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[http://www.arbovax.com/ Arbovax, Inc. ] is a company based in Raleigh, North Carolina developing vaccines for arthropod borne viral diseases such as Dengue (Breakbone Fever), Chikungunya, West Nile, Eastern Equine Encephalitis, Western Equine Encephalitis and Yellow Fever. Using novel technology first discovered by the company founders while at the University of Texas, and now with strong ties to North Carolina State University, the company has developed potential vaccine candidates for Dengue and Chikungunya.

The Challenge of Arthropod Borne Disease


 * Insect (arthropod) borne diseases (zoonosis) affect hundreds of millions of people annually worldwide. Insects, as disease transmission vectors, play an important role in the transmission of disease by serving as a hospitable resevoir for the disease and as a conduit between hosts. Viruses, bacteria, and parasites all may be transmitted from an insect vector to an appropriate mammalian host, such as humans or other large animals. Probably the best known arthropod borne parasitical disease is Malaria, causing approximately 700,000 deaths annually. A common bacterial zoonosis is Lyme disease.


 * In order for an insect to transmit disease as a vector, that insect must become infected from an infected host, the disease pathogen must replicate without harming the insect, and then when the insect contacts or bites a host, that pathogen must be capable of infecting the host. The insect only needs to be infected once but then may infect many hosts during its period of infectivity, then other insects may become infected by biting the inrected host, and the cycle repeats in a potentially exponential fashion.


 * The focus of Arbovax, however, is on diseases caused by viruses (arboviruses) spread by insects, primarily mosquitoes. There are more than 700 arbovirus linked diseases with about 200 affecting humans and a like number affecting animals. While most produce mild or inconsequential symptoms with negligible sequelae, a number of these diseases have high morbidity and mortality both for human hosts and non-human hosts. These diseases are primarily diseases of the tropical zones where insect populations remain relatively stable throughout the year and the hosts remain outdoors and accessible to the vector. However, the range of these diseases is expanding with travel to and from the tropics and an extension of the range of the vector insects.

Arbovax Technology


 * Arbovax' technology involves creating an attenuated virus mutant, more specifically a host range mutant, that 'appears' to the host to be a 'wild type' virus. This 'appearance' is actually the collection of exposed glycoprotein epitopes on the surface of the virus that initially indentifies this virus as a pathogen to the host, and is later used to create specific, neutralizing antibodies in the host for long range protection (immunization) against a future infection. It is generally believed that a wild type virus creates the strongest and longest lasting immunity, assuming the host survives the initial infection, thus the goal to present to the host a vaccine that closely resembles wild type virus.


 * The host surviving the initial infection is crucial of course, and Arbovax addresses this by changing part of the virus that is involved with infection and replication in the host and leaving the wild type glycoprotein epitopes used to create immunity, unchanged. By combining 'wild type' high immunogenicity and low virulence (low infectivity) an efficient vaccine is created.


 * As an added benefit, the mutations that Arbovax technology imposes upon the arbovirus do not affect the virus' ability to reproduce in the insect vector, and therefore the vaccine can be produced in quantity in an insect cell reactor at reduced cost compared to other vaccine technologies.

Virology 101


 * Viruses are odd little sui generis collections of genetic material (RNA or DNA) in a protein container, or 'capsid', often surrounded by an envelope made of phospholipids and proteins. They do not fit the standard definitions for living organisms; indeed they are called 'biologic agents' and they rely exclusively on other organisims for reproduction through infection, and once created do not grow. They merely wait for the opportunity to infect another organism. Their method of reproduction involves hijacking a host cell's replication structures to produce virus components; this is usually fatal to the infected cell but by that time many thousands of viruses have been reproduced.


 * A viral infection involves the virus initially coming into contact with an appropriate target cell. Once the virus 'identifies' an appropriate target cell using the epitopes expressed on the cell surface, the virus quickly fuses with the cell membrane and with extreme violence (of limited magnitude), injects the viral genetic material into the cell. (This is a description of the release of the 'high energy' component, or potential energy component, of viral particles that is a function of their tightly folded internal genetic structure.)


