Skin delivery of hapten and neurokinin-1 receptor antagonists by microneedle arrays targets neurogenic inflammation and prevents contact dermatitis

Contact dermatitis (CD) is a chronic inflammatory disease caused by type-1 immunity. Skin exposure to haptens stimulates the secretion of Substance-P (SP) and initiates the neurogenic inflammation that intensifies CD. Neurokinin-1 receptor (NK1R)-signaling by SP or hemokinin-1 (HK1) amplifies immune responses. Nonetheless, the role and therapeutic implications of the NK1R-SP-HK1 axis in CD remain unclear. We show that SP, HK-1 and the NK1R are required for CD. Specific deletion of the NK1R in keratinocytes decreased the rapid release of IL-1β and IL-6 at the site of contact sensitization which impaired the innate and adaptive immunity of CD whereas deletion of the receptor in dendritic cells (DC) prevented only the adaptive immune response of the disease. Therefore, we hypothesized that blockade of NK1R during sensitization would be a feasible immunosuppressive intervention to treat CD. We developed a system of microneedle arrays (MNA) that co-deliver hapten and NK1R antagonists into mouse skin. This immunosuppressive approach resulted in decreased skin migration and lymph node homing of stimulatory dermal DC transporting the hapten from the sensitization site. Conversely, the immunosuppressive MNA did not affect the migration and lymph node homing of epidermal Langerhans cells (LC), and depletion of LC resulted in loss of the NK1R antagonist beneficial effects. In addition, immunosuppressive MNA caused deletion of hapten-specific T cells and increased T-regulatory cells, which prevented CD-onset and -relapses in a hapten-specific manner. Our findings indicate that immune-regulation by engineering localized skin neuroimmune-networks can be used to treat cutaneous diseases that, like CD are caused by type-1 immunity.

Neurokinin A blocks the ABCA1 channel to promote IL-10-dependent mast cell regulation

Cutaneous mast cells (MCs) reside in close proximity to peripheral sensory nerve fibers and are susceptible to regulation by neuropeptides. The tachykinin family member, Neurokinin A (NKA) binds with highest affinity to the Neurokinin 2 Receptor, expressed on MCs. MCs are poised to respond to NKA, but its role in the MC biology is, to our knowledge, under-explored. The objective of this study was to evaluate the effects of NKA on bone marrow (BM) MCs and peritoneal (P)MCs in vitro and in the murine model of passive cutaneous anaphylaxis (PCA) in vivo. Neurokinin A inhibited FceRI-initiated phosphorylation and nuclear localization of STAT5, and release of TNF and IL-13 in an IL-10-dependent manner. NKA affected the MC secretome, abrogating ABCA1-dependent release of the cysteine protease, calpain. Extracellular calpain, in turn, degraded IL-10. In vivo, NKA administration reduced PCA, inhibiting edema, and induction of inflammatory cytokines and in a manner that relied on MC derived-IL-10. Likewise, direct inhibition of the ABCA1 phenocopied the effects of NKA, reducing IgE-initiated MC responses in vitro and in vivo. In conclusion, NKA minimizes IgE-initiated inflammation though an IL-10-dependent mechanism and inhibits ABCA1-dependent release of the IL-10 degrading enzyme, calpain. This study illuminates a novel tier of neuropeptide mediated MC regulation through the ABCA1. Strategies interfering with the ABCA1 may be promising therapeutics for targeting MCs in cutaneous inflammatory diseases.

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.

Keratinocyte-Polyamines and Dendritic Cells: A Bad Duet for Psoriasis

The role of keratinocyte metabolism in psoriasis is not fully elucidated. In this issue of Immunity, Lou et al. describe that interleukin-17 (IL-17) re-programs the urea cycle in keratinocytes increasing polyamines that stabilize RNA-Ag-complexes that upon cellular turnover activate dendritic cells, which amplify psoriasis inflammation.

