Gene Therapy through Virology

The virus is one of natures most resilient and abundant creatures. Since their discovery in the late 1800s by Dmitri Ivanovsky, over 5000 of these biological agents have been specifically described, though there are millions more that have yet to be studied in detail. Viruses are microscopic (they fall in the range of 20-400 nanometers in diameter), acellular, compilations of genetic material, proteins, and the occasional lipid (generally the lipid coat acts to protect the virus when it finds itself outside of its target cell) that have to infect the cells of another organisms in order to replicate themselves. They are not limited to any particular type of organism, infecting the cells of plants, animals, and bacteria alike. A virus infestation can be widespread and devastating, with many of histories pandemics being attributed to the virus. We even find record of its destructive effects in recent news, as evidenced by the current Ebola outbreak in Guinea (Poon, 2014).

The virus is thought to have evolved from the plasmid. Plasmids are circles of DNA that can shift into and out of cells. The virus is particularly important to evolution because it contributes to genetic diversity through its method of horizontal gene transfer and constant mutation.

There are two types of viruses that affect humans, DNA and RNA. Aside from the obvious difference of the sugars utilized by these two types of viruses (ribose versus deoxyribose) DNA viruses are double stranded, replicate in the nucleus, and their process is similar to how the host cell would normally replicate (i.e. through the splitting apart of the double helix and the utilization of RNA polymerase). RNA viruses are single stranded, replicate in the cytoplasm and their mutation rate is much higher due to the highly unstable, single strand structure.

Viruses typically enter the human body through the avenue of a vector. A vector is anything that carries the virus; it does not necessarily have to be negatively affected by the virus (for example: mosquitoes carry the virus that causes Chikungunya fever, but that virus doesn’t kill them). This can be an infected insect or human fluids, such as saliva, or fecal matter. While different types of viruses have various replication techniques, there are six fundamental steps in viral replication: attachment, penetration, uncoating, replication, assembly, and lysing of the cell. Attachment occurs when the proteins on the outside of the viral shell attach to the protein receptors of the cellular target, it is similar in nature to a key fitting into a keyhole. After the virus has attached it then moves onto the next phase of penetration. This step involves the passing of the viral genome into the cell either through destruction of part of the cell wall (this generally occurs when viruses attack plants, because of their rigid cellular wall structure), or through some sort of opening, like a pore. The virus then goes through the process of uncoating, in order to expose either the viral DNA or viral RNA. To do this the viral capsid is removed, either through dissolving the coating using the virus’s own enzymes, or the capsid will just release itself. The viral genetic material then begins to replicate itself. Depending on the type of virus, this will occur in either the nucleus or the cytoplasm and will utilize the cell’s own replication materials. After replication, the virus assembles its new selves, which then proceed to burst forth from their host cell, killing it in the process. It must be noted, that not all viruses kill the cell. HIV is enveloped by the cell membrane, and then buds off of it.

Viruses can cause a variety of problems, aside from cellular destruction caused by replication. Many of them evolve very quickly (influenza, HIV) which allows for them to outsmart man made immunization techniques and the human bodies own natural defense techniques. This can cause huge issues for humans. Viral infections can lead to death of the host organism, and as stated earlier, have been known to be the culprits behind some of histories most infamous epidemics. The influenza virus alone causes anywhere from 250,000-500,000 deaths per year, globally ("Influenza (seasonal)," 2014). In fact, the 1918 flu pandemic was estimated to have killed over 100 million people on a global scale. The Yellow Fever has been around for centuries and still kills thousands. Viral infections can also lead to certain types of cancers. Both Merkel cell carcinoma and liver cancer have been implicated as having been caused by viral infections. The final fear is that viruses can be used as a method of biological warfare. The virus is such an effective specimen in causing deleterious effects on a given population, that some fear that countries will use it in times of warfare.

Even though the virus seems to be an entirely negative agent, the virus model can also be utilized for human and environmental benefit. One of the reasons viruses are so successful is because of their ability to quickly mutate. One way that viruses accomplish such a high mutation rate is through the method of antigenic drift. Antigenic drift is when the genes in a virus that code for antibody binding sites, undergo a high number of mutations (Hampson, 2002). For all practical purposes, this essentially creates a new virus. The effect of this drift successfully makes all of the antibodies that the host built up during the previous viral attack, entirely useless. The host cell therefore, loses its immunity.

This idea has been applied toward creating strategies for a more effective tumor immunotherapy. One study in particular focused on how antigenic drift affects tumor cells. They found that the tumor cells in mice they were studying were displaying antigenic properties in order to evade Cytotoxic T Lymphocyte therapy. One of the main discoveries made was that “the antigenicity of tumors can be altered by antigenic drift. Thus, much like viruses, tumor cells can evade T cell-mediated destruction through mutations…” (Xue-Feng, Jinqing, Ou, Pan & Yang, 2003). By working with this idea of tumor cells as containing properties similar to those of the virus, inferences (and potential lines of research) can be made that therapies utilized for viruses, may be useful as a springboard to research therapies for various cancers. This also allows researchers to focus on how to predict antigenic shift in tumor cells, in order to try to stop replication of these harmful cells early on.

