Control of Mycobacterial Infections in Mice Expressing Human Tumor Necrosis Factor (TNF) but Not Mouse TNF

Reverse Genetics Applied to Immunobiology of Tumor Necrosis Factor, a Multifunctional Cytokine

Tumor necrosis factor (TNF) is one of many cytokines - protein molecules responsible for communication between the cells of immune system. TNF was discovered and given its grand name because of its striking antitumor effects in experimental systems, but its main physiological functions in the context of whole organism turned out to be completely unrelated to protection against tumors. This short review discusses "man-made" mouse models generated by early genome-editing technologies, which enabled us to establish true functions of TNF in health and certain diseases as well as to unravel potential strategies for improving therapy of TNF-dependent diseases.

TNF hampers intestinal tissue repair in colitis by restricting IL-22 bioavailability

Successful treatment of chronic inflammatory diseases integrates both the cessation of inflammation and the induction of adequate tissue repair processes. Strikingly, targeting a single proinflammatory cytokine, tumor necrosis factor (TNF), induces both processes in a relevant cohort of inflammatory bowel disease (IBD) patients. However, the molecular mechanisms underlying intestinal repair following TNF blockade during IBD remain elusive. Using a novel humanized model of experimental colitis, we demonstrate that TNF interfered with the tissue repair program via induction of a soluble natural antagonist of IL-22 (IL-22Ra2; IL-22BP) in the colon and abrogated IL-22/STAT3-mediated mucosal repair during colitis. Furthermore, membrane-bound TNF expressed by T cells perpetuated colonic inflammation, while soluble TNF produced by epithelial cells (IECs) induced IL-22BP expression in colonic dendritic cells (DCs) and dampened IL-22-driven restitution of colonic epithelial functions. Finally, TNF induced IL-22BP expression in human monocyte-derived DCs and levels of IL22-BP correlated with TNF in sera of IBD patients. Thus, our data can explain how anti-TNF therapy induces mucosal healing by increasing IL-22 availability and implicates new therapeutic opportunities for IBD.

Interleukin-13 overexpressing mice represent an advanced pre-clinical model for detecting the distribution of anti-mycobacterial drugs within centrally necrotizing granulomas

The Mycobacterium tuberculosis-harboring granuloma with a necrotic center surrounded by a fibrous capsule is the hallmark of tuberculosis (TB). For a successful treatment, antibiotics need to penetrate these complex structures to reach their bacterial targets. Hence, animal models reflecting the pulmonary pathology of TB patients are of particular importance to improve the preclinical validation of novel drug candidates. M. tuberculosis-infected interleukin-13-overexpressing (IL-13^tg) mice develop a TB pathology very similar to patients and, in contrast to other mouse models, also share pathogenetic mechanisms. Accordingly, IL-13^tg animals represent an ideal model for analyzing the penetration of novel anti-TB drugs into various compartments of necrotic granulomas by matrix-assisted laser desorption/ionization–mass spectrometry imaging (MALDI-MS imaging). In the present study, we evaluated the suitability of BALB/c IL-13^tg mice for determining the antibiotic distribution within necrotizing lesions. To this end, we established a workflow based on the inactivation of M. tuberculosis by gamma irradiation while preserving lung tissue integrity and drug distribution, which is essential for correlating drug penetration with lesion pathology. MALDI-MS imaging analysis of clofazimine, pyrazinamide, and rifampicin revealed a drug-specific distribution within different lesion types, including cellular granulomas, developing in BALB/c wild-type mice, and necrotic granulomas in BALB/c IL-13^tg animals, emphasizing the necessity of preclinical models reflecting human pathology. Most importantly, our study demonstrates that BALB/c IL-13^tg mice recapitulate the penetration of antibiotics into human lesions. Therefore, our workflow in combination with the IL-13^tg mouse model provides an improved and accelerated evaluation of novel anti-TB drugs and new regimens in the preclinical stage.

