Genetic Engineering and Its Applications
Gene Therapy
Perhaps the most exciting application of genetic engineering is gene therapy in humans.
Gene therapy aims to treat, cure, and prevent diseases caused by a single defective gene by introducing a therapeutic or functional gene into the patient.
The insertion of a functional gene is intended to replace and repair the defective gene, correct the genetic anomaly, or provide these cells with a new feature that addresses the inadequacies of cells in a given tissue.
Types of Gene Therapy
There are two types of gene therapy: somatic and germline.
Somatic gene therapy: It attempts to correct a disease by treating some cells of the body (soma) of the sick person, so that the existence of a few transgenic cells may be enough to reduce symptoms of the disease. To enter target cells, therapeutic vectors are used, usually viruses, which are transferred in different ways.
Gene therapy for the germline: This involves introducing transgenic cells into a fertilized egg so that any therapeutic gene will be part of the genetic code of all body cells, including future germline cells. Although this type of genetic engineering is done in laboratory mice, to date, it has not been done in humans. Germline gene therapy, which tries to correct defects in the patient and future generations, is also associated with complex ethical problems. Many people from different social sectors believe that the manipulation of human genes would be too close to designing “babies on demand” or eugenics, which is the deliberate practice of genetic improvement of humankind.
Besides the ethical problems, enormous technical barriers must be overcome before the full potential of gene therapy to cure inherited diseases can be realized. However, it is a tool to treat many diseases.
It is currently investigating the use of transgenic cells as a therapy for certain cancers, diabetes, Alzheimer’s, or Parkinson’s.
Techniques of Cloning: Reproductive Cloning
As you know, cloning is the process by which organisms produce genetically identical copies of themselves and identical to the original organism from which they come.
Some living things can reproduce asexually and give rise to exact copies of themselves or natural clones. If you’ve grown a plant from a cutting from another plant, you have made a clone. But can we make a copy of an adult animal by cloning one of its cells?
Current biotechnology allows us to create animal clones by a technique known as reproductive cloning.
This technique involves removing the nucleus of an egg from a donor animal and replacing it with the nucleus from a somatic cell from the animal to be cloned, a method called nuclear transplantation. Thus, an “artificial” embryo is created, which is subsequently implanted in the uterus of a female of the same species to complete its embryonic development. The resulting organism is genetically identical to the individual from which the somatic cell nucleus was used.
In 1996, a group of Scottish scientists, led by Professor Ian Wilmut, achieved, after 277 failed attempts, the first mammal cloned from an adult cell, Dolly the sheep. Since that time, the cloning of many other mammals, such as mice, cats, cows, horses, and pigs, has been demonstrated.
However, cloning is still at a craft level! In all cases, only a small percentage of cloned embryos develop normally to birth, and many cloned animals, like Dolly, suffer from various diseases and premature death.
Stem Cells or Stem Cells
The body of any mammal, including humans, is made up of billions of cells of over one hundred different types. Of these cell types, the stem cell is unique.
Stem cells (from English, stem cell/s) are undifferentiated cells that can divide indefinitely to produce both new stem cells and, under appropriate conditions, differentiate into one or more specialized cell types, e.g., muscle cells, blood, or liver cells.
Types of Stem Cells
Not all stem cells are equal. They differ from each other by their degree of plasticity, i.e., their ability to give rise to cells of very different types.
- Embryonic stem cells (ESC): After a sperm fertilizes an egg, a zygote is formed, a single totipotent cell that can generate, through successive cell divisions, the full range of hundreds of different cells of the new body and, therefore, any tissue, including those that give rise to the placenta.
- The resulting cells of the first divisions of the zygote are also totipotent, but as new cells are formed and become increasingly specialized, the range of cell types that may arise shrinks. A few days after fertilization, the first specialization begins. The early embryo is then integrated by a series of cells that form a nearly hollow sphere called a blastocyst, in which you can see two types of cells: those that form the surface layer, which will give rise to the placenta, and those occupying part of the interior, which are embryonic stem cells.
- Embryonic stem cells (ESCs) are pluripotent cells because, although they alone cannot give rise to the whole organism (they need the placenta), they are the origin of all cell types and tissues of the adult individual.
- Adult stem cells (ASC): They are found in many adult body tissues, such as blood or skin. Their main function is to replace dying cells within an organ or tissue.
- Adult stem cells (ASCs) are multipotent cells that can give rise to many cell types but not all.
- Other types of stem cells: Besides the cells described so far, there are other types of stem cells. These include fetal stem cells, which are cells that can be isolated from fetuses whose development has been interrupted by natural causes or medical reasons; stem cells extracted from the umbilical cord after birth, which are adult cells similar to those of embryonic origin; and embryonic germ cells (EGCs), which are the mother cells of germ cells (eggs and sperm) and that, in culture, are capable of giving rise to all adult cell types.
Applications of Stem Cells: A Hope in Biomedicine
Stem cells have many uses both in research and in medical and therapeutic projects. Some applications of the studies being done with stem cells are:
- Testing toxins and new drugs with therapeutic potential: Currently, cancer cell lines are being used to analyze potential anticancer drugs.
- Studying the early stages of embryonic development and genetic control.
- Cell therapy and transplantation: Today, there are therapies based on the use of adult stem cells used to repair damaged organs and tissues with promising results. Transplantation of bone marrow stem cells is perhaps the best-known regenerative therapy and is applied to treat leukemia and other cancers and for heart muscle repair in patients with various heart diseases. The discovery of reserves of stem cells in the adult brain that can form different kinds of nerve cells that are capable of regenerating neurons is a major stimulus for the development of novel regenerative therapies that could benefit many patients with nervous system disorders.
However, for some scientists, true regenerative medicine will begin when they can use embryonic stem cells, especially embryonic cells derived from the patient. Thus, clinical application in the future could solve two major problems associated with current transplantation: donor shortage and preventing rejection of transplanted tissue since a patient could be transplanted with their own tissue (autologous). But how are embryonic stem cells obtained from an individual who is already born when these cells come from embryos?
To obtain embryonic stem cells, therapeutic cloning should be used, a technique that is exceptionally complex and involves numerous ethical and legal problems, despite having no purpose of cloning people but to create a cloned embryo from which to obtain cells for medical purposes.
The alleged human cloning for therapeutic purposes would be to transplant the nucleus from an adult cell from a patient to an enucleated egg from a female donor. Thus, it would create an embryo from which embryonic stem cells would be extracted. These pluripotent cells would be differentiated in the laboratory to generate the needed tissue to be transplanted without rejection in the patient.