#scichallenge2017 #scienceincypriotschools Cystic Fibrosis and gene therapy
WHAT IS CYSTIC FIBROSIS?
Cystic Fibrosis (CF) is a genetic disease of which causes the body to create extremely
thick, sticky mucus. The unhealthily thick mucus is produced by the layers of cells
that line hollow organs and glands called epithelial cells. The function of these cells is
to produce mucus and other secretions. Normally, epithelial cells make clear, thin
mucus that keeps surfaces lubricated and helps prevent disease by trapping potential
infectious organisms. These epithelial cells are normally found in the respiratory
tract, and are lined with cilia, thin hair-like structures that continuously beat and
sweep the mucus up and out of the respiratory tract.
In CF patients, the mucus produced by these epithelial cells is so thick and sticky that
is it not able to be swept out of the respiratory tract by the cilia. This causes a build-
up of mucus within the airways, enabling a trapped disease – causing organisms to
reproduce and this leads to infections.
CF patients also have trouble digesting food. In the gastrointestinal tract, the thick
mucus blocks the ducts leaving the pancreas, therefore digestive enzymes that are
produced are not able to reach the intestines to break any food down. This makes it
difficult for the patients to digest their food and obtain enough nutrients. The lungs
and the pancreas are the most infected organs although other organs such as the liver,
the sweat glands and the reproductive organs are commonly affected too.
It is a chronic inherited disease, which means that it inherited genetically from
parents that are both carriers of the faulty CFTR gene, the gene responsible for CF. If
both parents are carriers, there is a 1 in 4 chance that their child will have CF.
DIFFERENCES BETWEEN HEALTHY PATIENTS
AND CF PATIENTS
WHAT IS THE CFTR PROTEIN?
The protein CFTR – Cystic Fibrosis Transmembrane Conductance
Regulator is found in all epithelial cells, including those in the
lungs. Its job is to balance the flow of water and chloride ions
in and out of epithelial cells. When the gene is mutated, like in
CF patients, the protein doesn’t work properly and causes
changes to the ion balance of cells. This change can cause
symptoms such as salty sweat, which can result in dehydration
in CF patients, as well as the production of thick mucus.
THE PREVALENCE OF CF AROUND THE WORLD
CF is a disease present all over the world. In Europe,
particularly, CF is extremely prevalent in Ireland, the
Netherlands, Switzerland, Belgium, Denmark and Czech
In America, CF is transpired to 1 in 2,500 to 3,500 Caucasian
infants; it is the most lethal disease affecting Caucasian
The problem with CF is the short life span of the patients with
the disease. They have an average life span of 37.5 years.
VIRUSES…THE GOOD GUYS?
Viruses are usually the cause of our colds or our trouble-making
flus, which make us feel weak and ailing. They have specialised
surface proteins that allow them to sneak into cells causing
infection. What if we could use viruses and their mode of
infection as a transfer vehicle to genetically engineer and “fix”
mutated cells? What if we could insert a functional copy of a
gene within the virus’s genome, enabling it to infect host
(human) cells and allow the recovery of cell function to take
place? This could be a revolutionary approach to treating
genetic diseases such as Cystic Fibrosis.
VIRAL VECTOR WEAKNESSES
Viral vectors could help cure the disease, but scientists need further research
into this treatment option. There are a lot of consequences to consider while
trying to find a way to cure CF, for example which virus would be best suitable
and safe, making sure there are no harmful consequences. To fix the DNA, the
gene CFTR is needed to enter the cells, to replace the faulty gene sequence
with the healthy copy. There are possible viruses to choose from which must
cover certain factors:
The virus must target airways cells; no virus can infect all types of cells.
The virus must be able to infect cells that divide infrequently, like airway
The virus must be effective and must infect a high number of cells to make a
significant change to the patient’s condition.
The virus must be sneaky; it should be able to infect cells without triggering
the immune system. Triggering the immune system would cause the death of
the viral vectors.
In this case, Adeno-associated viruses (AAV) are compatible for the procedure;
and scientists have used them before. The reason this therapy has not worked is
because the virus failed to assimilate into the cells genomic information. They
formed only low and momentary quantities of CFTR gene activity. Scientists are
still trying to understand why it went wrong and are trying to improve this
HOW DO THEY DO IT?
In gene therapy, the virus is used as a transport vehicle to deliver the
healthy gene to the patients’ affected cells expressing the faulty gene. Here
are the steps:
1. Scientists cut out the pathogenic genes that the virus expresses using
restriction endonuclease enzymes. Doing this makes the virus non-
2. The healthy copy of the CFTR protein is then ‘glued’ into the viral
genome using enzymes called DNA ligases.
3. The DNA produced is recombinant, and the virus is now called transgenic.
4. The transgenic viruses are left to replicate in petri dishes.
5. They are administered to the patients using an inhaler.
No one is immune to viruses; even bacteria can be infected by viruses.
Bacteriophage viruses are viruses which infect specific bacteria and use them to
reproduce, coming from the Greek word “φαγεῖν” meaning “to eat”, and the
word bacteria, translating to ‘‘Bacteria – eater’’. The phage – depending on what
type, uses a specific cycle to infect a host bacterium. There are two cycles that
the phage can choose from:
The LYTIC Cycle: occurs when the phage inserts its genetic information into
the bacterium and replicates more copies of its genome. Once this is done,
new virus particles form and the phage explodes, killing the bacterial cell. The
new viruses produced are released and able to infect further cells.
The LYSOGENIC Cycle: begins when the phage injects its genetic material into
the bacterial cell, which fuses and becomes a part of the bacterial genome.
Each time the bacteria divide, the virus’s genome is also replicated. When
enough copies of the viral genome have been made, the virus assembles
particles that destroy the bacterium, and switch to the LYTIC cycle.
OTHER TREATMENTS FOR CF
There are other treatments used to help CF patients be comfortable and free from
infections. There are many different therapies, but the main ones consist of
treatments such as airway clearance techniques, medications, oral pancreatic
enzymes and mucus thinners.
In chest physical therapy, a technique that involves clapping with cupped hands on
the back and the front of the chest is used to loosen thick mucus. It enables the
mucus to be coughed up, out of the respiratory tract.
Pancreatic enzymes are a necessary supplement which helps in the breakdown and
digestion of fats which can be disrupted if the pancreatic ducts are blocked.
Other medications comprise of inhaled antibiotics which are commonly used after
all the above treatments. They are usually used after a bronchodilator, which helps
in the removal of mucus from the bronchi, clearing the airways. Antibiotics are
taken to fight off any bacterial infections.
The mentioned method of gene therapy which uses
viral vectors as transport vehicles to get a healthy copy
of the gene inside the cell, replacing the faulty gene,
was unsuccessful. Although it failed, scientists are
working to improve this technique and will hopefully
find a way to extend patients’ life span in the future,
as well as find a way to cure Cystic Fibrosis.