Peptide‐Pulsed Immature Dendritic Cells Reduce Response to β Cell Target Antigens and Protect NOD Recipients from Type I Diabetes

Our previous work demonstrated peptide-pulsed mature myeloid dendritic cells (DC) presenting β cell antigens induce tolerance. Here we determine whether immature DC (iDC) presenting dominant (insulin β9-23 chain, proinsulin C19-A3) or ignored (glutamic acid decarboxylase 65 78-97 ) antigen determinants promote tolerance. Nonobese diabetic (NOD) mice were given injections of either unpulsed or peptide-pulsed myeloid iDC beginning at 9 weeks of age for 3 consecutive weeks. Diabetes incidence in recipients of unpulsed iDC was comparable to unmanipulated animals (∼80%), whereas GAD65 78-97 pulsed iDC recipients were protected from the disease (P = 0.05). We also analyzed splenic T cell proliferation responses to the panel of studied peptides in diabetic and nondiabetic recipients. When stimulated with insulin or proinsulin peptide, nondiabetic mice receiving the peptide-pulsed iDC had a 21- to 31-fold or 3.9- to 9.0-fold reduction in T cell response, respectively, as compared to the response of diabetic unpulsed recipients. However, only a 2.6- to 3.1-fold reduction in response to β chain peptide, and a 1.5-to 3.4-fold reduction in proinsulin response were observed in diabetic mice receiving peptide-pulsed iDC. The reduction was not specific to the immunizing peptide, as reduced proliferation was observed to other diabetes-target peptides. We conclude that protective iDC-based therapies require target antigen presentation, and ignored determinants may be preferable perhaps due to an available naive T cell repertoire. In addition, iDC presenting peptides induce a nonspecific reduction in T cell responses to β cell antigens, possibly through the induction of regulatory T cells.