Transmembrane TNF and Its Receptors TNFR1 and TNFR2 in Mycobacterial Infections

Tumor necrosis factor (TNF) is one of the main cytokines regulating a pro-inflammatory environment. It has been related to several cell functions, for instance, phagocytosis, apoptosis, proliferation, mitochondrial dynamic. Moreover, during mycobacterial infections, TNF plays an essential role to maintain granuloma formation. Several effector mechanisms have been implicated according to the interactions of the two active forms, soluble TNF (solTNF) and transmembrane TNF (tmTNF), with their receptors TNFR1 and TNFR2. We review the impact of these interactions in the context of mycobacterial infections. TNF is tightly regulated by binding to receptors, however, during mycobacterial infections, upstream activation signalling pathways may be influenced by key regulatory factors either at the membrane or cytosol level. Detailing the structure and activation pathways used by TNF and its receptors, such as its interaction with solTNF/TNFRs versus tmTNF/TNFRs, may bring a better understanding of the molecular mechanisms involved in activation pathways which can be helpful for the development of new therapies aimed at being more efficient against mycobacterial infections.

Current Perspectives on the Role of TNF in Hematopoiesis Using Mice With Humanization of TNF/LT System

TNF is a multifunctional cytokine with its key functions attributed to inflammation, secondary lymphoid tissue organogenesis and immune regulation. However, it is also a physiological regulator of hematopoiesis and is involved in development and homeostatic maintenance of various organs and tissues. Somewhat unexpectedly, the most important practical application of TNF biology in medicine is anti-TNF therapy in several autoimmune diseases. With increased number of patients undergoing treatment with TNF inhibitors and concerns regarding possible adverse effects of systemic cytokine blockade, the interest in using humanized mouse models to study the efficacy and safety of TNF-targeting biologics in vivo is justified. This Perspective discusses the main functions of TNF and its two receptors, TNFR1 and TNFR2, in steady state, as well as in emergency hematopoiesis. It also provides a comparative overview of existing mouse lines with humanization of TNF/TNFR system. These genetically engineered mice allow us to study TNF signaling cascades in the hematopoietic compartment in the context of various experimental disease models and for evaluating the effects of various human TNF inhibitors on hematopoiesis and other physiological processes.

The structure of myeloid cell-specific TNF inhibitors affects their biological properties

Spatial organization and conformational changes of antibodies may significantly affect their biological functions. We assessed the effect of mutual organization of the two V_H H domains within bispecific antibodies recognizing human TNF and the surface molecules of murine myeloid cells (F4/80 or CD11b) on TNF retention and inhibition. TNF-neutralizing properties in vitro and in vivo of MYSTI-2 and MYSTI-3 antibodies were compared with new variants with interchanged V_H H domains and different linker sequences. The most effective structure of MYSTI-2 and MYSTI-3 proteins required the Ser/Gly-containing 'superflexible' linker. The orientation of the modules was crucial for the activity of the proteins, but not for MYSTI-3 with the Pro/Gln-containing 'semi-rigid' linker. Our results may contribute toward the development of more effective drug prototypes.

Altered composition and functional profile of high-density lipoprotein in leprosy patients

The changes in host lipid metabolism during leprosy have been correlated to fatty acid alterations in serum and with high-density lipoprotein (HDL) dysfunctionality. This is most evident in multibacillary leprosy patients (Mb), who present an accumulation of host lipids in Schwann cells and macrophages. This accumulation in host peripheral tissues should be withdrawn by HDL, but it is unclear why this lipoprotein from Mb patients loses this function. To investigate HDL metabolism changes during the course of leprosy, HDL composition and functionality of Mb, Pb patients (paucibacillary) pre- or post-multidrug therapy (MDT) and HC (healthy controls) were analyzed. Mb pre-MDT patients presented lower levels of HDL-cholesterol compared to HC. Moreover, Ultra Performance Liquid Chromatography-Mass Spectrometry lipidomics of HDL showed an altered lipid profile of Mb pre-MDT compared to HC and Pb patients. In functional tests, HDL from Mb pre-MDT patients showed impaired anti-inflammatory and anti-oxidative stress activities and a lower cholesterol acceptor capacity compared to other groups. Mb pre-MDT showed lower concentrations of ApoA-I (apolipoprotein A-I), the major HDL protein, when compared to HC, with a post-MDT recovery. Changes in ApoA-I expression could also be observed in M. leprae-infected hepatic cells. The presence of bacilli in the liver of a Mb patient, along with cell damage, indicated hepatic involvement during leprosy, which may reflect on ApoA-I expression. Together, altered compositional and functional profiles observed on HDL of Mb patients can explain metabolic and physiological changes observed in Mb leprosy, contributing to a better understanding of its pathogenesis.

