We have made amazing progress in our understanding of how genes work and how to work with genes,even though we have a
long way to go. We can extract DNA from cells and isolate specific genes from the mass of DNA.
Once the genes are isolated,they can be copied millions of time by putting them into microorganisms like bacteria or
yeast,which will faithfully replicate them each time the cells divide. Or,they can be incubated with a supply of DNA building
blocks and enzymes in a laboratory device (the PCR machine) where they will copy themselves over and over.
Genes,once remote,inaccessibile bits of DNA,can now be identified,isolated from cells,and copied into whatever quantities
needed. Minute amounts of these genes can be put into cells of living organisms where,amazingly,the genes will often enter
the neucleus,latch onto and become part of the chromosomes ,and function as though they were meant to be there.
This process of adding functional genes to cells,called genetic transformation,is the reason why we are now able to make
so many different genetically modified organisms.
Almost all GMOs are now at the research stage and not cleared for commer cial use. However,a few,like corn,wheat,and
soybeans,are now widely used in agrilculture,and many other modified plants and animals are waiting in the wings.
How is it possible to put genes,minute DNA molecules,into cells so small that they are invisible to the naked eye?
the utimate goal is to bring about a gene-based therapeutic result,the transfer of genes to people so that the genes will
express proteins that will treat or cure illness.
We need some kind of vector,something that can carry the genes into the target cells. Sometimes genes can be introduced
into cells by wrapping them in tiny spheres of fatty material called liposomes. These will soak through cell membranes,carrying
their DNA cargo inside.
There,in a small percentage of cases the genes will incorporate themselves into the cell's genome. DNA can even be coated
onto microscopic gold particles and literally shot into cells using a device known as a gene gun.
In most of the instances that pertain to human RA research,DNA carriers have been kindly provided by nature in the form
of viruses. Viruses are not living organism. So small they cannot be seen even with the ordinary laboratory microscope,they
are merely bits of RNA or DNA wrapped in a bit of protein
They can propagate themselves only by entering a living cell and taking it over,forcing it to make viral copies. To use
viruses as vectors,researchers disable the parts of the viral genetic instructions that allow the viruses to replicate in
living cells and wrap the genes that they want to transfer inside the virus protein coat.
Then,when the viruses are mingled with cells,perhaps in a test tube in the laboratory,or inside an animal or human joint,the
viruses will slip into those cells,releasing the experimental genes.
Gene therapy experiments use a variety of viral types,each of which has advantages and disadvantages. One of the real
challenges in developing an efficient means of gene therapy for RA,or any other disease,is devising a vector,viral or otherwise,that
is safe and effective.
In human clinical study using genetic manipulation related to treating human diseases carried out with more than four
thousand human volunteers. Most of the procedures were of the gene-addition variety. The researchers attempted to put normal
genes into cells that harbored defective forms of those genes.
By 2000 there were six thousand people in three dozen countries undergoing gene therapy experiments. Most were directed
against cancer,but included at least twentytwo other conditions,including,cystic fibrosis,hemophilia,coronary artery disease,AIDS,and
three trials of gene therapy for RA.
Genes are in charge of making proteins. They do not actually stitch together the long chains of amino acids that form
the proteins. That assembly is done outside the neucleus,on the surface of roughly spherical granules,the ribosomes,which
are scattered throut the cell.
Each cell has thousands of these granules,scenes of a constant buzz of activity as proteins are put together and sent
off to various parts of the cell to fulfill their appointed tasks. The sequence of the thousands of building blocks making
up the genes,called bases,signified by the initials A,T,G, or C ,determines the sequence of thousands of the twenty different
amino acid building blocks.
How is the knowledge of the gene base sequence transmitted to the ribsomes? A mirror image copy of the gene is made,in
the form of another molecule called RNA. This "messenger" RNA,carrying the information about the base sequence of the gene,moves
out to the ribosomes,drapes across them,and the protein chains are assembled one amino acid at a time along the length of
the messenger RNA, according to its particular base sequence. The process of making RNA,the faithful messenger carrying the
genetic code for protein manufacture,is known as transcription.
Here, is where controls operate that make it possible for the cell to be fine-tuned,organized,dynamic living entity.
In any given cell,there are lots of genes that are always turned on,sending messenger RNA to make proteins that the cell needs
to have in constant supply.
However,for most genes there is a strict set of controls that regulate their actions. Most genes do not get transcribed,i.e.,they
cannot make a length of messenger RNA and send it off to make proteins,unless the genes receive specific signals to do so.
Those signals vary widely and can be environmental (e.g.,temperature or light) or internal (e.g.,hormones or cytokines).
A cell know what is going on outside of it only when it receives and interprets chemical cues that arrive at its outer border,the
delicate cell membrane. One category of such cues include chemicals that turn genes on and off.
How is it possible to switch genes on and off? It turns out that a gene includes not only a stretch of DNA that can be
transcribed into messenger RNA,but another piece of DNA next to that called the promoter,almost like a trigger needed to "fire"
the gene. When a chemical signal arrives at the cell membrane, it attaches to,a compatible protein receptor on the membrane,like
a hand fitting into a glove.