Blockade of the neurokinin-1 receptor in keratinocytes prevents neuroinflammation and decreases innate and adaptive immune responses in the skin

Substance P (SP) is a proinflammatory neuropeptide that following Ag entrance in peripheral tissues signals via the neurokinin 1 receptor (NK1R) to initiate innate and support adaptive cellular immune responses. These mechanisms underlie chronic skin inflammatory disorders like contact dermatitis (CD). Here we propose to develop an immunosuppressive method to prevent and treat CD by blocking the effects of SP during skin sensitization with haptens. We utilized microneedle arrays to efficiently deliver the hapten 2,4-dinitrocholorobencene (DNCB) and NK1R antagonists simultaneously to the skin of C57/BL6 mice. This approach, restrained neuroinflammation, increased T regulatory cells and decreased the viability of Th1 and Tc1 biased cells in the draining lymph nodes. Together these effects inhibited local and systemic CD and prevented its relapses. Using the Cre-Lox P system, we demonstrate that specific deletion of the NK1R in keratinocytes but not in leukocytes inhibited the sensitization phase of CD by blocking the release of IL-1β and IL-6. Whereas deletion of the receptor in keratinocytes or in dendritic cells was necessary to abrogate the adaptive cellular immunity. Our data demonstrate the possibility of preventing the development of cellular immunity by engineering the skin microenvironment to restrain the effects of neuroinflammatory peptides accounting for the onset of chronic skin inflammatory diseases.

The pseudo-allergy receptor, MrgprB2/X2 is controlled by neurokinin A and the neurokinin 2 receptor in human and mouse skin

Within the skin, mast cells (MCs) and sensory neurons form a cohesive unit that plays an important role in initiating immune responses. Neuropeptides such as neurokinin A and substance P direct MC function by initiating signaling through neurokinin (NK) receptors, and Mas related G-protein receptors (Mrgpr)s. Neurokinin A, in particular, is thought to signal through the NK2R. Recent studies highlight the importance of the MrgprB2 (mouse) and MrgprX2 (human) in the MC response to pseudo-allergens, secretagogues and substance P. To date, a relationship between neurokinin receptors and the MrgprB2/X2 has not been investigated. In this study, we hypothesize that MrgprB2/X2 expression is controlled by the NK2R and its high affinity ligand, neurokinin A. In mice, we show that administration of neurokinin A diminishes MrgprB2 expression. Surprisingly, antagonism of the NK2R also downregulates MrgprB2 expression and in NK2R-deficient mice, MrgprB2 expression is markedly diminished. In contrast, co-administration of neurokinin A and a NK2R antagonist markedly increases MrgprB2 expression. In human skin explants, NK2R antagonism has minimal effect on MrgprX2 expression, but co-administration of neurokinin A and a NK2R antagonist upregulates MrgprX2 expression, as seen in murine skin. These data demonstrate that NK2R-signaling influences MrgprB2/X2 expression and, in absence of the NK2R, neurokinin A interacts with an unknown receptor to increase MrpgrB2/X2 expression. Collectively, these data uncover a novel role for NK2R signaling in the regulation of MrgprB2/X2. These important findings have implications for patients with dysregulated mast cell function initiated through the MrgprX2.

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.

Neurokinin A renders mast cells responsive to autocrine IL-10

Interleukin (IL)-10 is produced by skin-resident mast cells (MCs). However, little is known about mechanisms regulating IL-10 production by MCs. In this study, we investigated the capacity for tissue-derived factors, such as neuropeptides, to regulate IL-10 release from MCs. Neurokinin A (NKA), a tachykinin family member, is highly expressed in the skin, but few studies have addressed its impact on immune cells. In this study, we specifically hypothesized that NKA would affect IL-10 levels in MCs. We investigated the effects of NKA in vitro using bone marrow (BM)MCs, loaded with IgE then activated with cross-linking antigen. Neurokinin A affected three levels of IL-10 regulation in IgE-activated BMMCs: 1) NKA augmented IL-10R expression, 2) NKA increased IL-10 transcription 3) NKA decreased release of an IL-10-degrading protease, without affecting degranulation. Neurokinin A potently reduced IL-4, IL-6 and IL-13 transcription and STAT5 phosphorylation. Neutralization of IL-10 reversed the effects of NKA on transcription and on STAT5 phosphorylation. In the skin, intradermal administration of NKA into MC-sufficient mice upregulated expression of IL-10 RNA, while NKA had no effect on IL-10 RNA when administered into mice lacking cutaneous MCs. We used the murine passive cutaneous anaphylaxis (PCA) model to investigate the relationship between NKA and IgE-initiated MC activation in the skin. Neurokinin A reduced early and late PCA in a manner requiring MC-derived IL-10. Collectively, we have identified a novel mechanism through which the neuropeptide, NKA, acts on MCs to regulate IL-10, broadening our understanding of the role of neuropeptides in MC function.