Effects of myeloid cell-restricted TNF inhibitors in vitro and in vivo

Systemic TNF neutralization can be used as a therapy for several autoimmune diseases. To evaluate the effects of cell type-restricted TNF blockade, we previously generated bispecific antibodies that can limit TNF secretion by myeloid cells (myeloid cell-specific TNF inhibitors or MYSTIs). In this study several such variable domain (VH) of a camelid heavy-chain only antibody-based TNF inhibitors were compared in relevant experimental models, both in vitro and in vivo. Pretreatment with MYSTI-2, containing the anti-F4/80 module, can restrict the release of human TNF (hTNF) from LPS-activated bone marrow-derived macrophage (BMDM) cultures of humanized TNF knock-in (mice; hTNFKI) more effectively than MYSTI-3, containing the anti-CD11b module. MYSTI-2 was also superior to MYSTI-3 in providing in vivo protection in acute toxicity model. Finally, MYSTI-2 was at least as effective as Infliximab in preventing collagen antibody-induced arthritis. This study demonstrates that a 33 kDa bispecific mini-antibody that specifically restricts TNF secretion by macrophages is efficient for amelioration of experimental arthritis.

Novel functions of inactive rhomboid proteins in immunity and disease

iRhoms are related to a family of intramembrane serine proteinases called rhomboids but lack proteolytic activity. In mammals, there are two iRhoms, iRhom1 and iRhom2, which have similar domain structures and overlapping specificities as well as distinctive functions. These catalytically inactive rhomboids are essential regulators for the maturation and trafficking of the disintegrin metalloprotease ADAM17 from the endoplasmic reticulum to the cell surface, and are required for the cleavage and release of a variety of membrane-associated proteins, including the IL-6 receptor, l-selectin, TNF, and EGFR ligands. iRhom2-dependent regulation of ADAM17 function has been recently implicated in the development and progression of several autoimmune diseases including rheumatoid arthritis, lupus nephritis, as well as hemophilic arthropathy. In this review, we discuss our current understanding of iRhom biology, their implications in autoimmune pathologies, and their potential as therapeutic targets.

Properties of Fluorescent Far-Red Anti-TNF Nanobodies

Upregulation of the expression of tumor necrosis factor (TNF-α, TNF) has a significant role in the development of autoimmune diseases. The fluorescent antibodies binding TNF may be used for personalized therapy of TNF-dependent diseases as a tool to predict the response to anti-TNF treatment. We generated recombinant fluorescent proteins consisting of the anti-TNF module based on the variable heavy chain (VHH) of camelid antibodies fused with the far-red fluorescent protein Katushka (Kat). Two types of anti-TNF VHH were developed: one (BTN-Kat) that was bound both human or mouse TNF, but did not neutralize their activity, and a second (ITN-Kat) that was binding and neutralizing human TNF. BTN-Kat does not interfere with TNF biological functions and can be used for whole-body imaging. ITN-Kat can be evaluated in humanized mice or in cells isolated from humanized mice. It is able to block human TNF (hTNF) activities both in vitro and in vivo and may be considered as a prototype of a theranostic agent for autoimmune diseases.

Intrinsic TNFR2 signaling in T regulatory cells provides protection in CNS autoimmunity

In spite of TNF involvement in the pathogenesis of multiple sclerosis (MS), systemic TNF neutralization in MS patients was not successful. One of the possible reasons is that TNF possesses both pathogenic and protective features that may be related to TNFR1 versus TNFR2 receptor engagement. This study uncovers one of such protective functions of TNF mediated by intrinsic TNFR2 signaling in T_reg cells. In mice bearing humanized TNF and TNFR2 genetic loci, TNFR2 ablation restricted to T_reg cells led to reduced capacity to control Th17 cell responses, exacerbated experimental autoimmune encephalomyelitis (EAE) development, and affected the maintenance of T_reg cells. These findings provide support for the emerging role of TNFR2 signaling in autoimmunity, as demonstrated here in mice with conditional inactivation of TNFR2.

