Decreased numbers of blood dendritic cells and defective function of regulatory T cells in antineutrophil cytoplasmic antibody-associated vasculitis

Use of gene-modified regulatory T-cells to control autoimmune and alloimmune pathology: is now the right time?

Adoptive immunotherapy using genetically targeted T-cells has recently begun to achieve impressive clinical impact in selected tumor types. Furthermore, long-term follow-up studies indicate thus far that integrating viral vectors do not elicit clinically evident genotoxicity in T-cells, unlike hematopoietic stem cells. The optimism engendered by this clinical experience provides a platform for consideration of the extended use of this technology in other disease types. One area of particular interest entails the harnessing of regulatory T-cells (Tregs) in order to down-regulate unwanted immune responses. Increasing evidence supports the efficacy of this approach in pre-clinical models of autoimmune disease and allograft rejection. Nonetheless, questions remain about optimal host cell, transgene cargo, phenotypic stability of engineered cells in vivo and potential for toxicity. Here, we review the evidence that genetically engineered Tregs can effectively dampen pathogenic immune responses and critically evaluate the prospects for clinical development of this approach.

Patients with antineutrophil cytoplasmic antibody-associated vasculitis have defective Treg cell function exacerbated by the presence of a suppression-resistant effector cell population

OBJECTIVE

The development of pathogenic antineutrophil cytoplasmic antibodies (ANCAs) can result in systemic small vessel vasculitis. However, the breakdown in immune tolerance that results in the induction and persistence of ANCAs is not well understood. We undertook this study to test our hypothesis that abnormal T cell regulation is central to disease pathogenesis in patients with ANCA-associated vasculitis (AAV).

METHODS

Peripheral blood samples were obtained from 62 patients with AAV and 19 healthy controls for flow cytometric analysis of CD4+ T cell populations. Functional T cell studies were performed with fluorescence-activated cell sorted CD4+ T cell populations stimulated with anti-CD3/anti-CD28.

RESULTS

We demonstrated two separate abnormalities in T cell regulation in patients with AAV. First, we showed that the Treg cell frequency was increased in the peripheral blood of patients with active disease, but Treg cells from patients with AAV had decreased suppressive function. Treg cells from patients with active disease disproportionately used a FoxP3 isoform lacking exon 2, which might alter Treg cell function. Second, we identified a CD4+ T cell population with increased frequency that was resistant to Treg cell suppression, produced proinflammatory cytokines, and was antigen experienced.

CONCLUSION

AAV is associated with disruption of the suppressive Treg cell network and with increased frequency of a distinct proinflammatory effector T cell subset that comprises the majority of peripheral CD4+ T cells.

Impaired blood dendritic cell numbers and functions after aneurysmal subarachnoid hemorrhage

Previous Presentation

Portions of this study were presented at the Annual Congress of Société Française d’Anesthésie et de Réanimation in Paris, September 2012.

Background

Toll-like receptor (TLR) agonists are promising therapy for the prevention of nosocomial infections in critical ill patients. We aimed to analyze the TLR-reactivity of circulating dendritic cells (DC) as assessed by cytokine production after an ex vivo challenge with TLR agonists in aneurysmal subarachnoid hemorrhage (SAH) patients.

Methods and Findings

A single-center prospective observational study took place in one intensive care unit of a teaching hospital. Blood samples were harvested on days 2, 5 and 10 in 21 severe SAH patients requiring mechanical ventilation and 17 healthy controls. DC production of cytokines (Tumour Necrosis Factor, TNF-α; Interleukin, IL-12; and Interferon, IFN-α) was assessed by intracellular immunostaining on TLR-3, 4, 7/8 and 9 stimulations. SAH patients had decreased numbers of blood myeloid (mDCs) and plasmacytoid DCs (pDCs) on days 2, 5 and 10. Compared with the healthy controls, the frequency of mDCs producing TNF-α after TLR-3 stimulation was decreased in the SAH patients. The frequency of myeloid DCs producing IL-12 after TLR-3 and 4 stimulations was also decreased in the SAH patients. In contrast, the mDCs response to TLR-7/8 was not impaired in the SAH patients. The frequency of pDCs producing TNF-α⁺ and IFN-α⁺ on TLR-7/8 stimulation were reduced at all of the tested times in the SAH patients, whereas reactivity to TLR-9 was preserved. On day 2, the pDCs from non-survivor patients (n = 8) had a decreased ability to produce IFN-α on TLR-9 stimulation compared with the survivors.