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 A augments SynCAM expression and IL-10 release from mast cells

Cutaneous mast cells (MCs) initiate innate and adaptive immune responses. In the skin, MCs reside proximal to peripheral nerve fibers, forming a functional synapse mediated, in part, by Synaptic Cell Adhesion Molecule (SynCAM). Within the synapse, MC function is likely affected by the release of soluble neuropeptides. We and others have demonstrated that the immune functions of MCs are affected by the neuropeptides from the tachykinin family. Substance P promotes MC-inflammatory functions, whereas the role of neurokinin A (NKA) in MC biology is hereto unknown. In this study, the capacity for NKA to regulate MC stasis and IgE-initiated MC activation was evaluated. In bone marrow derived (BM) MCs, NKA increased expression of SynCAM, but not expression of other cell adhesion molecules, such as ICAM or NCAM. In IgE-activated MCs, NKA did not affect SynCAM expression. However, NKA promoted IL-10 secretion resulting in the inhibition of IgE-initiated STAT5 phosphorylation and nuclear localization, leading to the inhibition of type 2 cytokine release. STAT5 phosphorylation was restored in NKA treated BMMCs by neutralizing IL-10. In vivo, intradermal administration of NKA increased the density of MCs in the skin. In spite of this increase in MCs, NKA reduced IgE-initiated passive cutaneous anaphylaxis. Our data indicates that NKA strengthens the formation of the MC-neuron synapse and down-regulates MC pro-inflammatory functions.

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.

The neuropeptide, neurokinin A, has divergent effects on mast cell function

Mast cells (MCs) play a critical role in initiation of cutaneous type 2 immune responses. In the cutaneous microenvironment, sensory nerve fibers form a cohesive unit with MCs. In this unit, MC function is likely affected by neuropeptides, such as neurokinin A (NKA). NKA is abundant in the skin, but the affects of NKA on cutaneous MCs have not been extensively reported. NKA signals preferentially through the neurokinin-2 receptor (NK2R). We hypothesized that NKA/NK2R interactions influence cutaneous MC function. The effect of NKA on MCs was evaluated in vivo using the MC/IgE-specific passive cutaneous anaphylaxis (PCA) model. NKA reduced IgE-initiated changes in ear thickness. Likewise, NK2R antagonism enhanced IgE-initiated ear thickness in the PCA model. Intracellular pathways mediating the effects of NKA were delineated using bone marrow derived MCs (BMMCs). BMMCs expressed NK2R protein constitutively and NK2R expression was up-regulated by IgE. Functionally, NKA increased the percentage of IgE-activated MCs releasing granules but repressed transcription and release of the type 2 cytokines, IL-4 and IL-13. Mechanistically, IgE-mediated granule release has been attributed to increased STAT3 activation, whilst IL-4 and IL-13 transcription in MCs is attributed to STAT5 activation. NKA augmented STAT3 phosphorylation in IgE-activated MCs but reduced STAT5 phosphorylation. In sum, NKA modifies IgE-initiated STAT3 and STAT5 activity, granule release and cytokine transcription in MCs in vitro and inhibits MC function in vivo. These data demonstrate a role for NKA in the regulation of MC processes involved in type 2 mediated allergic disorders.

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.

Skin-resident effector memory CD8+CD28− T cells exhibit a pro-fibrotic phenotype in patients with systemic sclerosis

Loss of CD28 expression by CD8+ T cells occurs with age and during chronic inflammatory conditions. CD8+CD28− T cells are a heterogeneous cell subpopulation whose function ranges from immunosuppressive to effector. Here we analyzed the role of CD8+CD28− T cells in the pathogenesis of systemic sclerosis (SSc), a connective tissue disorder characterized by autoimmunity, vasculopathy and extensive cutaneous and visceral fibrosis. We show that the frequency of CD8+CD28− T cells is increased in the blood and affected skin of SSc patients, independent of patient age, and correlates with the extent of skin fibrosis. We found that the majority of skin-tropic CD8+CD28− T cells are resident in the skin lesions of patients in the early stage of the disease, exhibit an effector memory phenotype and present a strong cytolytic activity ex vivo. Skin-resident and circulating SSc CD8+CD28− T cells produce high levels of the pro-fibrotic cytokine IL-13, which induces collagen production by normal and SSc dermal fibroblasts. Thus, our findings indicate that CD8+CD28− T cells represent a pathogenic T-cell subset in SSc and likely play a critical role in the early stage of SSc skin disease.

