Chapter 10 – Medical Biotechnology

•Gene therapy

•New gene therapy approaches

•Stem cells and Therapeutic Cloning

•Vaccines

•Tissue engineering and xenotransplantation

•Drug delivery and nanotechnology

Two types of gene therapy (adding a normal gene to correct a specific gene disorder)

• Ex vivo -cells are removed from the body, the gene of interest is inserted into them, the cells are cultured to increase cell numbers, and they are returned to the body by infusion or transplantation (time consuming and expensive)

• In vivo -a gene is introduced directly into specific cells within the body (quick and inexpensive), but targeting certain cells (e.g., bone marrow stem cells) is difficult

Consider somatic vs germline gene therapy; the later is currently banned.Note that gene therapy is limited to somatic cells and disorders that arecaused by a single gene.

Vectors/methods used to deliver genes in Human Gene Therapy

• Retroviruses

• Adenoviruses

• Adeno-associated viruses

• Herpes simplex virus

• Liposomes

• Naked DNA

Human gene therapy(# clinical trials 1990-1999)

• AIDS (19)• Amyotrophic lateral

sclerosis• Cancer (280)-p53• Cardiovasc. dis. (20)• Cystic fibrosis (24)• Familial

hypercholesterolemia• Gaucher disease (3)

• Hemophilia A (2)• Hemophilia B (2)• Hunters disease• Multiple sclerosis• Muscular dystrophy• Rheumatoid arthritis• Severe combined

immunodeficiency (3)

Severe Combined ImmunoDeficiency (SCID)• See http://www.scid.net/about.htmHow is ADA deficiency treated?There are no real cures for ADA deficiency, but doctors

have tried to restore ADA levels and improve immune system function with a variety of treatments:

• Bone marrow transplantation from a biological match (for example, a sibling) to provide healthy immune cells

• Transfusions of red blood cells (containing high levels of ADA) from a healthy donor

• Enzyme replacement therapy, involving repeated injections of the ADA enzyme

• Gene therapy - to insert synthetic DNA containing a normal ADA gene into immune cells

6-yr-old Ashanthi DeSilva-SCID sufferer treated with gene therapy-coloring at home in N Olmstead, OH (March 1993).

Cystic fibrosis transmembrane conductance regulator protein (CFTR)

CFTR involved with chloride ion transport out of cells; if defective Cl- builds up inside cells and draws water inside resulting in a sticky, sugar-rich extracellular mucus.

Is gene therapy safe?

• What do you think?

• Jesse Gelsinger storyJesse Gelsinger (June 18, 1981 - September 17, 1999) was the first person publicly identified as having died in a

clinical trial for gene therapy. He was 18 years old. Gelsinger suffered from ornithine transcarbamylase deficiency, an X-linked genetic disease of the liver, whose victims are unable to metabolize ammonia - a byproduct of protein breakdown. The disease is usually fatal at birth, but Gelsinger had not inherited the disease; in his case it was the result of a genetic mutation and as such was not as severe - some of his cells were normal which enabled him to survive on a restricted diet and special medications.

Gelsinger joined a clinical trial run by the University of Pennsylvania that aimed to correct the mutation. On Monday, September 13 1999, Gelsinger was injected with adenoviruses carrying a corrected gene in the hope that it would manufacture the needed enzyme. He died four days later, apparently having suffered a massive immune response triggered by the use of the viral vector used to transport the gene into his cells. This led to multiple organ failure and brain death. Gelsinger died on Friday, September 17th at 2:30 PM.

A Food and Drug Administration (FDA) investigation concluded that the scientists involved in the trial, including the lead researcher Dr. James M. Wilson (U Penn), broke several rules of conduct:

Inclusion of Gelsinger as a substitute for another volunteer who dropped out, despite having high ammonia levels that should have led to his exclusion from the trial

Failure by the university to report that two patients had experienced serious side effects from the gene therapy

Failure to mention the deaths of monkeys given a similar treatment in the informed consent documentation.

The University of Pennsylvania later issued a rebuttal [1], but paid the parents an undisclosed amount in settlement. The Gelsinger case was a severe setback for scientists working in the field.

New Approaches to Gene Therapy

• Antisense RNA

• Ribozymes

• RNA interference (RNAi)

• Spliceosome-mediated RNA trans-splicing

• Triplex helix oligonucleotide therapy

Inhibition of translation of specific RNA by antisense nucleic acid molecules

Promoter antisense cDNA poly A addition signal

antisense oligonucleotide

mRNA

-antisenseRNA complex

Ribozymes: A. Hammerhead B. Hairpin

RNA interference (RNAi)

A cellular nuclease binds to the dsRNA cleaving it into ssRNAs of 21-23 nucleotides each.A cellular nuclease binds to the dsRNA cleaving it into ssRNAs of 21-23 nucleotides each.

The nuclease-RNA oligonucleotide complex binds and cleaves specific mRNA.The nuclease-RNA oligonucleotide complex binds and cleaves specific mRNA.

dsRNA

Binding of dsRNA-specific nuclease

cleavage

mRNA is cleaved!

Nuclease-ssRNA complexHybridizes to mRNA

sense

antisense

Stem Cells

• Stem cells are the progenitors of many different cell types, depending upon which type of stem cell is used (e.g., bone marrow stem cells, neural stem cells, embryonic stem cells)

• Stem cell therapy-the goal is to repair damaged tissue (e.g. Parkinson’s disease, spinal cord injury)

Other topics covered in the chapter, but not in lecture

• Vaccines

• Tissue engineering

• Xenotransplantation

• Drug delivery and biosensors

• Nanotechnology