Previous attempts to use gene therapy as a cancer treatment have foundered -- the genes didn't always end up in the part of the body where they were needed.

Now researchers have found a way to inject magnetic nanoparticles directly into a class of white blood cells known as monocytes.

An external magnet over a cancerous tumour then draws in the magnetised cells to the area where they are needed.

"The use of nanoparticles to enhance the uptake of therapeutically armed cells by tumours could herald a new era in gene therapy -- one in which delivery of the gene therapy vector to the diseased site is much more effective," said Professor Claire Lewis of the University of Sheffield, a lead researcher.

"This new technique could also be used to help deliver therapeutic genes in other diseases like arthritic joints or ischemic heart tissue."

Although the concept of magnetic targeting is not new, this is one of the first successful applications of the idea.

"Though the concept of magnetic targeting for drug and gene delivery has been around for decades, major technical hurdles have prevented its translation into a clinical therapy," said Professor Jon Dobson from the University of Keele, a fellow researcher.

"By harnessing and enhancing the monocytes' innate targeting abilities, this technique offers great potential to overcome some of these barriers and bring the technology closer to the clinic."

Gene therapy has shown great promise, although clinical trials have revealed serious problems -- children have developed leukaemia as a result of treatment, and an adult patient died during a 1999 trial.

"We would hope that this will be safer because we are using a natural mechanism in the body and patients' own white blood cells to deliver the gene therapy," Professor Lewis said.

"We're simply amplifying that with this magnetic approach."