TNF is a multifunctional cytokine involved in autoimmune disease pathogenesis that exerts its effects through two distinct TNF receptors, TNFR1 and TNFR2. While TNF- and TNFR1-deficient (but not TNFR2-deficient) mice show very similar phenotypes, the significance of TNFR2 signaling in health and disease remains incompletely understood. Recent studies implicated the importance of the TNF/TNFR2 axis in T regulatory (T_reg) cell functions. To definitively ascertain the significance of TNFR2 signaling, we generated and validated doubly humanized TNF/TNFR2 mice, with the option of conditional inactivation of TNFR2. These mice carry a functional human TNF-TNFR2 (hTNF-hTNFR2) signaling module and provide a useful tool for comparative evaluation of TNF-directed biologics. Conditional inactivation of TNFR2 in FoxP3⁺ cells in doubly humanized TNF/TNFR2 mice down-regulated the expression of T_reg signature molecules (such as FoxP3, CD25, CTLA-4, and GITR) and diminished T_reg suppressive function in vitro. Consequently, T_reg-restricted TNFR2 deficiency led to significant exacerbation of experimental autoimmune encephalomyelitis (EAE), accompanied by reduced capacity to control Th17-mediated immune responses. Our findings expose the intrinsic and beneficial effects of TNFR2 signaling in T_reg cells that could translate into protective functions in vivo, including treatment of autoimmunity.

Transmembrane TNF and Partially TNFR1 Regulate TNFR2 Expression and Control Inflammation in Mycobacterial-Induced Pleurisy

Pleural tuberculosis is one of the most frequent forms of extra-pulmonary tuberculosis observed in patients infected with Mycobacterium tuberculosis. Tumor Necrosis Factor (TNF) is a crucial cytokine needed to control tuberculosis infection that remains a leading cause of morbidity and mortality worldwide. TNF blockade compromises host immunity and may increase the risk of reactivation of latent infection resulting in overt pulmonary, pleural and extra-pulmonary tuberculosis. While TNF signaling is mainly considered pro-inflammatory, its requirement for the anti-inflammation process involved in the resolution of infection and tissue repair is less explored. Our study analyzes the role of TNF and TNF receptors in the control of the inflammatory process associated with Bacillus Calmette-Guérin (BCG)-induced pleurisy. This study shows that the absence of TNF causes exacerbated inflammation in the pleural cavity of BCG-infected mice which is controlled by the transmembrane TNF (tmTNF) expression. The lack of TNF is associated with an impaired cellular expression and shedding of TNFR2 in the pleural cavity. The presence of tmTNF restores the normal expression of TNFR2 on myeloid cells during BCG-induced pleurisy. We also show that absence of TNFR1 affects the expression of TNFR2 on pleural cells and inflammation in the pleural cavity of BCG-infected mice. In conclusion, tmTNF but not soluble TNF prevents pleural cavity inflammation leading to attenuation and the resolution of the inflammatory process caused by mycobacterial pleurisy in association with the expression of TNFR2 on myeloid cells.

[Cytokine neutralization at specific cellular source : A new therapeutic paradigm? German Version]

BACKGROUND

Currently, treatment of autoimmune diseases is based on manipulation of general control mechanisms, including those mediated by immunoregulatory cytokines. This approach is non-curative and may cause unwanted side effects due to numerous beneficial and non-redundant functions of a particular cytokine.

METHODS

Techniques of reverse genetics, such as conditional gene targeting, were employed to uncover the contributions of two proinflammatory and immunomodulatory cytokines, tumour necrosis factor (TNF) and interleukin 6 (IL-6), in various disease states.

