Differential effects of decoy receptor- and antibody-mediated tumour necrosis factor blockage on FoxP3 expression in responsive arthritis patients

Get Spliced: Uniting Alternative Splicing and Arthritis

Immune responses demand the rapid and precise regulation of gene protein expression. Splicing is a crucial step in this process; ~95% of protein-coding gene transcripts are spliced during mRNA maturation. Alternative splicing allows for distinct functional regulation, as it can affect transcript degradation and can lead to alternative functional protein isoforms. There is increasing evidence that splicing can directly regulate immune responses. For several genes, immune cells display dramatic changes in isoform-level transcript expression patterns upon activation. Recent advances in long-read RNA sequencing assays have enabled an unbiased and complete description of transcript isoform expression patterns. With an increasing amount of cell types and conditions that have been analyzed with such assays, thousands of novel transcript isoforms have been identified. Alternative splicing has been associated with autoimmune diseases, including arthritis. Here, GWASs revealed that SNPs associated with arthritis are enriched in splice sites. In this review, we will discuss how alternative splicing is involved in immune responses and how the dysregulation of alternative splicing can contribute to arthritis pathogenesis. In addition, we will discuss the therapeutic potential of modulating alternative splicing, which includes examples of spliceform-based biomarkers for disease severity or disease subtype, splicing manipulation using antisense oligonucleotides, and the targeting of specific immune-related spliceforms using antibodies.

Characteristics of patients with difficult-to-treat rheumatoid arthritis in a French single-centre hospital

OBJECTIVES

To compare the features of difficult-to-treat rheumatoid arthritis (D2TRA) patients using two different definitions according to the previous failure of targeted therapies.

METHODS

We stratified consecutive RA patients treated at Cochin Hospital into two groups, a D2TRA group and a non-D2TRA group, according to two definitions of D2TRA. Both definitions defined D2TRA as RAs failing at least two targeted therapies, with a different mechanism of action for the EULAR-D2TRA definition or without prejudging the mechanism of action and for the Alternative D2TRA definition.

RESULTS

We included 320 consecutive RA patients. We identified 76 EULAR-D2TRA and 244 non-DTRA patients, and 120 Alternative D2TRA and 200 non-DTRA patients. Compared with non-D2TRA, D2TRA patients from both definitions were more likely to have lower socioeconomic level, positive rheumatoid factor, interstitial lung disease, higher DAS28-CRP and were more likely to respond to rituximab and Janus kinase inhibitors. Although EULAR and Alternative D2TRA patients displayed similar clinical and biological features, they were characterized by different therapeutic profiles. We observed fewer patients receiving methotrexate in the Alternative D2TRA group (53% vs 64%, P = 0.046). Patients with Alternative D2TRA not fulfilling the EULAR definition (n = 44) had all received two successive first-line TNF inhibitors, a monoclonal antibody and a soluble receptor, and were comparable to EULAR-D2TRA patients with regards to all other characteristics.

CONCLUSION

Low socioeconomic status, diabetes, interstitial lung disease and absence of combination with methotrexate allow identification of D2TRA. In addition, the inclusion as 'early-D2TRA' of patients failing two TNF inhibitors in the EULAR definition of D2TRA would facilitate the rapid identification of D2TRA patients.

Co-Expression of FOXP3FL and FOXP3Δ2 Isoforms Is Required for Optimal Treg-Like Cell Phenotypes and Suppressive Function

FOXP3 is the master transcription factor in both murine and human FOXP3⁺ regulatory T cells (Tregs), a T-cell subset with a central role in controlling immune responses. Loss of the functional Foxp3 protein in scurfy mice leads to acute early-onset lethal lymphoproliferation. Similarly, pathogenic FOXP3 mutations in humans lead to immunodysregulation, polyendocrinopathy, enteropathy, and X-linked (IPEX) syndrome, which are characterized by systemic autoimmunity that typically begins in the first year of life. However, although pathogenic FOXP3 mutations lead to overlapping phenotypic consequences in both systems, FOXP3 in human Tregs, but not mouse, is expressed as two predominant isoforms, the full length (FOXP3FL) and the alternatively spliced isoform, delta 2 (FOXP3Δ2). Here, using CRISPR/Cas9 to generate FOXP3 knockout CD4⁺ T cells (FOXP3KO^GFP CD4+ T cells), we restore the expression of each isoform by lentiviral gene transfer to delineate their functional roles in human Tregs. When compared to FOXP3FL or FOXP3Δ2 alone, or double transduction of the same isoform, co-expression of FOXP3FL and FOXP3Δ2 induced the highest overall FOXP3 protein expression in FOXP3KO^GFP CD4+ T cells. This condition, in turn, led to optimal acquisition of Treg-like cell phenotypes including downregulation of cytokines, such as IL-17, and increased suppressive function. Our data confirm that co-expression of FOXP3FL and FOXP3Δ2 leads to optimal Treg-like cell function and supports the need to maintain the expression of both when engineering therapeutics designed to restore FOXP3 function in otherwise deficient cells.

Alternative Splicing of FOXP3-Virtue and Vice

FOXP3 is the lineage-defining transcription factor of CD4+ CD25+ regulatory T cells. While many aspects of its regulation, interaction, and function are conserved among species, alternatively spliced FOXP3 isoforms are expressed only in human cells. This review summarizes current knowledge about alternative splicing of FOXP3 and the specific functions of FOXP3 isoforms in health and disease. Future perspectives in research and the therapeutic potential of manipulating alternative splicing of FOXP3 are discussed.