Regulatory T-cell stability and functional plasticity in health and disease

FOXP3-expressing regulatory T cells (T_reg ) are indispensable for immune homeostasis and tolerance, and in addition tissue-resident T_reg have been found to perform noncanonical, tissue-specific functions. For optimal tolerogenic function during inflammatory disease, T_reg are equipped with mechanisms that assure lineage stability. T_reg lineage stability is closely linked to the installation and maintenance of a lineage-specific epigenetic landscape, specifically a T_reg -specific DNA demethylation pattern. At the same time, for local and directed immune regulation T_reg must possess a level of functional plasticity that requires them to partially acquire T helper cell (T_H ) transcriptional programs-then referred to as T_H -like T_reg . Unleashing T_H programs in T_reg , however, is not without risk and may threaten the epigenetic stability of T_reg with consequently pathogenic ex-T_reg contributing to (auto-) inflammatory conditions. Here, we review how the T_reg -stabilizing epigenetic landscape is installed and maintained, and further discuss the development, necessity and lineage instability risks of T_H 1-, T_H 2-, T_H 17-like T_reg and follicular T_reg .

Cancer immunotherapies transition endothelial cells into HEVs that generate TCF1+ T lymphocyte niches through a feed-forward loop

The lack of T cell infiltrates is a major obstacle to effective immunotherapy in cancer. Conversely, the formation of tumor-associated tertiary-lymphoid-like structures (TA-TLLSs), which are the local site of humoral and cellular immune responses against cancers, is associated with good prognosis, and they have recently been detected in immune checkpoint blockade (ICB)-responding patients. However, how these lymphoid aggregates develop remains poorly understood. By employing single-cell transcriptomics, endothelial fate mapping, and functional multiplex immune profiling, we demonstrate that antiangiogenic immune-modulating therapies evoke transdifferentiation of postcapillary venules into inflamed high-endothelial venules (HEVs) via lymphotoxin/lymphotoxin beta receptor (LT/LTβR) signaling. In turn, tumor HEVs boost intratumoral lymphocyte influx and foster permissive lymphocyte niches for PD1^- and PD1⁺TCF1⁺ CD8 T cell progenitors that differentiate into GrzB⁺PD1⁺ CD8 T effector cells. Tumor-HEVs require continuous CD8 and NK cell-derived signals revealing that tumor HEV maintenance is actively sculpted by the adaptive immune system through a feed-forward loop.

Adjuvant Radiotherapy After Radical Cystectomy for Patients with High-risk Muscle-invasive Bladder Cancer: Results of a Multicentric Phase II Trial

BACKGROUND

High-risk muscle-invasive bladder cancer (MIBC) has a poor prognosis. Old trials showed that external beam radiotherapy (EBRT) after radical cystectomy (RC) decreases the incidence of local recurrences but induces severe toxicity.

OBJECTIVE

To evaluate the toxicity and local control rate after adjuvant EBRT after RC delivered with volumetric arc radiotherapy.

DESIGN, SETTING, AND PARTICIPANTS

This is a multicentric phase 2 trial. From August 2014 till October 2020, we treated 72 high-risk MIBC patients with adjuvant EBRT after RC. High-risk MIBC is defined as ≥pT3-MIBC ± lymphovascular invasion, fewer than ten lymph nodes removed, pathological positive lymph nodes, or positive surgical margins.

INTERVENTION

Patients received 50 Gy in 25 fractions with intensity-modulated radiotherapy to the pelvic lymph nodes ± cystectomy bed.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The primary outcome is acute toxicity. We report on local relapse-free rate (LRFR), clinical relapse-free survival (CRFS), overall survival (OS), and bladder cancer-specific survival (BCSS).

RESULTS AND LIMITATIONS

The median follow-up is 18 mo. Forty-two patients (61%) developed acute grade 2 gastrointestinal (GI) toxicity. Four patients (6%) had acute grade 3 GI toxicity. One patient had grade 5 diarrhea and vomiting due to obstruction at 1 mo. Two-year probabilities of developing grade ≥3 and ≥2 GI toxicity were 17% and 76%, respectively. Urinary toxicity, assessed in 17 patients with a neobladder, was acceptable with acute grade 2 and 3 urinary toxicity reported in 53% (N = 9) and 18% (N = 3) of the patients, respectively. The 2-yr LRFR is 83% ± 5% and the 2-yr CRFS rate is 43% with a median CRFS time of 12 mo (95% confidence interval: 3-21 mo). Two-year OS and BCSS are 52% ± 7% and 62% ± 7%, respectively. Shortcomings are the nonrandomized study design and limited follow-up.

