ABSTRACT: Originally discovered as a T cell-activating molecule, 4-1BB (CD137) is now also recognized as an activator of non-T cells, thus imparting a new dimension to its potential in vivo effects. 4-1BB expression is seen on a variety of non-T cells including activated dendritic cells (DCs), monocytes, neutrophils, B cells and natural killer (NK) cells, and promotes their individual effector functions. The T cell- and non-T cell-activating ability of 4-1BB may be the basis of its powerful anti-cancer, anti-autoimmune and anti-viral effects. Here we discuss the consequence and importance of 4-1BB signaling in non-T cells. We consider its effects on immune regulation, and the distinct and/or overlapping pathways involved in these responses, as well as possible therapeutic applications.
Project description:4-1BB ligand (4-1BBL) and its receptor, 4-1BB, are both induced on T cells after activation, but little is known about the role of 4-1BBL. In this study we show that 4-1BBL can transmit signals that limit T cell effector activity under tolerogenic conditions. Cross-linking 4-1BBL inhibited IL-2 production in vitro, primarily with suboptimal TCR stimulation. Furthermore, naive 4-1BBL-deficient OT-II transgenic T cells displayed a greater conversion to effector T cells in vivo when responding to soluble OVA peptide in wild-type hosts, whereas development of Foxp3(+) regulatory T cells was not altered. A greater number of effector T cells also differentiated from naive wild-type OT-II T cells when transferred into 4-1BB-deficient hosts, suggesting that APC-derived 4-1BB is likely to trigger 4-1BBL. Indeed, effector T cells that could not express 4-1BBL accumulated in larger numbers in vitro when stimulated with 4-1BB-expressing mesenteric lymph node dendritic cells. 4-1BBL was expressed on T cells when Ag presentation was limiting, and 4-1BBL was aberrantly expressed at very high levels on T cells that could not express 4-1BB. Trans-ligation, Ab capture, and endocytosis experiments additionally showed that T cell-intrinsic 4-1BB regulated internalization of membrane 4-1BBL, implying that the strong induction of 4-1BB on T cells may counteract the suppressive function of 4-1BBL by limiting its availability. These data suggest that 4-1BBL expressed on T cells can restrain effector T cell development, creating a more favorable regulatory T cell to effector cell balance under tolerogenic conditions, and this may be particularly active in mucosal barrier tissues where 4-1BB-expressing regulatory dendritic cells present Ag.
Project description:The most conspicuous function of plastids is the oxygenic photosynthesis of chloroplasts, yet plastids are super-factories that produce a plethora of compounds that are indispensable for proper plant physiology and development. Given their origins as free-living prokaryotes, it is not surprising that plastids possess their own genomes whose expression is essential to plastid function. This semi-autonomous character of plastids requires the existence of sophisticated regulatory mechanisms that provide reliable communication between them and other cellular compartments. Such intracellular signaling is necessary for coordinating whole-cell responses to constantly varying environmental cues and cellular metabolic needs. This is achieved by plastids acting as receivers and transmitters of specific signals that coordinate expression of the nuclear and plastid genomes according to particular needs. In this review we will consider the so-called retrograde signaling occurring between plastids and nuclei, and between plastids and other organelles. Another important role of the plastid we will discuss is the involvement of plastid signaling in biotic and abiotic stress that, in addition to influencing retrograde signaling, has direct effects on several cellular compartments including the cell wall. We will also review recent evidence pointing to an intriguing function of chloroplasts in regulating intercellular symplasmic transport. Finally, we consider an intriguing yet less widely known aspect of plant biology, chloroplast signaling from the perspective of the entire plant. Thus, accumulating evidence highlights that chloroplasts, with their complex signaling pathways, provide a mechanism for exquisite regulation of plant development, metabolism and responses to the environment. As chloroplast processes are targeted for engineering for improved productivity the effect of such modifications on chloroplast signaling will have to be carefully considered in order to avoid unintended consequences on plant growth and development.
