Monitoring FoxP3 expression in Tolerance to Factor VIII (128.4)

Abstract

Abstract The FoxP3 transcription factor has emerged as a marker for regulatory T cells in the mouse. Our lab has identified a gene therapy based approach that allows us to abrogate the immune response in models for autoimmune diseases and the deleterious immune response in hemophilic patients being treated with factor VIII. Utilizing the FoxP3-GFP knock-in mouse that has been mated to our hemophilic fVIII−/− mouse, we are able to monitor fluctuations in the FoxP3 by flow cytometry. We have observed a relative increase in FoxP3 when tolerance is induced and a relative decrease when an immune response is initiated towards fVIII. We have also developed an in vitro model to follow FoxP3 as it changes in different populations with certain stimuli. Thus, we found that ~75% of CD4+CD25+ cells in a resting population are FoxP3 positive and 12% of all CD4+ cells are FoxP3+. After a single day of stimulation of splenocytes with soluble anti-CD3 antibody, nearly all the CD4+ cells become CD4+CD25+ while less than 6% remain FoxP3+. When presentation of anti-CD3 via Fc receptors is blocked, activation (monitored by CD25 levels) is abrogated, but FoxP3 levels also decrease. While this drop in the frequency of FoxP3 expression in CD4 T cells can be explained in part by the activation of the CD4+CD25− effector cells, we propose that anti-CD3 antibody is also actively diminishing FoxP3 levels in the regulatory T cell population. Supported by HL061883.