The Type and Frequency of Immunoregulatory CD4⁺ T-Cells Govern the Efficacy of Antigen-Specific Immunotherapy in Nonobese Diabetic Mice

Abstract

Antigen-specific immunotherapy, an approach to selectively block autoimmune diabetes, generally declines in nonobese diabetic (NOD) mice as disease progresses. To define the parameters influencing the efficacy of antigen-specific immunotherapy once diabetes is established, plasmid DNA (pDNA) vaccination was used to suppress autoimmune-mediated destruction of syngeneic islet grafts in diabetic NOD recipients. pDNAs encoding a glutamic acid decarboxylase 65 (GAD65)-Ig molecule (pGAD65), interleukin (IL)-4 (pIL4), and IL-10 (pIL10) significantly delayed the onset of recurrent diabetes compared with pGAD65+pIL10-vaccinated recipients. Despite differences in efficacy, a similar frequency of GAD65-specific CD4⁺ T-cells secreting IL-4, IL-10, or interferon-γ were detected in mice treated with pGAD65+pIL4+pIL10 and pGAD65+pIL10. However, the frequency of FoxP3-expressing CD4⁺CD25⁺CD62L^hi T-cells was increased in the renal and pancreatic lymph nodes of diabetic recipients vaccinated with pGAD65+pIL4+pIL10. These immunoregulatory CD4⁺CD25⁺ T-cells (CD4⁺CD25⁺ Treg) exhibited enhanced in vivo and in vitro suppressor activity that partially was transforming growth factor-β dependent. Furthermore, duration of islet graft protection in pGAD65+pIL4+pIL10-vaccinated diabetic recipients correlated with the persistence of CD4⁺CD25⁺ Treg. These data demonstrate that the frequency and maintenance of FoxP3-expressing CD4⁺CD25⁺ Treg influence antigen-induced suppression of ongoing β-cell autoimmunity in diabetic recipients.