RESULTS

Several non-redundant functions of TNF from distinct cellular sources were identified. TNF from myeloid cells is pathogenic in several autoimmune diseases, whereas TNF produced by T cells showed non-redundant protective functions in experimental arthritis and in a Mycobacterium tuberculosis infection model. To test the idea of selective pharmacological inhibition of "bad" TNF produced by myeloid cells while sparing "good" TNF produced by T lymphocytes, a myeloid-specific TNF inhibitor (MYSTI) was designed - a recombinant mini-antibody with dual specificity that can bind to the surface molecule F4/80 on myeloid cells and to TNF. In vitro experiments confirmed retention of TNF on the surface of TNF-producing cells and in vivo experiments indicated that MYSTI can protect mice from lethal TNF-mediated hepatotoxicity. MYSTI is also effective in experimental arthritis.

CONCLUSION

The proposed therapeutic strategy may be more effective than systemic anti-cytokine therapy in several human autoimmune diseases, as it would preserve the potentially beneficial effects of the same cytokine produced by other cell types. Such bispecific biological agents may become interesting tools for experimental studies and, eventually, drug development.

VHH-Based Bispecific Antibodies Targeting Cytokine Production

Proinflammatory cytokines, such as TNF, IL-6, and IL-1, play pathogenic roles in multiple diseases and are attractive targets for biologic drugs. Because proinflammatory cytokines possess non-redundant protective and immunoregulatory functions, their systemic neutralization carries the potential for unwanted side effects. Therefore, next-generation anti-cytokine therapies would seek to selectively neutralize pathogenic cytokine signaling, leaving normal function intact. Fortunately, the biology of proinflammatory cytokines provides several such opportunities. Here, we discuss various applications of bispecific antibodies targeting cytokines with specific focus on selective TNF neutralization targeted directly to the surface of specific populations of monocytes and macrophages. These bispecific antibodies combine an anti-TNF VHH with VHHs or scFvs directed against abundant surface molecules on myeloid cells and serve to limit the bioavailability of TNF produced by these cells. Such reagents may become prototypes of a novel class of anti-cytokine biologics.

Animal Models for Tuberculosis in Translational and Precision Medicine

Tuberculosis (TB) is a health threat to the global population. Anti-TB drugs and vaccines are key approaches for TB prevention and control. TB animal models are basic tools for developing biomarkers of diagnosis, drugs for therapy, vaccines for prevention and researching pathogenic mechanisms for identification of targets; thus, they serve as the cornerstone of comparative medicine, translational medicine, and precision medicine. In this review, we discuss the current use of TB animal models and their problems, as well as offering perspectives on the future of these models.

Cytokine neutralization at specific cellular source : A new therapeutic paradigm?

BACKGROUND

Currently, treatment of autoimmune diseases is based on manipulation of general control mechanisms, including those mediated by immunoregulatory cytokines. This approach is non-curative and may cause unwanted side effects due to numerous beneficial and non-redundant functions of a particular cytokine.

METHODS

Techniques of reverse genetics, such as conditional gene targeting, were employed to uncover the contributions of two proinflammatory and immunomodulatory cytokines, tumour necrosis factor (TNF) and interleukin 6 (IL-6), in various disease states.

RESULTS

Several non-redundant functions of TNF from distinct cellular sources were identified. TNF from myeloid cells is pathogenic in several autoimmune diseases, whereas TNF produced by T cells showed non-redundant protective functions in experimental arthritis and in a Mycobacterium tuberculosis infection model. To test the idea of selective pharmacological inhibition of "bad" TNF produced by myeloid cells while sparing "good" TNF produced by T lymphocytes, a myeloid-specific TNF inhibitor (MYSTI) was designed-a recombinant mini-antibody with dual specificity that can bind to the surface molecule F4/80 on myeloid cells and to TNF. In vitro experiments confirmed retention of TNF on the surface of TNF-producing cells and in vivo experiments indicated that MYSTI can protect mice from lethal TNF-mediated hepatotoxicity. MYSTI is also effective in experimental arthritis.

CONCLUSION

The proposed therapeutic strategy may be more effective than systemic anti-cytokine therapy in several human autoimmune diseases, as it would preserve the potentially beneficial effects of the same cytokine produced by other cell types. Such bispecific biological agents may become interesting tools for experimental studies and, eventually, drug development.