 * Once the genetic material is inside the cell it quickly finds its way to the ribosomes and nucleus where the genetic material produces proteins and more genetic material that quickly fold into the native virus shape as it attaches to the inside of the cell membrane, then exudes through the membrane, taking a bit of the membrane along as it's capsid. This viral folding is very important to virulence and involves bonding between specific nucleosides; these chemical bonds contain a large amount of energy that is released as these bonds break during injection into the host cell. Altering the nucleoside bonds, and thus the folding structure, can have profound effect upon the virulence of the virus.

For further general information about viruses, see "Introduction to Viruses", or for more detail see the article "Virus"
 * This is a brief description of the traditional view of viral infection, however, viruses can also infect target immune system cells through endocytosis as may be the case with T lymphocytes and HIV infection.

General Overview of Vaccine Technologies


 * Live Pathogen Vaccines


 * Live pathogen vaccines can be very effective but they may represent an unacceptable risk of morbidity and mortality, especially for those diseases that do not require a vector for transmission, such as measles.


 * Killed Pathogen Vaccines


 * These can be effective and have no risk of causing disease, however, the process of killing the pathogen often denatures characteristic proteins and alters the epitopes or appearance to the host, and threfore may not produce strong or long lasting immunity.


 * Attenuated Pathogen Vaccines


 * Attenuated vaccines are "weakened" pathogens that do not efficiently infect the host. This technology traditionally relies upon normal mutations that occur with each generation to create, over many generations (serial passage), a pathogen that has mutated such that it no longer effectively infects the host. Unfortunately, these mutations are not predictable as to location in the genome and they can affect the immunogenicity (epitope presentation). Even more alarming is the possiblity of 'reversion to wild type' should the pathogen mutate back to wild type virulence as it replicates in the host. This has been documented with the Sabin oral polio vaccine (live attenuated virus). (Of note, even though Arbovax' vaccines are considered 'attenuated', because of the specific technology used, there is no chance of reversion to wild type virus).


 * Chimeric Vaccines


 * Chimeras are combinations of pieces of pathogens joined together to create an infectious particle that doesn't cause significant disease. Often parts of pathogenic viruses are fused wtih common viruses, such as adenoviruses, but these have proven to be of limited effectiveness, probably because the chimera does not present wild type epitopes to the host and has limited replication in the host. In addition, they are expensive to produce because they do not replicate naturally.


 * Subunit Vaccines'''


 * Subunit vaccines are non-infectious pieces of pathogens, mainly proteins or glycoproteins, presented to the host to produce an immune response. They do not replicate in the host, do not mirror the epitopes of the wild type pathogen, and require a relatively large amount of the inocculum. Recombinant vaccines are subunit vaccines in which a protein or other antigen is added to, and expressed by, another virus such as adenovirus. These recombinant viruses contain both epitopes of the carrier virus (i.e. adenovirus) and the selected epitopes added to or expressed by this virus, and does not appear as a wild type virus to the vaccinee. Conjugated subunit vaccines are those created by attaching the antigenic epitopes to large protein carrier molecules but these can cause sensitization reactions. Tetanus toxoid is an example of a conjugated subunit vaccine, although it is directed at a protein target and not a viral target.

Immunology in a Nutshell


 * An infection is a battle between a host organism and a pathogen; usually the pathogen has the upper hand early on, but the host organism quickly responds to the pathogenic threat on multiple fronts. If the pathogen is able to replicate faster than the host can neutralize and remove the pathogen, the host is killed. However, if the host is able to slow down or eliminate pathogen replication, the host can usually clear the body of the pathogen within a few days. The host response depends on recognizing the pathogen as 'not-host', then initiating a cascade of non-specific and specific responses to the infection of the pathogen.

Recognition of 'non-host' and subsequent response by the host is the essence of immunology.

Recognition of 'non-Host'

Immunology in a Nutshell Host vs. Other Humoral vs cell mediated defense Presentation and recognition

Current Methods of Creating Vaccines Wild Type Innoculation Attenuated Virus Chimeric Formulations Subunit formulations