Maria-Luisa del Rio

CD103− and CD103+ Bronchial Lymph Node Dendritic Cells Are Specialized in Presenting and Cross-Presenting Innocuous Antigen to CD4+ and CD8+ T Cells

Dendritic cells (DC) are able to capture, process, and present exogenous Ag to CD8+ T lymphocytes through MHC class I, a process referred to as cross-presentation. In this study, we demonstrate that CD103+ (CD11chighCD11blow) and CD103− (CD11cintCD11bhigh) DC residing in the lung-draining bronchial lymph node (brLN) have evolved to acquire opposing functions in presenting innocuous inhaled Ag. Thus, under tolerogenic conditions, CD103− DC are specialized in presenting innocuous Ag to CD4+ T cells, whereas CD103+ DC, which do not express CD8α, are specialized in presenting Ag exclusively to CD8+ T cells. In CCR7-deficient but not in plt/plt mice, Ag-carrying CD103+ DC are largely absent in the brLN, although CD103+ DC are present in the lung of CCR7-deficient mice. As a consequence, adoptively transferred CD8+ T cells can be activated under tolerizing conditions in plt/plt but not in CCR7-deficient mice. These data reveal that CD103+ brLN DC are specialized in cross-presenting innocuous inhaled Ag in vivo. Because these cells are largely absent in CCR7−/− mice, our findings strongly suggest that brLN CD103+ DC are lung-derived and that expression of CCR7 is required for their migration from the lung into its draining lymph node.

Development and functional specialization of CD103+ dendritic cells

Summary:  CD103 (αE) integrin expression distinguishes a population of dendritic cells (DCs) that can be found in many if not all lymphoid and non‐lymphoid organs. CD103+ DCs display distinct functional activities. Migratory CD103+ DCs derived from skin, lung, and intestine efficiently present exogenous antigens in their corresponding draining lymph nodes to specific CD8+ T cells through a mechanism known as cross‐presentation. On the T cells they prime, intestinal CD103+ DCs can drive the induction of the chemokine receptor CCR9 and α4β7 integrin, both known as gut‐homing receptors. CD103+ DCs also contribute to control inflammatory responses and intestinal homeostasis by fostering the conversion of naive T cells into induced Foxp3+ regulatory T cells, a mechanism that relies on transforming growth factor‐β and retinoic acid signaling. This review discusses recent findings that identify murine CD103+ DCs as important regulators of the immune response.

Induction of Tolerance to Innocuous Inhaled Antigen Relies on a CCR7-Dependent Dendritic Cell-Mediated Antigen Transport to the Bronchial Lymph Node

Allergic airway diseases such as asthma are caused by a failure of the immune system to induce tolerance against environmental Ags. The underlying molecular and cellular mechanisms that initiate tolerance are only partly understood. In this study, we demonstrated that a CCR7-dependent migration of both CD103+ and CD103− lung dendritic cells (DC) to the bronchial lymph node (brLN) is indispensable for this process. Although inhaled Ag is amply present in the brLN of CCR7-deficient mice, T cells cannot be tolerized because of the impaired migration of Ag-carrying DC and subsequent transport of Ag from the lung to the draining lymph node. Consequently, the repeated inhalation of Ag protects wild-type but not CCR7-deficient mice from developing allergic airway diseases. Thus, the continuous DC-mediated transport of inhaled Ag to the brLN is critical for the induction of tolerance to innocuous Ags.

CX3CR1+ c-kit+ bone marrow cells give rise to CD103+ and CD103- dendritic cells with distinct functional properties.

Dendritic cells (DC) represent a rather heterogeneous cell population with regard to morphology, phenotype, and function and, like most cells of the immune system, are subjected to a continuous renewal process. CD103+ (integrin αE) DC have been identified as a major mucosal DC subset involved in the induction of tissue-specific homing molecules on T cells, but little is known about progenitors able to replenish this DC subset. Herein we report that lineage (lin)−CX3CR1+c-kit+ (GFP+c-kit+) bone marrow cells can differentiate to either CD11c+CD103− or CD11c+CD103+ DC in vitro and in vivo. Gene expression as well as functional assays reveal distinct phenotypical and functional properties of both subsets generated in vitro. CD103− DC exhibit enhanced phagocytosis and respond to LPS stimulation by secreting proinflammatory cytokines, whereas CD103+ DC express high levels of costimulatory molecules and efficiently induce allogeneic T cell proliferation. Following adoptive transfer of GFP+c-kit+ bone marrow cells to irradiated recipients undergoing allergic lung inflammation, we identified donor-derived CD103+ DC in lung and the lung-draining bronchial lymph node. Collectively, these data indicate that GFP+c-kit+ cells contribute to the replenishment of CD103+ DC in lymphoid and nonlymphoid organs.

