Extensive Amplification of Human Regulatory T Cells Alters Their Functional Capacities and Targets Them to the Periphery

Single-cell insights into immune dysregulation in rheumatoid arthritis flare versus drug-free remission

Immune-mediated inflammatory diseases (IMIDs) are typically characterised by relapsing and remitting flares of inflammation. However, the unpredictability of disease flares impedes their study. Addressing this critical knowledge gap, we use the experimental medicine approach of immunomodulatory drug withdrawal in rheumatoid arthritis (RA) remission to synchronise flare processes allowing detailed characterisation. Exploratory mass cytometry analyses reveal three circulating cellular subsets heralding the onset of arthritis flare - CD45RO+PD1hi CD4+ and CD8+ T cells, and CD27+CD86+CD21- B cells - further characterised by single-cell sequencing. Distinct lymphocyte subsets including cytotoxic and exhausted CD4+ memory T cells, memory CD8+CXCR5+ T cells, and IGHA1+ plasma cells are primed for activation in flare patients. Regulatory memory CD4+ T cells (Treg cells) increase at flare onset, but with dysfunctional regulatory marker expression compared to drug-free remission. Significant clonal expansion is observed in T cells, but not B cells, after drug cessation; this is widespread throughout memory CD8+ T cell subsets but limited to the granzyme-expressing cytotoxic subset within CD4+ memory T cells. Based on our observations, we suggest a model of immune dysregulation for understanding RA flare, with potential for further translational research towards novel avenues for its treatment and prevention.

GITR and TIGIT immunotherapy provokes divergent multicellular responses in the tumor microenvironment of gastrointestinal cancers

BACKGROUND

Understanding the mechanistic effects of novel immunotherapy agents is critical to improving their successful clinical translation. These effects need to be studied in preclinical models that maintain the heterogenous tumor microenvironment (TME) and dysfunctional cell states found in a patient's tumor. We investigated immunotherapy perturbations targeting co-stimulatory molecule GITR and co-inhibitory immune checkpoint TIGIT in a patient-derived ex vivo system that maintains the TME in its near-native state. Leveraging single-cell genomics, we identified cell type-specific transcriptional reprogramming in response to immunotherapy perturbations.

METHODS

We generated ex vivo tumor slice cultures from fresh surgical resections of gastric and colon cancer and treated them with GITR agonist or TIGIT antagonist antibodies. We applied paired single-cell RNA and TCR sequencing to the original surgical resections, control, and treated ex vivo tumor slice cultures. We additionally confirmed target expression using multiplex immunofluorescence and validated our findings with RNA in situ hybridization.

RESULTS

We confirmed that tumor slice cultures maintained the cell types, transcriptional cell states and proportions of the original surgical resection. The GITR agonist was limited to increasing effector gene expression only in cytotoxic CD8 T cells. Dysfunctional exhausted CD8 T cells did not respond to GITR agonist. In contrast, the TIGIT antagonist increased TCR signaling and activated both cytotoxic and dysfunctional CD8 T cells. This included cells corresponding to TCR clonotypes with features indicative of potential tumor antigen reactivity. The TIGIT antagonist also activated T follicular helper-like cells and dendritic cells, and reduced markers of immunosuppression in regulatory T cells.

CONCLUSIONS

We identified novel cellular mechanisms of action of GITR and TIGIT immunotherapy in the patients' TME. Unlike the GITR agonist that generated a limited transcriptional response, TIGIT antagonist orchestrated a multicellular response involving CD8 T cells, T follicular helper-like cells, dendritic cells, and regulatory T cells. Our experimental strategy combining single-cell genomics with preclinical models can successfully identify mechanisms of action of novel immunotherapy agents. Understanding the cellular and transcriptional mechanisms of response or resistance will aid in prioritization of targets and their clinical translation.

GITR and TIGIT immunotherapy provokes divergent multi-cellular responses in the tumor microenvironment of gastrointestinal cancers

Understanding the cellular mechanisms of novel immunotherapy agents in the human tumor microenvironment (TME) is critical to their clinical success. We examined GITR and TIGIT immunotherapy in gastric and colon cancer patients using ex vivo slice tumor slice cultures derived from cancer surgical resections. This primary culture system maintains the original TME in a near-native state. We applied paired single-cell RNA and TCR sequencing to identify cell type specific transcriptional reprogramming. The GITR agonist was limited to increasing effector gene expression only in cytotoxic CD8 T cells. The TIGIT antagonist increased TCR signaling and activated both cytotoxic and dysfunctional CD8 T cells, including clonotypes indicative of potential tumor antigen reactivity. The TIGIT antagonist also activated T follicular helper-like cells and dendritic cells, and reduced markers of immunosuppression in regulatory T cells. Overall, we identified cellular mechanisms of action of these two immunotherapy targets in the patients' TME.

