Neurokinin-1 Receptor Signaling Is Required for Efficient Ca2+ Flux in T-Cell-Receptor-Activated T Cells

Efficient Ca²⁺ flux induced during cognate T cell activation requires signaling the T cell receptor (TCR) and unidentified G-protein-coupled receptors (GPCRs). T cells express the neurokinin-1 receptor (NK1R), a GPCR that mediates Ca²⁺ flux in excitable and non-excitable cells. However, the role of the NK1R in TCR signaling remains unknown. We show that the NK1R and its agonists, the neuropeptides substance P and hemokinin-1, co-localize within the immune synapse during cognate activation of T cells. Simultaneous TCR and NK1R stimulation is necessary for efficient Ca²⁺ flux and Ca²⁺-dependent signaling that sustains the survival of activated T cells and helper 1 (Th1) and Th17 bias. In a model of contact dermatitis, mice with T cells deficient in NK1R or its agonists exhibit impaired cellular immunity, due to high mortality of activated T cells. We demonstrate an effect of the NK1R in T cells that is relevant for immunotherapies based on pro-inflammatory neuropeptides and its receptors.

The neurokinin 1 receptor (NK1R) induces Ca²⁺ flux in excitable cells. Here, Morelli et al. show that NK1R signaling in T cells promotes optimal Ca²⁺ flux triggered by TCR stimulation, which is necessary to sustain T cell survival and the efficient Th1- and Th17-based immunity that is relevant for immunotherapies based on pro-inflammatory neuropeptides.

Graft-derived extracellular vesicles transported across subcapsular sinus macrophages elicit B cell alloimmunity after transplantation

Despite the role of donor-specific antibodies (DSAs) in recognizing major histocompatibility complex (MHC) antigens and mediating transplant rejection, how and where recipient B cells in lymphoid tissues encounter donor MHC antigens remains unclear. Contrary to the dogma, we demonstrated here that migration of donor leukocytes out of skin or heart allografts is not necessary for B or T cell allosensitization in mice. We found that mouse skin and cardiac allografts and human skin grafts release cell-free donor MHC antigens via extracellular vesicles (EVs) that are captured by subcapsular sinus (SCS) macrophages in lymph nodes or analog macrophages in the spleen. Donor EVs were transported across the SCS macrophages, and donor MHC molecules on the EVs were recognized by alloreactive B cells. This triggered B cell activation and DSA production, which were both prevented by SCS macrophage depletion. These results reveal an unexpected role for graft-derived EVs and open venues to interfere with EV biogenesis, trafficking, or function to restrain priming or reactivation of alloreactive B cells.

Oral administration of lipoteichoic acid from Lactobacillus rhamnosus GG overcomes UVB-induced immunosuppression and impairs skin tumor growth in mice

There is increasing evidence of the relevant connection and regulation between the gut and skin immune axis. In fact, oral administration of lipoteichoic acid (LTA) from Lactobacillus rhamnosus GG (LGG) prevents the development of UV-induced skin tumors in chronically exposed mice. Here we aim to evaluate whether this LTA is able to revert UV-induced immunosuppression as a mechanism involved in its anti-tumor effect and whether it has an immunotherapeutic effect against cutaneous squamous cell carcinoma. Using a mouse model of contact hypersensitivity, we demonstrate that LTA overcomes UV-induced skin immunosuppression. This effect was in part achieved by modulating the phenotype of lymph node resident dendritic cells (DC) and the homing of skin migratory DC. Importantly, oral LTA reduced significantly the growth of established skin tumors once UV radiation was discontinued, demonstrating that it has a therapeutic, besides the already demonstrated preventive antitumor effect. The data presented here strongly indicates that oral administration of LTA represents a promising immunotherapeutic approach for different conditions in which the skin immune system is compromised.

Restraining neuroinflammation during antigen delivery as an immunosuppressive approach to prevent and treat contact dermatitis

Neuroinflammation promotes the initiation and sustains chronic inflammatory disorders. Substance-P, released by sensory neurons, is the prototype neuropeptide that signals via the neurokinin 1 receptor (NK1R) to enhance cellular immunity. We observed that NK1RKO or SPKO mice do not develop contact dermatitis (CD). Hence, we hypothesized that limiting neuroinflammation during Ag entrance induces an immune-suppressive environment to prevent T cell priming and eliminate memory T cells that cause CD. We co-delivered OVA or 2,4-dinitrocholorobencene (DNCB) and two different NK1R antagonists during sensitization of a DTH reaction induced to C57/BL6 mice reconstituted or not with OTI and OTII cells. For efficient skin delivery, we generated microneedle arrays loaded with OVA or DNCB and NK1R antagonists. We demonstrate that our approach prevents the innate and adaptive immunity accounting for the initiation of CD and mitigates pre-existing pathogenic memory T cells that cause local or systemic CD relapses. Mechanistic studies demonstrate that NK1R antagonists suppress the release of pro-inflammatory cytokines in the skin, promote the death of activated CD4 Th1 and CD8 T-cells, and generate Tregs in the skin draining lymph nodes. Our data demonstrates that controlling neuroinflammation during Ag entrance prevents the generation of pathogenic effector and memory T cells accounting for the initiation and relapses of chronic inflammatory skin disorders like CD. NIH R01 AR068249 and AR071277 to ATL and LDF.

