Saturday, May 22, 2010

What are the areas needing Efficient Gene Delivery

Today an enormous amount of genetic information is available from databases, which are continuously fed by worldwide genome sequencing programs. Every day, the human genome-sequencing program alone provides new information about human genes with potential therapeutic value. On a diagnostic level, this will allow detecting “genetic defects” and also a prediction as to which amino acid in a given protein is concerned. However, unless the change in amino acids is meaningless or the malformed protein can be replaced, this information has limited therapeutic impact since curing the DNA defect is at present not possible. Another aspect concerns the large number of genes with unknown function. Since it is not possible to predict the three dimensional structure of a protein, let alone its biological function (interactions with other biological substances), from its amino acid sequence, the only way to “mine” the genetic information consists in a laborious transfection of a mammalian cell with the gene in question to enable said cell to produce the protein. Subsequently this allows studying the activity of the protein either directly within the cell or in vitro once enough of the material has been produced for further characterization.

The problem of quickly producing a certain amount of protein for further characterization and study is a major bottleneck in several areas of the life sciences and the related bioindustry. The list of sequenced genes for which the function of the corresponding protein is poorly understood is long. In addition, it is fairly easy to mutate genes in vitro, so a variety of new proteins can be encoded, some of which might have considerable therapeutic value. In contrast to the quick generation of new genes, the establishing of a stable recombinant production cell line requires at least a year for transfection, screening/amplification and scale up due to the difficulties of inserting the gene stably into a transcriptionally active region of the cell's chromosomal DNA. Recently, a much faster method -transient transfection - has been discussed as a means to produce quickly (within days) milligrams of a given protein. In this case, the foreign DNA is not inserted into the genome of the cell. The method, which until recently was only used for the production of smaller amounts of proteins through-out, had been shown to be compatible with at least the 1 L scale. If transfections could be established at the 100 liter scale or more, gram amounts of any protein could be produced within days. Screening of putative biopharmaceuticals but also basic research would profit enormously. Such large-scale transfections have not yet been achieved.

Gene therapy is another domain where efficient transfer of genes is essential. Many severe human diseases are caused by a genetic defect leading to the mal- or over-/ under-expression of the corresponding protein. Patients could be permanently cured if the missing genes could be transferred in a functional form into the concerned organs. Delivery of genes to specific tissues could become the most efficient medical treatment in the future, but for obvious reasons, the establishment of a very safe and well-controlled method for gene delivery is imperative.

Tags: Bio Technology, Bio Genetics, Gene Delivery

Monday, May 3, 2010

Understanding of Bioartificial Organ Rejection

The process of rejection may begin with the diffusion of immunogens from the graft across the membrane barrier. There are several possible sources for these antigens, including molecules shed from the cell surface, protein secreted by live cells and cytoplasmic protein liberated from dead cells. Recognition and display of these antigens by antigen presenting cells initiates the cellular and humoral immune response. The former leads to activation of cytotoxic cells, macrophages and other cells of the immune system. These cells must be prevented from contacting grafted tissue, a requirement relatively easy to meet. More difficult is keeping out components of the humoral immune response. These include cytokines, for example, interleukin-1, which can have detrimental effects on beta cells, as well as the antibodies formed as a response to the antigens, which have leaked across the barrier. In addition, there may always be some antibodies already present in the antibody spectrum of the blood serum which correspond to cell surface antigens (e.g., major histocompatibility complexes) on allo- or xenografts. Antibodies produced during preexisting autoimmune disease, such as type I diabetes, might also bind to surface antigens on allogeneic cells. Finally, macrophages and certain other immune cells can secrete low-molecular weight reactive metabolites of oxygen and nitrogen including free radicals, hydrogen peroxide, and nitric oxide that are toxic to cells in a nonspecific manner. These agents can diffuse large distances if their lifetime exceeds 1s.

Any attempts to evaluate biocompatibility in vitro would show some lack of predictability for in vivo experiments. Therefore, implantation experiments are necessary to correlate these phenomena. The majority of experiments have been performed on rodents, and there are only a few reports on systematic experiments in large animal models. The choice of an animal model should reflect the human situation. In diabetes research, the diabetic BB-rat, NOD-mice and STZ-treated mice have generally been accepted to be a representative animal model of autoimmune diabetes.

Tags: Bio Technology, Bio Genetics, Organ Rejection