Gene therapy is an extremely promising field of research. The benefits are vast and even include the potential eradication of certain genetic diseases such as cystic fibrosis and Parkinson’s disease. Many physicians believe that it will change the face of medicine, by creating a shift from treating the symptoms of a disease to an entirely prevention based practice. Gene therapy works by utilizing an empty virus in order to replace a faulty gene with its healthy twin. This is done by removing the harmful part of the virus, injecting it into some model organism (generally a mouse) and allowed to replicate. The newly replicated viruses are then taken from the mouse and injected into the patient (for instance, an individual who has cancer). The virus goes to the target cells (in this example the cells are cancerous) and replicates. After it has infected all of the cancer cells, the physician gives the patient medicine that is meant to kill the original virus. Because this virus is now in all of the cancer cells it will, theoretically, kill all of the cancer cells as well. While gene therapy is still in the testing phase, it is currently the only promising lead towards finding cures for genetic disorders.

One of the reasons that gene therapy is so strongly championed is that it is truly working toward finding a cure for these particular diseases, as opposed to treating the systemic effects of a disease like many chemical treatments do. As stated earlier, many in the health care profession believe that gene therapy will turn medicine into a prevention-based practice, as well as enact profound steps towards the eradication of all genetic diseases. Some believe that gene therapy is the “final frontier,” so to speak, of medical advancement.

While the positive benefits of gene therapy have the potential to create huge changes in the treatment of human genetic disorders, there are also some very profound negative implications. There is the possibility of a negative immune system response. If the immune system were to react with an exaggerated response, it can lead to large amounts of inflammation and, in a particularly sick individual, systemic organ failure. The virus structure can also be difficult to accurately control, which can lead to the virus attacking and damaging healthy cells. Additionally, there is also the possible risk of infection and tumor growth.

When looking outside of the obvious physical hesitancies, depending on the patient, there are also potential moral dilemmas. For example the idea of screening a fetus for genetic defects, and using those results as a determining factor in continuing a pregnancy, doesn’t sit well with many religious individuals. There is also the science fiction-esque concept of the “designer baby.” This is the idea that one can use gene therapy techniques to create what they perceive to be the perfect human. Even the possibility of an organization utilizing the virus to enact biological warfare has to be considered when discussing the potential side effects of the potent virus structure.

Even with all of the negative implications, it is hard to deny gene therapy’s potential. This is the first time in human history that we have had the very real possibility to entirely eradicate human genetic disorders and diseases. One of the major break throughs that lead to this life changing therapy technique was the mapping of the human genome.

When the project first launched in 1990, its original goal was to only map the nucleotides in the human subject. After completing that first goal, the research has extended beyond itself to study and map the proteins, SNPs, and individual genomes of the human race. By pushing the mapping technology to its outer limits, this project has also lead to the ability for an individual to have their own personal genome mapped (Harmon, 2010). This type of personalization enables researchers to develop techniques like gene therapy for individuals suffering from rare genetic disorders. The ability to quickly, and affordably, map an individual patients genome has led to the idea of a genome bank. There are both positive and negative implications for this as well. One of the positive aspects of having your genome stored in the cloud is that it would allow for easy access by any healthcare provider. This would enable them to have an intimate look at all of your individual aspects. There is also the promise of gathering enough individual genomes, and utilizing them to track trends and to investigate specific disease states. Some to question the ethical nature of having this type of information stored and easily accessed by the scientific community. The question of who owns the information is one that looms overhead, as well. Does the patient own their genetic information, or does the scientific community own it? What good does a person’s genome do if it is not being utilized for humanities greater good?

Even though this large collections of information has allowed for an increasingly intimate look into the make up of the human body, it hasn’t really given us a whole lot of answers. There is a seemingly endless amount of research regarding correlations between certain physical characteristics and the A,C,G,and T’s that they are made up of, but there needs to be more advances into the therapy aspect of this. After decades of mucking through the mountains of information that the Human Genome Project provided us with, scientists are just now beginning to utilize the genome to explore and refine cures for genetic diseases.

References

Harmon, K. (2010, June 28). Genome sequencing for the rest of us. Scientific American,

Hampson, A. (2002). Influenza virus antigens and antigenic drift. Influenza, 49-86.

Poon, L. (2014, April 1). Why is Guinea's Ebola outbreak so unusual? NPR, Retrieved from http://www.npr.org/blogs/health/2014/04/01/297884573/why-is-guineas-ebola-outbreak-so-unusual

World Health Organization, (2014). Influenza (seasonal). Retrieved from website: http://www.who.int/mediacentre/factsheets/fs211/en/

Xue-Feng, B., Jinqing, L., Ou, L., Pan, Z., & Yang, L. (2003). Antigenic drift as a mechanism for tumor evasion of destruction by cytolytic t lymphocytes. Journal of Clinical Investigation, 111(10), 1487-1496. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC155049/