Gene Therapy
The gene therapy is a therapeutic strategy is to penetrate genes in cells or tissues an individual to treat a disease . Gene therapy aims to replace or complement an allele defective mutant allele with a functional or overexpress a protein whose activity would have a therapeutic impact.
History
The concept of gene therapy - to repair or modify the genetic heritage to treat a disease - is actually raised by the scientific community in the late 1960's [ 1] . But if all the theoretical elements are present, the level of technology does not yet realize practically this approach. Improved knowledge about the links between certain mutated genes and certain diseases, the creation of gene transfer system secure from viruses, improvement technology for manipulating DNA - in short all the advances of this fabric of concepts and techniques that we now call biotechnology - allow this theoretical idea to emerge as a first clinical trial initiated by S. Rosenberg in the United States in the late 1980s. The 1990s and early twenty-first th century saw hatched a string of clinical trials in a variety of diseases: cancer, heart and vascular diseases, viral infections, hereditary immune deficiencies, ... associated with a major public enthusiasm ( including through the Telethon ) and investors. Poorly served by a communication from doing little things into the ground realities and assumptions, facing industrial players or patients who expect immediate positive results, gene therapy is quickly confronted with the bitter observation emerging from this period : no real benefit was observed for the 4000 patients enrolled in the 400 to 600 tests conducted during this period. Communication difficulties between the scientific community and the academic industry, a gradual withdrawal of venture capitalists on gene therapy approaches, a mistrust regarding the real potential of this strategy marks the entry of gene therapy in e XXI century. The success of therapeutic protocol Alain Fischer on the treatment of bubble children suffering from severe immunodeficiency in the 2000s, formally demonstrating the interest of the concept but tempered by some serious side effects, fails to fully revive efforts various players in this field (see below). Today, in a more mature phase, less publicized, more thoughtful, more aware many years - even decades - to ensure that this idea forms part of a routine therapy, many international teams continue to work to make gene therapy an additional tool in the range of hospital treatments.
Many diseases are potential targets of gene therapy
While this concept is born the idea of \u200b\u200btreating inherited disorders he was quickly directed toward the treatment of all diseases, hereditary or not, in which it was possible to imagine that some genes were defective or that it was possible to envisage a role for novel genes. Cancers, viral infections, pain, heart disease, attacks the nervous system trauma, ... Conceptually it is not a disease that could not benefit from gene therapy approach, either through a strategy of restoring a faulty gene activity or by the production of an additional activity that may have a therapeutic impact . Almost since the first clinical trial (Which then was interested in cancer treatment), we observe that about 70% of the trials focused on cancer treatment, approximately 20% over the conventional treatment of hereditary diseases, and 10% on various conditions such as viral infections. About 1400 clinical trials have been made internationally. If gambling statistics is tempting, but we must be careful to draw clear conclusions from the overall analysis of these protocols concerned with pathologies, technologies and concepts very diverse.
Carrying a gene: the problem of gene therapy vectors
Once the gene selected for its therapeutic potential against a disease, a critical step in gene therapy is to enter the new information genetics in the patient's body. In this spirit, is called gene therapy vector system while allowing the transfer of this gene in a cell. The vectors used in gene therapy and genetically modified cells by these vectors are classified as Organizations Genetically Modified . The patients are not considered in this classification according to a European directive which excludes humans automatically .
Viral vectors
The use of modified viruses to carry a gene therapy based on the observation efficiency of viruses to transfer their own genetic material into human cells. To produce viral vectors are used genetically modified virus, called secure. The principle is to eliminate sequences of viruses that encode proteins, including those associated with a possible pathogenic behavior of the virus, and keep only those that are used to construct the virus particle and ensure the infection cycle. The virus genome is rebuilt to carry the therapeutic gene sequences. Viral proteins that potentially fail to train therapeutic viral particles are provided by cells called producing or packaging during the production phase vectors.
adenoviral vectors
The adenovirus is a DNA virus. It has the feature to enter its genetic material into the target cell without waiting for mitosis (cell division) and without inserting new genetic information into the genome of the target cell. Although widely used in many clinical trials, researchers are still unable to date to completely get rid of its genes, thus maintaining a character potentially pathogenic vector constructs.
