Pathophysiological characteristics of preproinsulin-specific CD8+ T cells in subjects with juvenile-onset and adult-onset type 1 diabetes: A 1-year follow-up study

Retina-arrestin specific CD8+ T cells are not implicated in HLA-A29-positive birdshot chorioretinitis

BACKGROUND

HLA-A29-positive birdshot chorioretinitis (BCR) is an inflammatory eye disorder that is generally assumed to be caused by an autoimmune response to HLA-A29-presented peptides from retinal arrestin (SAG), yet the epitopes recognized by CD8+ T cells from patients remain to be identified.

OBJECTIVES

The identification of natural ligands of SAG presented by HLA-A29. To quantify CD8+ T cells reactive to antigenic SAG peptides presented by HLA-A29 in patients and controls.

METHODS

We performed mass-spectrometry based immunopeptidomics of HLA-A29 of antigen-presenting cell lines from patients engineered to express SAG. MHC-I Dextramer technology was utilised to determine expansion of antigen-specific CD8+ T cells reactive to SAG peptides in complex with HLA-A29 in a cohort of BCR patients, HLA-A29-positive controls, and HLA-A29-negative controls.

RESULTS

We report on the naturally presented antigenic SAG peptides identified by sequencing the HLA-A29 immunopeptidome of antigen-presenting cells of patients. We show that the N-terminally extended SAG peptide precursors can be trimmed in vitro by the antigen-processing aminopeptidases ERAP1 and ERAP2. Unexpectedly, no enhanced antigen engagement by CD8+ T cells upon stimulation with SAG peptides was observed in patients or HLA-A29-positive controls. Multiplexed HLA-A29-peptide dextramer profiling of a case-control cohort revealed that CD8+ T cells specific for these SAG peptides were neither detectable in peripheral blood nor in eye biopsies of patients.

CONCLUSIONS

Collectively, these findings demonstrate that SAG is not a CD8+ T cell autoantigen and sharply contrast the paradigm in the pathogenesis of BCR. Therefore, the mechanism by which HLA-A29 is associated with BCR does not involve SAG.

The many faces of islet antigen-specific CD8 T cells: clues to clinical outcome in type 1 diabetes

Immune monitoring enables a better understanding of disease processes and response to therapy, but has been challenging in the setting of chronic autoimmunity because of unknown etiology, variable and protracted kinetics of the disease process, heterogeneity across patients and the complexity of immune interactions. To begin to parse this complexity, we focus here on type 1 diabetes (T1D) and CD8 T cells as a cell type that has features that are associated with different stages of disease, rates of progression and response to therapy. Specifically, we discuss the current understanding of the role of autoreactive CD8 T cells in disease outcome, which implicates particular CD8 functional subsets, rather than unique antigens or total number of autoreactive T cells. Next, we discuss how autoreactive CD8 T‐cell features can be reflected in measures of global CD8 T cells, and then pull these concepts together by highlighting immune therapies recently shown to modulate both CD8 T cells and disease progression. We end by discussing outstanding questions about the role of specific subsets of autoreactive CD8 T cells in disease progression and how they may be optimally modulated to treat and prevent T1D.

Autoreactive CD8+ T cell exhaustion distinguishes subjects with slow type 1 diabetes progression

Although most patients with type 1 diabetes (T1D) retain some functional insulin-producing islet β cells at the time of diagnosis, the rate of further β cell loss varies across individuals. It is not clear what drives this differential progression rate. CD8+ T cells have been implicated in the autoimmune destruction of β cells. Here, we addressed whether the phenotype and function of autoreactive CD8+ T cells influence disease progression. We identified islet-specific CD8+ T cells using high-content, single-cell mass cytometry in combination with peptide-loaded MHC tetramer staining. We applied a new analytical method, DISCOV-R, to characterize these rare subsets. Autoreactive T cells were phenotypically heterogeneous, and their phenotype differed by rate of disease progression. Activated islet-specific CD8+ memory T cells were prevalent in subjects with T1D who experienced rapid loss of C-peptide; in contrast, slow disease progression was associated with an exhaustion-like profile, with expression of multiple inhibitory receptors, limited cytokine production, and reduced proliferative capacity. This relationship between properties of autoreactive CD8+ T cells and the rate of T1D disease progression after onset make these phenotypes attractive putative biomarkers of disease trajectory and treatment response and reveal potential targets for therapeutic intervention.

