Sahil Adriouch

Bio: Sahil Adriouch is an academic researcher from French Institute of Health and Medical Research. The author has contributed to research in topics: Immune system & NAD+ kinase. The author has an hindex of 27, co-authored 67 publications receiving 3135 citations. Previous affiliations of Sahil Adriouch include Paris Diderot University & University of Rouen.

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

Abstract: 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.

Cutting edge: a natural P451L mutation in the cytoplasmic domain impairs the function of the mouse P2X7 receptor.

Abstract: The P2X7 receptor (P2X 7 R) is an ATP-gated channel that mediates apoptosis of cells of the immune system. The capacity of P2X 7 R to form large pores depends on its large cytoplasmic tail, which harbors a putative TNFR-related death domain. Previous transfection studies indicated that mouse P2X 7 R forms pores much less efficiently than its counterparts from humans and rats. In this study, we demonstrate that an allelic mutation (P451L) in the predicted death domain of P2X 7 R confers a drastically reduced sensitivity to ATP-induced pore formation in cells from some commonly used strains of mice, i.e., C57BL/6 and DBA/2. In contrast, most other strains of mice, including strains derived from wild mice, carry P451 at this position as do rats and humans. The effects of the P451L mutation resemble those of the E496A mutation in human P2X 7 R. These P2X 7 R mutants may provide useful tools to decipher the molecular mechanisms leading to pore formation.

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

Abstract: 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.

Extracellular NAD and ATP: Partners in immune cell modulation.

Abstract: Extracellular NAD and ATP exert multiple, partially overlapping effects on immune cells. Catabolism of both nucleotides by extracellular enzymes keeps extracellular concentrations low under steady-state conditions and generates metabolites that are themselves signal transducers. ATP and its metabolites signal through purinergic P2 and P1 receptors, whereas extracellular NAD exerts its effects by serving as a substrate for ADP-ribosyltransferases (ARTs) and NAD glycohydrolases/ADPR cyclases like CD38 and CD157. Both nucleotides activate the P2X7 purinoceptor, although by different mechanisms and with different characteristics. While ATP activates P2X7 directly as a soluble ligand, activation via NAD occurs by ART-dependent ADP-ribosylation of cell surface proteins, providing an immobilised ligand. P2X7 activation by either route leads to phosphatidylserine exposure, shedding of CD62L, and ultimately to cell death. Activation by ATP requires high micromolar concentrations of nucleotide and is readily reversible, whereas NAD-dependent stimulation begins at low micromolar concentrations and is more stable. Under conditions of cell stress or inflammation, ATP and NAD are released into the extracellular space from intracellular stores by lytic and non-lytic mechanisms, and may serve as ‘danger signals–to alert the immune response to tissue damage. Since ART expression is limited to naive/resting T cells, P2X7-mediated NAD-induced cell death (NICD) specifically targets this cell population. In inflamed tissue, NICD may inhibit bystander activation of unprimed T cells, reducing the risk of autoimmunity. In draining lymph nodes, NICD may eliminate regulatory T cells or provide space for the preferential expansion of primed cells, and thus help to augment an immune response.

The Inflammasomes: Guardians of the Body

Abstract: The innate immune system relies on its capacity to rapidly detect invading pathogenic microbes as foreign and to eliminate them. The discovery of Toll-like receptors (TLRs) provided a class of membrane receptors that sense extracellular microbes and trigger antipathogen signaling cascades. More recently, intracellular microbial sensors have been identified, including NOD-like receptors (NLRs). Some of the NLRs also sense nonmicrobial danger signals and form large cytoplasmic complexes called inflammasomes that link the sensing of microbial products and metabolic stress to the proteolytic activation of the proinflammatory cytokines IL-1β and IL-18. The NALP3 inflammasome has been associated with several autoinflammatory conditions including gout. Likewise, the NALP3 inflammasome is a crucial element in the adjuvant effect of aluminum and can direct a humoral adaptive immune response. In this review, we discuss the role of NLRs, and in particular the inflammasomes, in the recognition of microbial and danger components and the role they play in health and disease.

