cancer causing viruses and its vaccine

Cancer causing viruses and its vaccine

 Today we discussing about cancer and its vaccination

Cancer:

Cancer , known medically as a malignant neoplasm, is a broad group of diseases involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invading nearby parts of the body. The cancer may also spread to more distant parts of the body through the lymphatic system or bloodstream. Not all tumors are cancerous; benign tumors do not invade neighboring tissues and do not spread throughout the body. There are over 200 different known cancers that affect humans.

Viruses:

Viruses also have the ability to cause cancer by altering cell genes. Cancer viruses change cells by integrating their genetic material with the host cell's DNA. The infected cell is regulated by the viral genes and gains the ability to undergo abnormal new growth. Several viruses have been linked to certain types of cancer in humans. The Epstein-Barr virus has been linked to Burkitt's lymphoma, the hepatitis B virus has been linked to liver cancer, and the human papilloma viruses have been linked to cervical cancer.

Viruses and Cancer:

Cancer (Latin cancer, crab) is one of our most serious medical problems and the focus of an immense amount of interest and research.A tumor (Latin tumere, to swell) is a growth or lump of tissue resulting from neoplasia or abnormal new cell growth and reproduction due to a loss of regulation. Tumor cells have aberrant shapes and altered plasma membranes that contain distinctive tumor antigens. They may invade surrounding tissues to form unorganized cell masses. They often lose the specialized metabolic activities characteristic of differentiated tissue cells and rely greatly upon anaerobic metabolism. This reversion to a more primitive or less differentiated state is called anaplasia. There are two major types of tumors with respect to overall form or growth pattern. If the tumor cells remain in place to form a compact mass, the tumor is benign. In contrast, malignant or cancerous tumor cells can actively spread throughout the body in a process known as metastasis, often by floating in the blood and establishing secondary tumors. Some cancers are not solid, but cell suspensions. For example, leukemias are composed of malignant white blood cells that circulate throughout the body. Indeed, dozens of kinds of cancers arise from a variety of cell types and afflict all kinds of organisms.
At present, viruses have been implicated in the genesis of atleast eight human cancers:
1 ) The Epstein-Barr virus (EBV) is one of the best-studied human cancer viruses. EBV is a herpes virus and the cause of two cancers. Burkitt’s lymphoma is a malignant tumor of
the jaw and abdomen found in children of central and western Africa. EBV also causes nasopharyngeal carcinoma. Both the virus particles and the EBV genome have been found within tumor cells; Burkitt’s lymphoma patients also have high blood levels of antibodies to EBV.Interestingly there is some reason to believe that a person also must have had malaria to develop Burkitt’s lymphoma. Environmental factors must play a role, because EBV does
not cause much cancer in the United States despite its prevalence. Possibly this is due to a low incidence of malaria in the United States.
2) Hepatitis B virus appears to be associated with one form of liver cancer (hepatocellular carcinoma) and can be integrated into the human genome.
3) Hepatitis C virus causes cirrhosis of the liver, which can lead to liver cancer.
4) Human herpes virus 8 is associated with the development of Kaposi’s sarcoma.
5) Some strains of human papilloma viruses have been linked to cervical cancer.
6) At least two retroviruses, the human T-cell lymphotropic virus I (HTLV-1) and HTLV-2, seem able to cause cancer, adult T-cell leukemia, and hairy-cell leukemia, respectively  Other retrovirus-associated cancers may well be discovered in the future.It appears that viruses can cause cancer in several ways. They may bring oncogenes into a cell and insert them into its
genome. Rous sarcoma virus (a retrovirus) carries an src gene that codes for tyrosine kinase. This enzyme is located mainly in the plasma membrane and phosphorylates the amino acid tyrosine in several cellular proteins. It is thought that this alters cell growth and behavior. Since the activity of many proteins is regulated by phosphorylation and several other oncogenes also code for protein kinases, many cancers may result at least partly from altered cell regulation due to changes in kinase activity. The human T-cell lymphotropic viruses, HTLV-1 and HTLV-2, seem to transform T cells by producing a regulatory protein that sometimes activates genes involved in cell division as well as stimulating virus reproduction. Some oncogenic viruses carry one or more very effective promoters oenhancers. If these viruses integrate themselves next to a cellular oncogene, the promoter or enhancer will stimulate its transcription,leading to cancer.
Causes of Cancer:
Cancer results from the development of abnormal properties in normal cells that enable them to grow excessively and spread to other locations. This abnormal development can be caused by mutations that occur from factors such as chemicals, radiation, ultraviolet light, and chromosome replication errors. These mutagens alter DNA by changing nucleotide bases and can even change the shape of DNA. The altered DNA produces errors in DNA replication, as well as errors in protein synthesis. These changes influence cell growth, cell division, and cell aging.
Cancer Cell Properties:
Cancer cells have characteristics that differ from normal cells.

•    Cell Reproduction

Cancer cells acquire the ability to reproduce uncontrollably. These cells may have gene mutations or chromosome mutations that affect the reproductive properties of the cells. Cancer cells gain control of their own growth signals and continue to multiply unchecked. They don't experience biological aging and maintain their ability to replicate and grow.
•    Cell Communication
Cancer cells lose the ability to communicate with other cells through chemical signals. They also lose sensitivity to anti-growth signals from surrounding cells. These signals normally restrict cellular growth.

•    Cell Adhesion

 Cancer cells lose the adhesion molecules that keep them bonded to neighboring cells. Some cells have the ability to metastasize or spread to other areas of the body through the blood or lymph fluid. Once in the bloodstream, cancer cells release chemical messengers called chemokines that enable them to pass through blood vesselsinto the surrounding tissues.
•    Cell Specialization
Cancer cells are unspecialized and do not develop into cells of a specific type. Similar to stem cells, cancer cells proliferate or replicate many times, for long periods of time. Cancer cell proliferation is rapid and excessive as these cells spread through out the body.

•    Cell Death

 When the genes in a normal cell are damaged beyond repair, certain DNA checking mechanisms signal for cell destruction. Mutations that occur in gene checking mechanisms allow for the damages to go undetected. This results in the loss of the cell's ability to undergo programmed cell death.
Retroviruses:
Retroviruses are viruses with an RNA genome (RNA viruses), that replicate by way of reversetranscription of their RNA into DNA. These viruses penetrate their cell host intact. Once inside, their capsid protein coat is removed, releasing a single stranded RNA genome. An RNA-dependent DNA polymerase, encoded by the virus, generates a complementary DNA strand which becomes integrated into the host cell genome and serves as the template for the synthesis of new viral RNA genomes. Protein synthesis from these genomes results in development of new viral progeny which are released slowly from the host cell by budding, thereby not causing lysis and death of the infected cell, but allowing ongoing replication of new viruses.
Retroviruses are responsible for causing some forms of leukemia (a type of cancer) in humans, and the virus that causes AIDs (HIV) is a retrovirus. Despite this, retroviruses are also useful tools for protein engineering, used for introducing new genes into a host cell. These types of virus integrate into host DNA at random sites, however, therefore the locations for gene insertions cannot (as yet) be controlled.
Discovering the First Cancer-Causing Virus: A farmer had brought him a hen with a large lump in her breast. Rous, a pathologist, diagnosed the lump as a sarcoma a tumor of cells in the connective tissue. He first tested whether the tumor could be transplanted into chickens closely related to the original one. It could, and with each passing, the tumor became more aggressive. To find out whether an infectious agent caused the cancer, Rous prepared an extract he minced a sample of the tumor tissue in saline solution and passed this through a filter to eliminate bacteria and tumor cells. Then he injected the extract into healthy chickens. Contrary to his expectations, it produced new tumors.
Describing these experiments, Rous suggested that the tumor-inducing agent was "a minute parasitic organism"a virus. There are two types of cancers caused by viruses: acutely transforming or slowly transforming cancers. In acutely transforming viruses, the virus carries an overactive oncogene, and the infected cell becomes cancerous as soon as the overactive viral gene is expressed. In contrast, in slowly transforming viruses, the virus genome is inserted near a previously existing proto-oncogene in the genome of the infected cell. The virus causes overexpression of that proto-oncogene, which typically induces uncontrolled cell division. Because the virus' genes might not insert near enough to a proto-oncogene to trigger the cancerous changes, and, even if optimally located, it might take some time to become activated, slowly transforming viruses usually cause tumors much longer after infection than the acutely transforming viruses.
Infection by some hepatitis viruses, especially hepatitis B and hepatitis C, can induce a chronic viral infection that leads to liver cancer in about 1 in 200 of people infected with hepatitis B each year (more in Asia, fewer in North America), and in about 1 in 45 of people infected with hepatitis C each year. People with chronic hepatitis B infection are more than 200 times more likely to develop liver cancer than uninfected people. Liver cirrhosis, whether from chronic viral hepatitis infection or alcohol abuse or some other cause, is independently associated with the development of liver cancer, and the combination of cirrhosis and viral hepatitis presents the highest risk of liver cancer development. Because chronic viral hepatitis is so common, and liver cancer so deadly, liver cancer is one of the most common causes of cancer-related deaths in the world, and is especially common in East Asia and parts of sub-Sarahan Africa.
Human papillomaviruses (HPV) are another particularly common cancer-causing virus. HPV is well known for causing genital warts and essentially all cases of cervical cancer, but it can also infect and cause cancer in several other parts of the body, including the larynx, lining of the mouth, nose, and throat, anus, and esophagus. The Papanicolaou smear ("Pap" smear) is a widely used cancer screening test for cervical cancer. DNA-based tests to identify the virus are also available.
Herpesviruses are a third group of common cancer-causing viruses. Two types of herpesviruses have been associated with cancer: the Epstein-Barr virus (EBV) and human herpesvirus 8 (HHV-8). EBV appears to cause all nonkeratinizing nasopharyngeal carcinomas and some cases of lymphoma, including Burkitt’s lymphoma the association is especially strong in Africa—and Hodgkin’s disease. EBV has also been found in a variety of other types of cancer cells, although its role in causing these other cancers is not well established. HHV-8 causes all cases of Kaposi’s sarcoma, and has been found in some cases of a cancer-related condition called Castleman's disease. Studies involving other kinds of cancer, particularly prostate cancer, have been inconsistent. Both of these herpesviruses are commonly found in cancerous cells of primary effusion lymphoma. Herpesviruses also cause cancer in animals, especially leukemias and lymphomas.
HIV does not directly cause cancer, but it is associated with a number of malignancies, especially Kaposi's sarcoma, non-Hodgkin's lymphoma, anal cancer and cervical cancer. Kaposi's sarcoma is caused by human herpesvirus 8. AIDS-related cases of anal cancer and cervical cancer are commonly caused by human papillomavirus. After HIV destroys the immune system, the body is no longer able to control these viruses, and the infections manifest as cancer. Certain other immune deficiency states (e.g. common variable immunodeficiency and IgA deficiency) are also associated with increased risk of malignancy.
Cancer vaccines:
Preventative vaccines, like those that protect against viruses or the flu, are given before a person becomes sick.  In recent years, scientists have been attempting to develop therapeutic vaccines, with the first successful prostate cancer vaccine called Provenge approved in 2010 by the US FDA.  In contrast to preventive vaccines the therapeutic cancer vaccines are given to a person who already has the disease. Therapeutic cancer vaccines are designed to treat cancer by boosting the immune system to fight against the cancer.
Cancer vaccines are active immunotherapies because they are meant to trigger the patient's immune system to respond. Cancer vaccines are targeted because they do not just boost the immune system in general, but because they cause the immune system to attack the cancer cells, honing in on one or more specific tumor antigens.

Examples of Cancer vaccines

         The examples of Cancer vaccines include: Tumor cell vaccines, Antigen Vaccines, Dendritic cell vaccines (Provenge), Anti-idiotype vaccines, DNA vaccines, Vector-based vaccines.   
A cancer vaccine may contain cancer cells, parts of cells, or purified tumor-specific antigens and is designed to increase the targeted immune response against cancer cells already present in the patient. A cancer vaccine may be combined with other substances or cells called adjuvants that help boost the immune response even further.
Cancer vaccines generally fall into two categories: a) cell-based cancer vaccines, which are created using cells from the patient's own cancer that have been presented to and cultured with the patient's own immune system cells.  These activated immune cells from the patient are delivered back to the same patient with other proteins (e.g., IL-2) to further facilitate immune activation of these tumor antigen primed immune cells; and b) vector-based cancer vaccines in which an engineered virus, or other vector, is used to introduce cancer specific proteins and other molecules to the patient in order to stimulate the patient's immune system to recognize the tumor cells and fight the cancer.
Both approaches are designed to stimulate the patient's own immune system to attack tumor cells.