Neurokinin 1 receptor-signaling sustains T-cell survival during thymus development and following T-cell activation in secondary lymphoid organs

T-cell receptor (TCR)-signaling triggers intracellular Ca2+ increase required for NFAT1/2-mediated IL-2 secretion. This pathway is necessary for thymocyte maturation and survival of activated T cells in secondary lymphoid organs (SLOs). In T cells, cellular Ca2+ levels are regulated by TCR- and G-protein coupled receptor (GPCR)-signaling via the PLCγ and PLCβ subunits, respectively. Nevertheless, the GPCR(s) involved in this phenomenon has not been identified. The neurokinin-1 receptor (NK1R) is a GPCR that induces Ca2+ flux in neurons, and NK1R-signaling by the neuropetides substance P (SP) and hemokinin 1 (HK1) promotes T-cell immunity. We studied the role of NK1R-signaling in T-cell development in the thymus and after T-cell priming in SLOs. By Imagestream, we found that the NK1R and its ligands localize at the site of dendritic cell (DC)-T cell contact. Following CD3-signaling, the NK1R was required for optimal Ca2+flux and NFAT-mediated IL-2 secretion in T cells, effects that were abrogated in NK1RKO or SP/HK1double KO T cells. In the thymus, absence of NK1R resulted in decreased maturation and survival of TCR+ double positive CD4 CD8, single positive CD4, and single positive CD8thymocytes. In SLOs, the NK1R was required for survival of Ag-activated CD4 Th1 and CD8 T cells. In vivo, in a skin model of Th1-DTH induced in NK1RKO T-cell or HK-1/SPdouble KOT-cell bone marrow chimeras, 73±5% of activated CD4 and CD8 T cells died during priming in skin-draining SLOs, and the remaining T cells died in the skin following elicitation. We conclude that the NK1R cooperates with the TCR to increase intracellular Ca2+ necessary for thymocyte maturation and survival of activated T cells in SLOs.

NIH R01 AR068249 and AR071277 to ATL and LDF.

Cross-dressing of recipient Ag-presenting cells with donor exosomes trigger direct T-cell allosensitization in transplantation

The idea that donor dendritic cells (DCs) from the graft present donor MHC Ag to naïve T cells has been challenged. Evidence suggests that donor DCs are undetectable or found are low numbers in graft-draining lymphoid organs. Thus, the aim of our study is to elucidate how donor MHC molecules are recognized so efficiently by recipient naïve T cells.

Results

After transplantation of CD45.2 BALB/c hearts in CD45.1 B6 mice, very few donor DCs were detected in the spleen, and no donor DCs were found in lymph nodes draining BALB/c skin grafted in B6 mice. In both cases, donor intact MHC molecules were detected by electron microscopy on exosomes attached to recipient conventional DCs in graft-draining lymphoid organs. The transferred MHC Ag induced proliferation and differentiation of CD8 T cells against the BALB/c H2Ld Ag. Cultures of BALB/c DCs with B6 DCs with inhibitors of exosome release (Rab27a siRNA) confirmed that passage of BALB/c MHC occurred via exosomes. Importantly, transfer of exosomes released by donor DCs (unlike other types of vesicles) promoted maturation of recipient DCs. By high resolution confocal microscopy, BALB/c DCs, engineered to release RFP+ exosomes and injected in CD11c-YFP B6 mice, transferred RFP+ exosomes to recipient YFP+ DCs in lymph nodes and spleen. Accordingly, depletion of recipient DCs in CD11c-DTR B6 recipients prevented presentation of donor intact MHC Ag to T cells and delayed heart allograft rejection.

Conclusion

Our results elucidate the ultrastructural basis of the still elusive semi-direct pathway of allorecognition, by demonstrating that donor exosomes (released by the graft or donor migrating DCs) cross-dress recipient APCs and promote the potent T-cell allosensitization seen in transplantation.

The neurokinin 1 receptor and its agonists recruited at the DC-T cell synapse are necessary to promote the survival of activated T cells in vivo

Initiation of cellular immunity relies on T cell activation by Ag-presenting dendritic cells (DCs). By signaling via the neurokinin-1 receptor (NK1R), the neuropeptides hemokinin-1 (HK-1) and substance P (SP) potentiate cellular immunity by mechanisms not fully elucidated. Although SP is mainly secreted by sensory nerves, it is also synthesized and released by T cells. Here, we investigated the role of NK1R and autocrine SP and HK-1 on T cell activation. Using Imagestream flow cytometry (Amnis) to visualize couplets of OVA loaded WT or SP/HK1double KO DCs and responder OT-II CD4 T cells, we observed that the NK1R, SP and HK-1 colocalize with phalloidin at the site of DC-T cell contact. Following CD3/CD28 activation in vitro, we demonstrate that T cells express the full-length NK1R, and that NK1R signaling induces Ca2 flux, activation of calcineurin, NFAT1/2 and NFκB, which results in IL-2 secretion and survival of CD4 and CD8 T cells. These effects were abrogated in NK1RKO orSP/HK1double KO T cells, or by soluble NK1R antagonists. Addition of exogenous SP or HK-1 to CD3/CD28 activated WT T cells did not increase IL-2 secretion indicating that autocrine SP and HK1 released at the DC-T cell synapse suffice to promote T cell survival. In a model of skin DTH in NK1RKO or HK-1/SPdouble KOT cell chimeras, 73 ± 5% of activated (CD44high) CD4 and CD8 T cells die in the draining lymph nodes after priming, and 79%± 7% of the remaining T cells recruited to the skin die in situ following elicitation. In summary, NK1R signaling by autocrine SP and HK1 at the DC-T cell synapse is necessary for the survival of activated T cells and the development of potent cellular immunity.

Graft-infiltrating host dendritic cells play a key role in organ transplant rejection

Successful engraftment of organ transplants has traditionally relied on preventing the activation of recipient (host) T cells. Once T-cell activation has occurred, however, stalling the rejection process becomes increasingly difficult, leading to graft failure. Here we demonstrate that graft-infiltrating, recipient (host) dendritic cells (DCs) play a key role in driving the rejection of transplanted organs by activated (effector) T cells. We show that donor DCs that accompany heart or kidney grafts are rapidly replaced by recipient DCs. The DCs originate from non-classical monocytes and form stable, cognate interactions with effector T cells in the graft. Eliminating recipient DCs reduces the proliferation and survival of graft-infiltrating T cells and abrogates ongoing rejection or rejection mediated by transferred effector T cells. Therefore, host DCs that infiltrate transplanted organs sustain the alloimmune response after T-cell activation has already occurred. Targeting these cells provides a means for preventing or treating rejection.

