VISTA deficiency protects from immune complex-mediated glomerulonephritis by inhibiting neutrophil activation

Expression and function of VISTA on myeloid cells

V-domain containing Ig Suppressor of T cell Activation (VISTA) is predominantly expressed on myeloid cells and functions as a ligand/receptor/soluble molecule. In inflammatory responses and immune responses, VISTA regulates multiple functions of myeloid cells, such as chemotaxis, phagocytosis, T cell activation. Since inflammation and immune responses are critical in many diseases, VISTA is a promising therapeutic target. In this review, we will describe the expression and function of VISTA on different myeloid cells, including neutrophils, monocytes, macrophages, dendritic cells (DCs), myeloid-derived suppressor cells (MDSCs). In addition, we will discuss whether the functions of VISTA on these cells impact the disease processing.

Phosphatidylinositol 3-Kinase δ Deficiency Protects From Antimyeloperoxidase Vasculitis

OBJECTIVE

Antineutrophil cytoplasmic antibody-associated vasculitis (AAV) is a systemic autoimmune disease in which glomerulonephritis is an important manifestation. Antibodies against myeloperoxidase (MPO) or proteinase 3 are thought to be important in pathogenesis. Phosphoinositide 3-kinase δ (PI3Kδ) mediates a number of effects in lymphocytes, but its role in myeloid cell responses is less clear. Therefore, this study was undertaken to assess this in a preclinical model of glomerulonephritis induced by the transfer of antibodies to MPO.

METHODS

D910A mice with inactive PI3Kδ were compared with wild-type controls. Disease protocols allowed for a comparison of experimental groups in the setting of both mild and more severe disease. Adoptive transfer experiments were performed, with flow cytometric analysis of digested kidneys taken at the end of the experiment.

RESULTS

With mild disease, D910A mice had fewer glomerular macrophages, fewer glomerular neutrophils, and reduced albuminuria compared with wild-type controls. With more severe disease, they also had fewer glomerular crescents and lower serum creatinine levels, indicating protection from acute kidney injury. Adoptive transfer experiments showed a defect in the recruitment of D910A monocytes to the diseased kidney.

CONCLUSION

Mice with inactive PI3Kδ were protected from anti-MPO vasculitis. This is due to cell intrinsic defect in the recruitment of monocytes to the kidney. These findings suggest that PI3Kδ is a potential therapeutic target in AAV.

Myeloid expression of the anti-apoptotic protein Mcl1 is required in anti-myeloperoxidase vasculitis but myeloperoxidase inhibition is not protective

Antibodies to neutrophil and monocyte myeloperoxidase and proteinase 3 are a feature of anti-neutrophil cytoplasmic antibody vasculitis, a disease with significant morbidity for which new treatments are needed. Mice with a myeloid-specific deletion of the anti-apoptotic protein Mcl1 have reduced numbers of circulating neutrophils. Here, we assessed if myeloid-specific Mcl1 was required in murine anti-myeloperoxidase vasculitis and whether inhibition of myeloperoxidase was protective. In a murine model of anti-neutrophil cytoplasmic antibody vasculitis, induced by anti-myeloperoxidase antibody, mice with a myeloid-specific deletion of Mcl1 were protected from disease. They had fewer crescents, neutrophils, and macrophages in the glomeruli, lower serum creatinine levels and reduced albuminuria compared with controls. At baseline and day six after disease induction they had fewer circulating neutrophils than controls. At day six there were also fewer circulating monocytes. Myeloperoxidase inhibition with AZD5904 had no effect on histological or biochemical parameters of disease, and there was also no reduction in albuminuria at day one, two, five or seven after disease induction. These findings persisted when disease was induced without granulocyte-colony stimulating factor, which increases disease severity. A second myeloperoxidase inhibitor, AZM198, also showed no evidence of an effect, although both AZD5904 and AZM198 inhibited human neutrophil extracellular trap formation in vitro. Thus, our results show that while myeloid-specific Mcl1 is required in this model of anti-myeloperoxidase vasculitis, myeloperoxidase inhibition is not protective.

Distinct immune stimulatory effects of anti-human VISTA antibodies are determined by Fc-receptor interaction

