Generation and characterization of antagonistic anti-human CD39 nanobodies

CD39 is the major enzyme controlling the levels of extracellular adenosine triphosphate (ATP) via the stepwise hydrolysis of ATP to adenosine diphosphate (ADP) and adenosine monophosphate (AMP). As extracellular ATP is a strong promoter of inflammation, monoclonal antibodies (mAbs) blocking CD39 are utilized therapeutically in the field of immune-oncology. Though anti-CD39 mAbs are highly specific for their target, they lack deep penetration into the dense tissue of solid tumors, due to their large size. To overcome this limitation, we generated and characterized nanobodies that targeted and blocked human CD39. From cDNA-immunized alpacas we selected 16 clones from seven nanobody families that bind to two distinct epitopes of human CD39. Among these, clone SB24 inhibited the enzymatic activity of CD39. Of note, SB24 blocked ATP degradation by both soluble and cell surface CD39 as a 15kD monomeric nanobody. Dimerization via fusion to an immunoglobulin Fc portion further increased the blocking potency of SB24 on CD39-transfected HEK cells. Finally, we confirmed the CD39 blocking properties of SB24 on human PBMCs. In summary, SB24 provides a new small biological antagonist of human CD39 with potential application in cancer therapy.

Time-resolved role of P2X4 and P2X7 during CD8+ T cell activation

CD8+ T cells are a crucial part of the adaptive immune system, responsible for combating intracellular pathogens and tumor cells. The initial activation of T cells involves the formation of highly dynamic Ca2+ microdomains. Recently, purinergic signaling was shown to be involved in the formation of the initial Ca2+ microdomains in CD4+ T cells. In this study, the role of purinergic cation channels, particularly P2X4 and P2X7, in CD8+ T cell signaling from initial events to downstream responses was investigated, focusing on various aspects of T cell activation, including Ca2+ microdomains, global Ca2+ responses, NFAT-1 translocation, cytokine expression, and proliferation. While Ca2+ microdomain formation was significantly reduced in the first milliseconds to seconds in CD8+ T cells lacking P2X4 and P2X7 channels, global Ca2+ responses over minutes were comparable between wild-type (WT) and knockout cells. However, the onset velocity was reduced in P2X4-deficient cells, and P2X4, as well as P2X7-deficient cells, exhibited a delayed response to reach a certain level of free cytosolic Ca2+ concentration ([Ca2+]i). NFAT-1 translocation, a crucial transcription factor in T cell activation, was also impaired in CD8+ T cells lacking P2X4 and P2X7. In addition, the expression of IFN-γ, a major pro-inflammatory cytokine produced by activated CD8+ T cells, and Nur77, a negative regulator of T cell activation, was significantly reduced 18h post-stimulation in the knockout cells. In line, the proliferation of T cells after 3 days was also impaired in the absence of P2X4 and P2X7 channels. In summary, the study demonstrates that purinergic signaling through P2X4 and P2X7 enhances initial Ca2+ events during CD8+ T cell activation and plays a crucial role in regulating downstream responses, including NFAT-1 translocation, cytokine expression, and proliferation on multiple timescales. These findings suggest that targeting purinergic signaling pathways may offer potential therapeutic interventions.

The role of the ATP-adenosine axis in ischemic stroke

In ischemic stroke, the primary neuronal injury caused by the disruption of energy supply is further exacerbated by secondary sterile inflammation. The inflammatory cascade is largely initiated by the purine adenosine triphosphate (ATP) which is extensively released to the interstitial space during brain ischemia and functions as an extracellular danger signaling molecule. By engaging P2 receptors, extracellular ATP activates microglia leading to cytokine and chemokine production and subsequent immune cell recruitment from the periphery which further amplifies post-stroke inflammation. The ectonucleotidases CD39 and CD73 shape and balance the inflammatory environment by stepwise degrading extracellular ATP to adenosine which itself has neuroprotective and anti-inflammatory signaling properties. The neuroprotective effects of adenosine are mainly mediated through A₁ receptors and inhibition of glutamatergic excitotoxicity, while the anti-inflammatory capacities of adenosine have been primarily attributed to A_2A receptor activation on infiltrating immune cells in the subacute phase after stroke. In this review, we summarize the current state of knowledge on the ATP-adenosine axis in ischemic stroke, discuss contradictory results, and point out potential pitfalls towards translating therapeutic approaches from rodent stroke models to human patients.

Microglia and meningeal macrophages depletion delays the onset of experimental autoimmune encephalomyelitis

In multiple sclerosis and the experimental autoimmune encephalomyelitis (EAE) model, both resident microglia and infiltrating macrophages contribute to demyelination as well as spontaneous remyelination. Nevertheless, the specific roles of microglia versus macrophages are unknown. We investigated the influence of microglia in EAE using the colony stimulating factor 1 receptor (CSF-1R) inhibitor, PLX5622, to deplete microglial population and Ccr2^RFP/+ fms^EGFP/+ mice, to distinguish blood-derived macrophages from microglia. PLX5622 treatment depleted microglia and meningeal macrophages, and provoked a massive infiltration of CCR2⁺ macrophages into demyelinating lesions and spinal cord parenchyma, albeit it did not alter EAE chronic phase. In contrast, microglia and meningeal macrophages depletion reduced the expression of major histocompatibility complex II and CD80 co-stimulatory molecule in dendritic cells, macrophages and microglia. In addition, it diminished T cell reactivation and proliferation in the spinal cord parenchyma, inducing a significant delay in EAE onset. Altogether, these data point to a specific role of CNS microglia and meningeal macrophages in antigen presentation and T cell reactivation at initial stages of EAE.

Macrophages and glia are the dominant P2X7-expressing cell types in the gut nervous system-No evidence for the role of neuronal P2X7 receptors in colitis

The blockade or deletion of the pro-inflammatory P2X7 receptor channel has been shown to reduce tissue damage and symptoms in models of inflammatory bowel disease, and P2X7 receptors on enteric neurons were suggested to mediate neuronal death and associated motility changes. Here, we used P2X7-specific antibodies and nanobodies, as well as a bacterial artificial chromosome transgenic P2X7-EGFP reporter mouse model and P2rx7^-/- controls to perform a detailed analysis of cell type-specific P2X7 expression and possible overexpression effects in the enteric nervous system of the distal colon. In contrast to previous studies, we did not detect P2X7 in neurons but found dominant expression in glia and macrophages, which closely interact with the neurons. The overexpression of P2X7 per se did not induce significant pathological effects. Our data indicate that macrophages and/or glia account for P2X7-mediated neuronal damage in inflammatory bowel disease and provide a refined basis for the exploration of P2X7-based therapeutic strategies.