Immune phenotype of the CD4+ T cells in the aged lymphoid organs and lacrimal glands

Aging is associated with a massive infiltration of T lymphocytes in the lacrimal gland. Here, we aimed to characterize the immune phenotype of aged CD4⁺ T cells in this tissue as compared with lymphoid organs. To perform this, we sorted regulatory T cells (Tregs, CD4⁺CD25⁺GITR⁺) and non-Tregs (CD4⁺CD25^negGITR^neg) in lymphoid organs from female C57BL/6J mice and subjected these cells to an immunology NanoString® panel. These results were confirmed by flow cytometry, live imaging, and tissue immunostaining in the lacrimal gland. Importantly, effector T helper 1 (Th1) genes were highly upregulated on aged Tregs, including the master regulator Tbx21. Among the non-Tregs, we also found a significant increase in the levels of EOMES^med/high, Tbet^negIFN-γ⁺, and CD62L⁺CD44^negCD4⁺ T cells with aging, which are associated with cell exhaustion, immunopathology, and the generation of tertiary lymphoid tissue. At the functional level, aged Tregs from lymphoid organs are less able to decrease proliferation and IFN-γ production of T responders at any age. More importantly, human lacrimal glands (age range 55-81 years) also showed the presence of CD4⁺Foxp3⁺ cells. Further studies are needed to propose potential molecular targets to avoid immune-mediated lacrimal gland dysfunction with aging.

Prevention of Allograft Rejection by Use of Regulatory T Cells With an MHC-Specific Chimeric Antigen Receptor

CD4⁺ CD25^high FOXP3⁺ regulatory T cells (Tregs) are involved in graft-specific tolerance after solid organ transplantation. However, adoptive transfer of polyspecific Tregs alone is insufficient to prevent graft rejection even in rodent models, indicating that graft-specific Tregs are required. We developed a highly specific chimeric antigen receptor that recognizes the HLA molecule A*02 (referred to as A2-CAR). Transduction into natural regulatory T cells (nTregs) changes the specificity of the nTregs without alteration of their regulatory phenotype and epigenetic stability. Activation of nTregs via the A2-CAR induced proliferation and enhanced the suppressor function of modified nTregs. Compared with nTregs, A2-CAR Tregs exhibited superior control of strong allospecific immune responses in vitro and in humanized mouse models. A2-CAR Tregs completely prevented rejection of allogeneic target cells and tissues in immune reconstituted humanized mice in the absence of any immunosuppression. Therefore, these modified cells have great potential for incorporation into clinical trials of Treg-supported weaning after allogeneic transplantation.

Sarcoidosis: Immunopathogenesis and Immunological Markers

Sarcoidosis is a multisystem granulomatous disorder invariably affecting the lungs. It is a disease with noteworthy variations in clinical manifestation and disease outcome and has been described as an “immune paradox” with peripheral anergy despite exaggerated inflammation at disease sites. Despite extensive research, sarcoidosis remains a disease with undetermined aetiology. Current evidence supports the notion that the immune response in sarcoidosis is driven by a putative antigen in a genetically susceptible individual. Unfortunately, there currently exists no reliable biomarker to delineate the disease severity and prognosis. As such, the diagnosis of sarcoidosis remains a vexing clinical challenge. In this review, we outline the immunological features of sarcoidosis, discuss the evidence for and against various candidate etiological agents (infective and noninfective), describe the exhaled breath condensate, a novel method of identifying immunological biomarkers, and suggest other possible immunological biomarkers to better characterise the immunopathogenesis of sarcoidosis.

Regulatory T cells with reduced repressor capacities are extensively amplified in pulmonary sarcoid lesions and sustain granuloma formation

Sarcoidosis can evolve into a chronic disease with persistent granulomas accompanied by progressive fibrosis. While an unlimited inflammatory response suggests an impaired immune control in sarcoid lesions, it stands in contrast to the massive infiltration with CD4(+)CD25(high)FoxP3(+) regulatory T cells. We here revealed that those Treg cells in affected lung lesions were mainly derived from activated natural Treg cells with GARP (LRRC32)-positive phenotype but exhibited reduced repressor capacities despite high IL-10 and TGF-beta 1 levels. The repressive capacity of blood Treg cells, in contrast, was not impaired compared to age-matched healthy donors. Treg derived cells in granuloma lesions have undergone extensive rounds of amplifications indicated by shortened telomeres compared to blood Treg cells of the same patient. Lesional Treg derived cells moreover secreted pro-inflammatory cytokines including IL-4 which sustains granuloma formation through fibroblast amplification and the activation of mast cells, the latter indicated by the expression of membrane-bound oncostatin M.