Skin-Resident Effector Memory CD8+CD28- T Cells Exhibit a Profibrotic Phenotype in Patients with Systemic Sclerosis

Loss of CD28 expression by CD8⁺ T cells occurs with age and during chronic inflammatory conditions. CD8⁺CD28^- T cells are a heterogeneous cell subpopulation whose function ranges from immunosuppressive to effector. Here we analyzed the role of CD8⁺CD28^- T cells in the pathogenesis of systemic sclerosis (SSc), a connective tissue disorder characterized by autoimmunity, vasculopathy, and extensive cutaneous and visceral fibrosis. We show that the frequency of CD8⁺CD28^- T cells is increased in the blood and affected skin of SSc patients, independent of patient age, and correlates with the extent of skin fibrosis. We found that most skin-tropic CD8⁺CD28^- T cells are resident in the skin lesions of patients in the early stage of the disease, exhibit an effector memory phenotype, and present a strong cytolytic activity ex vivo. Skin-resident and circulating SSc CD8⁺CD28^- T cells produce high levels of the profibrotic cytokine IL-13, which induces collagen production by normal and SSc dermal fibroblasts. Thus, our findings indicate that CD8⁺CD28^- T cells represent a pathogenic T-cell subset in SSc and likely play a critical role in the early stage of SSc skin disease.

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.

Neurokinin A reduces FcɛRI-triggered inflammation mediated by cutaneous mast cells

Mast cells (MCs) are potent effector cells in atopic diseases, like asthma and atopic dermatitis. In the skin, MCs reside in the dermis, in close proximity to sensory nerves. In this shared geographical space, MCs and neurons may have evolved common mechanisms for responding to noxious stimuli and for maintaining homeostasis, including responsiveness to neuropeptides. Sensory nerves release neuropeptides with immune functions including the tachykinin family member, neurokinin A (NKA). Recent studies highlight immune functions for NKA but a role for NKA in MC biology has not been explored. NKA signals with high affinity through the neurokinin 2 receptor (NK2R) that has been reported to be anti-inflammatory in the skin. In the current study, we hypothesized that NKA would dampen MC activation initiated by FcɛRI. Our data demonstrated that, in vitro, mouse bone marrow (BM) derived MCs expressed low levels of the NK2R, which was upregulated following FcɛRI activation and maintained by STAT3 signaling. The addition of NKA to MC cultures downregulated surface expression of the prototypical MC markers, FcɛRIα and c-Kit. This effect was overcome with IgE and cross-linking antigen (Ag). NKA alone did not affect degranulation or cytokine release. But, NKA increased the percentage of MCs releasing granules in response to IgE + Ag, while decreasing the secretion of IL-4, IL-13 and IL-6 in response to IgE + Ag. In vivo, intradermal administration of NKA reduced IgE-dependent MC functions in a murine model of passive cutaneous anaphylaxis. Our data suggest that NKA reduces the inflammatory capacity of MCs and that activation of the NKA/NK2R axis has a therapeutic potential for MC mediated atopic diseases.

Hemokinin-1 and Substance P provide adjuvancy for T cell activation and survival necessary for innate and adaptive cellular immune responses

Chronic inflammatory and autoimmune disorders rely on the generation of efficient T cell responses. The pro-inflammatory neuropeptides, hemokinin-1 (HK-1) and substance P (SP) potentiate cellular immunity by signaling via the neurokinin-1 receptor (NK1R) expressed in leukocytes, including T cells. HK-1 is secreted by leukocytes while SP is released by sensory nerves and tissue resident cells. The role of NK1R signaling in the effector functions of T cells remains ill understood. We investigated the effects of signaling via the NK1R in the population of activated T-cells. In vitro, we compared the effects of HK-1 and SP on the survival and effector functions of wild type (WT) and NK1RKO CD4 and CD8 T cells. In vivo, we compared the effect of NK1R-signaling on T cells by using a delayed-type hypersensitivity (DTH) model in hosts with selective deletion of the NK1R in T cells. We demonstrate that NK1R-signaling is necessary for the generation, and maintenance of the survival and effector functions of CD4 and CD8 T cells. T cells secreted HK-1 and SP to promote self-activation and survival. Signaling via the NK1R resulted in Ca2+-influx in T cells, and that effect was impaired in NK1RKO T cells. Downstream, NK1R signaling activated the Ca2+-dependent NFAT1 and NFAT2 pathways, with the consequent increases in the synthesis and secretion of IL-2 that sustained T cell survival. In addition, NK1R-signaling stimulated the MAPK (c-Fos and c-Jun) and NF-kB pathways resulting in T cell activation. In vivo, DTH assays were significantly compromised in mice with selective deletion of NK1R+ T cells compared to WT. Our results elucidate the role and mechanisms of specific NK1R-T cell signaling in the generation and maintenance of potent T cell responses.