Origin, distribution, and function of three frequent coding polymorphisms in the gene for the human P2X7 ion channel

P2X7, an ion channel gated by extracellular ATP, is widely expressed on the plasma membrane of immune cells and plays important roles in inflammation and apoptosis. Several single nucleotide polymorphisms have been identified in the human P2RX7 gene. In contrast to other members of the P2X family, non-synonymous polymorphisms in P2X7 are common. Three of these occur at overall frequencies of more than 25% and affect residues in the extracellular “head”-domain of P2X7 (155 Y/H), its “lower body” (270 R/H), and its “tail” in the second transmembrane domain (348 T/A). Comparison of the P2X7 orthologues of human and other great apes indicates that the ancestral allele is Y—R—T (at 155–270–348). Interestingly, each single amino acid variant displays lower ATP-sensitivity than the ancestral allele. The originally published reference sequence of human P2X7, often referred to as “wildtype,” differs from the ancestral allele at all three positions, i.e. H—H—A. The 1,000 Genome Project determined the sequences of both alleles of 2,500 human individuals, including roughly 500 persons from each of the five major continental regions. This rich resource shows that the ancestral alleles Y155, R270, and T348 occur in all analyzed human populations, albeit at strikingly different frequencies in various subpopulations (e.g., 25%–59% for Y155, 59%–77% for R270, and 13%–47% for T348). BLAST analyses of ancient human genome sequences uncovered several homozygous carriers of variant P2X7 alleles, possibly reflecting a high degree of inbreeding, e.g., H—R—T for a 50.000 year old Neanderthal, H—R—A for a 24.000 year old Siberian, and Y—R—A for a 7,000 year old mesolithic European. In contrast, most present-day individuals co-express two copies of P2X7 that differ in one or more amino acids at positions 155, 270, and 348. Our results improve the understanding of how P2X7 structure affects its function and suggest the importance of considering P2X7 variants of participants when designing clinical trials targeting P2X7.

CD38-specific nanobodies allow in vivo imaging of multiple myeloma under daratumumab therapy

RATIONALE

Recent studies have demonstrated the feasibility of CD38-specific antibody constructs for in vivo imaging of multiple myeloma. However, detecting multiple myeloma in daratumumab-pretreated patients remains difficult due to overlapping binding epitopes of the CD38-specific imaging antibody constructs and daratumumab. Therefore, the development of an alternative antibody construct targeting an epitope of CD38 distinct from that of daratumumab is needed. We report the generation of a fluorochrome-conjugated nanobody recognizing such an epitope of CD38 to detect myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

METHODS

We conjugated the CD38-specific nanobody JK36 to the near-infrared fluorescent dye Alexa Fluor 680. The capacity of JK36AF680 to bind and detect CD38-expressing cells pretreated with daratumumab was evaluated on CD38-expressing tumor cell lines in vitro, on primary myeloma cells from human bone marrow biopsies ex vivo, and in a mouse tumor model in vivo.

RESULTS

Fluorochrome-labeled nanobody JK36AF680 showed specific binding to CD38-expressing myeloma cells pretreated with daratumumab in vitro and ex vivo and allowed for specific imaging of CD38-expressing xenografts in daratumumab-pretreated mice in vivo.

CONCLUSIONS

Our study demonstrates that a nanobody recognizing a distinct, non-overlapping epitope of CD38 allows the specific detection of myeloma cells under daratumumab therapy in vitro, ex vivo, and in vivo.

Evaluation of nanobody-based biologics targeting purinergic checkpoints in tumor models in vivo

Adenosine triphosphate (ATP) represents a danger signal that accumulates in injured tissues, in inflammatory sites, and in the tumor microenvironment. ATP promotes tumor growth but also anti-tumor immune responses notably via the P2X7 receptor. ATP can also be catabolized by CD39 and CD73 ecto-enzymes into immunosuppressive adenosine. P2X7, CD39 and CD73 have attracted much interest in cancer as targets offering the potential to unleash anti-tumor immune responses. These membrane proteins represent novel purinergic checkpoints that can be targeted by small drugs or biologics. Here, we investigated nanobody-based biologics targeting mainly P2X7, but also CD73, alone or in combination therapies. Blocking P2X7 inhibited tumor growth and improved survival of mice in cancer models that express P2X7. P2X7-potentiation by a nanobody-based biologic was not effective alone to control tumor growth but enhanced tumor control and immune responses when used in combination with oxaliplatin chemotherapy. We also evaluated a bi-specific nanobody-based biologic that targets PD-L1 and CD73. This novel nanobody-based biologic exerted a potent anti-tumor effect, promoting tumor rejection and improving survival of mice in two tumor models. Hence, this study highlights the importance of purinergic checkpoints in tumor control and open new avenues for nanobody-based biologics that may be further exploited in the treatment of cancer.

Effective targeting of microglial P2X7 following intracerebroventricular delivery of nanobodies and nanobody-encoding AAVs

The P2X7 ion channel is a key sensor for extracellular ATP and a key trigger of sterile inflammation. Intravenous injection of nanobodies that block P2X7 has shown to be beneficial in mouse models of systemic inflammation. P2X7 has also emerged as an attractive therapeutic target for inflammatory brain diseases. However, little is known about the ability of nanobodies to cross the BBB. Here we evaluated the ability of P2X7-specific nanobodies to reach and to block P2X7 on microglia following intravenous or intracerebral administration. For this study, we reformatted and sequence-optimized P2X7 nanobodies for higher stability and elevated isoelectric point. Following injection of nanobodies or nanobody-encoding adeno-associated viral vectors (AAV), we monitored the occupancy and blockade of microglial P2X7 in vivo using ex vivo flow cytometry. Our results show that P2X7 on microglia was within minutes completely occupied and blocked by intracerebroventricularly injected nanobodies, even at low doses. In contrast, very high doses were required to achieve similar effects when injected intravenously. The endogenous production of P2X7-antagonistic nanobodies following intracerebral or intramuscular injection of nanobody-encoding AAVs resulted in a long-term occupancy and blockade of P2X7 on microglia. Our results provide new insights into the conditions for the delivery of nanobodies to microglial P2X7 and point to AAV-mediated delivery of P2X7 nanobodies as a promising strategy for the treatment of sterile brain inflammation.

P2×7 is expressed on human innate-like T lymphocytes and mediates susceptibility to ATP-induced cell death

Extracellular ATP activates the P2×7 receptor, leading to inflammasome activation and release of pro-inflammatory cytokines in monocytes. However, a detailed analysis of P2×7 receptor expression and function in the human T cell compartment has not been reported. Here, we used a P2×7-specific nanobody to assess cell membrane expression and function of P2×7 on peripheral T lymphocyte subsets. The results show that innate-like T cells, which effectively react to innate stimuli by secreting high amounts of pro-inflammatory cytokines, have the highest expression of P2×7 in the human T cell compartment. Using Tγδ cells as example for an innate-like lymphocyte population, we demonstrate that these cells are more sensitive to P2×7 receptor activation than conventional T cells, affecting fundamental cellular mechanisms like calcium signaling and ATP-induced cell death. The increased susceptibility of innate-like T cells to P2×7-mediated cell death provides a mechanism to control their homeostasis under inflammatory conditions. Understanding the expression and function of P2×7 on human immune cells is essential to assume the benefits and consequences of newly developed P2×7-based therapeutic approaches. This article is protected by copyright. All rights reserved.

Nt5e deficiency does not affect post-stroke inflammation and lesion size in a murine ischemia/reperfusion stroke model

Extracellular ATP released to the ischemic brain parenchyma is quickly metabolized by ectonucleotidases. Among them, the ecto-5′-nucleotidase CD73 encoded by Nt5e generates immunosuppressive adenosine. Genetic deletion of Nt5e led to increased infarct size in the murine photothrombotic stroke model. We aimed at validating this result using the transient middle cerebral artery occlusion (tMCAO) stroke model that represents pathophysiological aspects of penumbra and reperfusion. Three days after tMACO, we did not detect a difference in stroke size between CD73-deficient (CD73^−/−) and control mice. Consistent with this finding, CD73^−/− and control mice showed comparable numbers and composition of brain-infiltrating leukocytes measured by flow cytometry. Using NanoString technology, we further demonstrated that CD73^−/− and control mice do not differ regarding glia cell gene expression profiles. Our findings highlight the potential impact of stroke models on study outcome and the need for cross-validation of originally promising immunomodulatory candidates.

