Chemistry: molecular biology and microbiology – Virus or bacteriophage – except for viral vector or...
Reexamination Certificate
2001-03-09
2002-10-22
Yucel, Remy (Department: 1636)
Chemistry: molecular biology and microbiology
Virus or bacteriophage, except for viral vector or...
C435S239000, C435S325000, C435S199000, C435S069100, C435S456000
Reexamination Certificate
active
06468777
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the production and stabilization of functional biological materials, such as proteins, viral agents, or other biological agents or products, including, but not limited to, enzymes, hormones, growth factors, structural proteins, tumor suppressor agents, nucleic acids and nucleic acid probes, vaccines, antigens, antibiotics, lipids, simple and complex carbohydrates, alcohols and other solvents and the products of those methods. Such functional biological materials are useful for the manufacture of vaccines and diagnostic assays or tests, for example.
The production of viruses, viral antigens, and other viral products useful for manufacturing of products such as vaccines and diagnostic assays, however, is expensive, time consuming and requires a high level of technical expertise. Viruses must be propagated in living eucaryotic cells. Eucaryotic cells that can be infected with a particular virus are said to be “permissive” for that virus. However, most eucaryotic cells are not permissive for any given virus, and no techniques exist to predict permissiveness. Additionally, cells that are permissive for virus production may have different levels of permissiveness. Some cell lines may produce large amounts of virus while others may permit only a low level of viral replication. Therefore, to determine the optimal cells for virus production, a sometimes large and often time-consuming empirical study of many cell lines must be performed. Further complicating matters, the optimal cell line may not be from the host (e.g., human cells for viruses affecting humans) from which the virus was obtained. Frequently, no suitable cell line exists for a virus from a particular host.
Cell lines are preferable to primary cell cultures from a host because of their stability, immortality, known characteristics, and behavior that has been defined by long experience. The requirements for use of such cell lines in viral production has led to development of a large number of exotic cell lines that are used to produce various viruses. For example, Canine Distemper Virus (CDV), a morbillivirus, grows well in Vero cells (i.e. African Green Monkey kidney cells) but is not propagated in cells from dogs, while Bovine Leukemia Virus (BLV) is produced from a cell line derived from bat lung tissue.
Unfortunately, growth of viruses in cell lines far removed from the host and tissue normally infected may cause such viruses to act in a fashion that is far removed from their normal behavior.
Further, the complex pathology for the virus can make the manufacture of viruses extremely difficult. For example, CDV and Human Measles Virus (HMV) are closely related viruses. Both viruses act similarly when infecting their respective canine and human hosts. Both produce encephalitis and long-term sequelae in which the central nervous system is damaged or destroyed. The central nervous system disease in dogs that occurs many years after initial CDV infection is called old dog encephalitis (ODE). In humans, the corresponding condition is subacute sclerosing panencephalitis (SSPE). The cause of ODE and SSPE is directly related to the number of virions produced and cells affected during the encephalitic phase of the disease. This in turn is directly related to permissiveness of the brain cells and the ability of the host's immune system to rapidly respond to the virus. Dogs or humans whose brain viral titers reach exceptionally high levels may develop these long-term consequences many years later. In fact, the high viral titers in some infected patients can result in permanent production of a viral protein in brain cells, even after the infection has cleared. The immune system recognizes the viral protein as foreign and continues to attack it even though no viable virus has been produced for many years. Eventually the combat between the host's immune system and these aberrant cells creates enough damage to destroy the host's cognitive capacity. Dogs with ODE are usually euthanized. The outcome of SSPE in humans is a progressive dementia eventually followed by death. Because of this complex disease pathophysiology, use of manufactured viruses and viral products has been unsuccessful in stimulating immunity in vivo.
Since many viruses (such as CDV and HMV) infect brain cells, the permissiveness of brain cell lines is important in studying the pathophysiology of the resultant disease and in producing viruses for diagnostics and vaccines that exactly mimic virus characteristics during natural infection. However, few neural cell lines exist, and they only produce low levels of CDV or HMV. Therefore, these cell lines produce inadequate levels of the virus for study and are especially unsuitable for antigen or vaccine production. A method of modifying such cells or cell lines, and the cell lines themselves, is thus required that will support replication of viruses and viral products to high levels.
In addition to the problems associated with producing known viruses to useful titers, it is extremely difficult to search for an unknown virus because the cell type required for replication of the unknown virus is itself unknown. For example, there are a number of diseases of the central nervous system that may well be caused by undiscovered viral agents. The degenerative diseases of Creutzfield-Jacob Disease (CJD, affecting humans), scrapie (affecting sheep), and bovine spongiform encephalopathy (affecting cattle) all are very slow neurodegenerative diseases whose etiology remains unknown. To date, no causative agent for these diseases has been identified nor has any viral agent been propagated from infected human or animal brain tissue. This has lead to the promotion of various unorthodox hypotheses concerning disease etiology, including suggestions that a special protein (called a “prion”, suggested to be an agent capable of causing infection and reproducing without any genetic material) might serve as the infectious agent. However, no cell line that produces prions, even to high levels, has been shown to be infectious. Transgenic mice modified to produce prions are not infectious even when they present the diagnostic hallmarks of the disease. Thus, without means for identification of the infectious agent, no good diagnostic test can be produced for these diseases, and the production of a vaccine is impossible.
Recently, the need for improved ways for development of diagnostic tests and potential vaccines has become of pressing importance. For example, recently cattle in Great Britain were fed meal consisting of sheep and other animal offal. Bovine spongiform encephalopathy was subsequently recognized for the first time in these cattle. A number of humans were infected by eating meat from the infected cattle—constituting a route of infection which had not been previously recognized (now called “new variant CJD”, or nvCJD). Besides the tragic consequences to the infected humans, the slaughter of cattle caused massive economic damage. The finding of nvCJD also produced political repercussions involving the import, export and sale of food and other animal products that might come from infected cattle. Accordingly, the development of a good diagnostic test is required along with the production of an efficacious vaccine. To accomplish these and similar goals, permissive cell lines are required that will allow the propagation of neutrotrophic agents responsible for the etiology of slow dementias like CJD and nvCJD.
As the average age of a nation's population increases, the incidence of disease states like Alzheimer's also increases. Alzheimer's disease is a slowly progressing dementia necessitating difficult, long-term care for the patient. Costs associated with such long-term debilitating diseases can be devastating. Alzheimer's is not thought to be infectious. However, certain features of Alzheimer's have caused speculation that infection with an unconventional viral agent (similar to nvCJD) might cause the disease. It may also be possible that a
Dees H. Craig
Smolik John
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Katcheves Konstantina
Photogen, Inc.
Yucel Remy
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