VISTA (PD-1H) is an immune regulatory molecule considered part of the next wave of immuno-oncology targets. VISTA is an immunoglobulin (Ig) superfamily cell surface molecule mainly expressed on myeloid cells, and to some extent on NK cells and T cells. In previous preclinical studies, some VISTA-targeting antibodies provided immune inhibitory signals, while other antibodies triggered immune stimulatory signals. Importantly, for therapeutic antibodies, the isotype backbone can have a strong impact on antibody function. To elucidate the mode of action of immune stimulatory anti-VISTA antibodies, we studied three different anti-human VISTA antibody clones, each on three different IgG isotypes currently used for therapeutic antibodies: unaltered IgG1 (IgG1-WT), IgG1-KO (IgG1-LL234,235AA-variant with reduced Fc-effector function), and IgG4-Pro (IgG4- S228P-variant with stabilized hinge region). Antibody functionality was analysed in mixed leukocyte reaction (MLR) of human peripheral blood mononuclear cells (PBMCs), as a model system for ongoing immune reactions, on unstimulated human PBMCs, as a model system for a resting immune system, and also on acute myeloid leukemia (AML) patient samples to evaluate anti-VISTA antibody effects on primary tumor material. The functions of three anti-human VISTA antibodies were determined by their IgG isotype backbones. An MLR of healthy donor PBMCs was effectively augmented by anti-VISTA-IgG4-Pro and anti-VISTA-IgG1-WT antibodies, as indicated by increased levels of cytokines, T cell activation markers and T cell proliferation. However, in a culture of unstimulated PBMCs of single healthy donors, only anti-VISTA-IgG1-WT antibodies increased the activation marker HLA-DR on resting myeloid cells, and chemokine levels. Interestingly, interactions with different Fc-receptors were required for these effects, namely CD64 for augmentation of MLR, and CD16 for activation of resting myeloid cells. Furthermore, anti-VISTA-IgG1-KO antibodies had nearly no impact in any model system. Similarly, in AML patient samples, anti-VISTA-antibody on IgG4-Pro backbone, but not on IgG1-KO backbone, increased interactions, as a novel readout of activity, between immune cells and CD34+ AML cancer cells. In conclusion, the immune stimulatory effects of antagonistic anti-VISTA antibodies are defined by the antibody isotype and interaction with different Fc-gamma-receptors, highlighting the importance of understanding these interactions when designing immune stimulatory antibody therapeutics for immuno-oncology applications.

Experimentally Induced Anti-Myeloperoxidase Vasculitis Is Not Attenuated in Factor B or VISTA Deficient Mice

Background

Anti-neutrophil cytoplasmic antibody vasculitis is characterized by antibodies to myeloperoxidase or proteinase 3. Previous work in murine anti-myeloperoxidase vasculitis has shown a role for the alternative pathway complement component factor B and the anaphylatoxin C5a. However, mice deficient in properdin, which stabilizes the alternative pathway convertase, were not protected. V-Type immunoglobulin domain-containing suppressor of T-cell activation (VISTA)-deficient mice were protected in the nephrotoxic nephritis model but the role of VISTA in anti-myeloperoxidase vasculitis is unknown.

Objectives

This study had 2 aims. First, we attempted to reproduce previous findings on the role of factor B in anti-myeloperoxidase vasculitis. Second, we examined the role of VISTA in this model, in order to see if the protection in the nephrotoxic nephritis model extended to anti-myeloperoxidase vasculitis.

Methods

Anti-myeloperoxidase vasculitis was induced in wild type, factor B, or VISTA deficient mice. Disease was assessed by quantifying glomerular crescents and macrophages, in addition to albuminuria and serum creatinine.

Results

When wild type and factor B deficient mice were compared, there were no differences in any of the histological or biochemical parameters of disease assessed. Similarly, when wild type or VISTA deficient mice were compared, there were no differences.

Conclusions

Factor B deficient mice were not protected which is in contrast to previous studies. Therefore alternative pathway activation is not essential in this model, under the conditions used in this study. VISTA deficient mice were not protected, suggesting that therapies targeting VISTA may not be effective in vasculitis.

VISTA: A Promising Target for Cancer Immunotherapy?

Agents targeting the B7 family co-inhibitory receptors cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death protein-1 (PD-1), or its ligand (PD-L1), have a pivotal role in clinical practice. V-domain Ig suppressor of T-cell activation (VISTA) is a protein highly conserved between species, with a similar amino acid sequence to the B7 family members, characterized by a particularly structural homology to PD-1. It has been counted as an emerging target within the list of novel targetable immune checkpoints in oncology. Physiologically, VISTA exerts a regulatory function on the immune system at several levels, particularly by modulating T cells activation. Its altered activity plays a role in many autoimmune diseases, and its expression has been found to be prognostically implicated in different cancer types in preclinical models. We hereby present the main evidence on the value of VISTA as an immune checkpoint in solid and hematological malignancies. We also review its value as a potential target for cancer immunotherapy, by reporting the results of Phase I and II clinical trials assessing the use of drugs targeting VISTA. The complexity of its pathway, along with some unclear biological aspects concerning its molecular interactions, currently represent a limit to the applicability of VISTA as an effective biomarker for immunotherapy in oncology. A deeper characterization of this immune checkpoint may help defining its value within immune signatures of solid and hematological malignancies, and to design future therapeutic strategies.