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Infarct volume on day 3 after tMCAO was comparable among CD73^−/− and control mice

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Brain leukocyte infiltration on day 3 after tMCAO was similar in CD73^−/− and control mice

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Glial RNA expression profile on day 3 after tMCAO was similar in CD73^−/− and control mice

P2X4 and P2X7 are essential players in basal T cell activity and Ca2+ signaling milliseconds after T cell activation

Initial T cell activation is triggered by the formation of highly dynamic, spatiotemporally restricted Ca²⁺ microdomains. Purinergic signaling is known to be involved in Ca²⁺ influx in T cells at later stages compared to the initial microdomain formation. Using a high-resolution Ca²⁺ live-cell imaging system, we show that the two purinergic cation channels P2X4 and P2X7 not only are involved in the global Ca²⁺ signals but also promote initial Ca²⁺ microdomains tens of milliseconds after T cell stimulation. These Ca²⁺ microdomains were significantly decreased in T cells from P2rx4^-/- and P2rx7^-/- mice or by pharmacological inhibition or blocking. Furthermore, we show a pannexin-1-dependent activation of P2X4 in the absence of T cell receptor/CD3 stimulation. Subsequently, upon T cell receptor/CD3 stimulation, ATP release is increased and autocrine activation of both P2X4 and P2X7 then amplifies initial Ca²⁺ microdomains already in the first second of T cell activation.

Interleukin-10 improves stroke outcome by controlling the detrimental Interleukin-17A response

Background

Lymphocytes have dichotomous functions in ischemic stroke. Regulatory T cells are protective, while IL-17A from innate lymphocytes promotes the infarct growth. With recent advances of T cell-subtype specific transgenic mouse models it now has become possible to study the complex interplay of T cell subpopulations in ischemic stroke.

Methods

In a murine model of experimental stroke we analyzed the effects of IL-10 on the functional outcome for up to 14 days post-ischemia and defined the source of IL-10 in ischemic brains based on immunohistochemistry, flow cytometry, and bone-marrow chimeric mice. We used neutralizing IL-17A antibodies, intrathecal IL-10 injections, and transgenic mouse models which harbor a deletion of the IL-10R on distinct T cell subpopulations to further explore the interplay between IL-10 and IL-17A pathways in the ischemic brain.

Results

We demonstrate that IL-10 deficient mice exhibit significantly increased infarct sizes on days 3 and 7 and enlarged brain atrophy and impaired neurological outcome on day 14 following tMCAO. In ischemic brains IL-10 producing immune cells included regulatory T cells, macrophages, and microglia. Neutralization of IL-17A following stroke reversed the worse outcome in IL-10 deficient mice and intracerebral treatment with recombinant IL-10 revealed that IL-10 controlled IL-17A positive lymphocytes in ischemic brains. Importantly, IL-10 acted differentially on αβ and γδ T cells. IL-17A producing CD4⁺ αβ T cells were directly controlled via their IL-10-receptor (IL-10R), whereas IL-10 by itself had no direct effect on the IL-17A production in γδ T cells. The control of the IL-17A production in γδ T cells depended on an intact IL10R signaling in regulatory T cells (Tregs).

Conclusions

Taken together, our data indicate a key function of IL-10 in restricting the detrimental IL-17A-signaling in stroke and further supports that IL-17A is a therapeutic opportunity for stroke treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02316-7.

CD73-mediated adenosine production by CD8 T cell-derived extracellular vesicles constitutes an intrinsic mechanism of immune suppression

Immune cells at sites of inflammation are continuously activated by local antigens and cytokines, and regulatory mechanisms must be enacted to control inflammation. The stepwise hydrolysis of extracellular ATP by ectonucleotidases CD39 and CD73 generates adenosine, a potent immune suppressor. Here we report that human effector CD8 T cells contribute to adenosine production by releasing CD73-containing extracellular vesicles upon activation. These extracellular vesicles have AMPase activity, and the resulting adenosine mediates immune suppression independently of regulatory T cells. In addition, we show that extracellular vesicles isolated from the synovial fluid of patients with juvenile idiopathic arthritis contribute to T cell suppression in a CD73-dependent manner. Our results suggest that the generation of adenosine upon T cell activation is an intrinsic mechanism of human effector T cells that complements regulatory T cell-mediated suppression in the inflamed tissue. Finally, our data underscore the role of immune cell-derived extracellular vesicles in the control of immune responses.

Identification of the Mouse T Cell ADP-Ribosylome Uncovers ARTC2.2 Mediated Regulation of CD73 by ADP-Ribosylation

Mouse T cells express the ecto-ADP-ribosyltransferase ARTC2.2, which can transfer the ADP-ribose group of extracellular nicotinamide adenine dinucleotide (NAD⁺) to arginine residues of various cell surface proteins thereby influencing their function. Several targets of ARTC2.2, such as P2X7, CD8a and CD25 have been identified, however a comprehensive mouse T cell surface ADP-ribosylome analysis is currently missing. Using the Af1521 macrodomain-based enrichment of ADP-ribosylated peptides and mass spectrometry, we identified 93 ADP-ribsoylated peptides corresponding to 67 distinct T cell proteins, including known targets such as CD8a and CD25 but also previously unknown targets such as CD73. We evaluated the impact of ADP-ribosylation on the capability of CD73 to generate adenosine from adenosine monophosphate. Our results show that extracellular NAD⁺ reduces the enzymatic activity of CD73 HEK cells co-transfected with CD73/ARTC2.2. Importantly, NAD⁺ significantly reduced CD73 activity on WT CD8 T cells compared to ARTC2ko CD8 T cells or WT CD8 T cells treated with an ARTC2.2-blocking nanobody. Our study provides a comprehensive list of T cell membrane proteins that serve as targets for ADP-ribosylation by ARTC2.2 and whose function may be therefore affected by ADP-ribosylation.

ADP-Ribosylation Regulates the Signaling Function of IFN-γ

Murine T cells express the GPI-anchored ADP-ribosyltransferase 2.2 (ARTC2.2) on the cell surface. In response to T cell activation or extracellular NAD⁺ or ATP-mediated gating of the P2X7 ion channel ARTC2.2 is shed from the cell surface as a soluble enzyme. Shedding alters the target specificity of ARTC2.2 from cell surface proteins to secreted proteins. Here we demonstrate that shed ARTC2.2 potently ADP-ribosylates IFN-γ in addition to other cytokines. Using mass spectrometry, we identify arginine 128 as the target site of ADP-ribosylation. This residue has been implicated to play a key role in binding of IFN-γ to the interferon receptor 1 (IFNR1). Indeed, binding of IFN-γ to IFNR1 blocks ADP-ribosylation of IFN-γ. Moreover, ADP-ribosylation of IFN-γ inhibits the capacity of IFN-γ to induce STAT1 phosphorylation in macrophages and upregulation of the proteasomal subunit ß5i and the proteasomal activator PA28-α in podocytes. Our results show that ADP-ribosylation inhibits the signaling functions of IFN-γ and point to a new regulatory mechanism for controlling signaling by IFN-γ.

