New York, Nov 6 (IANS): US scientists have developed a new gene therapy that can help reduce the development of cancer cells that are an infrequent but dangerous by-product of gene therapies.

Gene therapy holds potential for treating genetic diseases by replacing defective genes with repaired ones.

It has shown promise in clinical trials but has also been set back by difficulties in delivering genes, getting them to work for a long time and safety issues.

The findings were converted into a stem cell gene therapy to target a life-threatening immune deficiency in newborns called Severe Combined Immunodeficiency (SCID-X1), also known as 'Boy in the Bubble Syndrome' -- a genetic disorder which results in an extreme vulnerability to infectious diseases.

"Our goal is to develop a safe and effective therapy for SCID-X patients and their families," said Grant Trobridge, Associate Professor at Washington State University.

The researchers developed a vector from a foamy retrovirus -- a natural choice for gene therapy because they work by inserting their genes into a host's genome.

The team altered it to change how it interacts with a target stem cell so it would insert itself into safer parts of the genome. They found that it integrated less often near potential cancer-causing genes.

Unlike other retroviruses, they don't normally infect humans. They also are less prone to activate nearby genes, including genes that might cause cancer.

The researchers expect that the therapy could be ready for clinical trials within five years.

The developments are published in the journal Scientific Reports.