Lorenzo Cosmi

Phenotypic and functional features of human Th17 cells

T helper (Th) 17 cells represent a novel subset of CD4+ T cells that are protective against extracellular microbes, but are responsible for autoimmune disorders in mice. However, their properties in humans are only partially known. We demonstrate the presence of Th17 cells, some of which produce both interleukin (IL)-17 and interferon (IFN)-γ (Th17/Th1), in the gut of patients with Crohns disease. Both Th17 and Th17/Th1 clones showed selective expression of IL-23R, CCR6, and the transcription factor RORγt, and they exhibited similar functional features, such as the ability to help B cells, low cytotoxicity, and poor susceptibility to regulation by autologous regulatory T cells. Interestingly, these subsets also expressed the Th1-transcription factor T-bet, and stimulation of these cells in the presence of IL-12 down-regulated the expression of RORγt and the production of IL-17, but induced IFN-γ. These effects were partially inhibited in presence of IL-23. Similar receptor expression and functional capabilities were observed in freshly derived IL-17–producing peripheral blood and tonsillar CD4+ T cells. The demonstration of selective markers for human Th17 cells may help us to understand their pathogenic role. Moreover, the identification of a subset of cells sharing features of both Th1 and Th17, which can arise from the modulation of Th17 cells by IL-12, may raise new issues concerning developmental and/or functional relationships between Th17 and Th1.

Role for Interferon‐γ in the Immunomodulatory Activity of Human Bone Marrow Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) inhibit the proliferation of HLA‐unrelated T lymphocytes to allogeneic stimulation, but the mechanisms responsible for this activity are not fully understood. We show here that MSCs suppress the proliferation of both CD4+ and CD8+ T lymphocytes, as well as of natural killer (NK) cells, whereas they do not have an effect on the proliferation of B lymphocytes. The antiproliferative effect of MSCs was not associated with any effect on the expression of cell‐activation markers, induction of cell apoptosis, or mimicry/enhancement of T regulatory cell activity. The suppressive activity of MSCs was not contact‐dependent and required the presence of interferon (IFN)‐γ produced by activated T cells and NK cells. Accordingly, even activated B cells became susceptible to the suppressive activity of MSCs in the presence of exogenously added IFN‐γ. The suppressive effect of IFN‐γ was related to its ability to stimulate the production by MSCs of indoleamine 2,3‐dioxygenase activity, which in turn inhibited the proliferation of activated T or NK cells. These findings suggest that the beneficial effect on graft‐versus‐host disease induced by in vivo coinfusion with the graft of MSCs may be due to the activation of the immunomodulatory properties of MSCs by T cell– derived IFN‐γ.

Human interleukin 17–producing cells originate from a CD161+CD4+ T cell precursor

We demonstrate that CD161 is a highly up-regulated gene in human interleukin (IL) 17 T helper cell (Th17) clones and that all IL-17–producing cells are contained in the CD161+ fraction of CD4+ T cells present in the circulation or in inflamed tissues, although they are not CD1-restricted natural killer T cells. More importantly, we show that all IL-17–producing cells originate from CD161+ naive CD4+ T cells of umbilical cord blood, as well as of the postnatal thymus, in response to the combined activity of IL-1β and IL-23. These findings implicate CD161 as a novel surface marker for human Th17 cells and demonstrate the exclusive origin of these cells from a CD161+CD4+ T cell progenitor.

An Alternatively Spliced Variant of CXCR3 Mediates the Inhibition of Endothelial Cell Growth Induced by IP-10, Mig, and I-TAC, and Acts as Functional Receptor for Platelet Factor 4

The chemokines CXCL9/Mig, CXCL10/IP-10, and CXCL11/I-TAC regulate lymphocyte chemotaxis, mediate vascular pericyte proliferation, and act as angiostatic agents, thus inhibiting tumor growth. These multiple activities are apparently mediated by a unique G protein–coupled receptor, termed CXCR3. The chemokine CXCL4/PF4 shares several activities with CXCL9, CXCL10, and CXCL11, including a powerful angiostatic effect, but its specific receptor is still unknown. Here, we describe a distinct, previously unrecognized receptor named CXCR3-B, derived from an alternative splicing of the CXCR3 gene that mediates the angiostatic activity of CXCR3 ligands and also acts as functional receptor for CXCL4. Human microvascular endothelial cell line-1 (HMEC-1), transfected with either the known CXCR3 (renamed CXCR3-A) or CXCR3-B, bound CXCL9, CXCL10, and CXCL11, whereas CXCL4 showed high affinity only for CXCR3-B. Overexpression of CXCR3-A induced an increase of survival, whereas overexpression of CXCR3-B dramatically reduced DNA synthesis and up-regulated apoptotic HMEC-1 death through activation of distinct signal transduction pathways. Remarkably, primary cultures of human microvascular endothelial cells, whose growth is inhibited by CXCL9, CXCL10, CXCL11, and CXCL4, expressed CXCR3-B, but not CXCR3-A. Finally, monoclonal antibodies raised to selectively recognize CXCR3-B reacted with endothelial cells from neoplastic tissues, providing evidence that CXCR3-B is also expressed in vivo and may account for the angiostatic effects of CXC chemokines.

