Scientists say they have discovered how to "switch off" autoimmune diseases such as multiple sclerosis.
Researchers at the University of Bristol, who describe the work as an "important breakthrough", say it could improve the lives of millions around the world.
In their research, published today in Nature Communications, the team reveal how to stop cells from attacking healthy body tissue.
The team discovered how cells convert from being aggressive to protecting against disease, rather than the body's immune system destroying its own tissue by mistake.
It is hoped the insight will lead to the widespread use of antigen-specific immunotherapy as treatment for many autoimmune disorders.
Conditions which could be affected by the research include multiple sclerosis (MS), type 1 diabetes, Graves' disease and systemic lupus erythematosus.
MS alone affects around 100,000 people in the UK and 2.5 million people worldwide.
Professor David Wraith, of the university's School of Cellular and Molecular Medicine, led the "exciting" research - which was funded by the Wellcome Trust.
"Insight into the molecular basis of antigen-specific immunotherapy opens up exciting new opportunities to enhance the selectivity of the approach while providing valuable markers with which to measure effective treatment," Professor Wraith said.
"These findings have important implications for the many patients suffering from autoimmune conditions that are currently difficult to treat."
In the study, scientists were able to selectively target the cells that cause autoimmune disease by dampening down their aggression against the body's own tissue, while converting them into cells capable of protecting against disease.
This type of conversion has previously been applied to allergies, in a treatment known as "allergic desensitisation", but its application to autoimmune disorders has only recently been appreciated.
The researchers have now revealed how the administration of fragments of the proteins that are normally the target for the attack leads to correction of the autoimmune response.
Their work also shows that effective treatment can be achieved by gradually increasing the dose of antigenic fragment injected.
In order to analyse how this type of immunotherapy works, the scientists looked inside the immune cells themselves to see which genes and proteins were turned off by the treatment.
They found changes in gene expression that help explain how effective treatment leads to conversion of aggressor into protector cells.
The outcome is to reinstate self-tolerance, where an individual's immune system ignores its own tissues while remaining fully armed to protect against infection.
Researchers say that by specifically targeting the cells at fault, the immunotherapeutic approach avoids the need for immune suppressive drugs.
These drugs are often associated with side effects such as infections, development of tumours and disruption of natural regulatory mechanisms.
The treatment approach is currently undergoing clinical development through biotechnology company Apitope, a spin-out from the University of Bristol.
"Sequential transcriptional changes dictate safe and effective antigen-specific immunotherapy" is published in Nature Communications today.