Gene Therapy

Gene therapy typically involves the transfer and expression of a therapeutic gene. The nucleic acid transfer needs to have a dominant effect on the cell's phenotype.

Gene Therapy using Stem Cells: Hematopoietic stem cells can be enriched by a procedure developed by I.L. Weissman and colleagues. In this procedure, a bone marrow sample is reacted with fluorescent monoclonal antibodies specific for antigens expressed on mature red and white blood cells. The labeled cells are then removed by flow cytometry with a fluorescence activated cell sorter leaving a number of stem cells in the sample. To further enrich the stem cells they can be incubated with various antibodies raised against cells likley to represent early differentiation stages in hematopoiesis (for example raised against antigen stem-cell antigen 1 in mice or CD34 which is present on 1-3% of hematopoeitic cells that can reconstitute the entire hematopoietic system in humans.) CellPro Inc. has reported successfull enrichment of CD34 stem cells using affinity chromatography. Such CD34 stem cells can be enriched and then engineered to replace any defective genes and then reintroduced back into the body. If some of the engineered stem cells are pluripotent, then all blood cells originating from those cells should have the healthy gene. In theory, patients would only need a single injection of the stem cells whereas if mature cells were used, multiple injections would be required.

Gene Delivery: There are various viral and nonviral methods of gene delivery. The viral methods include 1) retrovirus, 2) adenovirus and 3) adeno-associated virus. The non-viral methods of gene delivery include 1) liposomes, 2) particle bombardment, 3) direct injection and 4) electroporation.

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