Serum-free culture medium and IL-7 costimulation increase the sensitivity of ELISpot detection.

The identification of parameters maximizing detection sensitivity in ELISpot assays is important to transfer this technology into the clinical setting for identifying rare Ag-specific CD8(+) T cells. We have therefore considered human IFN-gamma CD8(+) T cell responses against viral epitopes to analyze different variables which could be critical during the epitope-specific stimulation period. Two parameters were found to greatly enhance detection sensitivity (i.e., to specifically increase epitope-driven signal while keeping background noise to a minimum): use of human serum-free vs. serum-supplemented culture medium (2.4-fold median increase) and addition of low dose IL-7 (1.5-fold increase). Incorporating both of these parameters into the ELISpot procedure proved capable of greatly amplifying (35.1-fold increase) the low grade CD8(+) T cell responses directed against beta-cell epitopes of type 1 diabetes patients, as compared to a previously optimized procedure using human serum-supplemented medium and low dose IL-2. Implementation of this ELISpot procedure should expedite development of "immune staging" protocols for autoimmune as well as tumor and infectious diseases.

HLA-B7-restricted islet epitopes are differentially recognized in type 1 diabetic children and adults and form weak peptide-HLA complexes.

The cartography of ß-cell epitopes targeted by CD8(+) T cells in type 1 diabetic (T1D) patients remains largely confined to the common HLA-A2 restriction. We aimed to identify ß-cell epitopes restricted by the HLA-B7 (B*07:02) molecule, which is associated with mild T1D protection. Using DNA immunization on HLA-B7-transgenic mice and prediction algorithms, we identified GAD and preproinsulin candidate epitopes. Interferon-γ (IFN-γ) enzyme-linked immunospot assays on peripheral blood mononuclear cells showed that most candidates were recognized by new-onset T1D patients, but not by type 2 diabetic and healthy subjects. Some epitopes were highly immunodominant and specific to either T1D children (GAD(530-538); 44% T cell-positive patients) or adults (GAD(311-320); 38%). All epitopes displayed weak binding affinity and stability for HLA-B7 compared with HLA-A2-restricted ones, a general feature of HLA-B7. Single-cell PCR analysis on ß-cell-specific (HLA-B7 tetramer-positive) T cells revealed uniform IFN-γ and transforming growth factor-ß (TGF-ß) mRNA expression, different from HLA-A2-restricted T cells. We conclude that HLA-B7-restricted islet epitopes display weak HLA-binding profiles, are different in T1D children and adults, and are recognized by IFN-γ(+)TGF-ß(+)CD8(+) T cells. These features may explain the T1D-protective effect of HLA-B7. The novel epitopes identified should find valuable applications for immune staging of HLA-B7(+) individuals.

Critical parameters in blood processing for T-cell assays: validation on ELISpot and tetramer platforms.

Assays detecting antigen (Ag)-specific T-cell responses in immune-mediated processes are increasingly employed to understand disease pathogenesis and immune staging. The quantity and quality of starting peripheral blood mononuclear cell (PBMC) preparations are important factors in the performance of such assays. We therefore compared final PBMC yield and function by modifying parameters at the blood drawing, storage and processing steps. While drawing blood in vacuum-driven tubes or syringes and separating PBMCs on density gradients using standard or membrane (Leucosep) tubesmade no difference, storing tubes for 18 h without any agitation led to PBMC preparations contaminated with granulocytes and decreased interferon (IFN)-gamma enzyme-linked immunospot (ELISpot) responses. Even agitated blood showed a trend towards reduced ELISpot responses and increased human leukocyte Ag (HLA) multimer readouts when stored for 18 h compared to 3 h. These changes were reduced by diluting blood prior to storage. Washing PBMCs with media containing 10% human serum increased PBMC yields by 40.5%, without affecting ELISpot responses and multimer counts. However, washes with > 10% human serum decreased multimer counts, with no additional improvement in PBMC yields. These findings may be relevant for optimizing and harmonizing PBMC processing procedures for T-cell assays.

The frequency and immunodominance of islet-specific CD8+ T-cell responses change after type 1 diabetes diagnosis and treatment.

OBJECTIVE: Islet-reactive CD8(+) T-cells play a key role in the pathogenesis of type 1 diabetes in the NOD mouse. The predominant T-cell specificities change over time, but whether similar shifts also occur after clinical diagnosis and insulin treatment in type 1 diabetic patients is unknown. RESEARCH DESIGN AND METHODS: We took advantage of a recently validated islet-specific CD8(+) T-cell gamma-interferon enzyme-linked immunospot (ISL8Spot) assay to follow responses against preproinsulin (PPI), GAD, insulinoma-associated protein 2 (IA-2), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) epitopes in 15 HLA-A2(+) adult type 1 diabetic patients close to diagnosis and at a second time point 7-16 months later. RESULTS: CD8(+) T-cell reactivities were less frequent at follow-up, as 28.6% of responses tested positive at type 1 diabetes diagnosis vs. 13.2% after a median of 11 months (P = 0.003). While GAD and IA-2 autoantibody (aAb) titers were unchanged in 75% of cases, the fraction of patients responding to PPI and/or GAD epitopes by ISL8Spot decreased from 60-67 to 20% (P < 0.02). The previously subdominant IA-2(206-214) and IGRP(265-273) peptides were newly targeted, thus becoming the immunodominant epitopes. CONCLUSIONS: Shifts both in frequency and in immunodominance of CD8(+) T-cell responses occur more rapidly than do changes in aAb titers. These different kinetics may suggest complementary clinical applications for T-cell and aAb measurements.