Immunological Mechanisms of Hematopoietic Stem Cell Transplantation in Multiple Sclerosis

Our goal is the elucidation of the mechanisms of action of autologous hematopoietic stem cell transplant (HSCT) and immunoablation by high-dose cyclophosphamide in multiple sclerosis (MS). The molecular pathogenesis of multiple sclerosis is poorly understood although T-cell mediated immune destruction of myelin is thought to be an important element. We hypothesize, and the results of previous studies suggest, that radical immuno-ablation characterized by a profound T cell depletion can arrest the progression of disease. Patients with MS with poor prognosis based on the rate of progression and refractoriness to approved treatments (interferon-beta, glatiramer acetate) will be enrolled in clinical trials at the collaborating institution (NWU-Dr. R. Burt; Dr. D Kerr, JHU) and will receive either immune ablation with cyclophosphamide and the antibody Campath-1 followed by reconstitution with autologous peripheral blood stem cells, a procedure similar to autologous bone marrow transplantation, or high-dose cyclophosphamide treatment without stem cell rescue. While the overall treatment-related mortality worldwide is approximately 10%, the collaborating institution and investigators have an outstanding safety record in performing the procedure with no fatal adverse events after having transplanted more than 30 transplants with a previously more aggressive regimen than the one that is in use now. The underlying rationale for this treatment is that immuno-ablation could eliminate myelin-reactive T cells which, in disease-susceptible individuals, may have been activated by previous exposure to environmental agents or other acquired mechanisms of immune dysregulation. In the proposed study we plan to address whether HSCT or immunoablation without stem cell rescue act beneficially in MS via the eradication of myelin-reactive T cells and reconstitution of a functional and non-autoimmune immune repertoire. To achieve this goal, we will compare peripheral blood T cell reactivities to myelin antigens before and after the treatment in 34 patients with MS. In parallel, to identify potential disease-mediating cells that do not recognize these myelin antigens, we will search for clonally expanded cells in the blood of MS patients before treatment employing molecular analysis of T cell receptor repertoire. Expanded T cell clones will be tracked during post-transplant follow-up of patients. If the eradication of certain clonotypes resulting from immuno-ablation correlates with disease remission, we will attempt to isolate these cells in culture from pre-treatment samples and determine their specificity using combinatorial peptide libraries. We would use the same approach in case of reappearance or new clonal expansions concomitant to disease relapses. We will combine these studies with a broader, unbiased approach that employs microarray technology to identify potential changes in gene expression profiles. This approach may also lead to the identification of novel therapeutic targets for pharmacological treatment.