Mouse mammary tumor virus
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Mouse mammary tumor virus (MMTV) is a milk transmitted retrovirus like the HTL viruses, HI viruses and BLV.
MMTV becomes propagated from mouse to offspring by nursing the own or foster nursed puppets. It is contained as a DNA provirus integrated in the DNA of milk lymphocytes. The viruses become transported through the gastrointestinal tract to the Peyer's patches where they infect the new host's lymphocytes.
As the infected mice develop mammary tumors in adulthood, MMTV has inspired the up to now unsuccessful search for a human breast cancer virus. But the tumors caused by MMTV are benign and in general do not metastasize. Especially they do not metastasize to the bones as it is typical for human breast cancer. That makes the virus not useful as a model for human breast cancer, a malignant disease.
The MMTV genome codes for three main genes, which are called gag, pol and env and an open reading frame called orf. But it does not carry an oncogene inducing tumors. Instead it causes tumors by insertional mutagenesis.
MMTV has not been found in human breast cancer. What has been found were traces of one or more viruses similar to MMTV. So it is emerging that many human breast cancers contain part of the env gene of a virus that is very close to MMTV, but not the same. This env gene sequences are not found in the other cells of the body what suggests that they are of foreign origin.
Nevertheless, MMTV is an interesting virus for human diseases. It has superantigenic properties which destroy part of the immune system of the infected mouse. The well documented MMTV pathogenesis helps to understand the action of superantigens in human disease.
