg cell with its cytoplasm and cellular machinery but without any genetic material.
The nucleus from the donor somatic cell is then inserted into this enucleated egg cell. Following the transfer, the reconstructed egg cell is stimulated to begin dividing as if fertilized.
If successful, this cell will develop into an early-stage embryo, specifically a blastocyst, which is a ball of about 100 cells. This blastocyst contains genetic material identical to the original somatic cell donor.
Reproductive Versus Therapeutic Cloning
The SCNT technique serves as the initial step for two distinct applications of human cloning: reproductive cloning and therapeutic cloning. The primary difference between these two lies in their ultimate goal and outcome. Both processes begin with the creation of a cloned embryo through SCNT, but their developmental paths diverge significantly after the blastocyst stage.
Reproductive cloning aims to create a complete, genetically identical organism. Reproductive cloning in humans would involve implanting the cloned blastocyst into a surrogate uterus, allowing it to develop into a fetus and eventually a baby. However, human reproductive cloning is not currently practiced and is widely prohibited globally due to ethical and safety concerns.
Conversely, therapeutic cloning does not intend to create a new organism. Its purpose is to generate embryonic stem cells from the cloned blastocyst for medical research or treatment.
In this process, the cloned embryo is allowed to develop only to the blastocyst stage, from which the inner cell mass, containing pluripotent stem cells, is then extracted. This extraction leads to the embryo’s destruction, a point of ethical debate.
Medical Promise of Therapeutic Cloning
Therapeutic cloning offers potential for advancements in medicine, primarily through patient-specific stem cells. These cells, being genetically identical to the patient, circumvent the problem of immune rejection often associated with organ or tissue transplants. This compatibility is an advantage for regenerative medicine.
One application is regenerative medicine, where these stem cells could develop into specialized tissues or organs to repair or replace damaged ones. This holds promise for treating conditions involving tissue degradation, such as severe burns, heart muscle damage, or spinal cord injuries.
Generating patient-specific cells could improve treatments for many diseases. Therapeutic cloning also allows for the creation of “disease in a dish” models.
By culturing patient-specific cell lines, researchers can study disease progression at a cellular level outside the human body. These models are valuable for drug testing, enabling scientists to screen potential medications for efficacy and toxicity on cells that precisely mimic the patient’s condition, potentially leading to more personalized and effective therapies for conditions like Parkinson’s disease, Alzheimer’s disease, or diabetes.
Ethical Considerations and Global Regulations
The scientific capabilities of human cloning, particularly reproductive cloning, have raised ethical questions and led to a global regulatory landscape. Concerns about human dignity, exploitation, and safety risks to the cloned individual and any surrogate mother are part of the ethical debate surrounding reproductive cloning. The high failure rates and health issues observed in animal cloning further underscore safety concerns for human application.
As a result, human reproductive cloning is widely prohibited or subject to strict moratoria in many countries and by international bodies. For instance, the United Nations adopted a nonbinding declaration calling on member states to prohibit all forms of human cloning incompatible with human dignity and life. This broad consensus reflects a global aversion to creating genetically identical human beings.
Therapeutic cloning, while also controversial due to the destruction of the embryo for stem cell extraction, faces a different regulatory environment. In some countries, it is permitted under strict regulations for research purposes, recognizing its potential medical benefits. These regulations often require explicit consent from donors and impose strict oversight on research practices, balancing scientific advancement with ethical boundaries.