Making anti-cytokine therapy more selective: Studies in mice

Cytokines are involved in a wide range of functions shaping the normal immune response, yet inflammatory changes in the immune system due to dysregulated cytokine signaling may lead to the induction of autoimmunity. Cytokine inhibitors have revolutionized the treatment of many autoimmune diseases in recent years. Systemic cytokine ablation, however, is often associated with the development of adverse side effects and some patients simply do not respond to therapy. TNF, IL-1 and IL-6 are the best characterized proinflammatory cytokines considered as the main therapeutic targets for the treatment of several autoimmune and inflammatory diseases. But can anti-cytokine therapy become more selective and thus more efficient? This mini-review discusses several recently emerging paradigms and summarizes current experimental attempts to validate them in mouse studies.

TNF Neutralization Results in the Delay of Transplantable Tumor Growth and Reduced MDSC Accumulation

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells (IMCs) that, under normal conditions, may differentiate into mature macrophages, granulocytes, and dendritic cells. However, under pathological conditions associated with inflammation, cancer, or infection, such differentiation is inhibited leading to IMC expansion. Under the influence of inflammatory cytokines, these cells become MDSCs, acquire immunosuppressive phenotype, and accumulate in the affected tissue, as well as in the periphery. Immune suppressive activity of MDSCs is partly due to upregulation of arginase 1, inducible nitric oxide synthase, and anti-inflammatory cytokines, such as IL-10 and TGF-β. These suppressive factors can enhance tumor growth by repressing T-cell-mediated anti-tumor responses. TNF is a critical factor for the induction, expansion, and suppressive activity of MDSCs. In this study, we evaluated the effects of systemic TNF ablation on tumor-induced expansion of MDSCs in vivo using TNF humanized (hTNF KI) mice. Both etanercept and infliximab treatments resulted in a delayed growth of MCA 205 fibrosarcoma in hTNF KI mice, significantly reduced tumor volume, and also resulted in less accumulated MDSCs in the blood 3 weeks after tumor cell inoculation. Thus, our study uncovers anti-tumor effects of systemic TNF ablation in vivo.

Cell-type-restricted anti-cytokine therapy: TNF inhibition from one pathogenic source

Overexpression of TNF contributes to pathogenesis of multiple autoimmune diseases, accounting for a remarkable success of anti-TNF therapy. TNF is produced by a variety of cell types, and it can play either a beneficial or a deleterious role. In particular, in autoimmunity pathogenic TNF may be derived from restricted cellular sources. In this study we evaluated the feasibility of cell-type-restricted TNF inhibition in vivo. To this end, we engineered MYSTI (Myeloid-Specific TNF Inhibitor)--a recombinant bispecific antibody that binds to the F4/80 surface molecule on myeloid cells and to human TNF (hTNF). In macrophage cultures derived from TNF humanized mice MYSTI could capture the secreted hTNF, limiting its bioavailability. Additionally, as evaluated in TNF humanized mice, MYSTI was superior to an otherwise analogous systemic TNF inhibitor in protecting mice from lethal LPS/D-Galactosamine-induced hepatotoxicity. Our results suggest a novel and more specific approach to inhibiting TNF in pathologies primarily driven by macrophage-derived TNF.

Innate myeloid cell TNFR1 mediates first line defence against primary Mycobacterium tuberculosis infection

TNF is crucial for controlling Mycobacterium tuberculosis infection and understanding how will help immunomodulating the host response. Here we assessed the contribution of TNFR1 pathway from innate myeloid versus T cells. We first established the prominent role of TNFR1 in haematopoietic cells for controlling M. tuberculosis in TNFR1 KO chimera mice. Further, absence of TNFR1 specifically on myeloid cells (M-TNFR1 KO) recapitulated the uncontrolled M. tuberculosis infection seen in fully TNFR1 deficient mice, with increased bacterial burden, exacerbated lung inflammation, and rapid death. Pulmonary IL-12p40 over-expression was attributed to a prominent CD11b⁺ Gr1^high cell population in infected M-TNFR1 KO mice. By contrast, absence of TNFR1 on T-cells did not compromise the control of M. tuberculosis infection over 6-months. Thus, the protective TNF/TNFR1 pathway essential for controlling primary M. tuberculosis infection depends on innate macrophage and neutrophil myeloid cells, while TNFR1 pathway in T cells is dispensable.