Improved Functionality of Exhausted Intrahepatic CXCR5+ CD8+ T Cells Contributes to Chronic Antigen Clearance Upon Immunomodulation

Chronic hepatotropic viral infections are characterized by exhausted CD8+ T cells in the presence of cognate antigen in the liver. The impairment of T cell response limits the control of chronic hepatotropic viruses. Immune-modulatory strategies are attractive options to re-invigorate exhausted T cells. However, in hepatotropic viral infections, the knowledge about immune-modulatory effects on the in-situ regulation of exhausted intrahepatic CD8+ T cells is limited. In this study, we elucidated the functional heterogeneity in the pool of exhausted CD8+ T cells in the liver of mice expressing the model antigen Ova in a fraction of hepatocytes. We found a subpopulation of intrahepatic CXCR5+ Ova-specific CD8+ T cells, which are profoundly cytotoxic, exhibiting efficient metabolic functions as well as improved memory recall and self-maintenance. The intrahepatic Ova-specific CXCR5+ CD8+ T cells are possibly tissue resident cells, which may rely largely on OXPHOS and glycolysis to fuel their cellular processes. Importantly, host conditioning with CpG oligonucleotide reinvigorates and promotes exhausted T cell expansion, facilitating complete antigen eradication. The CpG oligonucleotide-mediated reinvigoration may support resident memory T cell formation and the maintenance of CXCR5+ Ova-specific CD8+ T cells in the liver. These findings suggest that CpG oligodinucleotide may preferentially target CXCR5+ CD8+ T cells for expansion to facilitate the revival of exhausted T cells. Thus, therapeutic strategies aiming to expand CXCR5+ CD8+ T cells might provide a novel approach against chronic liver infection.

A P2rx7 Passenger Mutation Affects the Vitality and Function of T cells in Congenic Mice

Among laboratory mouse strains many genes are differentially expressed in the same cell population. As consequence, gene targeting in 129-derived embryonic stem cells (ESCs) and backcrossing the modified mice onto the C57BL/6 background can introduce passenger mutations in the close proximity of the targeted gene. Here, we demonstrate that several transgenic mice carry a P2rx7 passenger mutation that affects the function of T cells. By the example of P2rx4^tm1Rass we demonstrate that P2X4ko T cells express higher levels of P2X7 and are more sensitive toward the P2X7 activators ATP and NAD⁺, rendering these cells more vulnerable toward NAD-induced cell death (NICD) compared with wild type (WT). The enhanced NICD sensitivity confounded functional assays e.g. cytokine production and cell migration. Our results need to be considered when working with P2rx4^tm1Rass mice or other 129-based transgenic strains that target P2rx7 neighboring genes.

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T cells from 129 mice express higher level of P2X7 compared with T cells from B6 mice

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P2rx4^tm1Rass T cells express high level of P2X7 due to a P2rx7 passenger mutation

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P2rx4^tm1Rass T cells are highly susceptible to NAD-induced cell death (NICD)

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NICD susceptibility of P2rx4^tm1Rass T cells confounds the outcome of functional assays

Characterization of brain-derived extracellular vesicles reveals changes in cellular origin after stroke and enrichment of the prion protein with a potential role in cellular uptake

Extracellular vesicles (EVs) are important means of intercellular communication and a potent tool for regenerative therapy. In ischaemic stroke, transient blockage of a brain artery leads to a lack of glucose and oxygen in the affected brain tissue, provoking neuronal death by necrosis in the core of the ischaemic region. The fate of neurons in the surrounding penumbra region depends on the stimuli, including EVs, received during the following hours. A detailed characterization of such stimuli is crucial not only for understanding stroke pathophysiology but also for new therapeutic interventions. In the present study, we characterize the EVs in mouse brain under physiological conditions and 24 h after induction of transient ischaemia in mice. We show that, in steady-state conditions, microglia are the main source of small EVs (sEVs), whereas after ischaemia the main sEV population originates from astrocytes. Brain sEVs presented high amounts of the prion protein (PrP), which were further increased after stroke. Moreover, EVs were enriched in a proteolytically truncated PrP fragment (PrP-C1). Because of similarities between PrP-C1 and certain viral surface proteins, we studied the cellular uptake of brain-derived sEVs from mice lacking (PrP-KO) or expressing PrP (WT). We show that PrP-KO-sEVs are taken up significantly faster and more efficiently than WT-EVs by primary neurons. Furthermore, microglia and astrocytes engulf PrP-KO-sEVs more readily than WT-sEVs. Our results provide novel information on the relative contribution of brain cell types to the sEV pool in murine brain and indicate that increased release of sEVs by astrocytes together with elevated levels of PrP in sEVs may play a role in intercellular communication at early stages after stroke. In addition, amounts of PrP (and probably PrP-C1) in brain sEVs seem to contribute to regulating their cellular uptake.

Circulating Endothelial Cells as Promising Biomarkers in the Differential Diagnosis of Primary Angiitis of the Central Nervous System

Background: Diagnosis of primary angiitis of the central nervous system (PACNS) and discrimination of PACNS from its mimics, e. g., reversible cerebral vasoconstriction syndrome (RCVS) or moyamoya disease (MMD) as non-inflammatory vasculopathies, still remain challenging. Circulating endothelial cells (CEC) are well-established markers for endothelial damage and potential biomarkers in PACNS. This study aimed to investigate if CECs may also help to distinguish an active PACNS from its important differentials (RCVS, MMD).

Methods: CECs were assessed in 47 subjects. Twenty-seven patients with PACNS were included, seven with an active disease (aPACNS), 20 in remission (rPACNS). Seven patients with RCVS/MMD were analyzed. Thirteen healthy subjects served as controls (HC). CECs were measured by immunomagnetic isolation from peripheral venous blood. Mann-Whitney-U-Tests were applied for between-group comparisons. The Benjamini-Hochberg-procedure was applied to adjust for multiple comparisons.

Results: In aPACNS, CECs were significantly elevated compared to HC (480 vs. 40 CEC/ml, p < 0.001) and rPACNS (54 CEC/ml, p < 0.001). RCVS/MMD patients showed higher CEC levels (288 CEC/ml) than HC (p < 0.001), but lower than those in aPACNS (p = 0.017). An adjustment for multiple comparisons confirmed prior significant differences. An increased CEC value (cut-off 294 CEC/ml) is indicative for an active PACNS [sensitivity 100%, 95% confidence interval (CI) 63–100%; specificity 93%, CI 81–98%].

Conclusions: CECs may serve as biomarkers for diagnosis, treatment monitoring, and also for differential diagnosis of PACNS. CECs seem to be a marker of endothelial injury with higher levels in inflammatory than non-inflammatory vasculopathies. Larger patient samples are required to corroborate these findings.