Conclusions

These data suggest functional abnormalities of circulating pDCs and mDCs that could be important for immunomodulation after SAH.

Phagocytosis of apoptotic cells by macrophages in anti-neutrophil cytoplasmic antibody-associated systemic vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of autoimmune diseases, including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA). It is not known why ANCA develop, but it has been shown that they participate in pathogenesis by activating polymorphonuclear neutrophils (PMNs). In this study we hypothesize that dysregulation of phagocytosis in AAV leads to the accumulation of apoptotic neutrophils seen in association with blood vessels in AAV. These cells progress into secondary necrosis, contributing to tissue damage and autoantibody formation. Peripheral blood cells were counted, and phagocytosis was investigated using monocyte-derived macrophages (MØ) and PMNs from healthy blood donors (HBD), AAV patients and systemic lupus erythematosus (SLE) patients. Furthermore, the effect of serum was assessed. Phagocytosis was measured using flow cytometry. The results showed no deviation in monocyte subpopulations for AAV patients compared to HBDs, although there was a decrease in lymphocyte and pDC (plasmacytoid dendritic cell) populations (4·2 × 10(6) cells/l versus 10·4 × 10(6) cells/l, P < 0·001). The number of neutrophils was increased (6·0 × 10(9) cells/l versus 3·8 × 10(9) cells/l, P < 0·001). There were no differences found in the ability of MØs to engulf apoptotic cells, nor when comparing apoptotic PMNs to become engulfed. However, serum from AAV donors tended to decrease the phagocytosis ability of MØs (36%) compared to serum from HBDs (43%). In conclusion, there is no intrinsic dysfunction in the MØs or in the PMNs that have an effect on phagocytic activity, but ANCA may play a role by decreasing phagocytic ability.

Crescentic Glomerulonephritis: an update on Pauci-immune and Anti-GBM diseases

Crescentic glomerulonephritis (GN) in a renal biopsy is a widely accepted "critical diagnosis" in Anatomic Pathology practice. Prompt biopsy evaluation and notification of the referring physician is essential to facilitate rapid therapeutic intervention. The differential diagnostic categories of crescentic GN include pauci-immune GN, anti-glomerular basement membrane (GBM) nephritis and immune complex-mediated GN, distinguished from one another by immunofluorescence and electron microscopic study of the renal biopsy. Immune complex-mediated GN is characterized by abundant glomerular deposits and encompasses several diseases including but not limited to lupus nephritis, cryoglobulinemic GN and immunoglobulin A nephropathy. Pauci-immune GN, with paucity of deposits, correlates closely with antineutrophil cytoplasmic antibody disease due to the identifiable circulating pathogenic antineutrophil cytoplasmic antibody in most patients. Recent studies have identified other antibodies in pauci-immune GN and implicated infectious organisms in triggering autoimmunity in a susceptible host by molecular mimicry of host antigens. Anti-GBM nephritis is a rare but potentially life-threatening autoimmune disease with circulating antibodies against GBM epitopes in α3 chain of type IV collagen. It is characterized by a linear immunoglobulin G deposition along GBM on immunofluorescence microscopy. Environmental triggers including infections and solvent exposure seem to change the tertiary structure of the type IV collagen α345 hexamer in GBM, expose neoepitopes, and initiate autoimmunity. Even in light of advances in understanding of pathophysiology and serologic testing, renal biopsy remains the mainstay of diagnosis of crescentic GN.

Human FoxP3+ regulatory T cells in systemic autoimmune diseases

Since the characterization of CD4(+)CD25(+) regulatory T (Treg) cells in mice, significant progress has been made in the definitions of the phenotype and the function of human Treg cells in health and in pathological conditions. Recent advances in the field leading to a better molecular definition of Treg subsets in humans and the description of the dynamics of differentiation of Treg cells should bring new insights in the understanding of human chronic systemic autoimmune diseases. How Treg cells are compromised in these diseases is a challenging issue because the elucidation of the mechanisms leading to such anomaly might lead to promising novel therapeutic approaches.