PD-1/PD-L1, PD-1/PD-L2, and other co-inhibitory signaling pathways in transplantation

Transplantation of cells, tissues and vascularized solid organs is a successful therapeutic intervention for many end‐stage chronic diseases. The combination of co‐stimulatory blockade with the delivery of negative signals to T cells through co‐inhibitory receptors would provide a robust approach to modulating T‐cell receptor signaling and improving alloantigen‐specific control of transplant rejection. This approach based on fundamental knowledge of APC/T‐cell interactions may complement conventional therapies in the near future to reinforce long‐term allograft survival, and permit minimal immunosuppression. The focus of this review was primarily on two major co‐inhibitory signaling pathways, namely PD‐1/PD‐L1/PD‐L2 and BTLA/CD160/HVEM/LIGHT that have been thoroughly characterized in murine models of transplantation using genetically modified mice, specific monoclonal antibodies and fusion proteins.

Antibody-mediated signaling through PD-1 costimulates T cells and enhances CD28-dependent proliferation.

Programmed death‐1 (PD‐1, CD279) is a molecule expressed on activated T, B and myeloid cells. The role of the interaction of PD‐1 ligands (PD‐L1 and PD‐L2) with PD‐1 receptor and the type of signals (costimulatory or inhibitory) that are delivered is a subject of intense debate. Our study has characterized two monoclonal antibodies (mAb) against murine PD‐1, termed clone 1H10 and clone 4F10, that recognized different epitopes from that of anti‐PD‐1, clone J43. We showed that neither of them inhibited anti‐CD3‐mediated proliferation, but 1H10 mAb induced direct T cell proliferation in the absence of any other stimulus. Moreover, PD‐1 engagement with 1H10 mAb costimulated anti‐CD3‐mediated proliferation and enhanced anti‐CD3/CD28 proliferation on both CD4+ and CD8+ T cells in the low range of anti‐CD3 concentrations. Anti‐PD‐1‐mediated proliferation induced with 1H10 mAb was also observed in vivo on CD4+ and CD8+ T cells, when CFSE‐labeled splenocytes were adoptively transferred to irradiated syngeneic and allogeneic recipients. Overall, our data indicate that PD‐1 might not only deliver negative signals to T cells upon interaction through one of its ligands, PD‐L1 as reported, but also could costimulate T cells, suggesting a dual potential functional activity of the extracellular domains of this receptor.

Selective Blockade of Herpesvirus Entry Mediator–B and T Lymphocyte Attenuator Pathway Ameliorates Acute Graft-versus-Host Reaction

The cosignaling network mediated by the herpesvirus entry mediator (HVEM; TNFRSF14) functions as a dual directional system that involves proinflammatory ligand, lymphotoxin that exhibits inducible expression and competes with HSV glycoprotein D for HVEM, a receptor expressed by T lymphocytes (LIGHT; TNFSF14), and the inhibitory Ig family member B and T lymphocyte attenuator (BTLA). To dissect the differential contributions of HVEM/BTLA and HVEM/LIGHT interactions, topographically-specific, competitive, and nonblocking anti-HVEM Abs that inhibit BTLA binding, but not LIGHT, were developed. We demonstrate that a BTLA-specific competitor attenuated the course of acute graft-versus-host reaction in a murine F1 transfer semiallogeneic model. Selective HVEM/BTLA blockade did not inhibit donor T cell infiltration into graft-versus-host reaction target organs, but decreased the functional activity of the alloreactive T cells. These results highlight the critical role of HVEM/BTLA pathway in the control of the allogeneic immune response and identify a new therapeutic target for transplantation and autoimmune diseases.

Detection of protein on BTLAlow cells and in vivo antibody-mediated down-modulation of BTLA on lymphoid and myeloid cells of C57BL/6 and BALB/c BTLA allelic variants.

