Carbamazepine Induces Focused T Cell Responses in Resolved Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis Cases But Does Not Perturb the Immunopeptidome for T Cell Recognition.

Antiseizure medications (ASMs) are frequently implicated in T cell-mediated drug hypersensitivity reactions and cause skin tropic pathologies that range in severity from mild rashes to life-threatening systemic syndromes. During the acute stages of the more severe manifestations of these reactions, drug responsive proinflammatory CD8+ T cells display classical features of Th1 cytokine production (e.g. IFNγ) and cytolysis (e.g. granzyme B, perforin). These T cells may be found locally at the site of pathology (e.g. blister cells/fluid), as well as systemically (e.g. blood, organs). What is less understood are the long-lived immunological effects of the memory T cell pool following T cell-mediated drug hypersensitivity reactions. In this study, we examine the ASM carbamazepine (CBZ) and the CBZ-reactive memory T cell pool in patients who have a history of either Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) from 3-to-20 years following their initial adverse reaction. We show that in vitro drug restimulation of CBZ-reactive CD8+ T cells results in a proinflammatory profile and produces a mainly focused, yet private, T cell receptor (TCR) usage amongst human leukocyte antigen (HLA)-B*15:02-positive SJS or TEN patients. Additionally, we show that expression of these CBZ-reactive TCRs in a reporter cell line, lacking endogenous αßTCR, recapitulates the features of TCR activation reported for ASM-treated T cell lines/clones, providing a useful tool for further functional validations. Finally, we conduct a comprehensive evaluation of the HLA-B*15:02 immunopeptidome following ASM (or a metabolite) treatment of a HLA-B*15:02-positive B-lymphoblastoid cell line (C1R.B*15:02) and minor perturbation of the peptide repertoire. Collectively, this study shows that the CBZ-reactive T cells characterized require both the drug and HLA-B*15:02 for activation and that reactivation of memory T cells from blood results in a focused private TCR profile in patients with resolved disease.

Differential effects of γc cytokines on postselection differentiation of CD8 thymocytes.

The primary consequence of positive selection is to render thymocytes responsive to cytokines and chemokines expressed in the thymic medulla. In the present study, our main objective was to discover which cytokines could support the differentiation of positively selected thymocytes. To this end, we have developed an in vitro model suitable for high-throughput analyses of positive selection and CD8 T-cell differentiation. The model involves coculture of TCR(hi)CD5(int)CD69(-) double-positive (DP) thymocytes with peptide-pulsed OP9 cells and γc-cytokines. We report that IL-4, IL-7, and IL-21 have nonredundant effects on positively selected DP thymocytes. IL-7 signaling phosphorylates STAT5 and ERK; induces Foxo1, Klf2, and S1pr1; and supports the differentiation of classic CD8 T cells. IL-4 activates STAT6 and ERK and supports the differentiation of CD8(int)PD-L1(hi)CD44(hi)EOMES(+) innate CD8 T cells. IL-21 is produced by thymic epithelial cells and the IL-21 receptor-α is strongly induced on DP thymocytes undergoing positive selection. IL-21 signaling phosphorylates STAT3 and STAT5, but not ERK, and does not support CD8 T-cell differentiation. However, IL-21 has a unique ability to up-regulate BCL-6, expand DP thymocytes undergoing positive selection, and increase the production of mature T cells. Our data suggest that injection of recombinant IL-21 might enhance thymic output in subjects with age- or disease-related thymic atrophy.

Nitric oxide and glucocorticoids synergize in inducing apoptosis of CD4⁺8⁺ thymocytes: implications for 'Death by Neglect' and T-cell function.

Thymic epithelial cells (TECs) play a central role in T-cell development by presenting self-antigens on MHC proteins. Double-positive (DP) thymocytes that fail to interact with TEC via their TCR die by 'Death by Neglect'. We demonstrated a role for TEC-derived glucocorticoids (GCs) in this process. In a previous study, we used an in vitro system recapitulating Death by Neglect, to demonstrate the involvement of nitric oxide (NO) and inducible NO synthase (iNOS) in this process. In this study, we show that NO synergizes with GCs to induce apoptosis of DP thymocytes in a fetal thymic organ culture. Also, DP thymocytes from iNOS⁻/⁻ mice are less sensitive to GC-induced apoptosis. Furthermore, the number of DP thymocytes in iNOS⁻/⁻ mice is higher than in wild-type mice, suggesting a role for NO in Death by Neglect. This phenomenon effects T-cell function profoundly: iNOS⁻/⁻ T cells do not respond to TCR-mediated activation signals, measured by up-regulation of CD69, IL-2R and IFNγ secretion. This failure to activate is a result of TCR incompetence because iNO⁻/⁻ T cells respond to TCR-independent stimuli (phorbol myristate acetate and calcium ionophore). This study suggests that NO and GCs synergize to execute TEC-induced death of DP thymocytes.

BAFF and selection of autoreactive B cells.

B cell activating factor (BAFF) is a crucial survival factor for transitional and mature B cells, and is a promising therapeutic target for systemic lupus erythematosus (SLE). A BAFF inhibitor, belimumab, is the first new drug in 50 years to be approved for the treatment of SLE. However, the mechanism of action of this drug is not entirely clear. In this review we will focus on the role of the BAFF-APRIL signaling pathway in the selection of autoreactive B cells, and discuss whether altered selection is the mechanism for the therapeutic efficacy of BAFF inhibition in SLE.