Donor dendritic cell-derived exosomes promote allograft-targeting immune response

The immune response against transplanted allografts is one of the most potent reactions mounted by the immune system. The acute rejection response has been attributed to donor dendritic cells (DCs), which migrate to recipient lymphoid tissues and directly activate alloreactive T cells against donor MHC molecules. Here, using a murine heart transplant model, we determined that only a small number of donor DCs reach lymphoid tissues and investigated how this limited population of donor DCs efficiently initiates the alloreactive T cell response that causes acute rejection. In our mouse model, efficient passage of donor MHC molecules to recipient conventional DCs (cDCs) was dependent on the transfer of extracellular vesicles (EVs) from donor DCs that migrated from the graft to lymphoid tissues. These EVs shared characteristics with exosomes and were internalized or remained attached to the recipient cDCs. Recipient cDCs that acquired exosomes became activated and triggered full activation of alloreactive T cells. Depletion of recipient cDCs after cardiac transplantation drastically decreased presentation of donor MHC molecules to directly alloreactive T cells and delayed graft rejection in mice. These findings support a key role for transfer of donor EVs in the generation of allograft-targeting immune responses and suggest that interrupting this process has potential to dampen the immune response to allografts.

Suppression of autoimmune diabetes by soluble galectin-1

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that targets the beta-cells of the pancreas. We investigated the ability of soluble galectin-1 (gal-1), an endogenous lectin that promotes T cell apoptosis, to down-regulate the T cell response that destroys the pancreatic beta-cells. We demonstrated that in nonobese diabetic (NOD) mice, gal-1 therapy reduces significantly the amount of Th1 cells, augments the number of T cells secreting IL-4 or IL-10 specific for islet cell Ag, and causes peripheral deletion of beta-cell-reactive T cells. Administration of gal-1 prevented the onset of hyperglycemia in NOD mice at early and subclinical stages of T1D. Preventive gal-1 therapy shifted the composition of the insulitis into an infiltrate that did not invade the islets and that contained a significantly reduced number of Th1 cells and a higher percentage of CD4(+) T cells with content of IL-4, IL-5, or IL-10. The beneficial effects of gal-1 correlated with the ability of the lectin to trigger apoptosis of the T cell subsets that cause beta-cell damage while sparing naive T cells, Th2 lymphocytes, and regulatory T cells in NOD mice. Importantly, gal-1 reversed beta-cell autoimmunity and hyperglycemia in NOD mice with ongoing T1D. Because gal-1 therapy did not cause major side effects or beta-cell toxicity in NOD mice, the use of gal-1 to control beta-cell autoimmunity represents a novel alternative for treatment of subclinical or ongoing T1D.

Distinct subsets of human skin dendritic cells differ on their ability to initiate Th17 responses (90.24)

Activated human cutaneous dendritic cells (DCs) have the ability to initiate Th1 and Th2 immunity. However, whether human cutaneous DCs are capable of biasing pro-inflammatory Th17 responses remains little understood. Utilizing human skin explants composed by both epidermis and dermis or epidermal or dermal sheets to collect activated skin-migratory DCs (smiDCs), we demonstrated that smiDCs stimulate allogeneic naïve CD4+ T cells to differentiate simultaneously into two distinct effector Th17 and Th1 populations with ability of skin homing and inducing severe tissue damage. Of the two main myeloid DC populations resident in the skin, the subset of epidermal skin-migratory Langerhans cells (smiLCs) were capable of inducing Th17 responses. This effect depended on the combined effects of IL-15 and stabilized IL-6 trans-signaling of naïve CD4+ T cells. Purified skin-migratory DDCs did not synthesize IL-15 and were unable to bias Th17 responses however, they acquired the ability to bias Th17 cells in co-cultures with CD4+ T cells supplemented with IL-15 and stabilized IL-6. Overall, our data demonstrate that human cutaneous LCs induce Th17 responses by mechanisms different from those previously described for mouse DCs and human monocytes and highlight the need to target clinical treatments based on these variations.

Supported by NIH grants: R01 CA100893 (ATL)

Dendritic cell (DC)- derived exosomes spread donor allo-antigen between recipient's DC following cardiac transplantation (141.11)

Exosomes are nanovesicles generated in multivesicular endosomes that are released to the extracellular space by different cell types. Since DC-derived exosomes (dexosomes) express MHC-peptide and costimulatory molecules, we investigated the role of dexosomes in elicitation of the anti-donor response in transplantation. Dexosomes were generated from bone marrow-derived DC and labeled with PKH67 for traffic studies. CD4+ TCRtg T cells (Thy1.1+) specific for the IEα52-68 (BALB/c)-IAb (B10) complex were CFSE-labeled and transferred i.v. to host Thy1.2+ B6 mice. Graft infiltrating DC were isolated from BALB/c (CD45.2+) cardiac grafts 3 days after transplantation in B6 (CD45.2+) recipients and genetically-engineered ex vivo to release exosomes expressing the reporter marker eGFP, and then transferred i.v. into host CD45.1+ B6 mice. We demonstrated that although graft-infiltrating leukocytes release exosomes ex vivo, they do not secrete enough exosomes in circulation to stimulate donor-reactive T-cells in lymphoid organs. Instead, migrating DCs (generated in vitro or isolated from allografts), once they home in the spleen, they transfer exosomes expressing eGFP to spleen-resident DCs. Thus, exchange of exosomes between DCs in lymphoid organs constitutes a mechanism by which passenger leukocytes transfer alloAg to recipient's APC and amplify generation of donor-reactive T-cells.