Project description:4-1BB (CD137, TNFRSF9), a member of the activation-induced tumor necrosis factor receptor family, is a powerful T-cell costimulatory molecule. It generally enhances CD8(+) T responses and even breaks the tolerance of CD8(+) T cells in an antigen-specific manner. In the present study we found that it was expressed in the placentas of pregnant mice and that its expression coincided with that of the immunesuppressive enzyme indoleamine 2,3-dioxygenase (IDO). Therefore, we investigated whether 4-1BB signaling is involved in fetal rejection using agonistic anti-4-1BB mAb and 4-1BB-deficient mice. Treatment with agonistic anti-4-1BB mAb markedly increased the rate of rejection of allogeneic but not syngeneic fetuses, and this was primarily dependent on CD8(+) T cells. Complement component 3 (C3) seemed to be the effector molecule because 4-1BB triggering resulting in accumulation of C3 in the placenta, and this accumulation was also reversed by anti-CD8 mAb treatment. These findings demonstrate that 4-1BB triggering breaks the tolerance of CD8(+) T cells to alloantigens in the placenta. Moreover, triggering 4-1BB protected the pregnant mice from Listeria monocytogenes (LM) infection, but led to rejection of semi-allogeneic fetuses. Therefore, given the cross-recognition of alloantigen by pathogen-reactive CD8(+) T cells, the true function of 4-1BB may be to reverse the hypo-responsiveness of pathogen-reactive CD8(+) T cells in the placenta in cases of infection, even if that risks losing the fetus.
Project description:When optimizing chimeric antigen receptor (CAR) therapy in terms of efficacy, safety, and broadening its application to new malignancies, there are two main clusters of topics to be addressed: the CAR design and the choice of transfected cells. The former focuses on the CAR construct itself. The utilized transmembrane and intracellular domains determine the signaling pathways induced by antigen binding and thereby the cell-specific effector functions triggered. The main part of this review summarizes our understanding of common signaling domains employed in CARs, their interactions among another, and their effects on different cell types. It will, moreover, highlight several less common extracellular and intracellular domains that might permit unique new opportunities. Different antibody-based extracellular antigen-binding domains have been pursued and optimized to strike a balance between specificity, affinity, and toxicity, but these have been reviewed elsewhere. The second cluster of topics is about the cellular vessels expressing the CAR. It is essential to understand the specific attributes of each cell type influencing anti-tumor efficacy, persistence, and safety, and how CAR cells crosstalk with each other and bystander cells. The first part of this review focuses on the progress achieved in adopting different leukocytes for CAR therapy.
Project description:Non-melanoma skin cancers (NMSC) have a higher incidence than all other cancers combined with cutaneous squamous cell carcinoma (cSCC), capable of metastasis, representing approximately 20% of NMSCs. Given the accessibility of the skin, surgery is frequently employed to treat localized disease, although certain localities, the delineation of clear margins, frequency and recurrence of tumors can make these cancers inoperable in a subset of patients. Other treatment modalities, including cryotherapy, are commonly used for individual lesions, with varying success. Immunotherapy, particularly with checkpoint antibodies, is increasingly a promising therapeutic approach in many cancers, offering the potential advantage of immune memory for protection against lesion recurrence. This review addresses a role for PD-1, 4-1BB and VISTA checkpoint antibodies as monotherapies, or in combination as a therapeutic treatment for both early and late-stage cSCC.
Project description:Costimulatory signals provided to T cells during antigen encounter have a decisive role in the outcome of immune responses. Here, we used chimeric receptors harboring the extracellular domain of mouse inducible T cell costimulator (mICOS) to study transcriptional activation mediated by cytoplasmic sequences of the major T cell costimulatory receptors CD28, 4-1BB, and CD2. The chimeric receptors were introduced in a T cell reporter platform that allows to simultaneously evaluate nuclear factor κB (NF-κB), NFAT, and AP-1 activation. Engagement of the chimeric receptors induced distinct transcriptional profiles. CD28 signaling activated all three transcription factors, whereas 4-1BB strongly promoted NF-κB and AP-1 but downregulated NFAT activity. CD2 signals resulted in the strongest upregulation of NFAT. Transcriptome analysis revealed pronounced and distinct gene expression signatures upon CD2 and 4-1BB signaling. Using the intracellular sequence of CD28, we exemplify that distinct signaling motifs endow chimeric receptors with different costimulatory capacities.