Characterization of proinsulin-specific regulatory T cells in type 1 diabetes at different ages of onset

BACKGROUND AND OBJECTIVES

Regulatory T cells (Tregs) play an important role in maintaining tolerance to self-antigens. Defects in the frequency and function of polyclonal Tregs have been reported in type 1 diabetes (T1D). However, characteristics of proinsulin (PI)-specific Tregs in human T1D have not yet been explored. Therefore, we aimed to characterize PI-specific Tregs in two distinct pathophysiological subtypes of T1D, juvenile-onset T1D (JOT1D) and adult-onset T1D (AOT1D), distinguished by the age of onset.

METHODS

Peripheral blood mononuclear cells of the recruited subjects were stimulated in vitro with PI-derived peptides. PI-specific Tregs were characterized by flow cytometry using the combination of markers CD25, CD137, FOXP3 and CD45RA.

RESULTS

Firstly, we observed similar frequencies of polyclonal Tregs in the T1D (n = 25) and healthy control (HC) (n = 20) subjects (P = 0.96), with a positive correlation between age and frequency of polyclonal Tregs (r = +0.35, P = 0.04). While the frequency of polyclonal Tregs was higher in AOT1D group (P = 0.02), both JOT1D (n = 14) and AOT1D groups (n = 11) had a comparable frequency of PI-specific Tregs in their peripheral blood. The frequency of PI-specific memory Tregs was significantly high in both the JOT1D (P = 0.02) and AOT1D (P = 0.009) groups compared to their respective HC groups (n = 10). Finally, we observed no significant difference in the expression of FOXP3 and IL-2 receptor in PI-specific Tregs in all the groups.

CONCLUSIONS

Unlike polyclonal Tregs, both T1D subtypes harbor comparable frequencies of PI-specific Tregs. Chronic antigen presentation results in a distinct memory-like phenotype of PI-specific Tregs in these subjects irrespective of the age of disease onset.

In vitro assessment of cord blood-derived proinsulin-specific regulatory T cells for cellular therapy in type 1 diabetes

BACKGROUND

Antigen-specific regulatory T cells (Tregs) have proven to be effective in reversing established autoimmunity in type 1 diabetes (T1D). Cord blood (CB) can serve as an efficient and safe source for Tregs for antigen-specific immunomodulation in T1D, a strategy that is yet to be explored. Therefore, we assessed the potential of CB in generation of proinsulin (PI)-specific Tregs by using HLA class II tetramers.

METHODS

We analyzed the frequency of PI-specific natural Tregs (nTregs) and induced Tregs (iTregs) derived from the CB as well as peripheral blood (PB) of patients with T1D and healthy control subjects. For this, CD4+CD25+CD127^low and CD4+CD25-T cells were cultured in the presence of PI-derived peptides, transforming growth factor (TGF)-β and rapamycin. PI-specific Tregs were then selected using allele-specific HLA II tetramers loaded with PI-derived peptides, followed by suppression assays.

RESULTS

Following stimulation, we observed that CB harbors a significantly higher frequency of PI-specific Tregs than PB of subjects with T1D (P = 0.0003). Further, the proportion of PI-specific Tregs was significantly higher in both the nTreg (P = 0.01) and iTreg (P = 0.0003) compartments of CB as compared with PB of subjects with T1D. In co-culture experiments, the PI-specific Tregs suppressed the proliferation of effector T cells significantly (P = 0.0006). The expanded nTregs were able to retain hypomethylation status at their Tregs-specific demethylated region (TSDR), whereas iTregs were unable to acquire the characteristic demethylation pattern.

CONCLUSION

Our study demonstrates that CB can serve as an excellent source for generation of functional antigen-specific Tregs for immunotherapeutic approaches in subjects with T1D.