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Team:UCL London/Medicine
From 2011.igem.org
Our Relevance - Medical Applications
Case Study (Pandemics)
In recent years there have been two pandemics: the 2005 H5N1 “Avian Influenza” and the 2009 H1N1 “Swine Flu”. Both of these diseases had their own implications about the future of global health.
H5N1 was more widely spread in the bird population causing the deaths of over 140 million domestic birds worldwide.[1] The incubation period for this virus ranges from 2 to 8 days and potentially as long as 17 days, which is longer than incubation periods for most other strains of influenza. It has a serial interval of 2-3 days.[2] As for its influence on the human population, the virus itself was highly pathogenic, 50% of the people reported infected. Once infected, if proper treatment such as a high enough dosage of antiviral drugs aren´t administered within 48 hours after the onset of symptoms, new strains of drug resistant viruses might develop and proliferate. Without any further means of treatment the patient would suffer a cytokine storm resulting in multiple organ failure, pulmonary haemorrhaging and even ventilator-associated pneumonia. H1N1 on the other hand had crossed the human to human barrier and became a worldwide epidemic in 4 months. It has an incubation period of an average of four days after which the host will become contagious until their symptoms subside. H1N1 symptoms were mild, not unlike those demonstrated when infected with seasonal flu. In both instances we were lucky that the virus in question had not mutated enough to become both highly pathogenic as well as easily transmitted amongst humans. However, it´s possible that next time we won´t be so fortunate, there could soon be another pandemic on our hands one which is deadly and easy to transmit. Every year we lose at least 5.5 million [3] lives to flu as well as other diseases such as malaria, tuberculosis and HIV. We must take care now to ensure that we have the resources necessary to make a quick and efficient retaliatory response.
How this problem is being dealt with
The way these types of diseases are being treated are with antiviral drugs (which are becoming increasingly ineffective) and vaccinations against the infection in question. There are four generations of vaccines being produced in the market currently: First-generation vaccines [4] were exclusively live, attenuated pathogens. Many a time one would get insufficient attenuation where the pathogens would revert to their wild type forms. This was especially dangerous when administered to an immunodeficient patient resulted in persistent infection. The pathogen could also be contaminated by other viruses. These types of vaccines lead to fetal damage as well. Because of these safety concerns, second-generation vaccines -- chemically or physically inactivated pathogens -- were later developed. Non-living vaccines were susceptible to contamination by toxins or chemicals and frequently triggered allergic reactions or autoimmune responses. Purified or synthetic proteins represent a third generation, consist of protein antigens that have either been produced in a heterologous expression system (e.g. bacteria or mammalian cells) or purified from large amounts of the pathogenic organism. The vaccinated person produces antibodies to the protein antigen, thus protecting him/her from disease. This strategy also eliminates the risk of active infection that can occur with live attenuated vaccines or even inactivated vaccines where inactivation is incomplete.[5] Recent advances in molecular biology and genetic engineering have led to the development of the fourth vaccine generation, which includes DNA and virus vector-based vaccines.
Typically customised yearly flu vaccines are created based on predictions of what strains might be present that year. This is done by taking antibodies from patients’ who´ve recovered from the disease and thus developed immunity not only to the viral strain they were infected by but also to other related strains for that disease. Then vaccines are developed for a chosen few of these strains and manufactured at a large scale. This can be done using several methods. The one most predominantly used is chicken egg-based manufacture.
The manufacture of vaccines is done in sterile fertilized chicken eggs, preferably from known uninfected stock. A live influenza virus and high-yielding donor strain is then injected into each egg, infecting the embryo. The eggs are incubated for several days before the virus protein is removed, purified and inactivated. The total process takes six months which could be a potential problem as manufacturing companies will not be able to respond quickly enough during a pandemic or when a new strain emerges.[6] There´s also a physical limitation of the availability of specialized eggs which would limit the supply of vaccines during a global influenza pandemic. Chicken egg based technologies can be transmitted from wild fowl (which are carriers of all type of Influenza A viruses) to poultry in which case it wouldn´t be possible to use eggs for vaccine manufacture. This production method is quite unreliable as the eggs could spoil or produce the virus at differing rates. Additionally it´s also possible to get mutation of the viral strain being grown which adds inconsistency to the overall yield and such contaminations could result in more side effects for the patient. Also, patients who are allergic to eggs, or are vegan aren´t able to receive vaccines produced using this method.
New non-egg based methods are currently being developed for safety and speed of manufacture as well. These methods are the third generation vaccines using baculovirus (BEVS)[7] or mammalian cell expression systems, as they are effective tools in creating recombinant proteins that can be used in vaccines. BEVS requires introduction of the desired gene into a nonessential region of the viral genome usually Autographa California multiple embedded nuclear polyhedrosis virus (AcMNPV) using a insect cell transfer vector (typically Spodoptera frugiperda Sf9 cells). The desired gene and virus are cotransfected in insect cells. Production of the foreign proteins is achieved when insect cell cultures are infected the resultant recombinant virus. These alternatives deal with the problem of egg allergies and viral impurities as the flu vaccine is produced in human mammalian kidney cells or tissue cultures which the body’s immune system is unlikely to reject. Cell-based manufacture of vaccines can also be rapidly expanded and scaled up in times of emergency by cloning a pure cell. Cell-based vaccine production uses cell lines grown in laboratories that are capable of hosting a growing virus. The virus is input into the cell, using the host´s machinery to replicate itself. The cells' outer walls are removed, harvested, purified, and inactivated. The vaccine can then be produced in merely a few of weeks. The polio vaccine is currently produced using the cell-based method.[8] However, the most promising option thus far is DNA vaccines.
