PATIENTS with crippling diseases such as multiple sclerosis should beware of expensive stem-cell "wonder cures" that have never been properly tested, leading medical research groups say today.

While stem cells offer great promise for treating many disorders, extravagant claims made for therapies costing more than £10,000 a time do not stand up to scientific scrutiny, they say.

In a letter to The Times, 14 medical charities and research funders warn patients that there is no evidence to support the benefits attributed to unorthodox stem-cell treatments, which could carry a risk of infection, immune system rejection and even cancer.

Premature use of stem cells to treat disease, before safety and effectiveness have been evaluated in clinical trials, also threatens to set back mainstream research that promises genuinely better therapies, they say. The signatories include Professor Colin Blakemore, chief executive of the Medical Research Council, Lord Patel, of the UK Stem Cell Bank, and the heads of the MS Society, the Parkinson’s Disease Society, the Juvenile Diabetes Research Foundation and the Alzheimer’s Society.

Stem cells have the capacity to form a wide variety of tissue types, and could be used to replace cells and organs that are damaged or destroyed in conditions such as MS, diabetes and Parkinson’s disease. The most powerful are found in embryos, but other less malleable types can also be extracted from the adult body and from umbilical cord blood.

Only a handful of treatments based on adult and cord blood stem cells have been licensed in the UK, principally for treating leukaemia and eye and skin disorders. But some foreign clinics offer stem-cell injections for other conditions, chiefly MS, and for cosmetic surgery.

Several dozen British MS patients have travelled to a centre in the Netherlands to receive cord blood stem cells from a Swiss company called Advanced Cell Therapeutics (ACT) at a cost of up to £13,500. The Dutch clinic is one of two under investigation by the authorities. The ACT procedure was banned in the Irish Republic this year, prompting the company to consider offering it in international waters on the Swansea to Cork ferry.

While some patients have claimed dramatic improvements and provided glowing testimonials, no scientific evidence has been published showing that the treatment works.

Most mainstream researchers are sceptical that the grafts perform as they are purported to, and ascribe apparent benefits to a short-lived placebo effect.

Scientists are concerned that desperate patients are being exploited. "We advise those who are desperate for cures or attracted to cosmetic surgery to be wary of claims being made by clinics offering these treatments," the letter says.

An accidental death from a treatment that has not been adequately assessed for safety could also turn public opinion against more carefully regulated stem-cell research. "We worry that those cutting corners risk discrediting the field as well as betraying patients," the letter says.

Professor Blakemore said that the potential of stem cells would best be realised by cautious progress and rigorous clinical trials. "This is a delicately poised field of research, with a difficult ethical background. Just one application of maverick stem-cell science that leads to cancer could set back the legitimate field by years, if not decades."

Professor Robin Lovell-Badge, a stem-cell expert of the National Institute for Medical Research, said that there was preliminary evidence that cord blood stem cells could form other kinds of cell, but these did not appear to have a long-term therapeutic effect. It was also hard to see how injecting them could ensure they reached the parts of the body where they were needed.

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