The trial results are preliminary and do not prove gene therapy could halt arthritis but they provide a strong indication the therapy could work and that it can be done safely, an issue that has generated controversy in recent years, reports UPI.

"These data demonstrate that it is possible to transfer genes to human joints ... in a safe and acceptable manner," the research team, headed by Christopher H. Evans, an orthopaedic surgeon at Harvard Medical School, said.

wrote in the online issue of the Proceedings of the National Academy of Sciences.

The safety of gene therapy - using a virus or other vector to insert a gene into cells to help correct a disease - has been called into question in recent years due to high-profile cases involving patient deaths or injuries.

In the current study the researchers used a vector that was linked to the death of three boys in another case and were keenly aware of the safety concerns surrounding this procedure.

They decided to extend their follow-up of patients who received the therapy to five years to minimize the possibility of undetected dangerous side effects.

"Because of the critical importance of safety in the application of gene therapy to non-lethal diseases, we delayed publication of these data until a five-year period had passed without clinical or molecular evidence of side-effects," the team wrote.

In the study, nine women ranging in age from 49 to 73 who were afflicted with rheumatoid arthritis underwent the gene-therapy procedure at the University of Pittsburgh School of Medicine from 1996 to 1999.

Two of four knuckles in their hand were injected with cells that had been modified with a gene known as IL-1 Ra, which is thought to block the inflammation process that occurs in rheumatoid arthritis. Two knuckles received untreated cells.

The researchers did not find any indication of serious side effects related to the gene-therapy procedure but did detect evidence indicating the technique could halt rheumatoid arthritis. The joints treated with the modified cells showed high levels of IL-1 Ra.

This indicated the gene-therapy procedure successfully inserted the gene into the synovial cells, which line joints and secrete a fluid that allows bones to move painlessly against each other. The cells also produced lesser amounts of chemicals that are known to induce inflammation in arthritis than their non-treated counterparts.