retroviral vectors
The retroviruses are used as vector in gene therapy because they can insert new genetic information into the genome of the target cell. The new gene is then transmitted from mother cells into daughter cells equally without "dilution" of genetic information in time. The genome of retroviruses is composed of molecules RNA (ribonucleic acid) instead of DNA as the genome of human cells. Infection by a retrovirus involves a step of reverse transcription of RNA in a fragment of DNA that can be associated (step of integration) to chromosomes after penetration into the cell nucleus. A combination of viral proteins and cell proteins target this step ensures the transfer of molecules of DNA the cell cytoplasm to the nucleus and integration into the host genome. Once integrated, the retrovirus genome DNA as it is stable and transmitted as a Mendelian manner any gene of the cell. While most trials were conducted with retrovirus vectors derived from mice, some clinical trials are currently underway using vectors derived from HIV virus (treatment of adrenoleukodystrophy by team-Aubourg Cartier in Paris since 2007, treatment of HIV infection in the United States since 2000), treatment of hemoglobinopathies by Team-Leboulch Beuzard in Paris. This latter type of vector, said vector lentiviral derived from a human virus but completely secure is a vector particularly popular. Indeed, it is able to genetically modify the cells to rest, opening opportunities to manipulate neurons, liver cells ... a range cell populations inaccessible to retroviral vectors derived from murine viruses. [ 7] Integration of retroviral vectors into the genome of the target cell, if it is a major asset for the perpetuation and transmission of genetic information, still represents a challenge in terms of security. Two clinical trials using retroviral vectors to modify murine hematopoietic cells (treatment of immune deficiency caused by a mutation carried by the gamma c chain of the receptor for interleukin-2 - see below - and treatment of disease Gaucher) led to the emergence of forms of leukemia patients.
vectors derived from AAV
AAV vectors (adeno associated virus ) are derived from known viruses associated with adenovirus. Viruses are unique to foster integration of their genome in the same spot on chromosome 19. Insertion uncontrolled can cause significant disturbances in cell function, these vectors were highly developed for their potential safe although they are only able to transferring small genes. Although construction of the vector from the virus overcomes this property of targeting the insertion of AAV derived viruses have been widely used clinically. Long considered harmless, unlike adenoviral and retroviral vectors (see below), their development has been promoted in recent years. [ 8] But the recent death in the summer of 2007 from a patient in a clinical trial for treatment of rheumatoid arthritis by vectors derived from AAV can also now Critics of this strategy to point the finger on what type of vehicle.
vectors derived from other viruses
Beyond these vectors frequently used in clinical practice, many attempts to use vectors from viruses described in the literature. There have been many works concerning the use of Herpes Simplex (HSV), the poxvirus (currently in clinical development), animal viruses related to HIV, influenza virus ... These various attempts witnessed by the lack of a viral vector universal pushing scientists to test new ways, and secondly the desire for some manufacturers to position themselves in the field with patent owners .
nonviral vectors
Various strategies have been developed to avoid recourse to viruses and use directly the DNA molecule.
- Most strategies combine chemical molecules (polycation, ...) and the DNA molecule to facilitate the crossing the membrane of cells and retraction of DNA molecules. These vectors produced by bacteria, easily purified, are not inert particles and the characters are potentially pathogenic viruses that cause viral vectors.
Unlike viral vectors, they are easier to produce, handle and store and are characterized as conventional pharmaceuticals. However, their efficiency is much lower than that of viruses to transfer genetic information into a large population of cells, making them difficult to use in certain cases (revision of a substantial part of tumor cells for example). In addition, they have only very limited capacity to integrate genetic information into the genome, making them useless for genetic changes in cell populations of perennial active proliferation. However, this technology can be perfectly adapted to certain therapeutic strategies based on a cascade of events from some genetically modified cells (activation of the immune system, for example).
- Recently, laboratory, magnetic nanoparticles ( driven to their targets by magnets ) were efficient vectors of interfering RNA (RNAi ) here used against cancer [ 10] . The first vectors tested were magnetic nanocrystals coated with a layer of fat or polymers are difficult to manufacture.
More recently, a nanoparticle called "LipoMag" (magnetic nanocrystals coated with oleic acid monoouche then a cationic lipid has effectively brought an RNAi cancer (Inhibitor of growth of tumor vessels), in mice with gastric tumors. In 9 out of 13 cases, the transfer was done more efficiently than previously used nanocrystals .
