Genetic Engineering and Human Health

Gene Therapy

Gene therapy is the way DNA can be manipulate to treat illnesses caused by damaged, mutated, or missing genes. The treatment of genetic illnesses has been extremely difficult because the root of the problem has been beyond our reach, until now. We are at the dawn of a new era. In recent years, the fields of engineering, biology, and technology have joined, propelling the science of genetic engineering forward with increasing speed. This has advanced the study, treatment, and diagnosis of genetic illnesses. Genetic engineers are developing safe and efficient therapies to correct, alter or fix a gene and then return it to the cell where it will integrate itself into the existing DNA.

Gene therapy is the way an altered gene is used to treat a genetic disease but this is extremely challenging. The problematic gene must be located, a specific corrective therapy developed, a viable vector to deliver the gene, and then the gene needs to integrate into the cell's transcription and translation, ultimately altering the DNA permanent way.

Before one can develop a therapy, one must understand the nature and origin of the genetic illness. Genetic therapies for monogenetic illnesses target the one defective gene that cause cystic fibrosis, CF, muscular dystrophy, MD, hemophilia, and sickle cell anemia. Some gene therapies can introduce genes into a cell that are encoded with a sequence to produce therapeutic proteins like insulin. ²⁹ Other therapies include replacing mutated genes with a healthy copy, silencing or inactivating the malfunctioning gene, and inserting a correcting gene, or a recombinant gene that will correct the problem or fight the disease. ³⁰

Recombinant DNA technology refers to the recombining the DNA molecules in an environment outside the cell, then returning the recombined, or altered, DNA to a host cell where it will hopefully replicate and be transcribed and translated into protein. The recombination procedure is accomplished by cutting a piece of DNA—often a carrier DNA or vector with the enzyme called restriction endonuclease and adding a new section of DNA into the region of the cut. The new DNA might contain an altered or improved gene. The process is completed by rejoining the DNA with the linking enzyme, ligase, to "glue" it back together.

After an appropriate therapy is determined, one must decide on a vector. There are many kinds of vectors each with specific characteristic to consider when choosing one for a particular delivery. ³¹ A good vector is able to deliver the therapeutic DNA into the nucleus of a cell safely and effectively. In order to do this, the cells need to be targeted and the gene needs to be delivered into the nucleus where the DNA is located. Once the gene is in the nucleus, the new gene must be "activated" and integrated into the existing DNA of the host cell. This means that its code needs to be transcribed and translated into the new protein. Lastly, this "activation" must be without harmful side effects such as an immune response or a toxic reaction, which would render the therapy unusable. ³² Retroviruses are good vectors because of their ability to enter and integrate their genetic material into the host cell. They contain single stranded RNA as the viral genetic material and use the host cell's transcription and translation mechanisms to replicate itself. Reverse transcription makes two copies of the viral RNA forming a double stranded DNA molecule, which integrates into the host genome. In the end, the virus's encoded proteins are then transcribed and translated. ³³

Silencing Genes: Small-Interfering RNA or siRNA

Diseases can be treated and cured by stopping the expression of a specific gene that is causing the illness. One therapy used to stop gene expression is the use of antisense therapies. Antisense therapies take a known gene sequence of a disease, and synthesize a strand of complementary nucleotides, or an oligonucleotide, which will bind to the mRNA of the targeted gene. When the antisense oligonucleotide binds to the mRNA, it is no longer able to translate its message. In this way, the gene is turned "off" unable to translate its genetic code into disease causing proteins. Therefore, a therapy can be developed for an illness by making an antisense oligonucleotide for the disease-causing gene. Although effective, the antisense oligonucleotides have a short life, which limits its use. ³⁴

Cutting- edge research led by Mark Saltzman of Yale University has shown great promise in the use of siRNA to silence cancer-causing genes. This work has implemented revolutionary biodegradable vectors improving the safety and effectiveness of delivery. The siRNA is a double stranded, small interfering RNA molecule that silences the expression of the gene like the antisense oligonucleotide, but its double stranded structure is more stable than the single antisense oligonucleotides and can last for several weeks. Si RNA binds to the complementary bases of mRNA transcript. As a result, it disables transcription by "interfering" with mRNA. ³⁵ In Saltzman's study, the isRNA was imbedded in biodegradable nanoparticle polymers to deliver the small-interfering RNA. The nanoparticles were densely loaded with siRNA and were able to silence the defective gene in a safe and effective way. The gene was silenced! This revolutionary work is offering great hope for the advancement of genetic therapies and changing the face of medicine as we know it . ³⁶