Concise Review: Mechanisms Behind Apoptotic Cell-Based Therapies Against Transplant Rejection and Graft versus Host Disease

The main limitations to the success of transplantation are the antigraft response developed by the recipient immune system, and the adverse side effects of chronic immunosuppression. Graft-versus-host disease (GVHD) triggered by donor-derived T lymphocytes against the recipient tissues is another serious obstacle in the field of hematopoietic stem cell transplantation. Several laboratories have tested the possibility of promoting antigen (Ag)-specific tolerance for therapy of graft rejection, GVHD, and autoimmune disorders, by developing methodologies that mimic the mechanisms by which the immune system maintains peripheral tolerance in the steady state. It has been long recognized that the silent clearance of cells undergoing apoptosis exerts potent immune-regulatory effects and provides apoptotic cell-derived Ags to those Ag-presenting cells (APCs) that internalize them, in particular macrophages and dendritic cells. Therefore, in situ-targeting of recipient APCs by systemic administration of leukocytes in early apoptosis and bearing donor Ags represents a relatively simple approach to control the antidonor response against allografts. Here, we review the mechanisms by which apoptotic cells are silently cleared by phagocytes, and how such phenomenon leads to down-regulation of the innate and adaptive immunity. We discuss the evolution of apoptotic cell-based therapies from murine models of organ/tissue transplantation and GVHD, to clinical trials. We make emphasis on potential limitations and areas of concern of apoptotic cell-based therapies, and on how other immune-suppressive therapies used in the clinics or tested experimentally likely also function through the silent clearance of apoptotic cells by the immune system. Stem Cells 2016;34:1142-1150.

Clinical implications of basic science discoveries: nociceptive neurons as targets to control immunity--potential relevance for transplantation

Increasing evidence indicates the existence of a complex cross-regulation between the most important biosensors of the human body: The immune and nervous systems. Cytokines control body temperature and trigger autoimmune disorders in the central nervous system, whereas neuropeptides released in peripheral tissues and lymphoid organs modulate inflammatory (innate) and adaptive immune responses. Surprisingly, the effects of nerve fibers and the antidromic release of its pro-inflammatory neuropeptides on the leukocytes of the immune system that mediate graft rejection are practically unknown. In the transplantation field, such area of research remains practically unexplored. A recent study by Riol-Blanco et al has revealed new details on how nociceptive nerves regulate the pro-inflammatory function of leukocytes in peripheral tissues. Although the mechanism(s) by which neuroinflammation affects the immune response against the allograft remains unknown, recent data suggest that this new area of research is worth exploring for potential development of novel complementary therapies for prevention/treatment of graft rejection.

Methods of analysis of dendritic cell-derived exosome-shuttle microRNA and its horizontal propagation between dendritic cells

Exosomes are extremely small (<100 nm) membrane vesicles, generated in the endocytic compartment that are released to the extracellular milieu by living cells. Although the biological function of exosomes in vivo remains unclear, they seem to function as mechanisms of cell-to-cell communication for horizontal transfer of proteins, antigens, prions, morphogens, mRNA, and noncoding regulatory RNAs, including microRNAs (miRNAs) (also known as exosome-shuttle miRNAs). Dendritic cells (DCs), the most potent professional antigen-presenting leukocytes of the immune system, release relatively high levels of exosomes and also interact with free exosomes present in the extracellular space. Therefore, DCs constitute a good model for the analysis of exosome-shuttle miRNAs and their horizontal propagation between cells. This chapter provides basic protocols for purification of exosomes released by mouse bone marrow-derived DCs, analysis of their miRNA content, and assessment of the function of exosome-shuttle miRNAs, once they are transferred to target/acceptor DCs.

Interleukin-13-producing CD8+ T cells mediate dermal fibrosis in patients with systemic sclerosis

OBJECTIVE

Fibrosis is a major contributor to morbidity and mortality in systemic sclerosis (SSc). T cells are the predominant inflammatory infiltrate in affected tissue and are thought to produce cytokines that drive the synthesis of extracellular matrix (ECM) proteins by fibroblasts, resulting in excessive fibrosis. We have previously shown that aberrant interleukin-13 (IL-13) production by peripheral blood effector CD8+ T cells from SSc patients correlates with the extent of skin fibrosis. The present study was undertaken to investigate the role of IL-13 production by CD8+ T cells in dermal fibrosis, an early and specific manifestation of SSc.

METHODS

ECM protein production by normal dermal fibroblasts cocultured with SSc CD8+ T cell supernatants was determined by quantitative polymerase chain reaction and Western blotting. Skin-homing receptor expression and IL-13 production by CD8+ T cells in the peripheral blood of SSc patients were measured by flow cytometry. IL-13+ and CD8+ cells in sclerotic skin were identified by immunohistochemistry.

RESULTS

IL-13-producing circulating CD8+ T cells from patients with SSc expressed skin-homing receptors and induced a profibrotic phenotype in normal dermal fibroblasts, which was inhibited by an anti-IL-13 antibody. High numbers of CD8+ T cells and IL-13+ cells were found in the skin lesions of SSc patients, particularly during the early inflammatory phase of the disease.

CONCLUSION

These findings show that IL-13-producing CD8+ T cells are directly involved in modulating dermal fibrosis in SSc. The demonstration that CD8+ T cells homing to the skin early in the course of SSc are associated with accumulation of IL-13 is an important mechanistic contribution to the understanding of the pathogenesis of dermal fibrosis in SSc and may represent a potential target for therapeutic intervention.

A peptide derived from endostatin ameliorates organ fibrosis

Fibroproliferative disorders such as idiopathic pulmonary fibrosis and systemic sclerosis have no effective therapies and result in significant morbidity and mortality due to progressive organ fibrosis. We examined the effect of peptides derived from endostatin on existing fibrosis and fibrosis triggered by two potent mediators, transforming growth factor-β (TGF-β) and bleomycin, in human and mouse tissues in vitro, ex vivo, and in vivo. We identified one peptide, E4, with potent antifibrotic activity. E4 prevented TGF-β-induced dermal fibrosis in vivo in a mouse model, ex vivo in human skin, and in bleomycin-induced dermal and pulmonary fibrosis in vivo, demonstrating that E4 exerts potent antifibrotic effects. In addition, E4 significantly reduced existing fibrosis in these preclinical models. E4 amelioration of fibrosis was accompanied by reduced cell apoptosis and lower levels of lysyl oxidase, an enzyme that cross-links collagen, and Egr-1 (early growth response gene-1), a transcription factor that mediates the effects of several fibrotic triggers. Our findings identify E4 as a peptide with potent antifibrotic activity and a possible therapeutic agent for organ fibrosis.

Coordinate stimulation of macrophages by microparticles and TLR ligands induces foam cell formation

Aberrant activation of macrophages in arterial walls by oxidized lipoproteins can lead to atherosclerosis. Oxidized lipoproteins convert macrophages to foam cells through lipid uptake and TLR signaling. To investigate the relative contributions of lipid uptake and TLR signaling in foam cell formation, we established an in vitro assay using liposomes of defined lipid compositions. We found that TLRs signaling through Toll/IL-1R domain-containing adapter inducing IFN-β promoted foam cell formation by inducing both NF-κB signaling and type I IFN production, whereas TLRs that do not induce IFN, like TLR2, did not enhance foam cell formation. Addition of IFN-α to TLR2 activator promoted robust foam cell formation. TLR signaling further required peroxisome proliferator-activated receptor α, as inhibition of peroxisome proliferator-activated receptor α blocked foam cell formation. We then investigated the ability of endogenous microparticles (MP) to contribute to foam cell formation. We found that lipid-containing MP promoted foam cell formation, which was enhanced by TLR stimulation or IFN-α. These MP also stimulated foam cell formation in a human skin model. However, these MP suppressed TNF-α production and T cell activation, showing that foam cell formation can occur by immunosuppressive MP. Taken together, the data reveal novel signaling requirements for foam cell formation and suggest that uptake of distinct types of MP in the context of activation of multiple distinct TLR can induce foam cell formation.