Agonistic signaling via the neurokinin 1 receptor and CD40 have a synergistic effect to promote dendritic cell survival and potent CTL responses (135.56)

Immune competent organs are richly innervated and pro-inflammatory neuropeptides released by nerve endings favor the initiation of innate and adaptive immune responses. By binding the neurokinin 1 receptor (NK1R), the pro-inflammatory neuropeptide substance P promotes immune cell survival and potent cellular immunity. Dendritic cells (DCs) express surface NK1R and the priming of T cell responses requires Ag presentation by DCs able to withstand apoptotic signaling. We hypothesized that signaling DCs via the NK1R prevents apoptosis of DCs favoring sustained DC-T cell contact and robust CTL responses. Using murine bone marrow-derived DCs (BMDCs) cultured with the NK1R agonist [Sar9Met(02)11]-SP (SarSP-DCs), we demonstrate that signaling via the NK1R utilizes the PI3K-Akt pathway to prolong the expression of anti-apoptotic molecules. Additionally, SarSP-DCs showed increased expression of surface CD40. Adoptive transfer of Ag-loaded SarSP-DCs showed enhanced longevity in local draining lymph nodes vs. control DCs, which was a result of a combination of signaling via the NK1R and CD40 molecules. Importantly, SarSP-DCs elicited potent CTL responses compared to control DCs. We conclude that agonistic signaling via the NK1R and CD40 have a synergistic effect that enhances DC survival and favors the generation of potent CTL responses.

Supported by NIH grant: R01 CA100893 (ATL)

Quiescent recipient splenic dendritic cells (DC) re-process therapeutic DC into alloantigen for presentation to and down-regulation of anti-donor T cells to prolong allograft survival (141.31)

Current dogma in transplantation presumes that therapeutic maturation-resistant dendritic cells (MR-DC) prevent allograft rejection by directly interacting with donor-reactive T-cells in vivo. However, this assumption remains untested. Our study therefore aimed to elucidate the mechanism by which donor MR-DC down-regulate the anti-donor response to prolong allograft survival in mice. We employed as prototypic donor MR-DC, bone marrow-derived DC treated with the active form of vitamin D3, 1α,25(OH)2D3. We demonstrate that donor-derived MR-DC prolonged cardiac allograft survival similarly as donor apoptotic or viable splenocytes, suggesting that different donor-derived cellular therapies share a common mechanism of action. We determined that once injected i.v., MR-DC were short-lived and failed to directly tolerize donor-reactive T-cells. Rather, apoptotic MR-DC were internalized and re-processed by quiescent recipient splenic CD11chiCD8α+ and CD11chiCD8- DC, which in turn induced deletion of effector T-cells and outgrowth of regulatory T-cells via the indirect pathway. Importantly, activated recipient DC induced robust T-cell activation via indirect presentation. Our data suggest that therapeutic DC, like other more practical cellular therapies, serve as a source of alloantigen for recipient quiescent DC that in turn down-regulate the anti-donor response to prolong allograft survival.

Differential capability of human cutaneous dendritic cell subsets to initiate Th17 responses

Human skin-migratory dendritic cells (DCs) have the ability to prime and bias Th1 and Th2 CD4+ T lymphocytes. However, whether human cutaneous DCs are capable of initiating proinflammatory Th17 responses remains undetermined. We report that skin-migratory DCs stimulate allogeneic naive CD4+ T cells that differentiate simultaneously into two distinct effector Th17 and Th1 populations capable of homing to the skin, where they induce severe cutaneous damage. Skin-migratory Langerhans cells (smiLCs) were the main cutaneous DC subset capable of inducing Th17 responses dependent on the combined effects of IL-15 and stabilized IL-6, which resulted in IL-6 trans-signaling of naive CD4+ T cells. Different from smiLCs, purified skin-migratory dermal DCs did not synthesize IL-15 and were unable to bias Th17 responses. Nevertheless, these dermal DCs were capable of differentiating Th17 cells in mixed leukocyte cultures supplemented with IL-15 and stabilized IL-6. Overall, our data demonstrate that human epidermal smiLCs induce Th17 responses by mechanisms different from those previously described and highlight the need to target clinical treatments based on these variations.

Dendritic cells expressing plasmacytoid marker PDCA-1 are Trojan horses during Toxoplasma gondii infection

Plasmacytoid dendritic cells (pDCs) play a key role in the innate immune response to viral infection, due largely to their ability to produce large quantities of type I IFNs. These cells are also notable for their ability to differentiate into conventional dendritic cells after appropriate stimulation. Here, we show that a splenic population of murine CD11c(+) cells expressing pDC markers Gr-1, B220, and PDCA-1 is preferentially parasitized after infection with the virulent RH strain of Toxoplasma gondii. Although these markers are closely associated with pDCs, the population we identified was unusual because the cells express CD11b and higher than expected levels of CD11c. By adoptive transfer of CD45.1-positive cells into CD45.2 congenic mice, we show that CD11c(+)Gr-1(+) cells migrate from the peritoneal cavity to the spleen. During infection, these cells accumulate in the marginal zone region. Recruitment of infected CD11c(+)Gr-1(+) cells to the spleen is partially dependent upon signaling through chemokine receptor CCR2. Intracellular cytokine staining demonstrates that infected, but not noninfected, splenic CD11c(+)Gr-1(+) dendritic cells are suppressed in their ability to respond to ex vivo TLR stimulation. We hypothesize that Toxoplasma exploits pDCs as Trojan horses, targeting them for early infection, suppressing their cytokine effector function, and using them for dissemination within the host.

Exosomes as a short-range mechanism to spread alloantigen between dendritic cells during T cell allorecognition

Exosomes are nanovesicles released by different cell types including dendritic cells (DCs). The fact that exosomes express surface MHC-peptide complexes suggests that they could function as Ag-presenting vesicles or as vehicles to spread allogeneic Ags for priming of anti-donor T cells during elicitation of graft rejection or induction/maintenance of transplant tolerance. We demonstrate that circulating exosomes transporting alloantigens are captured by splenic DCs of different lineages. Internalization of host-derived exosomes transporting allopeptides by splenic DCs leads to activation of anti-donor CD4 T cells by the indirect pathway of allorecognition, a phenomenon that requires DC-derived, instead of exosome-derived, MHC class II molecules. By contrast, allogeneic exosomes are unable to stimulate direct-pathway T cells in vivo. We demonstrate in mice that although graft-infiltrating leukocytes release exosomes ex vivo, they do not secrete enough concentrations of exosomes into circulation to stimulate donor-reactive T cells in secondary lymphoid organs. Instead, our findings indicate that migrating DCs (generated in vitro or isolated from allografts), once they home in the spleen, they transfer exosomes expressing the reporter marker GFP to spleen-resident DCs. Our results suggest that exchange of exosomes between DCs in lymphoid organs might constitute a potential mechanism by which passenger leukocytes transfer alloantigens to recipient's APCs and amplify generation of donor-reactive T cells following transplantation.