This sets off a cascade of chemical reactions inside the cell,the products of one reaction trigger the next reaction
and so on,resulting in the production of specific chemicals called transcription factors.
A transcription factor binds to a particular site promoter,and turns on the gene. It's the concept of the assembly line
again,one step leads to the next,which leads to the next,and then finally the finished product,an active gene. This step-by-step
process,starting with the cell receiving a signal and ending with a turned-on gene,is a key target for experimental genetic
regulation in RA
Now,scientists are learning more about the transcription factors that play a central role in activating the genes behind
the scenes,they are searching for ways to gain control over them. Almost inadvertently, physicians have been doing that to
a certain extent already. Several of the medications long used to treat RA act in part by blocking the activity of certain
The medications sulfasalazine,gold compounds,and glucocorticoids (steriods) all inhibit one of the transcription factors
central to inflammation. There are at least four groups of transcription factors that operate in RA. The specific factor influenced
by the above,nuclear factor kappaB (NF-kappaB) deserves particular emphasis because it is a pivotal regulator of inflammation.
NF-kappaB turns on the genes that make TNF-alpha and IL-1,those cytokines that perpetuate inflammation In RA both of
these cytokines are major driving forces behind the abnormal enlargement of the synovial membrane lining the joints,leading
to erosion of cartilage and bone. Another one of the effects that those cytokines have is to stimulate cells in the joint
to make even more NF-kappaB,forming a vicious cycle of inflammation.
The effect of this transcription factor reach even further. It even has a hand in helping to make molecules that assist
in attracting and grabbing onto inflamm atory white blood cells as they pass through the minute blood vessels surrounding
the joint,recruiting them to join the attack.
Given that these destructive cytokines are manufact ured by genes that are literally turned on by the transcription factor
NF-kappaB,it would seem logical to try to block that factor before the genes could be activated by it. If you are bothered
by the light,why not dismantle the light switch?
In one experimental study,scientists have blocked NF-kappaB by using pieces of DNA designed to latch onto the NF-kappaB,inactivating
it before it gets a chance to turn on genes. These approaches to blocking harmful gene products such as cytokines at the very
source of their manufacture may become a very useful tool in the management of RA.
The bones of our skeletal system are dynamic living tissues that can grow, adapt to stress,and repair themselves after
injury. Every bone is a rich dense matrix of collagen protein and minerals,mainly calcium phosphate,that envelops millions
of living cells. These cells lie buried within minute cavities in the bone.
These cells lie buried within minute cavities in the bone. The cavities are connected to each other by a complex series
of microscopic canals,used for carrying nutrition and waste disposal. Bone has a abundant blood supply, important not only
for nourishing the buried cells,but also for communicating with the bone's hollow interior.
There,protected by heavy surrounding walls,is the bone marrow: a rich,pulpy mass of tissue vital to our survival Yellow
marrow,which is mostly fatty tissue ,fills the large cavity in the shafts of the long boneslike -the femur of the leg,or
the humerus in the upper arm.
More important is the red marrow,packed into a honeycombed ends of the long bones,and filling the interior of many other
bones such as the pelvis and the sternum,the flat breastbone in the center of the chest.
Here in the red marrow special cells divide by the millions each second of our lives,replishing our blood cells. Blood
is actually a kind of connective tissue consisting of cells within a liquid,the blood plasma,which circulates through
the heart and blood vessels.
The blood carries vital nutrients to our other tissues and removes waste products of their metabolism. Blood cells include
the erythrocytes,the red blood cells,as well as the leukocytes,the white blood cells, crucial components of the immune system.
This process of blood production called hematopoiesis occurs in embryo and fetus in tissues such as the liver,thymus,and
spleen,as well as the red marrow.
After birth,the red marrow is primarily responsible for creating new blood , although tissues in the lympatic system
helps in the production of some white blood cells
The ancestors of all of one's blood cells is a single population of primitive, permanent red bone marrow residents,the
In the case of gene therapy,genes might be inserted into stem cells that could then be put into a person's bone marrow,where
they would be a permanent source of the proteins made gy the genes. Stem cells,once changed to either normal or even pathological
adult cell types in culture,could be used for drug screening and to study the basics of the disease process. The possibilities
of the numerous stem cell discoverious go beyond our immediate interest.
Laboratory research on animals is already underway to try to perfect a way to insert stem cells primed to replace tissues
lost to,for example, cancer, osteoporosis,injury or destruction by RA.
Not only may those stem cells replace tissues,they may carry with them genes that have been added to them in the laboratory,and
once in place,the cells will produce their gene-made proteins,perhaps proteins that may protect against disease that once
affected those tissues.
This newfound ability to remove and use mesenchymal stem cells from adult tissues is also important because it avoids
the controversy of using stem cells from human embryos. Since a series of research breakthroughs in 1998,human stem cell cultures
can be routinely grown from embryonic stem cells (ES cells) derived from the inner cell mass of the human embryo.
The inner cell mass is a cluster of cells enclosed in the hollow ball of cells that forms when the fertilized egg undergoes
repeated,rapid divisions. The inner cell mass is removed from human embryos that have been made in laboratory dishes in
the process known as in vitro fertilization.
ES cells have the potential to differentiate into all types of specialized cells in the organism