Administration vector
Numerous clinical trials of gene therapy have employed a protocol called "ex vivo", that is to say by taking the target cells of the individual and subjecting them to the vectors of gene transfer therapy outside the body. The cells are then reinjected into the patient. This allows researchers in some cases to assess the extent of genetic modification both in the percentage of cells genetically modified at the level of expression of therapeutic proteins, or pre-select specific cell populations (eg, blood stem cells). Nevertheless, some strategies, especially those aimed at eliminating tumors, or those designed to genetically modify the cells can not be manipulated outside the body, using an approach called vivo by directly injecting the vector into the targeted tissue , and letting it operate freely.
Strategies Unlimited
Gene therapy, like all approaches biotechnology, based on fundamental research. The biological mechanisms identified, and their underlying genetic origins, can devise strategies to repair or supplementation. The success of these strategies depends as much capacity to develop appropriate techniques (gene transfer effective, coherent expression of the gene, ...) that the accuracy with which the mechanisms are understood in question. Their limit is independent that the imagination of the scientific and medical community. In this spirit, we can distinguish several broad approaches.
A disease, a mutated gene, the flagship strategy of gene therapy
The "repair" of gene activity is planned or has been tested clinically in many diseases. Some immunodeficiencies linked to deficits in the gene encoding adenosine deaminase, or in the encoding chain gamma-c receptor Interleukin-2 (Fischer protocol, see below) or beta-thalassemia characterized by defects in synthesis of some globins can imagine the missing protein production by genetically modified hematopoietic cells. With haemophilia A and B are associated with defects in production of factors VIII and IX clotting chain that could be produced by muscle or liver cells releasing these factors in the blood. The treatment of cystic fibrosis is envisaged by the expression of the gene encoding the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) by some lung cells.
A disease, a genetic background poorly known "genes rescue 'possible
Some diseases are more complex in appearance. Thus, the treatment of Parkinson's disease is addressed in various ways since the link between the degeneration of neurons and a genetic mutation is not clearly established. For example it is proposed to express the glutamic acid decarboxylase (GAD), the decarboxylase of aromatic amino acid (AADC) or neurturin to the minimum limit degeneration.
cancer, a disease with genetics too complex
The cancer is primarily addressed through the concept of direct or indirect destruction of cancer cells . Many clinical protocols have been achieved by inserting into the cancer cells of genes encoding proteins sensitizing cancer cells to drugs. Thus, the gene encoding thymidine kinase Herpes simplex virus sensitizes the cells to a normally harmless product, the ganciclovir . Cancer cells are modified directly in the body by injecting vectors in vivo and ganciclovir is administered in a second time. Based more on changes in the basic research of the last twenty years, some approaches propose the use of natural protective mechanisms to eradicate cancer cells. Stimulation of the immune system by overexpression of cytokines (GM-CSF, Interferon ...), or restoration of biological chains called "programmed cell death or apoptosis (overexpression of p53 ...) are part of those strategies.
Blocking process by transferring a gene
Many biological blocking strategies have emerged in the 90s mainly to counter the HIV infection. Expression of mutated viral proteins (decoy) interfering with the natural proteins of the virus, expression of antisense RNA can inhibit translation of viral proteins, expression of molecules of natural protection of the cell (interferons, proteins trigger the apoptosis, ...), ... all these strategies are based on une interférence entre les diverses phases du cycle de multiplication du virus et une protéine ou un ARN dont la production est assurée par un vecteur exogène transféré dans les lymphocytes T du patient. Dans un autre domaine, de nombreux groupes travaillent sur l’expression de protéines impliquées dans les mécanismes immunitaires pour bloquer les rejets de greffe (production d’inhibiteur du complément, de cytokines immunosuppressives dérégulant le mécanisme de réponse immunitaire, d’inhibiteurs des interactions entre greffon et cellule immunitaires, …). Bien que peu développées certaines approches are also interested in the inhibition of pain with such an expression of the Pre-Proenkephalin.
Handle development
Recent approaches have brought about the expression of proteins involved in embryonic development (NeuroD protein or protein PDX1) to change the status of liver cells and transform almost in pancreatic cells to restore the patient diabetic cells capable of producing insulin regulated manner.