Effective Treatment of Inflammatory Disease Models with Exosomes Derived from Dendritic Cells Genetically Modified to Express IL-4

In this study, we demonstrate that genetically modified bone marrow-derived dendritic cells (DC) and exosomes derived from the DC, expressing either secreted IL-4 or membrane-bound IL-4, can reduce the severity and the incidence of established collagen-induced arthritis and inhibit inflammation of delayed-type hypersensitivity (DTH) in mice. The ability of the DC and DC-derived exosomes to suppress the DTH response was MHC class II and, in part, Fas ligand/Fas dependent. The DC-derived exosomes were internalized by CD11c(+) DC in the dermis at the site of injection and in the draining lymph node as well as by CD11c(+) DC and F4/80(+) macrophages in the spleen. Moreover, adoptive transfer of CD11c(+) or CD3(+) splenic cells from mice treated with exosomes showed significant reduction of footpad swelling in the DTH model. These results demonstrate that administration of DC/IL-4 or exosomes derived from DC/IL-4 are able to modulate the activity of APC and T cells in vivo through a MHC class II and partly Fas ligand/Fas-dependent mechanism, resulting in effective treatment of established collagen-induced arthritis and suppression of the DTH inflammatory response. Thus, APC-derived exosomes could be used therapeutically for the treatment of autoimmune disease and inflammatory disorders.

MHC Class II+ Exosomes in Plasma Suppress Inflammation in an Antigen-Specific and Fas Ligand/Fas-Dependent Manner

Exosomes are 50- to 100-nm vesicles that are formed within the late endocytic compartment and released from a variety of cell types. Previously, we demonstrated that exosomes derived from dendritic cells transduced with adenoviral vectors expressing IL-10, IL-4, or Fas ligand (FasL) produce anti-inflammatory exosomes able to reduce inflammation in a murine paw delayed-type hypersensitivity model, suppress the onset on murine collagen-induced arthritis, and reduce the severity of established collagen-induce arthritis. In this study, we examined the ability of endogenous, blood-borne exosomes to regulate the immune response. Exosomes isolated from plasma of mice immunized to keyhole limpet hemocyanin, but not from naive or OVA-immunized mice, were able to suppress the keyhole limpet hemocyanin-specific delayed-type hypersensitivity inflammatory response. The anti-inflammatory effect was mediated by MHC class II(+) plasma exosomes that were also FasL(+) and CD11b(+), but CD11c(-). Moreover, the anti-inflammatory effect of the MHC class II(+) plasma-derived exosomes was, in part, dependent upon the presence of FasL in the exosomes and Fas in the recipient mouse. These results suggest that exosomes in the plasma, produced by MHC class II(+) and CD11b(+) cells, have the ability to suppress the immune response in an Ag-specific manner in part through a Fas/FasL-dependent manner.

In vivo signaling through the neurokinin 1 receptor favors transgene expression by Langerhans cells and promotes the generation of Th1- and Tc1-biased immune responses

The proinflammatory capacities of the skin and the presence of high numbers of resident dendritic cells (DCs) constitute an ideal microenvironment for successful immunizations. Regardless of the ability of DCs to respond to local inflammatory signals in an immunostimulatory fashion, the immune functions of skin-resident DCs remain controversial, and epidermal Langerhans cells (LCs) have been referred to recently as anti-inflammatory/protolerogenic APCs. Substance P (SP), released by skin nerve fibers, is a potent proinflammatory neuropeptide that favors development of skin-associated cellular immunity. SP exerts its proinflammatory functions by binding with high affinity to the neurokinin 1 receptor (NK1R). In this study, we tested whether signaling skin cells via the NK1R promotes humoral and cellular immunity during skin genetic immunizations. We used the gene gun to deliver transgenic (tg) Ag to the skin of C57BL/6 mice and the selective NK1R agonist [Sar(9)Met (O(2)) (11)]-SP as a potential proinflammatory Th1-biasing adjuvant. Our strategy expressed tg Ag exclusively in the epidermis and induced a preferential migration of activated LCs to skin-draining lymph nodes. Local administration of the NK1R agonist during skin genetic immunizations increased significantly the expression of tg Ag by a mechanism involving the translocation of NF-kappaB into the nuclei of cutaneous DCs homing to skin-draining lymph nodes. Importantly, our immunization approach resulted in Th1 and T cytotoxic (CTL)-1 bias of effector T cells that supported cellular and Ab-mediated immune responses. We demonstrate that signaling skin cells via the NK1R provides the adjuvant effect which favors the immunostimulatory functions of LCs.

Growth factor-induced mobilization of dendritic cells in kidney and liver of rhesus macaques: implications for transplantation

Hematopoietic growth factors (HGF) mobilize potential tolerogenic cells in transplant donors. Fms-like tyrosine kinase 3 ligand (Flt3L) mobilizes stem cells and dendritic cells (DCs) in human and nonhuman primate blood. Blood and renal and liver biopsies were obtained from untreated and Flt3L-mobilized rhesus macaques. Flt3L increased the number of myeloid CD11c(hi) and plasmacytoid CD123(hi) precursors in blood and both myeloid CD11c(+) HLA-DR(+) fascin(+) (CD45RA(-)) DCs and putative plasmacytoid CD11c(lo) CD45RA(hi) DC precursors in liver and kidneys, without affecting organ function. DC in Flt3L-treated monkeys were concentrated in the glomeruli and interstitium of kidneys, and in the portal triads and parenchyma of liver. These DCs exhibited the phenotype of immature antigen-presenting cells (APCs; CD83(-) CD86(lo) CCR5(+) CCR7(-)). HGF-induced changes reversed significantly within 7 days of Flt3L withdrawal. Therapeutic protocols that mobilize donor hematopoietic cells should consider the influence of HGF on the APC constituency of prospective organ allografts.

