The study could provide further evidence of the Mouse Mammary Tumour Virus' (MMTV) role and opens up a number of important avenues for future research.
However, further studies on the effects of infection of human cells with MMTV as well as on the development of diagnostic procedures are needed and, if a role for the involvement of the virus in cancer can be shown, the development of an effective treatment.
The team from the Viennese Christian-Doppler-Laboratory for Gene Therapeutic Vector Development (University of Veterinary Medicine, Vienna), developed a recombinant MMTV carrying an inserted fluorescence gene.
These were able to successfully infect human cells of diverse origin, e.g. breast or cervix tumour derived cells.
The viruses multiplied and also infected further cells and could be seen under the microscope with the help of a fluorescent light source - proof of successful infection.
"The efficiency of infection of human cells was - in the best case - comparable with that obtained during infection of mouse cells, in the worst case only ten times lower," the study commented.
Infection requires intact MMTV envelope proteins and is blocked by heat inactivation or specific anti-viral neutralising antibodies.
News of this finding has rekindled the discussion about a possible role for MMTV in human breast cancer.
"MMTV can be anything from an innocent passenger to a possible factor involved in the development of breast cancer, although the reality probably lies somewhere in between these two extremes," said Dr Francoise Rouault, who has spent the last eight years researching MMTV.
After a number of scientific reports stretching back to the early 70's that an MMTV like agent may be involved in human breast cancer, it was only recently that MMTV DNA could be convincingly and reproducibly shown to be present in human breast cancer specimens.
Despite this intriguing finding suggestive of successful infection, other scientists said that the presence of MMTV DNA was merely due to contamination rather than infection.
Their arguments appeared to be bolstered by other studies showing that MMTV does not have the necessary key to successfully infect human cells.
Rouault said: "Although some research results suggest it - it has not been shown that MMTV directly causes human breast cancer."
"It is however known that MMTV can cause massive holes in the immune system and this may lead to a diminished ability of the body's natural defences to recognise and destroy cancer cells."
Even if MMTV turns out not to cause breast cancer in humans, the data is also exciting for a completely different reason since MMTV can also be engineered as a means of efficiently delivering therapeutic genes.
Indeed, this Trojan horse strategy may ironically prove particularly useful in the arsenal of weapons available for the future treatment of breast cancer.
The results are published in the recent issue of Cancer Research.