Evidence for a cross-talk between human neutrophils and Th17 cells

Interleukin-17A (IL-17A) and IL-17F are 2 of several cytokines produced by T helper 17 cells (Th17), which are able to indirectly induce the recruitment of neutrophils. Recently, human Th17 cells have been phenotypically characterized and shown to express discrete chemokine receptors, including CCR2 and CCR6. Herein, we show that highly purified neutrophils cultured with interferon-gamma plus lipopolysaccharide produce the CCL2 and CCL20 chemokines, the known ligands of CCR2 and CCR6, respectively. Accordingly, supernatants from activated neutrophils induced chemotaxis of Th17 cells, which was greatly suppressed by anti-CCL20 and anti-CCL2 antibodies. We also discovered that activated Th17 cells could directly chemoattract neutrophils via the release of biologically active CXCL8. Consistent with this reciprocal recruitment, neutrophils and Th17 cells were found in gut tissue from Crohn disease and synovial fluid from rheumatoid arthritis patients. Finally, we report that, although human Th17 cells can directly interact with freshly isolated or preactivated neutrophils via granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interferon-gamma release, these latter cells cannot be activated by IL-17A and IL-17F, because of their lack of IL-17RC expression. Collectively, our results reveal a novel chemokine-dependent reciprocal cross-talk between neutrophils and Th17 cells, which may represent a useful target for the treatment of chronic inflammatory diseases.

Phenotype, Localization, and Mechanism of Suppression of CD4 CD25 Human Thymocytes

Phenotypic markers, localization, functional activities, and mechanisms of action in vitro of CD4+CD25+ T cells, purified from postnatal human thymuses, were investigated. These cells showed poor or no proliferation in mixed lymphocyte culture (MLC), and suppressed in a dose-dependent fashion the proliferative response to allogeneic stimulation of CD4+CD25− thymocytes. Virtually all CD4+CD25+ thymocytes constitutively expressed cytoplasmic T lymphocyte antigen (CTLA)-4, surface tumor necrosis factor type 2 receptor (TNFR2), and CCR8. They prevalently localized to perivascular areas of fibrous septa and responded to the chemoattractant activity of CCL1/I-309, which was found to be produced by either thymic medullary macrophages or fibrous septa epithelial cells. After polyclonal activation, CD4+CD25+ thymocytes did not produce the cytokines interleukin (IL)-2, IL-4, IL-5, IL-13, interferon γ, and only a very few produced IL-10, but all they expressed on their surface CTLA-4 and the majority of them also transforming growth factor (TGF)-β1. The suppressive activity of these cells was contact dependent and associated with the lack of IL-2 receptor (IL-2R) α-chain (CD25) expression in target cells. Such a suppressive activity was partially inhibited by either anti–CTLA-4 or anti–TGF-β1, and was completely blocked by a mixture of these monoclonal antibodies, which were also able to restore in target T cells the expression of IL-2R α-chain and, therefore, their responsiveness to IL-2. These data demonstrate that CD4+CD25+ human thymocytes represent a population of regulatory cells that migrate in response to the chemokine CCL1/I-309 and exert their suppressive function via the inhibition of IL-2R α-chain in target T cells, induced by the combined activity of CTLA-4 and membrane TGF-β1.

