**3.1. Hematopoietic Stem Cell Transplantation(HST ) for T1D**

abolic responses to glucose challenge, and rapidly increased frequency of antigenpresenting cells in spleen and pancreatic lymph nodes. It was also found that ATG therapy dramatically increased the frequency and functional activity of CD4+CD25+ regulatory T cells. Adoptive transfer/cotransfer studies of T1D support that ATG therapy induces a stable and transferable immunomodulatory repertoire *in vivo*. This study indicates that an induc‐ tion of immunoregulation, rather than simple lymphocyte depletion, contributes to the ther‐ apeutic efficacy of ATG therapy [56]. The same group reported that ATG therapy combined with granulocyte-colony-stimulating factor (G-CSF) was remarkably effective at reversing newly diagnosed diabetes in NOD mice and more efficacious than either agent alone. This combination also afforded durable reversal from disease (>180 days post-onset) in animals having pronounced hyperglycemia (i.e., up to 500 mg/dL). Mechanistically, this combination therapy resulted in both immunological and physiological benefits, showing increased CD4/CD8 ratios and splenic regulatory T cells, as well as increased pancreatic β cell area and

Our unpublished data show that ATG therapy preferentially depletes naïve T cells, and memory T cells are relatively preserved. In addition, ATG therapy largely spares CD4+CD25+ regulatory T cells. Of interest, ATG therapy does not deplete antigen-specific T cells but alters T cell responses to the previously experienced antigens, showing increased levels of Th2 and IL-10-producing Tr1 cells, which might contribute to ATG therapy-in‐ duced T1D protection. In addition, post-ATG therapy CD4+CD25+ regulatory T cells display memory-like T cells phenotypically, suggesting that those regulatory T cells might play an

Based on the animal studies described above, a couple of clinical trials using ATG, or ATG combined with G-CSF in human T1D are ongoing (www.clinicaltrials.gov/NCT0116157, www.clinicaltrials.gov/NCT00515099). The assessment of the effectiveness of ATG therapy

T1D is characterized by the autoimmune destruction of insulin-producing β cells with loss of insulin secretion. Patients with T1D have absolute requirement of insulin for survival. While insulin is effective in lowering blood glucose, hypoglycemia, even life-threatening hy‐ poglycemia, is almost unavoidable with insulin treatment, as exogenous insulin cannot ex‐ actly mimic the profile of physiological insulin secretion. Other limitations of insulin therapy include inconvenience of daily life, physical pain and high economic costs caused

Therefore, other strategies have been explored to preserve or restore β cell function in the hope that endogenous insulin secretion will achieve better glycaemic control while reducing episodes of severe hypoglycemia. As discussed above, immunotherapy, in particular the use of immunomodulatory drugs has pulled much efforts. Both experimental and clinical data demonstrate that some agents like anti-CD20 and anti-CD3 antibodies are effective in delay‐

important role in ATG therapy-induced long-lasting T1D protective effect.

in human T1D await the outcomes from these clinical trials.

**3. Cellular therapy of type 1 diabetes**

by recurrent insulin injections.

attenuated pancreatic inflammation [57].

572 Type 1 Diabetes

The use of bone marrow transplantation (BMT) as a potential treatment for T1D was first proposed in animal study in 1985 [58], showing that allogenic bone marrow transplantation could prevent insulitis and overt diabetes in NOD mice. This concept was further substanti‐ ated by later animal study [59].

The first clinical trial to use hematopoietic stem cell transplantation in T1D patients was re‐ ported in 2003 [60]. The objective of the study was to stop autoimmune destruction of β cells with immunosuppressive drugs and to "re-set"the impaired immunologic system with a re‐ constituted one using autologous HSCs in the expectations of preserving residual β cell mass and facilitating endogenous mechanisms of β cell regeneration. With the above consid‐ erations, 15 newly diagnosed T1D patients were enrolled. All received high-dose immuno‐ suppression followed by autologous hematopoietic stem cell transplantation (AHST) within 6 weeks of diagnosis. During a 7- to 36-month follow-up (mean 18.8 months), 14 patients be‐ came insulin-free. β cell function was improved as evidenced by the increase in C-peptide levels. No significant adverse effects were observed. The mechanism concerning the benefi‐ cial effects of HST is proposed to be associated with the generation of a more tolerant im‐ mune system, which blocks the autoimmune destruction of residual β cells. This hypothesis appears to be consistent with a recent clinical observation showing that intra-pancreatic au‐ tologous bone marrow infusion has no beneficial effects on long-standing T1D patients with absence of β cell function [61].

To date, it is unclear whether the beneficial effects of HST can be sustained because of the lack of long-term follow-up study. Second, it is not known whether the beneficial effects of HST are due to immune reconstitution *via* stem cell differentiation or modulating the func‐ tion of existing immune cells. Therefore, randomized controlled trials with prolonged fol‐ low-up are needed to confirm the results of current studies and to evaluate the full potential of this regimen as a therapeutic option for T1D.