IDO expression by dendritic cells: tolerance and tryptophan catabolism.

Abstract: Indoleamine 2,3-dioxygenase (IDO) is an enzyme that degrades the essential amino acid tryptophan. The concept that cells expressing IDO can suppress T-cell responses and promote tolerance is a relatively new paradigm in immunology. Considerable evidence now supports this hypothesis, including studies of mammalian pregnancy, tumour resistance, chronic infections and autoimmune diseases. In this review, we summarize key recent developments and propose a unifying model for the role of IDO in tolerance induction.

Nanobodies: Natural Single-Domain Antibodies

Abstract: Sera of camelids contain both conventional heterotetrameric antibodies and unique functional heavy (H)-chain antibodies (HCAbs). The H chain of these homodimeric antibodies consists of one antigen-binding domain, the VHH, and two constant domains. HCAbs fail to incorporate light (L) chains owing to the deletion of the first constant domain and a reshaped surface at the VHH side, which normally associates with L chains in conventional antibodies. The genetic elements composing HCAbs have been identified, but the in vivo generation of these antibodies from their dedicated genes into antigen-specific and affinity-matured bona fide antibodies remains largely underinvestigated. However, the facile identification of antigen-specific VHHs and their beneficial biochemical and economic properties (size, affinity, specificity, stability, production cost) supported by multiple crystal structures have encouraged antibody engineering of these single-domain antibodies for use as a research tool and in biotechnology and medicine.

NAD+/NADH and NADP+/NADPH in Cellular Functions and Cell Death: Regulation and Biological Consequences

Abstract: Accumulating evidence has suggested that NAD (including NAD+ and NADH) and NADP (including NADP+ and NADPH) could belong to the fundamental common mediators of various biological processes, including energy metabolism, mitochondrial functions, calcium homeostasis, antioxidation/generation of oxidative stress, gene expression, immunological functions, aging, and cell death: First, it is established that NAD mediates energy metabolism and mitochondrial functions; second, NADPH is a key component in cellular antioxidation systems; and NADH-dependent reactive oxygen species (ROS) generation from mitochondria and NADPH oxidase-dependent ROS generation are two critical mechanisms of ROS generation; third, cyclic ADP-ribose and several other molecules that are generated from NAD and NADP could mediate calcium homeostasis; fourth, NAD and NADP modulate multiple key factors in cell death, such as mitochondrial permeability transition, energy state, poly(ADP-ribose) polymerase-1, and apoptosis-inducing factor; and fifth, NAD and NADP profoundly affect aging-influencing factors such as oxidative stress and mitochondrial activities, and NAD-dependent sirtuins also mediate the aging process. Moreover, many recent studies have suggested novel paradigms of NAD and NADP metabolism. Future investigation into the metabolism and biological functions of NAD and NADP may expose fundamental properties of life, and suggest new strategies for treating diseases and slowing the aging process.

A view on drug resistance in cancer

Abstract: The problem of resistance to therapy in cancer is multifaceted. Here we take a reductionist approach to define and separate the key determinants of drug resistance, which include tumour burden and growth kinetics; tumour heterogeneity; physical barriers; the immune system and the microenvironment; undruggable cancer drivers; and the many consequences of applying therapeutic pressures. We propose four general solutions to drug resistance that are based on earlier detection of tumours permitting cancer interception; adaptive monitoring during therapy; the addition of novel drugs and improved pharmacological principles that result in deeper responses; and the identification of cancer cell dependencies by high-throughput synthetic lethality screens, integration of clinico-genomic data and computational modelling. These different approaches could eventually be synthesized for each tumour at any decision point and used to inform the choice of therapy. A review of drug resistance in cancer analyses each biological determinant of resistance separately and discusses existing and new therapeutic strategies to combat the problem as a whole.