Intrinsic ability of GM+IL-4 but not Flt3L-induced rat dendritic cells to promote allogeneic T cell hyporesponsiveness

The influence of GM+IL-4 and Flt3 ligand (FL) on phenotype and function of BM-derived DC from Lewis rats was investigated. GM+IL-4-induced DC, despite expression of CD80/CD86, were less stimulatory than FL-induced DC that expressed low CD80/CD86 and were efficient stimulators of allogeneic T cells. GM+IL-4 DC were CD11b+ OX62lo, whereas FL DC were CD11blo OX62+. Following activation, GM+IL-4 DC produced IL-10 and IL-6, but no IL-12p70, and were resistant to further maturation. FL DC produced IL-12p70, IFN-alpha/beta, IL-10 and IL-6 and underwent maturation. Repeated stimulation of T cells with GM+IL-4 DC inhibited proliferation, cytokine production and induced early T cell apoptosis. FL DC-activated T cells produced large amounts of IFN-gamma/IL-10 and exhibited late T cell apoptosis/necrosis. In vivo, GM+IL-4 DC induced alloAg-specific hyporesponsiveness following T cell restimulation. These results demonstrate that GM+IL-4 DC display intrinsic regulatory properties, inducing passive-cell-death in T cells with potential for inactivation/regulation of alloreactive T cells in transplantation.

Dendritic Cells Expressing Transgenic Galectin-1 Delay Onset of Autoimmune Diabetes in Mice

Type 1 diabetes (T1D) is a disease caused by the destruction of the beta cells of the pancreas by activated T cells. Dendritic cells (DC) are the APC that initiate the T cell response that triggers T1D. However, DC also participate in T cell tolerance, and genetic engineering of DC to modulate T cell immunity is an area of active research. Galectin-1 (gal-1) is an endogenous lectin with regulatory effects on activated T cells including induction of apoptosis and down-regulation of the Th1 response, characteristics that make gal-1 an ideal transgene to transduce DC to treat T1D. We engineered bone marrow-derived DC to synthesize transgenic gal-1 (gal-1-DC) and tested their potential to prevent T1D through their regulatory effects on activated T cells. NOD-derived gal-1-DC triggered rapid apoptosis of diabetogenic BDC2.5 TCR-transgenic CD4+ T cells by TCR-dependent and -independent mechanisms. Intravenously administered gal-1-DC trafficked to pancreatic lymph nodes and spleen and delayed onset of diabetes and insulitis in the NODrag1(-/-) lymphocyte adoptive transfer model. The therapeutic effect of gal-1-DC was accompanied by increased percentage of apoptotic T cells and reduced number of IFN-gamma-secreting CD4+ T cells in pancreatic lymph nodes. Treatment with gal-1-DC inhibited proliferation and secretion of IFN-gamma of T cells in response to beta cell Ag. Unlike other DC-based approaches to modulate T cell immunity, the use of the regulatory properties of gal-1-DC on activated T cells might help to delete beta cell-reactive T cells at early stages of the disease when the diabetogenic T cells are already activated.

Transgenic Galectin-1 Induces Maturation of Dendritic Cells That Elicit Contrasting Responses in Naive and Activated T Cells

Dendritic cells (DC) are professional APC that control the balance between T cell immunity and tolerance. Genetic engineering of DC to regulate the outcome of the immune response is an area of intense research. Galectin (gal)-1 is an endogenous lectin that binds to glycoproteins and exerts potent regulatory effects on T cells. Consequently, gal-1 participates in central deletion of thymocytes and exerts therapeutic effects on experimental models of T cell-mediated autoimmune disorders and graft-vs-host disease. Together, these observations strongly indicate that engineering DC to express transgenic (tg) gal-1 may be beneficial to treat T cell-mediated disorders. In this study, we have investigated the impact of the expression of high levels of tg gal-1 on maturation/activation of DC and on their T cell stimulatory function. Murine DC were transduced with a recombinant adenovirus encoding hu gal-1 (gal-1-DC). Tg gal-1 was exported by a nonclassical pathway through exosomes and was retained on the DC surface inducing segregation of its ligand CD43. Expression of tg gal-1 triggered activation of DC determined by induction of a more mature phenotype, increased levels of mRNA for proinflammatory cytokines, and enhanced ability to stimulate naive T cells. Conversely, gal-1-DC induced rapid apoptosis of activated T cells. In vivo, gal-1-DC increased significantly the sensitization phase of contact hypersensitivity assays while inducing a drastic inhibition of the elicitation phase by triggering apoptosis of activated T cells in the dermis. Gal-1-DC represent a novel tool to control differentially the afferent and efferent arms of the T cell response.

Use of the inhibitory effect of apoptotic cells on dendritic cells for graft survival via T-cell deletion and regulatory T cells

Tolerance induction against donor allo-antigens (allo-Ag) remains one of the most challenging aspects of transplant immunology. The ability of dendritic cells (DC) to participate in immunity and tolerance makes them an excellent tool for tolerance induction. Here, we employed the immunosuppressive properties of apoptotic cells to deliver simultaneously an inhibitory signal and donor allo-Ag to recipient DC for treatment of allograft rejection. DC that captured apoptotic cells remained immature and activated deficiently anti-donor CD4(+) T cells that were unable to upregulate T-cell activation markers, to secrete IL-2 and IFN-gamma and to survive under homeostatic conditions due to low expression of Bcl-X(L), IL-7R and IL-15R. Administration of donor apoptotic cells decreased the systemic anti-donor T- and B-cell response and prolonged cardiac allograft survival in mice. The effect was donor specific and required the interaction of donor apoptotic cells with recipient quiescent CD8alpha(+) DC. When combined with CD40-CD154-blockade, administration of donor apoptotic cells resulted in indefinite graft survival mediated by generation of regulatory T cells. The use of the inhibitory effects of apoptotic cells on the anti-donor response provides a new approach to treat transplant rejection.