Cell cycle–dependent expression of CXC chemokine receptor 3 by endothelial cells mediates angiostatic activity

Endothelial cell receptors for the angiostatic chemokines IFN-gamma-inducible protein of 10 kDa (IP-10) and monokine induced by IFN-gamma (Mig) have not yet been identified, and the mechanisms responsible for the effects of these chemokines on angiogenesis are still unclear. IP-10 and Mig share a common functional receptor on activated T lymphocytes, named CXC chemokine receptor 3 (CXCR3). Using in situ hybridization and immunohistochemistry, we show that CXCR3 is expressed by a small percentage of microvascular endothelial cells in several human normal and pathological tissues. Primary cultures of human microvascular endothelial cells (HMVECs) likewise express CXCR3, although this expression is limited to the S/G2-M phase of their cell cycle. Both IP-10 and Mig, as well as the IFN-gamma-inducible T-cell alpha chemoattractant (I-TAC), which all share high-affinity binding for CXCR3, block HMVEC proliferation in vitro, an effect that can be inhibited by an anti-CXCR3 antibody. These data provide definitive evidence of CXCR3 expression by HMVEC and open new avenues for therapeutic interventions in all conditions in which an angiostatic effect may be beneficial.

Toll-Like Receptors 3 and 4 Are Expressed by Human Bone Marrow-Derived Mesenchymal Stem Cells and Can Inhibit Their T-Cell Modulatory Activity by Impairing Notch Signaling

Bone marrow (BM)‐derived mesenchymal stem cells (MSCs) are multipotent, nonhemopoietic progenitors that also possess regulatory activity on immune effector cells through different mechanisms. We demonstrate that human BM‐derived MSCs expressed high levels of Toll‐like receptors (TLRs) 3 and 4, which are both functional, as shown by the ability of their ligands to induce nuclear factor κB (NF‐κB) activity, as well as the production of interleukin (IL)‐6, IL‐8, and CXCL10. Of note, ligation of TLR3 and TLR4 on MSCs also inhibited the ability of these cells to suppress the proliferation of T cells, without influencing their immunophenotype or differentiation potential. The TLR triggering effects appeared to be related to the impairment of MSC signaling to Notch receptors in T cells. Indeed, MSCs expressed the Notch ligand Jagged‐1, and TLR3 or TLR4 ligation resulted in its strong downregulation. Moreover, anti‐Jagged‐1 neutralizing antibody and N[N‐(3,5‐difluorophenacetyl‐l‐alanyl)]‐S‐phenylglycine t‐butyl ester (DAPT), an inhibitor of Notch signaling, hampered the suppressive activity of MSCs on T‐cell proliferation. These data suggest that TLR3 and TLR4 expression on MSCs may provide an effective mechanism to block the immunosuppressive activity of MSCs and therefore to restore an efficient T‐cell response in the course of dangerous infections, such as those sustained by double‐stranded RNA viruses or Gram‐negative bacteria, respectively.

CD14+CD34low Cells With Stem Cell Phenotypic and Functional Features Are the Major Source of Circulating Endothelial Progenitors

Endothelial progenitor cells (EPCs) seem to be a promising tool for cell therapy of acute myocardial infarction, but their nature is still unclear. We show here that EPCs obtainable from peripheral blood (PB) derive from the adhesion-related selection in culture of a subset of CD14+ cells, which, when assessed by the highly-sensitive antibody-conjugated magnetofluorescent liposomes (ACMFL) technique, were found to express CD34. These CD14+CD34low cells represented a variable proportion at individual level of CD14+ cells, ranging from 0.6% to 8.5% of all peripheral-blood leukocytes, and constituted the dominant population among circulating KDR+ cells. By using the ACMFL technique, virtually all CD14+ cells present in the bone marrow were found to be CD14+CD34low double-positive cells. EPCs, as well as purified circulating CD14+CD34low cells, exhibited high expression of embryonic stem cell (SC) markers Nanog and Oct-4, which were downregulated in a STAT3-independent manner when they differentiated into endothelial cells (ECs). Moreover, circulating CD14+CD34low cells, but not CD14+CD34− cells, proliferated in response to SC growth factors, and exhibited clonogenicity and multipotency, as shown by their ability to differentiate not only into ECs, but also into osteoblasts, adipocytes, or neural cells. The results of this study may reconcile apparently contradictory data of the literature, showing the generation of PB-derived EPCs from either CD34+ or CD14+ cells. We suggest that the use of this previously unrecognized population of circulating CD14+CD34low cells, which exhibit both phenotypic and functional features of SCs, may be useful in improving cell-based therapies of vascular and tissue damage.

Th17 cells: new players in asthma pathogenesis

To cite this article: Cosmi L, Liotta F, Maggi E, Romagnani S, Annunziato F. Th17 cells: new players in asthma pathogenesis. Allergy 2011; 66: 989–998.