The MIDGE transfection vector technology
	Scientists at Mologen have developed a transfection vector which combines the advantages of viral-vectors (cell-specifity and high expression levels) with those of the plasmid vectors (no immunogenity or danger of virus recombination and relatively low costs).
	Structure and production of MIDGE vectors
	MIDGE minimalistic vectors contain only the expression cassette (promoter, coding sequence, and terminator/poly-A-site). They are smaller than plasmids by 50-80% and of linear covalently closed topology. MIDGE vectors are made in a three step process, in which the expression cassette is cut out of a suitable plasmid. The resulting fragment of double stranded DNA is then covalently closed at both ends by loops of single stranded DNA oligonucleotides at both ends so that a continuous, covalently closed molecule results. Graphical representation of MIDGE synthesis
Advantages of the MIDGE-Technology
	MIDGE is safe MIDGE vectors carry no sequence elements other than those needed for the medical objective of the gene transfer. Thus, there is no co-expression of antibiotic resistance genes from leaky bacterial promoters. Bacterial origins of replication and other sequence motives, which in bacteria tend to mediate integration or recombination, are completely absent in MIDGE. Therefore, integration into the genom of the host cell, of which the chances are very low already in plasmid DNA, is very unlikely to happen with MIDGE.
	MIDGE is selective The ease with which tissue specific ligands can be attached to the oligonucleotide loops makes the MIDGE-technology so versatile.
	In effect it brings back some of the "viral" selectivity and gene transfer activity to the enhanced safety of the naked DNA approach. Any vector will have to overcome two barriers before commencing gene expression: it has to get into the cell, and once within the cell, it has to reach the nucleus. A third, extracellular dimension of the problem is the delivery of the vector to the target cell population. MIDGE allows for the attachment of tissue-specific ligands, e.g. peptides with known receptors on clinically relevant cell populations. The covalent attachement of a single decapeptide to the naked vector has led to surprisingly large effects in its immunogenecity, resulting in a profound difference in the induced immune response both in magnitude and quality. As a result, peptide-linked MIGDE vectors have been shown in a mouse model to be at least as effective as a DNA prime-vaccinia boost model, the best immunisation regime known so far. Figure 1: MIDGE allows for the attachment of tissue-specific ligands for the active uptake of the entire vector molecule by receptor internalization into the cell cytoplasm. Nuclear import is mediated by nuclear localization sequences. A high level of gene expression is achieved.
	MIDGE is non-immunogenic In side-by-side comparison, MIDGE have shown several-fold increased expression of the encoded gene.
Summary
	Every vector described above has its merit. Scientists at Mologen believe, that the MIDGE vectors features an ideal combination of the advantages of all other vectors. MIDGE vectors are naked DNA, thus the dangers associated with viral vectors are of no concern At the same time, MIDGE vectors can be produce to target only specific cell types MIDGE vectors do not contain undesired sequences which could be hazardous to the patient No component of the MIDGE vector per se does elicit a significant immune response, thus avoiding undesired host reactions. Immuno stimulatory sequence content (such as CpG) can be chosen according to the objective of the gene transfer MIDGE vectors are relatively simple and inexpensive to produce and are stable in handling and in the patient’s body. MIDGE vectors have been tested successfully in a number of clinical trials.
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