Final Activity Report Summary - CD8 - TREAT (CD8+ T regs in allergen tolerance) Allergic diseases and asthma pose an important and increasing problem for approximately 40 % of the world population. These diseases seriously affect the life-quality of the patients and cause immense health care expenses, being sometimes even life threatening. Therefore, research that contributes to a better understanding of allergic diseases underlying mechanisms and to the development of therapies is of high public concern. The CD8 - TREAT project, supported by the Marie Curie activity of the European Union, was set up to improve therapy and prevention of allergic diseases by elucidating the immunological mechanisms underlying allergen tolerance. The principal idea was to invent treatment strategies that enhanced the organisms inherent capability to suppress inflammation. Currently, the treatments are mainly designed to control inflammation and disease symptoms. Thus, this project was intended to support suppression and to control immune responses in a more specific way instead of unspecific inhibition of inflammation. T cells with regulatory activity, the so called Treg cells, were shown to be of great importance for the control of immune responses to infectious agents as well as for the tolerance of harmless environmental antigens like allergens or of the body´s own constituents. Research which was performed at the Swiss Institute of Allergy and Asthma Research (SIAF) in Davos, Switzerland, during the last two years in the CD8 - TREAT project investigated the immune regulatory role of human CD8+ T cells. Our research work led to the identification of a new CD8+ T cell population with the characteristics of Treg cells in human tonsils. Because of their localisation at the gateway of the respiratory and alimentary tracts, tonsils were important for the discrimination between harmless and harmful potential pathogens. Surprisingly, cells expressing pro-inflammatory cytokines were also present in this regulatory population. Interestingly from a therapeutic point of view, it was possible to generate CD8+ T cells that possessed the capability to control other cells of the immune system. The project findings suggested that CD8+ Treg cells located in the tonsils were involved in the control of immune responses to up-taken antigens and might suppress other T cells even in a pro-inflammatory environment. However, further studies were needed to investigate how these cells contributed to tolerance. Relevant outcomes could lead to the development of immune modulating therapies in the future.