Nanobody-based CD38-specific heavy chain antibodies induce killing of multiple myeloma and other hematological malignancies

Rationale: CD38 is a target for the therapy of multiple myeloma (MM) with monoclonal antibodies such as daratumumab and isatuximab. Since MM patients exhibit a high rate of relapse, the development of new biologics targeting alternative CD38 epitopes is desirable. The discovery of single-domain antibodies (nanobodies) has opened the way for a new generation of antitumor therapeutics. We report the generation of nanobody-based humanized IgG1 heavy chain antibodies (hcAbs) with a high specificity and affinity that recognize three different and non-overlapping epitopes of CD38 and compare their cytotoxicity against CD38-expressing hematological cancer cells in vitro, ex vivo and in vivo. Methods: We generated three humanized hcAbs (WF211-hcAb, MU1067-hcAb, JK36-hcAb) that recognize three different non-overlapping epitopes (E1, E2, E3) of CD38 by fusion of llama-derived nanobodies to the hinge- and Fc-domains of human IgG1. WF211-hcAb shares the binding epitope E1 with daratumumab. We compared the capacity of these CD38-specific hcAbs and daratumumab to induce CDC and ADCC in CD38-expressing tumor cell lines in vitro and in patient MM cells ex vivo as well as effects on xenograft tumor growth and survival in vivo. Results: CD38-specific heavy chain antibodies (WF211-hcAb, MU1067-hcAb, JK36-hcAb) potently induced antibody-dependent cellular cytotoxicity (ADCC) in CD38-expressing tumor cell lines and in primary patient MM cells, but only little if any complement-dependent cytotoxicity (CDC). In vivo, CD38-specific heavy chain antibodies significantly reduced the growth of systemic lymphomas and prolonged survival of tumor bearing SCID mice. Conclusions: CD38-specific nanobody-based humanized IgG1 heavy chain antibodies mediate cytotoxicity against CD38-expressing hematological cancer cells in vitro, ex vivo and in vivo. These promising results of our study indicate that CD38-specific hcAbs warrant further clinical development as therapeutics for multiple myeloma and other hematological malignancies.

Astrocytes and Microglia Are Resistant to NAD+-Mediated Cell Death Along the ARTC2/P2X7 Axis

ADP-ribosylation of the P2X7k splice variant on mouse T cells by Ecto-ADP-ribosyltransferase ARTC2.2 in response to its substrate extracellular nicotinamide adenine dinucleotide (NAD⁺) triggers cell death. Since NAD⁺ is released as a danger signal during tissue damage, this NAD⁺-induced cell death (NICD) may impact the survival of other cell populations co-expressing P2X7 and of one of the ARTC2 isoforms (ARTC2.1, ARTC2.2). NICD of brain-resident, non-T cell populations has only been rudimentarily investigated. In this study, we evaluated the susceptibility of two glia cell populations, astrocytes and microglia, towards NICD. We found that astrocytes and microglia strongly upregulate cell surface levels of ARTC2.1 and ADP-ribosylation of cell surface proteins in response to treatment with lipopolysaccharide (LPS) and the mitogen-activated protein kinase kinase (MEK) 1 and 2 inhibitor U0126, but do not respond to extracellular NAD⁺ with P2X7 activation and induction of cell death. Furthermore, we found that astrocytes and microglia preferentially express the ADP-ribosylation-insensitive P2X7a splice variant, likely accounting for the resistance of these cells to NICD.

Generation and Characterization of Specific Monoclonal Antibodies and Nanobodies Directed Against the ATP-Gated Channel P2X4

The P2X4 channel is involved in different physiological and pathological conditions and functions in the nervous system. Despite the existence of several mouse models for which the expression of the gene was manipulated, there is still little information on the expression of the protein at the cellular level. In particular, supposedly specific available antibodies have often proved to recognize unrelated proteins in P2X4-deficient mice. Here, we used an in vivo DNA vaccine approach to generate a series of monoclonal antibodies and nanobodies specific for human, mouse, and rat P2X4 channels. We further characterized these antibodies and show that they solely recognize the native form of the proteins both in biochemical and cytometric applications. Some of these antibodies prove to specifically recognize P2X4 channels by immunostaining in brain or sensory ganglia slices, as well as at the cellular and subcellular levels. Due to their clonality, these different antibodies should represent versatile tools for further characterizing the cellular functions of P2X4 in the nervous system as well as at the periphery.

Generation and Function of Non-cell-bound CD73 in Inflammation

Extracellular adenine nucleotides participate in cell-to-cell communication and modulate the immune response. The concerted action of ectonucleotidases CD39 and CD73 plays a major role in the local production of anti-inflammatory adenosine, but both ectonucleotidases are rarely co-expressed by human T cells. The expression of CD39 on T cells increases upon T cell activation and is high at sites of inflammation. CD73, in contrast, disappears from the cellular membrane after activation. The possibility that CD73 could act in trans would resolve the conundrum of both enzymes being co-expressed for the degradation of ATP and the generation of adenosine. An enzymatically active soluble form of CD73 has been reported, and AMPase activity has been detected in body fluids of patients with inflammation and cancer. It is not yet clear how CD73, a glycosylphosphatidylinositol (GPI)-anchored protein, is released from the cell membrane, but plausible mechanisms include cleavage by metalloproteinases and shedding mediated by cell-associated phospholipases. Importantly, like many other GPI-anchored proteins, CD73 at the cell membrane is preferentially localized in detergent-resistant domains or lipid rafts, which often contribute to extracellular vesicles (EVs). Indeed, CD73-containing vesicles of different size and origin and with immunomodulatory function have been found in the tumor microenvironment. The occurrence of CD73 as non-cell-bound molecule widens the range of action of this enzyme at sites of inflammation. In this review, we will discuss the generation of non-cell-bound CD73 and its physiological role in inflammation.

P2X4 receptor controls microglia activation and favors remyelination in autoimmune encephalitis

Microglia survey the brain microenvironment for signals of injury or infection and are essential for the initiation and resolution of pathogen‐ or tissue damage‐induced inflammation. Understanding the mechanism of microglia responses during pathology is hence vital to promote regenerative responses. Here, we analyzed the role of purinergic receptor P2X4 (P2X4R) in microglia/macrophages during autoimmune inflammation. Blockade of P2X4R signaling exacerbated clinical signs in the experimental autoimmune encephalomyelitis (EAE) model and also favored microglia activation to a pro‐inflammatory phenotype and inhibited myelin phagocytosis. Moreover, P2X4R blockade in microglia halted oligodendrocyte differentiation in vitro and remyelination after lysolecithin‐induced demyelination. Conversely, potentiation of P2X4R signaling by the allosteric modulator ivermectin (IVM) favored a switch in microglia to an anti‐inflammatory phenotype, potentiated myelin phagocytosis, promoted the remyelination response, and ameliorated clinical signs of EAE. Our results provide evidence that P2X4Rs modulate microglia/macrophage inflammatory responses and identify IVM as a potential candidate among currently used drugs to promote the repair of myelin damage.

Current Approaches and Future Perspectives for Nanobodies in Stroke Diagnostic and Therapy

Antibody-based biologics are the corner stone of modern immunomodulatory therapy. Though highly effective in dampening systemic inflammatory processes, their large size and Fc-fragment mediated effects hamper crossing of the blood brain barrier (BBB). Nanobodies (Nbs) are single domain antibodies derived from llama or shark heavy-chain antibodies and represent a new generation of biologics. Due to their small size, they display excellent tissue penetration capacities and can be easily modified to adjust their vivo half-life for short-term diagnostic or long-term therapeutic purposes or to facilitate crossing of the BBB. Furthermore, owing to their characteristic binding mode, they are capable of antagonizing receptors involved in immune signaling and of neutralizing proinflammatory mediators, such as cytokines. These qualities combined make Nbs well-suited for down-modulating neuroinflammatory processes that occur in the context of brain ischemia. In this review, we summarize recent findings on Nbs in preclinical stroke models and how they can be used as diagnostic and therapeutic reagents. We further provide a perspective on the design of innovative Nb-based treatment protocols to complement and improve stroke therapy.