Project description:TRAF2 dependent K63-polyubiquitinations have been recently shown to connect CD137 (4-1BB) stimulation to NF-κB activation. In a search of deubiquitinase enzymes (DUBs) that could regulate such a signaling route, A20 and CYLD were found to coimmunoprecipitate with CD137 and TRAF2 complexes. Indeed, overexpression of A20 or CYLD downregulated CD137-elicited ubiquitination of TRAF2 and TAK1 upon stimulation with agonist monoclonal antibodies. Moreover, overexpression of A20 or CYLD downregulated CD137-induced NF-κB activation in cultured cells and in gene-transferred hepatocytes in vivo, while silencing these deubiquitinases enhanced CD137 costimulation of primary human CD8 T cells. Therefore A20 and CYLD directly downregulate the signaling from a T and NK-cell costimulatory receptor under exploitation for cancer immunotherapy in clinical trials.
Project description:4-1BB (CD137) is a TNF receptor superfamily (TNFRSF) member that is thought to undergo receptor trimerization upon binding to its trimeric TNF superfamily ligand (4-1BBL) to stimulate immune responses. 4-1BB also can bind to the tandem repeat-type lectin galectin-9 (Gal-9), and signaling through mouse (m)4-1BB is reduced in galectin-9 (Gal-9)-deficient mice, suggesting a pivotal role of Gal-9 in m4-1BB activation. Here, using sulfur-SAD phasing, we determined the crystal structure of m4-1BB to 2.2-Å resolution. We found that similar to other TNFRSFs, m4-1BB has four cysteine-rich domains (CRDs). However, the organization of CRD1 and the orientation of CRD3 and CRD4 with respect to CRD2 in the m4-1BB structure distinctly differed from those of other TNFRSFs. Moreover, we mapped two Asn residues within CRD4 that are N-linked glycosylated and mediate m4-1BB binding to Gal-9. Kinetics studies of m4-1BB disclosed a very tight nanomolar binding affinity to m4-1BBL with an unexpectedly strong avidity effect. Both N- and C-terminal domains of Gal-9 bound m4-1BB, but with lower affinity compared with m4-1BBL. Although the TNF homology domain (THD) of human (h)4-1BBL forms non-covalent trimers, we found that m4-1BBL formed a covalent dimer via 2 cysteines absent in h4-1BBL. As multimerization and clustering is a prerequisite for TNFR intracellular signaling, and as m4-1BBL can only recruit two m4-1BB monomers, we hypothesize that m4-1BBL and Gal-9 act together to aid aggregation of m4-1BB monomers to efficiently initiate m4-1BB signaling.
Project description:T cells engineered to express chimeric antigen receptors (CARs) targeting CD19 have produced impressive outcomes for the treatment of B cell malignancies, but different products vary in kinetics, persistence, and toxicity profiles based on the co-stimulatory domains included in the CAR. In this study, we performed transcriptional profiling of bulk CAR T cell populations and single cells to characterize the transcriptional states of human T cells transduced with CD3ζ, 4-1BB-CD3ζ (BBζ), or CD28-CD3ζ (28ζ) co-stimulatory domains at rest and after activation by triggering their CAR or their endogenous T cell receptor (TCR). We identified a transcriptional signature common across CARs with the CD3ζ signaling domain, as well as a distinct program associated with the 4-1BB co-stimulatory domain at rest and after activation. CAR T cells bearing BBζ had increased expression of human leukocyte antigen (HLA) class II genes, ENPP2, and interleukin (IL)-21 axis genes, and decreased PD1 compared to 28ζ CAR T cells. Similar to previous studies, we also found BBζ CAR CD8 T cells to be enriched in a central memory cell phenotype and fatty acid metabolism genes. Our data uncovered transcriptional signatures related to costimulatory domains and demonstrated that signaling domains included in CARs uniquely shape the transcriptional programs of T cells.