Syndecan-2 is a novel target of insulin-like growth factor binding protein-3 and is over-expressed in fibrosis

Extracellular matrix deposition and tissue scarring characterize the process of fibrosis. Transforming growth factor beta (TGFβ) and Insulin-like growth factor binding protein-3 (IGFBP-3) have been implicated in the pathogenesis of fibrosis in various tissues by inducing mesenchymal cell proliferation and extracellular matrix deposition. We identified Syndecan-2 (SDC2) as a gene induced by TGFβ in an IGFBP-3-dependent manner. TGFβ induction of SDC2 mRNA and protein required IGFBP-3. IGFBP-3 independently induced production of SDC2 in primary fibroblasts. Using an ex-vivo model of human skin in organ culture expressing IGFBP-3, we demonstrate that IGFBP-3 induces SDC2 ex vivo in human tissue. We also identified Mitogen-activated protein kinase-interacting kinase (Mknk2) as a gene induced by IGFBP-3. IGFBP-3 triggered Mknk2 phosphorylation resulting in its activation. Mknk2 independently induced SDC2 in human skin. Since IGFBP-3 is over-expressed in fibrotic tissues, we examined SDC2 levels in skin and lung tissues of patients with systemic sclerosis (SSc) and lung tissues of patients with idiopathic pulmonary fibrosis (IPF). SDC2 levels were increased in fibrotic dermal and lung tissues of patients with SSc and in lung tissues of patients with IPF. This is the first report describing elevated levels of SDC2 in fibrosis. Increased SDC2 expression is due, at least in part, to the activity of two pro-fibrotic factors, TGFβ and IGFBP-3.

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.

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.

Human skin culture as an ex vivo model for assessing the fibrotic effects of insulin-like growth factor binding proteins

Systemic sclerosis (SSc) is a connective tissue disease of unknown etiology. A hallmark of SSc is fibrosis of the skin and internal organs. We recently demonstrated increased expression of IGFBP-3 and IGFBP-5 in primary cultures of fibroblasts from the skin of patients with SSc. In vitro, IGFBP-3 and IGFBP-5 induced a fibrotic phenotype and IGFBP-5 triggered dermal fibrosis in mice. To assess the ability of IGFBPs to trigger fibrosis, we used an ex vivo human skin organ culture model. Our findings demonstrate that IGFBP-3 and IGFBP-5, but not IGFBP-4, increase dermal and collagen bundle thickness in human skin explants, resulting in substantial dermal fibrosis and thickening. These fibrotic effects were sustained for at least two weeks. Our findings demonstrate that human skin ex vivo is an appropriate model to assess the effects of fibrosis-inducing factors such as IGFBPs, and for evaluating the efficacy of inhibitors/therapies to halt the progression of fibrosis and potentially reverse it.

Helper function of memory CD8+ T cells: heterologous CD8+ T cells support the induction of therapeutic cancer immunity

In contrast to the well-established efficacy of preventive vaccines, the effectiveness of therapeutic vaccines remains limited. To develop effective vaccination regimens against cancer, we have analyzed the effect of effector and memory CD8+ T cells on the ability of dendritic cells to mediate the immunologic and antitumor effects of vaccination. We show that in contrast to effector CD8+ T cells that kill antigen-carrying dendritic cells, IFNgamma-producing memory CD8+ T cells act as "helper" cells, supporting the ability of dendritic cells to produce interleukin-12 (IL-12) p70. Promoting the interaction of tumor antigen-carrying dendritic cells with memory-type "heterologous" (tumor-irrelevant) CD8+ T cells strongly enhances the IL-12p70-dependent immunogenic and therapeutic effects of vaccination in the animals bearing established tumors. Our data show that the suppressive and helper functions of CD8+ T cells are differentially expressed at different phases of CD8+ T-cell responses. Selective performance of helper functions by memory (in contrast to effector) CD8+ T cells helps to explain the phenomenon of immune memory and facilitates the design of effective therapeutic vaccines against cancer and chronic infections.

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.

Professional antigen-presenting cells of the skin

The skin functions as an important pro-inflammatory and immune organ. Accordingly, the epidermis and dermis are highly populated by dendritic cells (DC), which are potent antigen-presenting cells (APC) with important immunostimulatory and migratory activities. Whereas the biological characteristics and immunological functions of epidermal DC known as Langernahs cells (LC) have been the focus of intense research in the past, less is known regarding their dermal counterparts named dermal dendritic cells (DDC). