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Study Shows Immune System Can Hurt As Well As Help Fight Cancer E-mail
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Researchers found that instead of fighting tumors, the protein C5a, which is produced during an immune response to a developing tumor, helps tumors build molecular shields against T-cell attack. Discovery could lead to new cancer treatments with fewer side effects

Researchers at the University of Pennsylvania School of Medicine have found that some proteins of the immune system can promote tumor growth. Investigators found that instead of fighting tumors, the protein C5a, which is produced during an immune response to a developing tumor, helps tumors build molecular shields against T-cell attack. These findings appeared online this week in Nature Immunology.

C5a is part of the complement system, one of the body's immune defenses against pathogens. When activated, the system's proteins rid the body of microbes and foreign cells. Many cancer treatments are aimed at boosting the immune system to kill tumors.

"Until now, everyone thought that the complement system was there to eliminate tumor cells. We found that in some conditions, the complement system can promote tumor growth, depending on the specific tumor and the specific environment in which the tumors are developing," says John Lambris, PhD, the Dr. Ralph and Sallie Weaver Professor of Research Medicine.

However, Penn researchers found that in a mouse model, activation of the complement system in tumor tissue leads to the generation of C5a, which recruits myeloid-derived suppressor cells (MDSC) to tumors. These MDSCs block the function of CD8+ T cells, which would normally dismantle a tumor.

Researchers also found that blocking the C5a receptor on cell surfaces impairs tumor growth at the same rate of Paclitaxel, a chemotherapy drug. This discovery could lead to new cancer treatments with far fewer side effects than chemotherapy, surmise the investigators.

"Researchers are trying to introduce immune therapies and anti-tumor vaccines, but most of these vaccines fail," says Lambris. "We show in this study a possible mechanism how to overcome this problem." Lambris and his team are conducting studies that apply the approaches outlined in this paper to five models of cancer.

In addition to Lambris, Penn co-authors are Maciej M. Markiewski, Robert A. DeAngelis, Salome K Ricklin-Lichtsteiner, Anna Koutoulaki, Fabian Benencia (now at the University of Ohio), and George Coukos, as well as Craig Gerard, Children's Hospital, Boston. The National Institutes of Health provided funding for this research.

This release and a related image can be viewed at http://www.uphs.upenn.edu/news/News_Releases/2008/09/immune-promote-tumor-growth.html

About Cancer

Cancer (medical term: malignant neoplasm) is the general name for a group of more than 100 diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not. The branch of medicine concerned with the study, diagnosis, treatment, and prevention of cancer is oncology.

Cancer cells can spread to other parts of the body through the blood and lymph systems. Most cancers are named for the organ or type of cell in which they start - for example, cancer that begins in the colon is called colon cancer; cancer that begins in basal cells of the skin is called basal cell carcinoma. Cancer types can be grouped into broader categories. The main categories of cancer include:
  • Carcinoma - a cancer which is derived from the lining cells, or epithelium, of an organ. There are 4 major types of epithelium in the body (Glandular, squamous, transitional, and pseudostratified). Some types are only found in a few select organs such as the lung (pseudostratified) or urinary bladder (transitional).  Carcinomas can arise from any of these epithelial types. For example, breast carcinoma is most commonly derived from the lining cells of the milk producing glands. A carcinoma with a glandular growth pattern is an adenocarcinoma.  Common adenocarcinomas include prostate, colon, and breast.  A carcinoma with a growth pattern resembling the squamous lining cells is termed a squamous cell carcinoma.  Common squamous cell carcinomas are found in the esophagus and skin.  However, any of these organs may have either type of carcinoma arising from it, although these latter diagnoses are exceedingly rare.
  • Central nervous system cancers - cancers that begin in the tissues of the brain and spinal cord.
  • Leukemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
  • Lymphoma - a cancer derived from the white blood cells that are present in the lymphoid tissues of the body.  These sites most commonly include the lymph nodes and spleen. However, lymphomas may arise from any organ and body site.
  • Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.

Today, millions of people are living with cancer or have had cancer. The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking, limiting time in the sun, being physically active, and eating a better diet. Half of all men and one-third of all women in the US will develop cancer during their lifetimes.

Although doctors often cannot explain why one person develops cancer and another does not, research shows that certain risk factors increase the chance that a person will develop cancer. Nearly all cancers are caused by abnormalities in the genetic material of the transformed cells. These abnormalities may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or viruses, bacteria, and certain hormones. Other cancer-promoting genetic abnormalities may be randomly acquired through errors in DNA replication, or are inherited, and thus present in all cells from birth.  Other common risk factors for cancer include:
  • Growing Older
  • Family history of cancer
  • Poor diet, lack of physical activity, or being overweight
  • Alcohol


 

 
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