A Missing PD-L1/PD-1 Coinhibition Regulates Diabetes Induction by Preproinsulin-Specific CD8 T-Cells in an Epitope-Specific Manner

作者：Schuster Cornelia; Brosi Helen; Stifter Katja; Boehm Bernhard O; Schirmbeck Reinhold^*

来源：PLos One, 2013, 8(8): e71746.

DOI：10.1371/journal.pone.0071746

Coinhibitory PD-1/PD-L1 (B7-H1) interactions provide critical signals for the regulation of autoreactive T-cell responses. We established mouse models, expressing the costimulator molecule B7.1 (CD80) on pancreatic beta cells (RIP-B7.1 tg mice) or are deficient in coinhibitory PD-L1 or PD-1 molecules (PD-L1(-/-) and PD-1(-/-) mice), to study induction of preproinsulin (ppins)-specific CD8 T-cell responses and experimental autoimmune diabetes (EAD) by DNA-based immunization. RIPB7.1 tg mice allowed us to identify two CD8 T-cell specificities: pCI/ppins DNA exclusively induced K-b/A(12-21)-specific CD8 T-cells and EAD, whereas pCI/ppins Delta A(12-21) DNA (encoding ppins without the COOH-terminal A(12-21) epitope) elicited K-b/B22-29-specific CD8 T-cells and EAD. Specific expression/processing of mutant ppins Delta A(12-21) (but not ppins) in non-beta cells, targeted by intramuscular DNA-injection, thus facilitated induction of (K)b/B22-29-specific CD8 T-cells. The A(12-21) epitope binds K-b molecules with a very low avidity as compared with B22-29. Interestingly, immunization of coinhibition-deficient PD-L1(-/-) or PD-1(-/-) mice with pCI/ppins induced K-b/A(12-21)-monospecific CD8 T-cells and EAD but injections with pCI/ppins Delta A(12-21) did neither recruit K-b/B22-29-specific CD8 T-cells into the pancreatic target tissue nor induce EAD. Ppins Delta A(12-21)/(K-b/B22-29)-mediated EAD was efficiently restored in RIP-B7.1(+)/PD-L1(-/-) mice, differing from PD-L1(-/-) mice only in the tg B7.1 expression in beta cells. Alternatively, an ongoing beta cell destruction and tissue inflammation, initiated by ppins/(K-b/A(12-21))-specific CD8 T-cells in pCI/ppins+pCI/ppins Delta A(12-21) co-immunized PD-L1(-/-) mice, facilitated the expansion of ppins Delta A(12-21)/(K-b/B22-29)-specific CD8 T-cells. CD8 T-cells specific for the high-affinity K-b/B22-29-(but not the low-affinity K-b/A(12-21))-epitope thus require stimulatory help from beta cells or inflamed islets to expand in PD-L1-deficient mice. The new PD-1/PD-L1 diabetes models may be valuable tools to study under well controlled experimental conditions distinct hierarchies of autoreactive CD8 T-cell responses, which trigger the initial steps of beta cell destruction or emerge during the pathogenic progression of EAD.

• 出版日期2013-8-19