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

Abstract

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. RIP-B7.1 tg mice allowed us to identify two CD8 T-cell specificities: pCI/ppins DNA exclusively induced Kb/A12–21-specific CD8 T-cells and EAD, whereas pCI/ppinsΔA12–21 DNA (encoding ppins without the COOH-terminal A12–21 epitope) elicited Kb/B22–29-specific CD8 T-cells and EAD. Specific expression/processing of mutant ppinsΔA12–21 (but not ppins) in non-beta cells, targeted by intramuscular DNA-injection, thus facilitated induction of Kb/B22–29-specific CD8 T-cells. The A12–21 epitope binds Kb 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 Kb/A12–21-monospecific CD8 T-cells and EAD but injections with pCI/ppinsΔA12–21 did neither recruit Kb/B22–29-specific CD8 T-cells into the pancreatic target tissue nor induce EAD. PpinsΔA12–21/(Kb/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/(Kb/A12–21)-specific CD8 T-cells in pCI/ppins+pCI/ppinsΔA12–21 co-immunized PD-L1−/− mice, facilitated the expansion of ppinsΔA12–21/(Kb/B22–29)-specific CD8 T-cells. CD8 T-cells specific for the high-affinity Kb/B22–29- (but not the low-affinity Kb/A12–21)-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.

Exploring the induction of preproinsulin-specific Foxp3+ CD4+ Treg cells that inhibit CD8+ T cell-mediated autoimmune diabetes by DNA vaccination

“…1b,c ; Supplementary Fig. S1a, b ) 37 38 . To investigate whether the modified ppinsΔA 12-21 antigen induces a prophylactic immunity, we immunized PD-L1 −/− or PD-1 −/− mice with pCI/ppinsΔA 12-21 followed by an injection with the diabetogenic pCI/ppins vector at day 12 post vaccination.…”

“…1a ) 37 . A vector-encoded, mutant ppinsΔA12-21 antigen (lacking the critical K b /A12-21 epitope) did not induce autoimmune diabetes in PD-L1 −/− or PD-1 −/− mice 38 . We thus hypothesized that the mutant pCI/ppinsΔA12-21 vector could elicit a prophylactic, Treg cell-mediated immunity in PD-L1 −/− and PD-1 −/− mice and protect them from autoimmune diabetes induced by a subsequent injection of the diabetogenic pCI/ppins vector.…”

“…The major advantage of DNA-based immunization is the flexibility in the design of vectors and the manipulation of endogenous antigen expression and/or antigen processing/presentation in distinct cellular compartments by molecular engineering. We have established a novel diabetes model in coinhibition-deficient PD-L1 −/− (B7-H1 −/− ) 35 and PD-1 −/− mice 36 to characterize the ppins-specific induction (or prevention) of autoreactive CD8 + T cells 37 38 . A single injection of ppins-encoding (pCI/ppins) DNA into PD-1- or PD-L1-deficient mice efficiently induced severe autoimmune diabetes 37 .…”

A dominant insulin-specific and islet-destructive T-cell response is sufficient to activate CD8 T cells directed against the fatty-acid receptor GPR40

“…The injection of pCI/ppins, 6,7 but not of pCI/GPR40, into PD-L1 −/− mice induced autoimmune diabetes ( Fig. 1g).…”

Transgenic expression of proinsulin to inactivate insulin-specific CD8+ T-cell responses in autoimmune diabetes

“…Likewise, accelerated onset and complete penetrance of diabetes by 15 weeks of age was observed for PD-1-deficient NOD mice, and islet-infiltrating CD8 + T cells displayed a strong IFN-γ bias (Wang et al, 2005). The PD-1/PD-L1 inhibitory pathway has also been implicated in a model of induced autoimmune diabetes in which RIP.B7-1 mice were administered preproinsulin-encoding plasmid DNA to induce preproinsulin-specific CD8 + T cells (Schuster et al, 2013). The relative affinity of epitopes derived from the preproinsulin-encoding DNA influenced co-stimulation dependence in that, CD8 + T cells specific for the lower affinity MHC-binding epitope, preproinsulin A12-21, became diabetogenic in the absence of transgenic B7-1 and PD-1 expression.…”