• Peter J Darlington, Tarik Touil, Jean-Sebastien Doucet, Denis Gaucher, Joumana Zeidan, Dominique Gauchat, Rachel Corsini, Ho Jin Kim, Martin Duddy, Farzaneh Jalili, Nathalie Arbour, Hania Kebir, Jacqueline Chen, Douglas L Arnold, Marjorie Bowman, Jack Antel, Alexandre Prat, Mark S Freedman, Harold Atkins, Rafick Sekaly, Remi Cheynier, Amit Bar-Or, and Canadian MS/BMT Study Group.
• Neuroimmunology Unit, Montreal Neurological Institute, McGill University, and Laboratory of Immunology, University of Montreal Hospital Research Centre, Montreal, Quebec, Canada.
• Ann. Neurol. 2013 Mar 1;73(3):341-54.

ObjectiveTo define changes in phenotype and functional responses of reconstituting T cells in patients with aggressive multiple sclerosis (MS) treated with ablative chemotherapy and autologous hematopoietic stem cell transplantation (HSCT).MethodsClinical and brain magnetic resonance imaging measures of disease activity were monitored serially in patients participating in the Canadian MS HSCT Study. Reconstitution kinetics of immune-cell subsets were determined by flow cytometry, whereas thymic function was assessed using T-cell receptor excision circle analyses as well as flow cytometry measurements of CD31+ recent thymic emigrants (RTEs). Functional assays were performed to track central nervous system-autoreactive antigen-specific T-cell responses, and the relative capacity to generate Th1, Th17, or Th1/17 T-cell responses.ResultsComplete abrogation of new clinical relapses and new focal inflammatory brain lesions throughout the 2 years of immune monitoring following treatment was associated with sustained decrease in naive T cells, in spite of restoration of both thymic function and release of RTEs during reconstitution. Re-emergence as well as in vivo expansion of autoreactive T cells to multiple myelin targets was evident in all patients studied. The reconstituted myelin-specific T cells exhibited the same Th1 and Th2 responses as preablation myelin-reactive T cells. In contrast, the post-therapy T-cell repertoire exhibited a significantly diminished capacity for Th17 responses.InterpretationOur results indicate that diminished Th17 and Th1/17 responses, rather than Th1 responses, are particularly relevant to the abrogation of new relapsing disease activity observed in this cohort of patients with aggressive MS following chemoablation and HSCT.Copyright © 2013 American Neurological Association.

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