The Research involved genetically engineering Mice to increase levels of the BAFF (B-Cell activating factor), which is utilised by the immune system to generate B-Cells (which produce antibodies). The Scientists subsequently observed that the Immune System of the Mice with the increased hormone level would alter the bodies response to cells that were not marked "self", by increasing the amount of "T" regulatory cells which are used by the body to suppress T-Cell activity (T-Cells are the body's "Killer" cells). It was also noted that the altered response did not seem to relate to a defect in the T-Cells themselves.
This discovery may lead to improved success rates in organ transplant patients by reducing the need for patients to be given immunosuppressive drugs which can sometimes have toxic affects and also prevent the body from fighting normal pathogens like bacteria and viruses.
Further Technical Detail can be found in the Journal of Immunology.