CONCLUSIONS

Adjuvant EBRT after RC can be administered without excessive severe toxicity.

PATIENT SUMMARY

In this report, we looked at the incidence of toxicity and local control after adjuvant external beam radiotherapy (EBRT) following radical cystectomy (RC) in high-risk muscle-invasive bladder cancer patients. We found that adjuvant EBRT was feasible and resulted in good local control. We conclude that these data support further enrollment of patients in ongoing trials to evaluate the place of adjuvant EBRT after RC.

Context-dependent effects of IL-2 rewire immunity into distinct cellular circuits

Interleukin 2 (IL-2) is a key homeostatic cytokine, with therapeutic applications in both immunogenic and tolerogenic immune modulation. Clinical use has been hampered by pleiotropic functionality and widespread receptor expression, with unexpected adverse events. Here, we developed a novel mouse strain to divert IL-2 production, allowing identification of contextual outcomes. Network analysis identified priority access for Tregs and a competitive fitness cost of IL-2 production among both Tregs and conventional CD4 T cells. CD8 T and NK cells, by contrast, exhibited a preference for autocrine IL-2 production. IL-2 sourced from dendritic cells amplified Tregs, whereas IL-2 produced by B cells induced two context-dependent circuits: dramatic expansion of CD8+ Tregs and ILC2 cells, the latter driving a downstream, IL-5-mediated, eosinophilic circuit. The source-specific effects demonstrate the contextual influence of IL-2 function and potentially explain adverse effects observed during clinical trials. Targeted IL-2 production therefore has the potential to amplify or quench particular circuits in the IL-2 network, based on clinical desirability.

Intratumoral DNA-based delivery of checkpoint-inhibiting antibodies and interleukin 12 triggers T cell infiltration and anti-tumor response

To improve the anti-tumor efficacy of immune checkpoint inhibitors, numerous combination therapies are under clinical evaluation, including with IL-12 gene therapy. The current study evaluated the simultaneous delivery of the cytokine and checkpoint-inhibiting antibodies by intratumoral DNA electroporation in mice. In the MC38 tumor model, combined administration of plasmids encoding IL-12 and an anti-PD-1 antibody induced significant anti-tumor responses, yet similar to the monotherapies. When treatment was expanded with a DNA-based anti-CTLA-4 antibody, this triple combination significantly delayed tumor growth compared to IL-12 alone and the combination of anti-PD-1 and anti-CTLA-4 antibodies. Despite low drug plasma concentrations, the triple combination enabled significant abscopal effects in contralateral tumors, which was not the case for the other treatments. The DNA-based immunotherapies increased T cell infiltration in electroporated tumors, especially of CD8⁺ T cells, and upregulated the expression of CD8⁺ effector markers. No general immune activation was detected in spleens following either intratumoral treatment. In B16F10 tumors, evaluation of the triple combination was hampered by a high sensitivity to control plasmids. In conclusion, intratumoral gene electrotransfer allowed effective combined delivery of multiple immunotherapeutics. This approach induced responses in treated and contralateral tumors, while limiting systemic drug exposure and potentially detrimental systemic immunological effects.

Unstable regulatory T cells, enriched for naïve and Nrp1neg cells, are purged after fate challenge

Regulatory T cells (T_regs) are indispensable for the control of immune homeostasis and have clinical potential as a cell therapy for treating autoimmunity. T_regs can lose expression of the lineage-defining Foxp3 transcription factor and acquire effector T cell (T_eff) characteristics, a process referred to as T_reg plasticity. The extent and reversibility of such plasticity during immune responses remain unknown. Here, using a murine genetic fate-mapping system, we show that T_reg stability is maintained even during exposure to a complex microbial/antigenic environment. Furthermore, we demonstrate that the observed plasticity of T_regs after adoptive transfer into a lymphopenic environment is a property limited to only a subset of the T_reg population, with the nonconverting majority of T_regs being resistant to plasticity upon secondary stability challenge. The unstable T_reg fraction is a complex mixture of phenotypically distinct T_regs, enriched for naïve and neuropilin-1-negative T_regs, and includes peripherally induced T_regs and recent thymic emigrant T_regs These results suggest that a "purging" process can be used to purify stable T_regs that are capable of robust fate retention, with potential implications for improving cell transfer therapy.

