Disruption of post-thymic tolerance in skin-reactive TCR transgenic mice through the interaction of lymphopenia and intestinal microbiota.

Autoimmune diseases often arise from conditions where the immune system is compromised. While lymphopenia-induced proliferation (LIP) is crucial for immune system development and maturation, it is also caused by environmental insults, such as infection, and becomes a risk factor for autoimmunity in adults. We used Dsg3H1 TCR transgenic mice, whose T cells are designed to recognize desmogrein-3, a skin antigen, to explore the impact of lymphopenia on post-thymic tolerance. Dsg3H1 mice are known to delete the most highly autoreactive T cells in the thymus, and develop only subtle immune-mediated pathology in the steady state. However, we found that transient lymphopenia induced by total body irradiation (TBI) or cyclophosphamide (CY) results in massive dermatitis in Dsg3H1 mice. The symptoms included expansion and development of self-reactive T cells, their differentiation into CD44high IL-17-producing helper T cells, and severe neutrophilic inflammation. Repopulation of FOXP3+ T regulatory cells after lymphopenia normally occurred, suggesting escape of skin-reactive conventional T cells from control by regulatory T cells. Furthermore, we found that a depletion of the intestinal microbiota by antibiotics prevents CY-induced dermatitis, indicating roles of the commensal intestinal microbiota in LIP and Th17 development in vivo. The current data suggested that post-thymic tolerance of Dsg3H1 mice is established on a fragile balance in the lymphoreplete immune environment and broken by the interplay between lymphopenia and intestinal microbiota. The dynamic phenotypes observed in Dsg3H1 mice prompt a re-evaluation of opportunistic lymphopenia together with the microbiota as pivotal environmental factors, impacting individuals with genetic predispositions for autoimmune diseases.

A protein kinase D inhibitor suppresses AKT on T cells and antagonizes cancer immunotherapy by anti-PD-1.

Antibodies that block the interaction between PD-1 and PD-1 ligands (anti-PD-1) are in clinical use for the treatment of cancer, yet their efficacy is limited. Pre-approved therapies that enhance the effect of anti-PD-1 in combination are beneficial. Small-molecule inhibitors that attenuate T cell receptor signaling are reported to prevent T cell exhaustion and induce memory T cells with stem cell potential, resulting in a durable effector T cell response in combination with anti-PD-1. In search of such targets, we focused on protein kinase D (PKD), which is suggested to be suppressive in both tumor growth and TCR signaling. We report that CRT0066101, a PKD inhibitor (PKDi), suppressed the growth of mouse tumors at a sub-micromolar concentration in vitro. Despite its inhibitory effects on tumors, a single treatment of tumor-bearing mice with PKDi did not inhibit, but rather accelerated tumor growth, and reversed the therapeutic effect of anti-PD-1. Mice treated with PKDi showed reduced T cell infiltration and defects in the generation of effector T cells, compared to those treated with anti-PD-1, suggesting that PKDi inhibited ongoing antitumor responses. Mechanistically, PKDi inhibited phosphorylation of AKT, a primary checkpoint that is reactivated by anti-PD-1. In conclusion, PKD is fundamentally required for T cell reactivation by anti-PD-1; therefore, inhibition of PKD is not appropriate for combination therapy with anti-PD-1. On the other hand, a single dose of PKDi was shown to strongly suppress experimental autoimmunity in mice, indicating that PKDi could be useful for the treatment of immune-related adverse events that are frequently reported in anti-PD-1 therapy.

TRIM28 Expression on Dendritic Cells Prevents Excessive T Cell Priming by Silencing Endogenous Retrovirus.

Acquired immune reaction is initiated by dendritic cells (DCs), which present Ags to a few naive Ag-specific T cells. Deregulation of gene expression in DCs may alter the outcome of the immune response toward immunodeficiency and/or autoimmune diseases. Expression of TRIM28, a nuclear protein that mediates gene silencing through heterochromatin, decreased in DCs from old mice, suggesting alteration of gene regulation. Mice specifically lacking TRIM28 in DCs show increased DC population in the spleen and enhanced T cell priming toward inflammatory effector T cells, leading to acceleration and exacerbation in experimental autoimmune encephalomyelitis. TRIM28-deficient DCs were found to ectopically transcribe endogenous retrovirus (ERV) elements. Combined genome-wide analysis revealed a strong colocalization among the decreased repressive histone mark H3K9me3-transcribed ERV elements and the derepressed host genes that were related to inflammation in TRIM28-deficient DCs. This suggests that TRIM28 occupancy of ERV elements critically represses expression of proximal inflammatory genes on the genome. We propose that gene silencing through repressive histone modification by TRIM28 plays a role in maintaining the integrity of precise gene regulation in DCs, which prevents aberrant T cell priming to inflammatory effector T cells.

Targeting abatacept-resistant T-helper-17 cells by aldehyde dehydrogenase inhibition.

IL-17-producing helper T (Th17) cells are long-lived and serve as central effector cells in chronic autoimmune diseases. The underlying mechanisms of Th17 persistence remain unclear. We demonstrated that abatacept, a CD28 antagonist, effectively prevented the development of skin disease in a Th17-dependent experimental autoimmune dermatitis model. Abatacept selectively inhibited the emergence of IL-7R-negative effector-phenotype T cells while allowing the survival and proliferation of IL-7R+ memory-phenotype cells. The surviving IL-7R+ Th17 cells expressed genes associated with alcohol/aldehyde detoxification and showed potential to transdifferentiate into IL-7R-negative effector cells. Inhibiting aldehyde dehydrogenase reduced IL-7R+ Th17 cells in vivo, independently of CD28, and exhibited additive effects when combined with abatacept. Our findings suggest that CD28 blockade prevents inflammation without eliminating persistent memory cells. These remaining memory cells can be targeted by other drugs, such as aldehyde dehydrogenase inhibitors, to limit their survival, thereby facilitating the treatment of chronic autoimmune diseases.