Monday, January 29, 2007

Infectious Cancer Cells

Some cancers are caused by infectious agents, such as viruses that cause cancer by infecting and transforming host cells. For example, Epstein-Barr virus (EBV) is implicated in Burkitt's lymphoma, nasopharyngeal carcinoma, and other cancers (review). For canine transmissible venereal tumor (CTVT), however, the tumor cell itself was thought to be the agent. To test this hypothesis, Murgia and colleagues isolated CTVT cells and non-cancerous blood cells from 40 different dogs on 5 continents, and determined their relationships by comparing nuclear and mitochondrial genetic markers. They conclude that all the tumors are clones of a single tumor that arose between 200 and 2,500 years ago. Although the tumor has a very unusual chromosome arrangement (aneuploid), it is stable. They also studied the highly polymorphic histocompatibility genes. Expression of histocompatibility proteins, which would block transplantation between different animals, is reduced but not extinguished on CTVT cells. Another study demonstrated that CTVT cells make TGF-beta1, which could also reduce the immune response. This surprising cell could provide ideas for inducing tolerance of allografts.
Claudio Murgia, Jonathan K. Pritchard, Su Yeon Kim, Ariberto Fassati, and Robin A. Weiss "Clonal Origin and Evolution of a Transmissible Cancer" Cell 126, 477–487, August 11, 2006

No comments: