Date of Graduation
8-2015
Document Type
Dissertation (PhD)
Program Affiliation
Immunology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Yeonseok Chung, Ph.D.
Committee Member
Rick A. Wetsel, Ph.D.
Committee Member
Stephen E. Ullrich, Ph.D.
Committee Member
Kimberly S. Schluns, Ph.D.
Committee Member
Ba-Bie Teng, Ph.D.
Committee Member
Dat Q. Tran, M.D.
Abstract
Excessive follicular helper T (Tfh) cell responses to self-antigens are associated with antibody-mediated autoimmune diseases in humans including systemic lupus erythematosus (SLE). Numeral and functional aberrations of T regulatory T (Treg) cells are common in patients with autoimmune diseases. Although different types of immunosuppressive agents have been used clinically to treat antibody-mediated autoimmune diseases, they generally have side effects due to the lack of target-specificity. To minimalize the adverse effects, there is a need to develop target-specific therapeutics which specifically control auto-reactive B cell responses and auto-reactive Tfh cell responses. Recent studies unveiled that Foxp3+ Treg cells expressing CXCR5 can migrate into the germinal center (GC) zone where they specifically suppress GC reactions in vivo, presumably by directly suppressing B cells and/or Tfh cells. These CXCR5+ Foxp3+ Treg cells are termed as follicular regulatory T (Tfr) cells. Due to their ability to specifically suppress Tfh cell and GC B cell responses, use of Tfr cells may be a promising target-specific therapy for the treatment of autoantibody-mediated autoimmune diseases. To evaluate the role of Tfr cells in autoantibody-mediated autoimmune diseases, we employed a BXD2 mouse model of spontaneous autoimmune lupus. Immune balance between Tfh and Tfr cell responses is crucial for the prevention of self-destructive antibody generation. However, the contribution of Tfh cells and Tfr cells to auto-reactive B cell responses in the BXD2 strain had not been evaluated. Therefore, we examined Tfh, Tfr and other relevant immune cellular responses in this autoimmune strain. We found no differences in both the frequency of Th17 cells and the levels of IL-17 in the circulation between wild-type and BXD2 mice. By contrast, the frequency of Tfh cells was significantly increased, and the numbers of Tfh cells were positively correlated with the levels of autoantibodies. In addition, we observed that IL-21-producing Tfh cells, but not IL-17-producing Th17 cells, efficiently promoted the production of IgG from BXD2 B cells in vitro. These results supported the role of Tfh cells in the development of auto-reactive B cell responses. In addition, the frequency of Tfr cells was reduced in BXD2 mice. Therefore, imbalance between Tfh cells and Tfr cells in BXD2 mice likely caused the self-destructive antibody generation, thereby providing additional support that Tfr cell-based immunotherapy may ameliorate antibody-mediated autoimmunity. Unfortunately, sufficient numbers of Tfr cells that will be required for immunotherapy will be difficult to obtain since they are only found in low frequency in vivo. To address this problem, we employed retroviral transduction of CXCR5 onto Foxp3+ Treg cells, which are more abundant and less difficult to purify than Tfr cells. We termed these engineered CXCR5 overexpressing Foxp3+ Treg cells as eTfr cells. We demonstrated that transduction of CXCR5 in the eTfr cells did not affect the expression of other genes important for Treg or Tfh cell function. Furthermore, eTFr cells migrated in response to CXCL13 and had T cell suppressive capacity in vitro, demonstrating that eTfr cells maintained critical Tfr cell-like properties in vitro and were potentially a cell source for Tfr cell-based immunotherapy. To test the therapeutic potential of the eTfr cells, we performed in vivo adoptive co-transfer experiments using TCRβ-deficient mice. Unfortunately, the results from these in vivo investigations were inconclusive, indicating the further refinement of the model system will be required to determine the viability of the eTfr therapeutic approach for the autoantibody-mediated autoimmune disease. In summary, we demonstrated that imbalance between Tfh cell and Tfr cells and IL-21, produced by Tfh cells, lead to auto-reactive GC B cell responses in BXD2 mice, suggesting that similar imbalances may have relevance in human autoantibody-mediated autoimmune diseases. Moreover, eTfr cells can migrate in response to CXCL13 and suppress T cell responses in vitro, supporting the possibility that eTfr cells may provide a novel immunotherapeutic approach for the treatment of antibody-mediated autoimmune disorders.
Keywords
Tfh, Tfr, Autoimmune disease, Autoantibody, BXD2, IL-21