Re-evaluation of neuronal P2X7 expression using novel mouse models and a P2X7-specific nanobody

The P2X7 channel is involved in the pathogenesis of various CNS diseases. An increasing number of studies suggest its presence in neurons where its putative functions remain controversial for more than a decade. To resolve this issue and to provide a model for analysis of P2X7 functions, we generated P2X7 BAC transgenic mice that allow visualization of functional EGFP-tagged P2X7 receptors in vivo. Extensive characterization of these mice revealed dominant P2X7-EGFP protein expression in microglia, Bergmann glia, and oligodendrocytes, but not in neurons. These findings were further validated by microglia- and oligodendrocyte-specific P2X7 deletion and a novel P2X7-specific nanobody. In addition to the first quantitative analysis of P2X7 protein expression in the CNS, we show potential consequences of its overexpression in ischemic retina and post-traumatic cerebral cortex grey matter. This novel mouse model overcomes previous limitations in P2X7 research and will help to determine its physiological roles and contribution to diseases.

The human body relies on a molecule called ATP as an energy source and as a messenger. When cells die, for example if they are damaged or because of inflammation, they release large amounts of ATP into their environment. Their neighbors can detect the outpouring of ATP through specific receptors, the proteins that sit at the cell’s surface and can bind external agents.

Scientists believe that one of these ATP-binding receptors, P2X7, responds to high levels of ATP by triggering a cascade of reactions that results in inflammation and cell death. P2X7 also seems to play a role in several brain diseases such as epilepsia and Alzheimer’s, but the exact mechanisms are not known. In particular, how this receptor is involved in the death of neurons is unclear, and researchers still debate whether P2X7 is present in neurons and in other types of brain cells.

To answer this, Kaczmarek-Hájek, Zhang, Kopp et al. created genetically modified mice in which the P2X7 receptors carry a fluorescent dye. Powerful microscopes can pick up the light signal from the dye and help to reveal which cells have the receptors. These experiments show that neurons do not carry the protein; instead, P2X7 is present in certain brain cells that keep the neurons healthy. For example, it is found in the immune cells that ‘clean up’ the organ, and the cells that support and insulate neurons. Kaczmarek-Hájek et al. further provide preliminary data suggesting that, under certain conditions, if too many P2X7 receptors are present in these cells neuronal damage might be increased. It is therefore possible that the brain cells that carry P2X7 indirectly contribute to the death of neurons when large amounts of ATP are released.

The genetically engineered mouse designed for the experiments could be used in further studies to dissect the role that P2X7 plays in diseases of the nervous system. In particular, this mouse model might help to understand whether the receptor could become a drug target for neurodegenerative conditions.

In Vivo Blockade of Murine ARTC2.2 During Cell Preparation Preserves the Vitality and Function of Liver Tissue-Resident Memory T Cells

On murine T cells, GPI-anchored ADP-ribosyltransferase 2.2 (ARTC2.2) ADP-ribosylates the P2X7 ion channel at arginine 125 in response to nicotinamide adenine dinucleotide (NAD⁺) released during cell preparation. We have previously shown that chronic gating of P2X7 by ADP-ribosylation reduces the vitality and function of regulatory T cells and natural killer T cells that co-express high levels of ARTC2.2 and P2X7. Here, we evaluated the expression of ARTC2.2 and P2X7 by effector and memory T cells in the liver of naïve mice and after infection with Listeria monocytogenes (Lm). We found that KLRG1⁻/CD69⁺ tissue-resident memory T cells (Trm) in the liver of naïve mice and 7 weeks after infection with Lm express high levels of ARTC2.2 and P2X7. Isolation of liver Trm and subsequent incubation at 37°C resulted in cell death of the majority of CD4⁺ and CD8⁺ Trm. Injection of the ARTC2.2-blocking nanobody s+16a 30 min prior to organ harvesting effectively prevented ADP-ribosylation of P2X7 during cell preparation and thereby prevented NAD-induced cell death of the isolated Trm upon subsequent incubation at 37°C. Consequently, preserving Trm vitality by s+16a injection enabled a highly sensitive in vitro cytokine expression profile analyses of FACS sorted liver Trm. We conclude that in vivo blockade of ARTC2.2 during cell preparation by nanobody s+16a injection represents a valuable strategy to study the role and function of liver Trm in mice.

Nanobodies that block gating of the P2X7 ion channel ameliorate inflammation

Ion channels are desirable therapeutic targets, yet ion channel-directed drugs with high selectivity and few side effects are still needed. Unlike small-molecule inhibitors, antibodies are highly selective for target antigens but mostly fail to antagonize ion channel functions. Nanobodies-small, single-domain antibody fragments-may overcome these problems. P2X7 is a ligand-gated ion channel that, upon sensing adenosine 5'-triphosphate released by damaged cells, initiates a proinflammatory signaling cascade, including release of cytokines, such as interleukin-1β (IL-1β). To further explore its function, we generated and characterized nanobodies against mouse P2X7 that effectively blocked (13A7) or potentiated (14D5) gating of the channel. Systemic injection of nanobody 13A7 in mice blocked P2X7 on T cells and macrophages in vivo and ameliorated experimental glomerulonephritis and allergic contact dermatitis. We also generated nanobody Dano1, which specifically inhibited human P2X7. In endotoxin-treated human blood, Dano1 was 1000 times more potent in preventing IL-1β release than small-molecule P2X7 antagonists currently in clinical development. Our results show that nanobody technology can generate potent, specific therapeutics against ion channels, confirm P2X7 as a therapeutic target for inflammatory disorders, and characterize a potent new drug candidate that targets P2X7.

IL-23 (Interleukin-23)-Producing Conventional Dendritic Cells Control the Detrimental IL-17 (Interleukin-17) Response in Stroke

BACKGROUND AND PURPOSE

Inflammatory mechanisms can exacerbate ischemic tissue damage and worsen clinical outcome in patients with stroke. Both αβ and γδ T cells are established mediators of tissue damage in stroke, and the role of dendritic cells (DCs) in inducing the early events of T cell activation and differentiation in stroke is not well understood.

METHODS

In a murine model of experimental stroke, we defined the immune phenotype of infiltrating DC subsets based on flow cytometry of surface markers, the expression of ontogenetic markers, and cytokine levels. We used conditional DC depletion, bone marrow chimeric mice, and IL-23 (interleukin-23) receptor-deficient mice to further explore the functional role of DCs.

RESULTS

We show that the ischemic brain was rapidly infiltrated by IRF4⁺/CD172a⁺ conventional type 2 DCs and that conventional type 2 DCs were the most abundant subset in comparison with all other DC subsets. Twenty-four hours after ischemia onset, conventional type 2 DCs became the major source of IL-23, promoting neutrophil infiltration by induction of IL-17 (interleukin-17) in γδ T cells. Functionally, the depletion of CD11c⁺ cells or the genetic disruption of the IL-23 signaling abrogated both IL-17 production in γδ T cells and neutrophil infiltration. Interruption of the IL-23/IL-17 cascade decreased infarct size and improved neurological outcome after stroke.

CONCLUSIONS

Our results suggest a central role for interferon regulatory factor 4-positive IL-23-producing conventional DCs in the IL-17-dependent secondary tissue damage in stroke.

