The Characterization of CD8+ T Cells as a Potential Mechanism of Disease in Immune Thrombocytopenia

Abstract

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by a low platelet count (less than 100 x 10^9 platelets/L) and an increased risk of bleeding. ITP is difficult to diagnose and manage due to the deficiencies in our understanding of the pathophysiological mechanisms leading to thrombocytopenia. Anti-platelet autoantibodies are believed to be the primary mechanism of thrombocytopenia in ITP. In this thesis, I demonstrate that autoantibodies can only be detected in half of all ITP patients; therefore, other mechanisms should be investigated. CD8+ T cells have been implicated as a mechanism of disease in ITP, but platelet-specific CD8+ T cells have yet to be identified. I have characterized CD8+ T cells in ITP patients and found that platelet-specific CD8+ T cells can be detected in ITP patients. These platelet-specific CD8+ T cells can also be detected in healthy individuals, so they are not specific to ITP. However, regulatory defects were observed in ITP patients and CD8+ T cell activity was elevated in ITP patients relative to healthy individuals and thrombocytopenic non-ITP patients. Investigating whether platelet-specific CD8+ T cells can actively participate in platelet destruction and underproduction will be an essential step towards better understanding the role of CD8+ T cells as a disease mechanism in ITP, which will lead to improvements in the management of ITP.