A mixed success, many failures, the first side effects
Most, if not all clinical trials of gene therapy since the early 1990s may be considered failures since they have only rarely and only briefly, improved clinical status of patients, and they never led to the development of therapeutic recognized and used internationally. Currently only one strategy, one used by Alain Fischer and Marina Cavazzana-Calvo, to address the failure to develop immune responses of newborns with severe immunodeficiency (SCID, Severe Combined Immunodeficiency) can be considered a success but with a complex situation as this strategy is sometimes causing serious side effects. In 1998-99, very young children with X-SCID with immunodeficiency (the "bubble baby") received a treatment to make their active T cells deficient. Specifically, the therapy was to insert a functional gene restores the functionality of a receptor for interleukin 2. The mutation of certain proteins to this receptor prevents these patients to have an effective immune response making them vulnerable to any opportunistic infections. Initially, the company proved to be a total success with healing patients [ 12] : most babies were out of their bubble and live normally. However, four of these patients on the score of children treated with this type of therapy have developed leukemia few years. Many data converge to suggest that the type of vector used could be integrated into sensitive areas genome and deregulating certain genes, such as protooncogene LMO2 [ 13] (a gene commonly found in activated natural lymphomas) could participate in these forms of leukemia induced. We can correlate this integration of vector multiplication anarchic yet undifferentiated white blood cells causing leukemia, it would be therefore a direct side effect attributable to the strategy itself. The majority of patients involved in various clinical trials of this type made by the world has not (yet) developed this type of leukemia.
This clinical trial "flagship" of gene therapy has several consequences. It was first shown that the concept of gene therapy was valid and that a strategy of manipulation of the genome could have a therapeutic impact. But it has also highlighted the need to improve strategies (use of new vectors limiting genotoxic inserts, reducing the amount of cells exposed to the vector and then reinfused to the patient to limit the risk of touching another gene. ..) and risks that could be associated with this strategy. Enfin, et de manière très inopportune, il a aussi fortement freiné le développement d'une thérapie génique qui commençait à souffrir d'une mauvaise réputation étant donné le peu de réussites observées dans les protocoles cliniques. Ces événements sont rentrés en synergie avec le décès d'un patient aux États-Unis en 1999, Jerry Jelsinger, lors de l'injection de fortes doses d'un vecteur dérivé d'un adénovirus, qui a ébranlé la communauté scientifique et médicale, et celui en 2007 d'un patient traité par un vecteur dérivé de AAV.
Les résultats de certains protocoles sont actuellement put forward in 2007-2008 including clinical trials on pathologies of vision, or infantile neuronal disease (late infantile neuronal LINCL or ceroid lipofuscinosis) where positive signs of clinical improvement are reported. The caution and these results are nonetheless not only confirm but also to improve in the future, since the announcement of a positive result does not necessarily mean that we is close to that required for therapeutic treatment can take place in a traditional hospital setting.
and Gene Therapy Company
While gene therapy works well in animal models (mice, dogs, ...), it is usually ineffective in humans because of the combination of several parameters: the inefficient vectors to transduce a significant percentage of cells, the difficulty of creating vectors that can replicate the complex kinetics of gene expression, sometimes the use of gene therapy due to inadequate conceptual errors regarding the mechanisms of disease The health of some patients for whom gene therapy could bring anything anyway ... This inefficiency makes it more acute consideration the ethical, sociological, and safe ... with an underlying issue: the research should they be arrested? The problems related to the risk of spreading the virus vector in the population, as well as a germline transmission (which would lead to send the sick child of the new genes during fertilization) are now virtually nonexistent, and Side effects, if they remain at the human drama, are generally very rare and do not justify a stop efforts R & D . Various bodies involved in the control trials in gene therapy (the AFSSAPS France, CAR U.S.) are beginning to adopt regulatory frameworks for optimal protection of the patient and his entourage, and we can consider today that gene therapy is "no more risky" than other experimental therapeutic approaches.
a sociological problem and ethics, any conventional medical approach based on biotechnology, is the cost and financial effort that the company agrees development of gene therapy. Yet exist a business perspective, the cost of gene therapy is currently provided by charities or government agencies, and especially by the industry. Regarded as a therapy for rich countries, unable to report a very positive either medically or commercially, and face the difficulties of financing the scientific research of many voices calling for a redistribution of money allocated to gene therapy, and stop investigations. The context is in fact not as Manichean as one might imagine. For example, if the Development of gene therapy is that rich countries, some studies based their concept on the use of naked DNA vector-type (non-viral) that could be easily produced, stored, sent and relatively low cost thus enabling countries poor access to treatments that today rely on heavy medication approaches financially.
source: wikipedia
0 comments:
Post a Comment