Sunday, March 27, 2011

Cancers Caused by Infectious Agents

We do not generally regard cancer as being contagious.  Although this is generally t rue, there are a growing number of cancers that have been shown to be caused by contagious agents, especially by specific viruses.  In the table below, the kinds of cancers caused by such agents are shown along with the microorganism implicated and their prevalence by location.


Causative Agent

Stomach (Gastric) Cancer

H. Pylori - Bacterium

Cervical Cancer

Human Papilloma Virus (HPV)

T-Cell Leukemia

HTLV-1 – related to the AIDS virus

Burkitt's Lymphoma

Epstein Barr Virus (EBV)

Kaposi's Sarcoma

HTLV-3 – AIDS Virus

Primary  Liver Cancer

Hepatitis B Virus (HBV)


In regards to the data listed in the table above, there is additional information associated with them:

  •          H.Pylori is a highly specialized and fairly ubiquitous bacterium that can survive in the harsh acidic environment of the stomach; it is found in the mucus layer on the inside of the stomach within those individuals who are infected.  For this reason, it is particularly difficult to treat with antibiotics.  It is found in about 2/3 of the world's population.  It has also been implicated in the onset of chronic gastritis and peptic ulcers.
  •          HPV has recently been implicated as the causative agent for cervical cancer.  Cervical Cancer is prevalent in sexually active women.  A vaccine against this virus has recently been developed.  It has been shown to be highly effective in preventing the onset of this cancer in young women. 
  •          EBV, the virus that causes Burkitt's lymphoma found predominantly in Africa, is the same virus that causes mononucleosis in individuals in the West.  The reason for this distinct difference in disease outcomes is poorly understood, but a genetic basis for this difference is likely.
  •          The AIDS virus is not directly responsible for the onset of Kaposi's sarcoma.  The disease is manifested in AIDS patients on account of their highly suppressed immune system due to infection with the AIDS virus that make AIDS patients especially susceptible to this cancer.
  •          Once an individual is infected with HBV as a result of close human contact with an infected individual, the virus can infect the liver without any noticeable symptoms.  This can be the case for many years before the onset of Liver cancer.   HBV is believed to account for 80% of primary liver cancer (cancer that originates in the liver).  It is a deadly cancer.  Fortunately, there is a vaccine against HBV infection, but there is currently no vaccine to prevent infection by the Hepatitis C Virus (HCV) that is also known to cause primary liver cancer. 

Monday, March 14, 2011

Disease-in-a-Dish – Another Application of Stem Cell Research

Stem cells have the capacity to be transformed into any specialized body cells under the right conditions.  This may seem very surprising, but there is an explanation that has at its roots in the nature of the genetic structure of living cells.  All cells in the human body, regardless of their structure and function, have the identical set of genes (genome).  If the genes determine the structure and function of cells, what, therefore, establishes the various unique and diverse tissue cell types such as liver, kidney, skin, etc.  The answer lies in what genes are expressed, turned on and what genes are not expressed, turned off.  The process of selectively turning genes on or off to produce specialized cell types is referred to as differentiation.  Stem cells are pluripotent – they are capable of becoming any specialized cell type under the appropriate conditions.

A considerable controversy erupted over the use of stem cells due to the fact that the source of these cells was from human embryos – so-called embryonic stem cells.  However, a new class of stem cells has been developed that are derived from the use of ordinary tissue cells treated with a cocktail of specific initializing factors that transform these cells to stem cells, so-called induced pluripotent stem cells (iPS) that have been shown to exhibit the same capacity as embryo-derived cells.

The following is a description of a direct application that utilizes iPS in a very interesting and potentially useful way.  Doctor K. Eggan and his colleagues from the Harvard Stem Cell Institute (HSCI) collected skin cells from two patients suffering from amyotrophic lateral sclerosis (ALS).  ALS is a degenerative disease of the nerve cells in the brain and spinal cord that control voluntary muscle movement also known as Lou Gehrig's disease.  These fibroblast cells were subsequently grown in culture and treated with the appropriate regulator genes to reprogram the cells to become iPS cells and thereby pluripotent  in behavior.  These iPS cells tend to clump into what is referred to as "embryoid bodies" and to these clumps were added retinoic acid and a compound that is known to accelerate cell division.  The result of the addition of these added factors was to successfully transform these embryoid bodies into motor neurons.

Since these newly derived nerve cells originated from patients with ALS, they retain all of the genetic properties and characteristics of the disease.  This affords an excellent opportunity to test these cells with drugs that may have potential therapeutic value for ALS patients. 

This  approach as outlined above is referred to as "disease-in-a-dish" and is an expansion of the pioneering efforts of Doctor Yamanaka from Japan.   It offers great promise in the study of such intractable diseases as ALS.