Insect lure helps scientists fish out drug targets
overcomes one of the bottlenecks in research into the immune system
- identifying the antigens in a disease that stimulate attack by
the immune system.
The scientists are already using the library-based technique to identify new drug targets in rheumatoid arthritis and develop cancer vaccines. The method extends a widely used technique, called library display, to more complex proteins.
"Our technique allows us to fish in a vast library of protein fragments for the specific ones that bind to T cells and trigger an immune-system attack," said John Kappler, an immunologist at the National Jewish Medical Research Centre and the Howard Hughes Medical Institute.
"We believe that researchers using this technique will extend its usefulness beyond T cells and antigens to interactions involving a wide variety of biologically important proteins," he added.
T cells carry receptors that can recognise a specific protein fragment or epitope. Cells known as antigen-presenting cells (APCs) display on their surfaces these epitopes, bound to a molecular class known as the major histocompatibility complex (MHC). When a T cell encounters a protein-MHC complex it latches on, becomes activated and mounts an immune response.
It is very difficult to determine experimentally what protein-MHC complex a particular T cell receptor binds, and so where the immune system is aiming its attack. But if this is known, it raises the possibility of designing drugs that block this target, switching off an inappropriate response in autoimmune disease or an allergic response.
Using genetic constructs and baculoviruses, the team created a library of insect cells, each one displaying a single MHC molecule holding a specific protein fragment. They then fished in this ocean with soluble T cell receptors containing fluorescent tags. When the receptors bound distinct MHC/protein complexes, the researchers isolated the insect cells displaying them.
They then sequenced DNA in the baculovirus infecting the insect cells, and identified the protein fragments that the receptor bound. In this way, they could identify the specific protein fragment any given T cell is designed to bind.
Kappler et al are currently working with other researchers to identify protein target in the autoimmune disease rheumatoid arthritis. Other researchers have identified specific T cells that are more common among patients with rheumatoid arthritis, but have been unable to identify the proteins in the body that they bind. If they can identify these proteins, it could have major implications for both prevention and treatment of the disease.
The authors of the study, which is published in the April issue of PloS Biology, also note that the technique is not limited to identifying epitopes, but could also be more widely applied to protein-protein interactions.
They are also working with other researchers who are developing cancer vaccines, as well as another group trying to identify the protein that works in concert with beryllium molecules to sensitise the immune system. Beryllium exposure can lead to a severe cell-mediated immune response that can lead to a chronic condition associated with progressive deterioration in lung function.
