Bone Marrow Transplantation

Bone Marrow is a soft tissue in the medullary cavities of bones. Immunodeficiency diseases are mainly concerned with the derivatives of marrow cells. So they can be cured by bone marrow transplantation. Eg. Severe combined immunodeficiency (SCID). Severe combined immunodeficiency is a genetic disease in man due to mutation in adenosine deaminase gene. Adenosine and deoxyadenosine get accumulated in the blood. These substances are toxic and Tcells. The sufferer dies within 3 years after birth.

The process of transplantation to treat SCID is:

A small piece of bone marrow is taken from a bone of patient suffering SCID. The marrow is macerated and cultured in supplemented Hank's Simm's medium.

Murine leukemia virus (MuLV), a retrovirus, is allowed to infect a mouse cell line. By reverse transcription, the RNA produces duplex DNA called proviral DNA. The proviral DNA is isolated from the mouse cells. Gag, poly and env gene in the proviral DNA are deleted. Aneomycin resistance gene (Neor)was inserted between the encapsidation region and viral replication sequence of the vector. The remedial gene adenosine deaminase gene is inserted near the encapsidation region of the vector to construct an rDNA.

Mouse cells in a culture are treatedwith the rDNA and calcium phosphate solution to intake the rDNA. This is called infesting. The infested mouse cells are again infected with a helper virus. The helper virus lacks encapsidation region. So it produce virus coat protein but its RNA cannot be packaged in to the protein coat. At the same time the rDNA has encapsidation region for packaging. So mRNA produced from the rDNA gets packaged in to the protein coat to form an infective virus particle.

The virus particles are isolated from the infested cells and allowed to infect T cells isolated from the marrowcells. The cells are incubated for a few days. The virus injects rDNA in to the cell, the RNA is made in to duplex DNA. The T cells in the culture is then treated with the antibiotic neomycin. T cells with rRNA are resistant to neomycin. The successful cells are washed with H2O and transfused back in to marrow of the patient's bone. The injection of individual cells in a suspension in to the bone marrow is called transfusion.

In another method, The Tcells are grown in to cell masses. The cell mass is placed in marrow of the patient's bone from which it was taken previously. This method is called autoplastic transplantation. The transplanted cells produce adenosine deaminase and cure SCID disease in the patient. T cells have short life time so repeated transfusions may be needed (2-7 times) to cure the disease.

Some of the diseases are: Chronic granulomatous disease. Fanconi anaemia, Hunter disease, Huler Syndrome, Purine nucleotide phophorylase deficiency, Sickle cell anaemia etc.

Liver transplantation

Ex vivo gene therapy using liver cells is called liver transplantation. Diseases such as familial hypercholesterolemia, hyperammonemia, etc. can be corrected by liver transplantation.

Familial hypercholesterolemia is characterized by high cholesterol level in blood and coronary artery disease. It is due to mutation in low density lipoprotein receptor gene (LDLR gene). The LDLR is produced in liver cells.

Some liver cells are taken from the patient and grown in vitro. LDLR gene is inserted in to retroviral DNA in a plasmid to construct a rDNA. The rDNA is transfested in to muse cells using calcium phosphate solution. The mouse cells are then infected with a helper retrovirus to form infective virus particles. The virus particles are then allowed to infect the liver cells. After proper screening, the liver cells containing the rDNA are transfused in to the liver of the patient. The remedial LDLR gene corrects the genetic disorder in the patient.

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