STEM CELL GENE MANIPULATION AND DELIVERY AS SYSTEMIC THEREPUTICS

P.AnushaM.Pharmacy

119A2S0302

What are stem cellsStem cells are the raw material from

which all of the body’s mature, differentiated cells are made. Stem cells give rise to brain cells, nerve cells, heart cells, pancreatic cells, etc. They have the potential to replace cell tissue that has been damaged or destroyed by severe illnesses.

They can replicate themselves over and over for a very long time.

Two Kinds of Stem CellsEmbryonic (also called “pluripotent”) stem

cells are capable of developing into all the cell types of the body.

Adult stem cells are more difficult to identify, isolate, and purify.

Stem cells based upon their sourceEmbryonic stem cells obtained from the

undifferentiated inner mass cells of a blastocyst, (an embryo that is between 50 to 150 cells)

Umbilical cord blood derived from the blood of the placenta and umbilical cord after birth

Adult stem cells undifferentiated cells found among differentiated cells of a specific tissue and are mostly multipotent cells Bone marrowAdipose tissueCNS stem cellsUmbilical Cord Blood

Embryonic Stem Cells:

Two Sources of Embryonic Stem Cells Excess fertilized eggs from IVF (in-vitro

fertilization) clinics

Therapeutic cloning (somatic cell nuclear transfer)

Stem cell therapy

Stem cell therapy is most often regarded as a means to provide replacement of specific cells for repair of a damaged or failing organ. Therefore, great efforts have been made to identify both ideal sources of cells, and those with the greatest differentiate potential, so that multiple cellular phenotypes can be obtained.

 

However, recentstudies have provided compelling evidence that, in some diseasestates, engraftment of transplanted stem cells may not, in fact, berequired to gain a therapeutic benefit.

 

stem cells exert their benefit by selectively seeking out areas of injury/damage within the

body and serving as a reservoir of cytokines and growth factors that promote repair of the endogenous cellular pool within the damaged organs.

These findings suggest that stem cells would be ideally suited as vehicles for delivering therapeutic genes or drugs to damaged/ diseased tissues.

Adult stem cell gene manipulation The prototypic example of adult stem cells, the hematopoietic stem cell. Although they are relatively rare in the human body, these cells can be readily isolated

from bone marrow or after mobilization into peripheral blood. After in vitro manipulation, these cells may be retransplanted into patients by

injection into the bloodstream, where they travel automatically to the place in the bone marrow in which they are functionally active.

Another adult bone marrow-derived stem cell type with potential use as a vehicle for gene transfer is the mesenchymal stem cell, which has the ability to form cartilage, bone, adipose (fat) tissue.

The traditional method to introduce a therapeutic gene into hematopoietic stem cells from bone marrow or peripheral blood involves the use of a vector derived from a certain class of virus, called a retrovirus.

However, these particular retroviral vectors were only capable of transferring the therapeutic gene into actively dividing cells. Since most adult stem cells divide at a relatively slow rate, efficiency was rather low.

Vectors derived from other types of retroviruses (lentiviruses) and adenoviruses have the potential to overcome this limitation, since they also target non-dividing cells.

The major drawback of these methods is “insertional mutagenesis.” and difficult to ex-vivo manipulation.

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embryonic stem cell gene manipulation

Following derivation, human embryonic stem cells areeasily accessible for controlled and specific geneticmanipulation. When this facility is combined with their rapid growth,

remarkable stability, and ability to mature in vitro into multiple cell types of the body, human embryonic stem cells are attractive potential tools for

gene therapy. First, human embryonic stem cells could be genetically manipulated to introduce the therapeutic gene. This gene may either be active or awaiting later activation, once the modified embryonic stem cell has differentiated into the desired cell type.

The therapeutic gene needs to be introduced into the

cell type used for therapy. Genes may be introduced

into cells by transfection or transduction.Transfection utilizes chemical or physical

methods to introduce new genes into cells.Transduction utilizes viral vectors for DNA

transfer. Viruses, by nature, introduce DNA or RNA into cells very efficiently.

parameter that must be carefully monitored is the random integration into the host genome, since this process can induce mutations or serious gene dysfunction.

However, several copies of the therapeuticgene may also be integrated into the genome, helpingto bypass positional effects and gene silencing. Positional effects are caused by certain areas within thegenome and directly influence the activity of theintroduced gene. Gene silencing refers to the phenomenonwhereby over time, most artificially introducedactive genes are turned off by the host cell, amechanism that is not currently well understood 

Gene silencing and positional effects can be avoided by to introduce the gene of interest specifically into a defined region of the genome by the gene targeting technique ( homologous recombination ).

Gene manipulated stem cell deliveryTherapeutic gene

The therapeuticgene is packagedinto a deliveryvehicle such asa retrovirus

and injectedinto the patient

Adult stem cells

embryonic stem cells

Genetically modified ES

Invitro differentiated stem cell

Adult stem cells areisolated and propagatedin the laboratory.

Therapeutic gene

The therapeutic geneis packaged into adelivery vehicle suchas a retrovirus andintroduced into thecells.

The genetically modifiedcells are reintroducedinto the patient

Direct delivery Cell based delivery

Applications of manipulated stem cells for delivery as systemic therapeuticsAny disease in which there is tissue degeneration

can be a potential candidate for stem cell therapies.

Alzheimer’s disease Parkinson’s disease Spinal cord injury Heart disease Severe burns Diabetes

Stem cells for Alzheimer’s disease Stem cells could, however, be genetically

modified so as to deliver substances to the Alzheimer brain, to stop cells from dying and stimulate the function of existing cells.

Manipulated stem cells for Parkinson's disease

Stem cells for diabetes

Drug TestingStem cells could allow scientists to test new drugs using

human cell line which could speed up new drug development.

Only drugs that were safe and had beneficial effects in cell line testing would graduate to whole animal or human testing.

It would allow quicker and safer development of new drugs.

Limbal stem Cell therapy The treatment is known

as limbal stem cell therapy, and the patients who received the treatment suffered from chemical burn or genetic disease know as aniridia

By replacing the limbal stem cells, the cornea begins to clear up as the cells are replaced with the healthy transparent layer again.

References

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