Human cloning involves the creation of a copy of a human cell or tissue that is genetically identical. The major types of human cloning include reproductive cloning and therapeutic cloning (National Human Genome Research Institute, 2009). Therapeutic cloning involves the use of cells from an adult to be used in medicine while reproductive cloning involves making cloned human beings. Cloning has been done on both animals and plants. When done on plants it has been used to raise genetically modified crops.
Gene therapy can occur in two forms somatic gene therapy and germline gene therapy. Somatic gene therapy involves removing cells from the patient and adding cloned genes to cells using a viral vector. The cells are amplified and those that have taken up the cloned gene are taken up. The transformed cells are then taken back into the patient (see figure 1). Some of the problems associated with this procedure include transgene integration and immune response killing the viral vector which may be marked as an intruder by the body’s immune system.
The procedure has been used in many clinical trials, mainly for treating cancer. The Adeno associated virus is commonly used in this case as it does not cause an immune response, it has the ability to enter non-dividing cells and it integrates into a particular location in the genome of its host (National Human Genome Research Institute, 2009). Germline gene therapy is different from somatic therapy in that the newly introduced gene is incorporated into all of the cells in the animal’s body. This includes the germline that gives rise to gametes.
The change that has occurred in the process is passed on to the next generation. To produce a transgenic animal, the embryo stem cells could be modified which is done by isolating stem cells and culturing them, adding DNA to cultured cells and selecting the transformed cells (National Human Genome Research Institute, 2009). Once selected, the transformed cells are injected into an early embryo and the embryo is implanted into the female. This produces mosaics in which some cells have different genotypes.
Heterozygotes are mated to produce homozygous individuals which are in turn mated to produce a transgenic strain (National Human Genome Research Institute, 2009). A transgenic animal could also be produced by direct DNA injection where the transgene is injected directly into the male pronucleus before the male and female have fused (National Human Genome Research Institute, 2009). The injected DNA integrates into a chromosome and the injected zygote is then implanted into a foster mother (see figure 2). In the figure the baby mouse has the transgene in every cell in its body.
Its expression depends on where the chromosome is integrated. Nowadays, however it is possible to have targeted gene insertion in some cases. Some of the medical applications of transgenic animals and plants include the production of model systems for the study of human disease for example where a certain gene product is lacking or where a certain gene has been over expressed or where there is a gene variant. An example of this the use of transplanted human stem cells by NIH scientists to improve the repair of bone injuries in rats (Guldberg, 2010).
Standardization of such a treatment it offers a possible alternative to bone grafting operations. One of the successes of stem cell transplants has been seen in the successful attempts of new hematopoietic stem cell (HSC) in reversing sickle cell anemia in children (Rodgers et al, 2009). Other applications include the production of medically important proteins, the production of vaccines and production of tissues and organs for transplantation. Transgenic plants are also used to improve crops. In spite of these advantages, the issue of cloning still remains controversial.