Clinical trials have indicated that autologous hematopoietic stem cell transplantation (HSCT) can persistently suppress inflammatory disease activity in a subset of patients with severe multiple sclerosis (MS), but the mechanism has remained unclear. To understand whether the beneficial effects on the course of disease are mediated by lympho-depletive effects alone or are sustained by a regeneration of the immune repertoire, we examined the long-term immune reconstitution in patients with MS who received HSCT. After numeric recovery of leukocytes, at 2-yr follow-up there was on average a doubling of the frequency of naive CD4+ T cells at the expense of memory T cells. Phenotypic and T cell receptor excision circle (TREC) analysis confirmed a recent thymic origin of the expanded naive T cell subset. Analysis of the T cell receptor repertoire showed the reconstitution of an overall broader clonal diversity and an extensive renewal of clonal specificities compared with pretherapy. These data are the first to demonstrate that long-term suppression of inflammatory activity in MS patients who received HSCT does not depend on persisting lymphopenia and is associated with profound qualitative immunological changes that demonstrate a de novo regeneration of the T cell compartment.

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High-dose immunosuppression and AHST were performed with acceptable toxicity in a small number of patients with newly diagnosed type 1 DM. With AHST, beta cell function was increased in all but 1 patient and induced prolonged insulin independence in the majority of the patients.

IMPORTANCE Hematopoietic stem cell transplantation (HSCT) represents a potentially useful approach to slow or prevent progressive disability in relapsing-remitting multiple sclerosis (MS). OBJECTIVE To compare the effect of nonmyeloablative HSCT vs disease-modifying therapy (DMT) on disease progression.

CCUMULATED CLINICAL EXPErience indicates that there is an inverse association between beta-cell function and chronic complications of type 1 diabetes mellitus (DM)-the higher the Cpeptide levels (an indirect measure of viable beta-cell function), the lower the incidence of microvascular complications of type 1 DM. 1 Since the establishment of the autoimmune etiology of type 1 DM in the late 1970s, many clinical trials analyzing the effects of different types of immune interventions demonstrated that beta-cell preservation is an achievable target in different degrees. 2,3 Based on the theory of possible reconstitution of immune tolerance after "immunologic reset" with autologous nonmyeloablative hematopoietic stem cell transplantation (HSCT), 4 in 2007, we reported a phase 1/2 trial evaluating the safety and metabolic effects of autologous nonmyeloablative HSCT in 15 patients with newly diagnosed type 1 DM. 5 The majority of pa-Author Affiliations are listed at the end of this article.