Regulated compartmentalization of programmed cell death-1 discriminates CD4+CD25+ resting regulatory T cells from activated T cells

More effective discrimination between CD4+CD25+ regulatory T cells (Treg) and activated T cells would significantly improve the current level of purification of Treg and their therapeutic application. We observed that approximately 90% of Treg (positive for the nuclear transcription factor Forkhead winged helix protein-3 and able to inhibit naive T cell proliferation) isolated from the spleens or lymph nodes of normal mice did not express significant levels of the inhibitory receptor programmed cell death-1 (PD-1) on their surface, but retained PD-1 intracellularly. An identical phenotype was also identified for human CD4+CD25(high) T cells isolated from peripheral blood of healthy volunteers. By contrast, activated T cells expressed high levels of surface PD-1 that paralleled up-regulation of CD25 during effector cell expansion. This distinction allowed us to isolate CD4+CD25+PD-1(-) T cells with suppressive activity from mice immunized with mature allogeneic dendritic cells. Although purification was limited to resting Treg because TCR ligation induced up-regulation of surface PD-1, this strategy nevertheless represents a valuable step toward more definitive characterization of Treg and their improved purification for therapeutic assessment.

Exosomes Derived from Genetically Modified DC Expressing FasL Are Anti-inflammatory and Immunosuppressive

We previously have demonstrated the ability of primary murine bone marrow-derived DC (BM-DC), genetically modified by adenoviral infection to express FasL, to inhibit progression of established collagen-induced arthritis (CIA) following systemic delivery. Here we demonstrate that exosomes derived from genetically modified BM-DC expressing FasL are able to inhibit inflammation in a murine footpad model of delayed-type hypersensitivity (DTH). Local administration of exosomes derived from DC expressing FasL (Exo/FasL) as well as the parental DC/FasL resulted in a significant reduction in swelling in both the treated and the untreated distal paw. However, both the DC/FasL and the Exo/FasL were unable to suppress the DTH response in lpr (Fas-deficient) mice. Gene transfer of FasL to BM-DC from gld (FasL-deficient) mice resulted in restoration of the ability of DC as well as DC-derived exosomes to suppress DTH. The ability of DC-derived exosomes and DC to suppress DTH responses was antigen specific and MHC class II dependent, but class I independent. The injected exosomes were found to be internalized into CD11c(+) cells at the site of injection and in the draining popliteal lymph node. Systemic injection of exosome/FasL into mice with established CIA resulted in significant disease amelioration. These results demonstrate that both systemic and local administration of exosomes derived from FasL-expressing DC are able to suppress antigen-specific immune responses through an MHC class II-dependent pathway, resulting in effective and sustained treatment of established collagen-induced arthritis and suppression of the DTH inflammatory response. These results suggest that DC/FasL-derived exosomes could be used clinically for the treatment of inflammatory and autoimmune diseases.

CCR and CC chemokine expression in relation to Flt3 ligand-induced renal dendritic cell mobilization

BACKGROUND

We investigated the expression and function of CC chemokine receptors (CCR) on highly-purified kidney and blood dendritic cells isolated from mice in which dendritic cells were mobilized with fms-like tyrosine 3 kinase ligand (Flt3L).

METHODS

CCR and CC chemokine expression were determined by RNase protection assay or flow cytometry, and dendritic cell migratory responses assayed using Transwell chambers. Chemokine production in renal tissue was detected by immunofluorescence staining. Trafficking of fluorochrome-labeled dendritic cells was monitored in vivo.

RESULTS

Freshly-isolated renal dendritic cells expressed mRNA for CCR1, 2, 5, and 7 and CCR1 and 5 protein. They did not migrate to inducible chemokines--CCL3 [macrophage inflammatory protein (MIP)-1alpha], CCL5 [regulated upon activation, normal T cell expressed and secreted (RANTES)], or CCL20 (MIP-3alpha). Following lipopolysaccharide (LPS) stimulation, the dendritic cells down-regulated CCR1, 2, and 5 expression, up-regulated or sustained signals for CCR7, and migrated to the constitutively expressed ligands CCL19 (MIP-3beta) and CCL21 (secondary lymphoid tissue chemokine). Normal kidneys expressed weak message for CCL2, 3, and 4, with stronger signals for CCL5 and 19. Intrarenal CCL5 production was enhanced by Flt3L administration, in association with marked increases in interstitial CD45+ mononuclear cells. Mobilized blood dendritic cells migrated to CCR2 and CCR5 ligands and trafficked to renal intertubular sites following adoptive (intravenous) transfer. Their migration to the CCR5 ligand MIP-1beta (CCL4) and homing to kidneys of Flt3L-treated recipients were inhibited by CCR5 antagonism.

CONCLUSION

These data implicate specific CCR and their ligands in regulation of the dendritic cell constituency of the kidney. CCR5 antagonism inhibits their directed migration and intrarenal accumulation.

Endocytosis, intracellular sorting, and processing of exosomes by dendritic cells

Exosomes are nanovesicles released by leukocytes and epithelial cells. Although their function remains enigmatic, exosomes are a source of antigen and transfer functional major histocompatibility complex (MHC)-I/peptide complexes to dendritic cells (DCs) for CD8(+) T-cell activation. Here we demonstrate that exosomes also are internalized and processed by immature DCs for presentation to CD4(+) T cells. Endocytosed exosomes are sorted into the endocytic compartment of DCs for processing, followed by loading of exosome-derived peptides in MHC-II molecules for presentation to CD4(+) T cells. Targeting of exosomes to DCs is mediated via milk fat globule (MFG)-E8/lactadherin, CD11a, CD54, phosphatidylserine, and the tetraspanins CD9 and CD81 on the exosome and alpha(v)/beta(3) integrin, and CD11a and CD54 on the DCs. Circulating exosomes are internalized by DCs and specialized phagocytes of the spleen and by hepatic Kupffer cells. Internalization of blood-borne allogeneic exosomes by splenic DCs does not affect DC maturation and is followed by loading of the exosome-derived allopeptide IEalpha(52-68) in IA(b) by host CD8alpha(+) DCs for presentation to CD4(+) T cells. These data imply that exosomes present in circulation or extracellular fluids constitute an alternative source of self- or allopeptides for DCs during maintenance of peripheral tolerance or initiation of the indirect pathway of allorecognition in transplantation.