Ecto-ADP-ribosyltransferase ARTC2.1 functionally modulates FcγR1 and FcγR2B on murine microglia

Mammalian ecto-ADP-ribosyltransferases (ecto-ARTs or also ARTCs) catalyze the ADP-ribosylation of cell surface proteins using extracellular nicotinamide adenine dinucleotide (NAD⁺) as substrate. By this post-translational protein modification, ecto-ARTs modulate the function of various target proteins. A functional role of ARTC2 has been demonstrated for peripheral immune cells such as T cells and macrophages. Yet, little is known about the role of ecto-ARTs in the central nervous system and on microglia. Here, we identified ARTC2.1 as the major ecto-ART expressed on murine microglia. ARTC2.1 expression was strongly upregulated on microglia upon co-stimulation with LPS and an ERK1/2 inhibitor or upon IFNβ stimulation. We identified several target proteins modified by ARTC2.1 on microglia with a recently developed mass spectrometry approach, including two receptors for immunoglobulin G (IgG), FcγR1 and FcγR2B. Both proteins were verified as targets of ARTC2.1 in vitro using a radiolabeling assay with ³²P-NAD⁺ as substrate. Moreover, ADP-ribosylation of both targets strongly inhibited their capacity to bind IgG. In concordance, ARTC2.1 induction in WT microglia and subsequent cell surface ADP-ribosylation significantly reduced the phagocytosis of IgG-coated latex beads, which was unimpaired in NAD⁺/DTT treated microglia from ARTC2.1^-/- mice. Hence, induction of ARTC2.1 expression under inflammatory conditions, and subsequent ADP-ribosylation of cell surface target proteins could represent a hitherto unnoticed mechanism to regulate the immune response of murine microglia.

Indoxyl Sulfate Affects Glial Function Increasing Oxidative Stress and Neuroinflammation in Chronic Kidney Disease: Interaction between Astrocytes and Microglia

Indoxyl sulfate (IS) is a protein-bound uremic toxin resulting from the metabolism of dietary tryptophan which accumulates in patients with impaired renal function, such as chronic kidney disease (CKD). IS is a well-known nephrovascular toxin but little is known about its effects on central nervous system (CNS) cells. Considering the growing interest in the field of CNS comorbidities in CKD, we studied the effect of IS on CNS cells. IS (15–60 μM) treatment in C6 astrocyte cells increased reactive oxygen species release and decreased nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activation, and heme oxygenase-1 (HO-1) and NAD(P)H dehydrogenase quinone 1 expression. Moreover, IS increased Aryl hydrocarbon Receptor (AhR) and Nuclear Factor-kB (NF-kB) activation in these cells. Similiar observations were made in primary mouse astrocytes and mixed glial cells. Inducible nitric oxide synthase and cyclooxygenase-2 (COX-2) expression, tumor necrosis factor-α and interleukin-6 release and nitrotyrosine formation were increased by IS (15–60 μM) in primary mouse astrocytes and mixed glial cells. IS increased AhR and NF-kB nuclear translocation and reduced Nrf2 translocation and HO-1 expression in primary glial cells. In addition, IS induced cell death in neurons in a dose dependent fashion. Injection of IS (800 mg/kg, i.p.) into mice induced histological changes and increased COX-2 expression and nitrotyrosine formation in thebrain tissue. Taken together, our results show a significant contribution of IS in generating a neurotoxic enviroment and it could also have a potential role in neurodegeneration. IS could be considered also a potential therapeutical target for CKD-associated neurodegenerative complications.

Nucleotide-Induced Membrane-Proximal Proteolysis Controls the Substrate Specificity of T Cell Ecto-ADP-Ribosyltransferase ARTC2.2

ARTC2.2 is a toxin-related, GPI-anchored ADP-ribosyltransferase expressed by murine T cells. In response to NAD(+) released from damaged cells during inflammation, ARTC2.2 ADP-ribosylates and thereby gates the P2X7 ion channel. This induces ectodomain shedding of metalloprotease-sensitive cell surface proteins. In this study, we show that ARTC2.2 itself is a target for P2X7-triggered ectodomain shedding. We identify the metalloprotease cleavage site 3 aa upstream of the predicted GPI anchor attachment site of ARTC2.2. Intravenous injection of NAD(+) increased the level of enzymatically active ARTC2.2 in serum, indicating that this mechanism is operative also under inflammatory conditions in vivo. Radio-ADP-ribosylation assays reveal that shedding refocuses the target specificity of ARTC2.2 from membrane proteins to secretory proteins. Our results uncover nucleotide-induced membrane-proximal proteolysis as a regulatory mechanism to control the substrate specificity of ARTC2.2.

P2X7 on Mouse T Cells: One Channel, Many Functions

The P2X7 receptor is an adenosine triphosphate (ATP)-gated cation channel that is expressed by several cells of the immune system. P2X7 is best known for its proinflammatory role in promoting inflammasome formation and release of mature interleukin (IL)-1β by innate immune cells. Mounting evidence indicates that P2X7 is also an important regulatory receptor of murine and human T cell functions. Murine T cells express a sensitive splice variant of P2X7 that can be activated either by non-covalent binding of ATP or, in the presence of nicotinamide adenine dinucleotide, by its covalent ADP-ribosylation catalyzed by the ecto-ADP-ribosyltransferase ARTC2.2. Prolonged activation of P2X7 by either one of these pathways triggers the induction of T cell death. Conversely, lower concentrations of ATP can activate P2X7 to enhance T cell proliferation and production of IL-2. In this review, we will highlight the molecular and cellular consequences of P2X7 activation on mouse T cells and its versatile role in T cell homeostasis and activation. Further, we will discuss important differences in the function of P2X7 on human and murine T cells.

Validation of nanobody and antibody based in vivo tumor xenograft NIRF-imaging experiments in mice using ex vivo flow cytometry and microscopy

This protocol outlines the steps required to perform ex vivo validation of in vivo near-infrared fluorescence (NIRF) xenograft imaging experiments in mice using fluorophore labelled nanobodies and conventional antibodies. First we describe how to generate subcutaneous tumors in mice, using antigen-negative cell lines as negative controls and antigen-positive cells as positive controls in the same mice for intraindividual comparison. We outline how to administer intravenously near-infrared fluorophore labelled (AlexaFluor680) antigen-specific nanobodies and conventional antibodies. In vivo imaging was performed with a small-animal NIRF-Imaging system. After the in vivo imaging experiments the mice were sacrificed. We then describe how to prepare the tumors for parallel ex vivo analyses by flow cytometry and fluorescence microscopy to validate in vivo imaging results. The use of the near-infrared fluorophore labelled nanobodies allows for non-invasive same day imaging in vivo. Our protocols describe the ex vivo quantification of the specific labeling efficiency of tumor cells by flow cytometry and analysis of the distribution of the antibody constructs within the tumors by fluorescence microscopy. Using near-infrared fluorophore labelled probes allows for non-invasive, economical in vivo imaging with the unique ability to exploit the same probe without further secondary labelling for ex vivo validation experiments using flow cytometry and fluorescence microscopy.

Tuning IL-2 signaling by ADP-ribosylation of CD25

Control of immunologic tolerance and homeostasis rely on Foxp3⁺CD4⁺CD25⁺ regulatory T cells (Tregs) that constitutively express the high affinity receptor for Interleukin-2, CD25. Tregs proliferate in response to injections of IL-2/anti-IL-2 antibody complexes or low doses of IL-2. However, little is known about endogenous mechanisms that regulate the sensitivity of CD25 to signaling by IL-2. Here we demonstrate that CD25 is ADP-ribosylated at Arg35 in the IL-2 binding site by ecto-ADP-ribosyltransferase ARTC2.2, a toxin-related GPI-anchored ecto-enzyme. ADP-ribosylation inhibits binding of IL-2 by CD25, IL-2- induced phosphorylation of STAT5, and IL-2-dependent cell proliferation. Our study elucidates an as-yet-unrecognized mechanism to tune IL-2 signaling. This newly found mechanism might thwart Tregs at sites of inflammation and thereby permit a more potent response of activated effector T cells.