Skin-homing CD4+ Foxp3+ T cells exert Th2-like function after staphylococcal superantigen stimulation in atopic dermatitis patients

BACKGROUND

The effect of staphylococcal superantigens (SsAgs) on cutaneous lymphocyte-associated antigen (CLA)(+) CD4(+) Foxp3(+) T cells of atopic dermatitis (AD) patients is unknown.

OBJECTIVE

To compare the effects of SsAgs on the ratio, function, and apoptosis of CCR6(+) subtype and CCR6(-) subtype of CLA(+) CD4(+) Foxp3(+) T cells among AD patients, asthma/allergic rhinitis (AR) patients without AD, and healthy subjects.

METHODS

Using immunofluorescence staining followed by flow cytometric analysis, we analysed peripheral blood mononuclear cells cultured with or without staphylococcal enterotoxin B (SEB) stimulation in 20 AD patients, 20 asthma/AR patients without AD, and 20 healthy subjects.

RESULTS

SEB decreased CCR6(+) /CCR6(-) ratio in CLA(+) CD4(+) Foxp3(+) T cells from AD patients and increased CCR6(+) /CCR6(-) ratio in those from healthy subjects. SEB induced the production of type 2 T helper cell (Th2) cytokine interleukin (IL)-5 in CCR6(-) subtype and anti-inflammatory cytokine IL-10 in CCR6(+) subtype of CLA(+) CD4(+) Foxp3(+) T cells. CLA(+) CD4(+) Foxp3(+) T cells from AD patients produced more IL-5 and less IL-10 after SEB stimulation than those from healthy subjects. CCR6(-) subtype of CLA(+) CD4(+) Foxp3(+) T cells from AD patients and CCR6(+) subtype of those cells from healthy subjects were more resistant to SEB-induced caspase-3 activation than the other subtype and those from other subjects.

CONCLUSIONS AND CLINICAL RELEVANCE

Despite a phenotype of regulatory T cells, skin-homing CD4(+) Foxp3(+) T cells of AD patients exert effector Th2-like function after SsAgs stimulation, which may aggravate allergic skin inflammation.

The ageing immune system and its clinical implications

Ageing is associated with multiple changes in many different components of the immune system. A healthy immune system exists in a state of balance between efficient effector responses against pathogens and tolerance to self antigens. This balance is changed with age; functions such as antigen recognition, phagocytosis, antigen presentation, chemotaxis, cytokine secretion and killing ability are all compromised. Aberrant cellular responses lead to an altered cytokine network with increases in inflammatory cytokines and decreases in anti-inflammatory cytokines leading to a pro-inflammatory state. Consequently older patients require extra care in diagnosis of infections as symptoms may be perturbed, resulting in unusual presentations of common conditions. The defects in immunity due to immunosenescence also mean that older patients require more care and screening than other patients in the same disease cohort. Though it is generally understood by clinicians that older patients are more at risk from multiple infections, the wider clinical effects of immunosenescence are less understood. The immune system is involved in several neurodegenerative conditions and the inflammatory conditions of immunosenescence may be a key factor in pathogenesis. Similarly, there is reason to believe that immunosenescence might be a key factor explaining the increased incidence of cancer in older age. With increasing understanding of the immune system's involvement in many of these pathological processes, and the contribution that immunosenescence makes to these, more efficient vaccines and novel therapies may be developed to prevent/treat these conditions.

Ulcerative typhlocolitis associated with Helicobacter mastomyrinus in telomerase-deficient mice

Telomerase deficiency induces early senescence and defects in proliferating cell populations, but in mice it has not been associated with inflammatory bowel disease. Genetically engineered mice lacking either telomerase reverse transcriptase (TERT) or telomerase RNA were examined for chronic diarrhea and wasting. Affected mice had pasty stools, thickened nondistensible colon walls, and contracted ceca. Histologically, the cecal mucosa was largely replaced by inflammatory infiltrate consisting of plasma cells, neutrophils, lymphocytes, and macrophages with marked widespread fibrosis and ulceration. Remaining epithelium was disorganized and hyperplastic, with multifocal dysplasia. Colonic mucosa was markedly hyperplastic with similar inflammation and epithelial dysplasia. Multifocal adenomatous hyperplasia, but no inflammation, was present in the small intestine. Microaerophilic spiral bacteria with 16S rRNA gene sequences identical to Helicobacter mastomyrinus were isolated from the colon and cecum. Severe granulomatous typhlocolitis without epithelial dysplasia developed in germ-free recombination-activating gene (RAG) knockout (KO) recipients of CD4+ T cells and inoculated with cecal contents from affected TERT KO mice and in specific pathogen-free recipient RAG KO mice and interleukin-10 KO mice inoculated with H mastomyrinus. Typhlocolitis in mice given H mastomyrinus was more severe than in mice given Helicobacter hepaticus. Telomerase-deficient mice are susceptible to helicobacter-associated typhlocolitis. H mastomyrinus causes severe disease in susceptible mouse strains.