Heart, but Not Skin, Allografts from Donors Lacking Flt3 Ligand Exhibit Markedly Prolonged Survival Time

Fms-like tyrosine kinase 3 ligand (Flt3L) administration leads to dramatic increases in dendritic cells (DC) in lymphoid and nonlymphoid tissues. Conversely, mice lacking Flt3L (Flt3L(-)/(-)) show severe reductions in both myeloid (CD11c(+)CD8alpha(-)) and lymphoid-related DC (CD11c(+)CD8alpha(+)) in the thymus and secondary lymphoid organs. In this study marked reductions in CD11c(+) interstitial cardiac DC and in dermal, but not epidermal, DC (Langerhans cells) were also observed. CD11c(+) cells that migrated from Flt3L(-/-) skin explants expressed lower surface MHC class II and costimulatory molecules and naive T cell allostimulatory activity than migratory wild-type (wt) C57BL/6 (B6) CD11c(+) cells. We examined the survival of Flt3L(-)/(-) heart or tail skin grafts (H2(b)) in allogeneic wt (BALB/c; H2(d)) recipients. The outcome of transplantation of BALB/c organs into Flt3L(-)/(-) recipients was also determined. Flt3L(-)/(-) mice rejected BALB/c heart or skin grafts with similar kinetics as B6 wt recipients. Trafficking of donor DC into host spleens or draining lymph nodes was markedly reduced after transplantation of Flt3L(-)/(-) heart, but not skin grafts, respectively. Compared with wt hearts, survival of Flt3L(-)/(-) hearts was markedly prolonged in BALB/c recipients (median survival time, 37 and 15 days, respectively; p < 0.001). Skin graft survival was unaffected. Rejection of Flt3L(-/-) hearts was precipitated by infusion of wt donor DC at the time of transplant. Thus, severe depletion of interstitial heart DC resulting from targeted gene disruption prolongs, but does not indefinitely extend, heart survival. Acute rejection of wt grafts in Flt3L(-/-) recipients reflects presumably an intact role of the direct pathway of allorecognition.

IN VIVO-MOBILIZED KIDNEY DENDRITIC CELLS ARE FUNCTIONALLY IMMATURE, SUBVERT ALLOREACTIVE T-CELL RESPONSES, AND PROLONG ORGAN ALLOGRAFT SURVIVAL1

BACKGROUND

Migratory antigen-presenting cells resident in kidneys may have tolerogenic potential. Difficulties inherent in their isolation have limited their characterization. The authors examined the phenotype and function of murine kidney dendritic cells (DC) mobilized in vivo by systemic administration of fms-like tyrosine 3 kinase ligand (Flt3L).

METHODS

Monoclonal antibody staining was used to characterize DC subsets in situ, immediately after their isolation, and after lipopolysaccharide stimulation. Cytokine and CC chemokine receptor (CCR) gene expression was analyzed by RNase protection assay. Mixed leukocyte reactions were performed to assess DC allostimulatory ability and also the function of putative T-regulatory cells. In vivo DC trafficking was monitored by fluorescence imaging of dye-labeled cells and the influence of renal DC on vascularized heart allograft survival was determined.

RESULTS

Flt3L induced a marked increase both in CD11cCD8alpha and in CD11cCD8alpha DC within the renal cortex and medulla. Rarer, CD11cB220 (precursor plasmacytoid) DC were also detected. Bulk freshly isolated DC exhibited no interleukin (IL)-12p35 mRNA, low surface co-stimulatory molecule expression, and CCR transcripts, consistent with immaturity. They elicited only weak allogeneic T-cell proliferative responses, and repeated stimulation induced CD4CD25 IL-10 T cells. In vivo, the freshly isolated DC failed to prime T cells of naive allogeneic hosts for anti-donor cytotoxic T-cell responses. When infused systemically, 1 week before organ transplantation, they prolonged graft survival without immunosuppressive therapy.

CONCLUSIONS

Hematopoietin-mobilized renal DC are functionally immature and exhibit tolerogenic potential. Mobilization of DC within kidneys is likely to affect their antigen-handling capacity, immunogenicity, and tolerogenic ability.

Internalization of circulating apoptotic cells by splenic marginal zone dendritic cells: dependence on complement receptors and effect on cytokine production

Under steady-state conditions, internalization of self-antigens embodied in apoptotic cells by dendritic cells (DCs) resident in peripheral tissue followed by DC migration and presentation of self-peptides to T cells in secondary lymphoid organs are key steps for induction and maintenance of peripheral T-cell tolerance. We show here that, besides this traffic of apoptotic cells mediated by peripheral tissue-resident DCs, splenic marginal zone DCs rapidly ingest circulating apoptotic leukocytes, process apoptotic cell-derived peptides into major histocompatibility complex class II (MHC-II) molecules, and acquire CD8alpha during their mobilization to T-cell areas of splenic follicles. Because apoptotic cells activate complement and some complement factors are opsonins for phagocytosis and play roles in the maintenance of peripheral tolerance, we investigated the role of complement receptors (CRs) in relation to phagocytosis of apoptotic cells by DCs. Apoptotic cell uptake by marginal zone DCs was mediated in part via CR3 (CD11b/CD18) and, to a lesser extent, CR4 (CD11c/CD18) and was reduced significantly in vivo in hypocomplementemic animals. Following phagocytosis of apoptotic cells, DCs exhibited decreased levels of mRNA and secretion of the proinflammatory cytokines interleukin 1alpha (IL-1alpha), IL-1beta, IL-6, IL-12p70, and tumor necrosis factor alpha (TNF-alpha), without effect on the anti-inflammatory mediator transforming growth factor beta1 (TGF-beta1). This selective inhibitory effect was at least partially mediated through C3bi-CD11b/CD18 interaction. Characterization of apoptotic cell/DC interaction and its outcome provides insight into the mechanisms by which apoptotic cells affect DC function without disrupting peripheral tolerance.