B- and T-lymphocyte attenuator (BTLA, CD272) is a polymorphic molecule belonging to the Ig superfamily (SF) that attenuates BCR and TCR-mediated signaling, and thereby functions as a negative regulator of lymphocyte activation. Herein, we report an anti-murine BTLA mAb (clone 4G12b) that remarkably detects protein expression on BTLA(low) cells such as naïve CD4(+) cells, CD8(+) T cells, dendritic cells (DC), as well as in NKT cells and for the first time, we found BTLA expression on DX5(dim) and DX5(bright) subsets of non-T NK cells in both C57BL/6 (B6) and BALB/c BTLA allelic variants. Anti-BTLA 4G12b mAb binds to an overlapping epitope to that recognized by anti-BTLA 6A6 mAb, but in contrast to the concept widely accepted of blocking activity of 6A6 mAb, surprisingly neither 4G12b nor 6A6 mAbs impeded murine HVEM-mIgG(2a).Fc recombinant fusion protein from interacting with BTLA-expressing cells. Lastly, in vivo administration of anti-BTLA 4G12b mAb induced a profound and lasting down-modulation of BTLA expression that led to BTLA receptor internalization with the potential utility of shutting down BTLA expression at any stage during the course of the immune response in both B6 and BALB/c strains of mice.

ITIM-dependent negative signaling pathways for the control of cell-mediated xenogeneic immune responses

Xenotransplantation is an innovative field of research with the potential to provide us with an alternative source of organs to face the severe shortage of human organ donors. For several reasons, pigs have been chosen as the most suitable source of organs and tissues for transplantation in humans. However, porcine xenografts undergo cellular immune responses representing a major barrier to their acceptance and normal functioning. Innate and adaptive xenogeneic immunity is mediated by both the recognition of xenogeneic tissue antigens and the lack of inhibition due to molecular cross‐species incompatibilities of regulatory pathways. Therefore, the delivery of immunoreceptor tyrosine‐based inhibitory motif (ITIM)‐dependent and related negative signals to control innate (NK cells, macrophages) and adaptive T and B cells might overcome cell‐mediated xenogeneic immunity. The proof of this concept has already been achieved in vitro by the transgenic overexpression of human ligands of several inhibitory receptors in porcine cells resulting in their resistance against xenoreactivity. Consequently, several transgenic pigs expressing tissue‐specific human ligands of inhibitory coreceptors (HLA‐E, CD47) or soluble competitors of costimulation (belatacept) have already been generated. The development of these robust and innovative approaches to modulate human anti‐pig cellular immune responses, complementary to conventional immunosuppression, will help to achieve long‐term xenograft survival. In this review, we will focus on the current strategies to enhance negative signaling pathways for the regulation of undesirable cell‐mediated xenoreactive immune responses.

B- and T-lymphocyte Attenuator Targeting Protects Against the Acute Phase of Graft Versus Host Reaction by Inhibiting Donor Anti-host Cytotoxicity

Background. B- and T-lymphocyte attenuator (BTLA) functions as a coinhibitory/costimulatory molecule that belongs to the immunoglobulin superfamily and exhibits a pattern of expression restricted to the hematopoietic compartment. Engagement of BTLA by its ligand, herpes virus entry mediator (HVEM), delivers negative signals to T cells, whereas engagement of HVEM receptor on T cells by surface BTLA expressed on other immune cells costimulates T activation. Previous work has reported that parental donor BTLA knock-out or HVEM knock-out T cells adoptively transferred into nonirradiated F1 recipient mice survived poorly, and the rejection of host hematopoietic cells was attenuated compared with F1 recipients receiving wild-type T cells. Methods. Parent into nonirradiated immunocompetent F1 murine model of acute graft versus host reaction, which is induced with the adoptive transfer of splenocytes from donor B6 mice (H-2b) into F1 recipients (BALB/c×B6, H-2d/b), was used as an experimental approach to test the therapeutic effect of targeting BTLA during the course of an allogeneic immune response. Results. We herein provide evidence that administration of an anti-BTLA monoclonal antibody leads to significant reduction of donor anti-host allogeneic immune response against bone marrow and thymus during the acute phase of graft versus host reaction in a parent into nonirradiated F1 murine model of alloreactivity. Anti-BTLA protection against donor anti-host hematopoietic cell rejection correlated with impaired anti-host cytotoxic T-lymphocyte activity than reduction in T-cell number infiltrating host tissues. Conclusions. These findings place BTLA receptor as a potential immunoregulatory target for the modulation of cytotoxic T-lymphocyte-mediated alloresponses.