Nanobodies as modulators of inflammation: potential applications for acute brain injury

Nanobodies are single domain antibodies derived from llama heavy-chain only antibodies (HCAbs). They represent a new generation of biologicals with unique properties: nanobodies show excellent tissue distribution, high temperature and pH stability, are easy to produce recombinantly and can readily be converted into different formats such as Fc-fusion proteins or hetero-dimers. Moreover, nanobodies have the unique ability to bind molecular clefts, such as the active site of enzymes, thereby interfering with the function of the target protein. Over the last decade, numerous nanobodies have been developed against proteins involved in inflammation with the aim to modulate their immune functions. Here, we give an overview about recently developed nanobodies that target immunological pathways linked to neuroinflammation. Furthermore, we highlight strategies to modify nanobodies so that they can overcome the blood brain barrier and serve as highly specific therapeutics for acute inflammatory brain injury.

Technical Advance: a new cell preparation strategy that greatly improves the yield of vital and functional Tregs and NKT cells

Release of NAD(+) during preparation of murine lymphocytes causes enzymatic ADP-ribosylation of cell-surface proteins on T cells, catalyzed by toxin-related ecto-ADP-ribosyltransferase, ARTC2. ADP-riboslyation activates the cytolytic P2X7 ion channel and affects, in particular, the vitality and function of Tregs and NKT cells. Here, we describe a simple method-injection of an ARTC2-blocking nanobody-to greatly improve Treg and NKT cell vitality and to preserve their function during in vitro assays and in adoptive-transfer experiments. Moreover, we present a method for the sorting of functional, primary NKT cells, based on coexpression of ARTC2 and NK1.1. Our results pave the way for the efficient ex vivo proliferation of Tregs and NKT cells and for new experimental and therapeutic uses of these important regulatory cells.

The art of blocking ADP-ribosyltransferases (ARTs): nanobodies as experimental and therapeutic tools to block mammalian and toxin ARTs

In 1901, the first Nobel Prize in Physiology or Medicine was awarded to Emil von Behring for his ground-breaking discovery of serum therapy: serum from horses vaccinated with toxin-containing culture medium of Corynebacterium diphtheriae contained life-saving 'antitoxins'. The molecular nature of the ADP-ribosylating toxin and the neutralizing antibodies were unraveled only 50 years later. Today, von Behring's antibody therapy is being refined with a new generation of recombinant antibodies and antibody fragments. Nanobodies, which are single-domain antibodies derived from the peculiar heavy-chain antibodies of llamas and other camelids, are emerging as a promising new class of highly specific enzyme inhibitors. In this review, we illustrate the potential of nanobodies as tools to block extracellular and intracellular ADP-ribosyltransferases (ARTs), using the toxin-related membrane-bound mammalian ecto-enzyme ARTC2 and the actin-ADP-ribosylating Salmonella virulence plasmid factor B toxin of Salmonella enterica as examples.

Extracellular NAD+ shapes the Foxp3+ regulatory T cell compartment through the ART2-P2X7 pathway

CD4(+)CD25(+)FoxP3(+) regulatory T cells (T reg cells) play a major role in the control of immune responses but the factors controlling their homeostasis and function remain poorly characterized. Nicotinamide adenine dinucleotide (NAD(+)) released during cell damage or inflammation results in ART2.2-mediated ADP-ribosylation of the cytolytic P2X7 receptor on T cells. We show that T reg cells express the ART2.2 enzyme and high levels of P2X7 and that T reg cells can be depleted by intravenous injection of NAD(+). Moreover, lower T reg cell numbers are found in mice deficient for the NAD-hydrolase CD38 than in wild-type, P2X7-deficient, or ART2-deficient mice, indicating a role for extracellular NAD(+) in T reg cell homeostasis. Even routine cell preparation leads to release of NAD(+) in sufficient quantities to profoundly affect T reg cell viability, phenotype, and function. We demonstrate that T reg cells can be protected from the deleterious effects of NAD(+) by an inhibitory ART2.2-specific single domain antibody. Furthermore, selective depletion of T reg cells by systemic administration of NAD(+) can be used to promote an antitumor response in several mouse tumor models. Collectively, our data demonstrate that NAD(+) influences survival, phenotype, and function of T reg cells and provide proof of principle that acting on the ART2-P2X7 pathway represents a new strategy to manipulate T reg cells in vivo.

A recombinant heavy chain antibody approach blocks ART2 mediated deletion of an iNKT cell population that upon activation inhibits autoimmune diabetes

The ectoenzyme ADP-ribosyltransferase 2.2 (ART2.2) can apoptotically delete various T-cell subsets. Depending on the involved apoptotic T-cell subset, enhanced ART2.2 activity could result in immunosuppression or autoimmunity. Diminished activity of the CD38 ectoenzyme that normally represents a counter-regulatory competitor for the NAD substrate represents one mechanism enhancing ART2.2 activity. Hence, it would be desirable to develop an agent that efficiently blocks ART2.2 activity in vivo. While the llama derived recombinant s+16 single domain antibody overcame the difficulty of specifically targeting the ART2.2 catalytic site potential therapeutic use of this reagent is limited due to short in vivo persistence. Thus, we tested if a modified version of s+16 incorporating the murine IgG1 Fc tail (s+16Fc) mediated long-term efficient in vivo suppression of ART2.2. We reasoned an ideal model to test the s+16Fc reagent were NOD mice in which genetic ablation of CD38 results in an ART2.2 mediated reduction in already sub-normal numbers of immunoregulatory natural killer T-(NKT) cells to a level that no longer allows them when activated by the super-agonist alpha-galactosylceramide (alpha-GalCer) to elicit effects inhibiting autoimmune type 1 diabetes (T1D) development. Treatment with s+16Fc efficiently mediated long-term in vivo inhibition of ART2.2 activity in NOD.CD38(null) mice, restoring their iNKT cell numbers to levels that upon alpha-GalCer activation were capable of inhibiting T1D development.

Single domain antibodies: promising experimental and therapeutic tools in infection and immunity

Antibodies are important tools for experimental research and medical applications. Most antibodies are composed of two heavy and two light chains. Both chains contribute to the antigen-binding site which is usually flat or concave. In addition to these conventional antibodies, llamas, other camelids, and sharks also produce antibodies composed only of heavy chains. The antigen-binding site of these unusual heavy chain antibodies (hcAbs) is formed only by a single domain, designated VHH in camelid hcAbs and VNAR in shark hcAbs. VHH and VNAR are easily produced as recombinant proteins, designated single domain antibodies (sdAbs) or nanobodies. The CDR3 region of these sdAbs possesses the extraordinary capacity to form long fingerlike extensions that can extend into cavities on antigens, e.g., the active site crevice of enzymes. Other advantageous features of nanobodies include their small size, high solubility, thermal stability, refolding capacity, and good tissue penetration in vivo. Here we review the results of several recent proof-of-principle studies that open the exciting perspective of using sdAbs for modulating immune functions and for targeting toxins and microbes.