NFIL3 mutations alter immune homeostasis and sensitise for arthritis pathology

OBJECTIVES

NFIL3 is a key immunological transcription factor, with knockout mice studies identifying functional roles in multiple immune cell types. Despite the importance of NFIL3, little is known about its function in humans.

METHODS

Here, we characterised a kindred of two monozygotic twin girls with juvenile idiopathic arthritis at the genetic and immunological level, using whole exome sequencing, single cell sequencing and flow cytometry. Parallel studies were performed in a mouse model.

RESULTS

The patients inherited a novel p.M170I in NFIL3 from each of the parents. The mutant form of NFIL3 demonstrated reduced stability in vitro. The potential contribution of this mutation to arthritis susceptibility was demonstrated through a preclinical model, where Nfil3-deficient mice upregulated IL-1β production, with more severe arthritis symptoms on disease induction. Single cell sequencing of patient blood quantified the transcriptional dysfunctions present across the peripheral immune system, converging on IL-1β as a pivotal cytokine.

CONCLUSIONS

NFIL3 mutation can sensitise for arthritis development, in mice and humans, and rewires the innate immune system for IL-1β over-production.

Insufficient IL-10 Production as a Mechanism Underlying the Pathogenesis of Systemic Juvenile Idiopathic Arthritis

Systemic juvenile idiopathic arthritis (sJIA) is a childhood-onset immune disorder of unknown cause. One of the concepts is that the disease results from an inappropriate control of immune responses to an initially harmless trigger. In the current study, we investigated whether sJIA may be caused by defects in IL-10, a key cytokine in controlling inflammation. We used a translational approach, with an sJIA-like mouse model and sJIA patient samples. The sJIA mouse model relies on injection of CFA in IFN-γ-deficient BALB/c mice; corresponding wild type (WT) mice only develop a subtle and transient inflammatory reaction. Diseased IFN-γ-deficient mice showed a defective IL-10 production in CD4⁺ regulatory T cells, CD19⁺ B cells, and CD3^-CD122⁺CD49b⁺ NK cells, with B cells as the major source of IL-10. In addition, neutralization of IL-10 in WT mice resulted in a chronic immune inflammatory disorder clinically and hematologically reminiscent of sJIA. In sJIA patients, IL-10 plasma levels were strikingly low as compared with proinflammatory mediators. Furthermore, CD19⁺ B cells from sJIA patients showed a decreased IL-10 production, both ex vivo and after in vitro stimulation. In conclusion, IL-10 neutralization in CFA-challenged WT mice converts a transient inflammatory reaction into a chronic disease and represents an alternative model for sJIA in IFN-γ-competent mice. Cell-specific IL-10 defects were observed in sJIA mice and patients, together with an insufficient IL-10 production to counterbalance their proinflammatory cytokines. Our data indicate that a defective IL-10 production contributes to the pathogenesis of sJIA.

MHC class II-peptide complexes displayed on activated T cells guide Treg suppression

Regulatory T cell (Treg) therapy is a promising strategy for extending allograft survival. Treg suppression requires initial T cell receptor (TCR)/peptide-MHC-II (pMHC-II) contacts, the nature of which remains elusive. As inflammation facilitates transfer of pMHC-II from antigen presenting cells (APCs) to activated T cells, we hypothesize that during transplantation associated inflammation, pMHC-II relocate on alloreactive T effector cells and serve as Treg activation signals. To test this, suppression assays were performed using murine CD4+ CD25− (Teff), CD90 depleted APCs, and CD4+ CD25+ Treg cells of different MHC haplotypes. We also used a transplantation model of skin allografts in RAG1 deficient mice injected with Teff and Treg cells from various MHC backgrounds. Data from more than 150 co-culture experiments show that Treg suppression occurs only when Treg and Teff share the same MHC-II, but independently of Treg matching with APC MHC-II. Further experiments demonstrate that pMHC-II complexes, displayed on activated Teff cells, are crucial to the induction of Treg suppression. In vivo results recapitulate the in vitro data: Treg suppression, leading to graft survival, occurs only when Teff and Treg cells are MHC-II matched. Collectively, these findings suggest that suppression of alloreactivity is directed by Treg TCR recognition of pMHC-II complexes exposed on Teff cells. The nature, origin (host vs. donor), and significance of MHC-II loaded peptides have yet to be established. Future studies to improve targeted Treg therapies for transplantation tolerance will focus on mechanisms coupling Treg function with Teff cell activation.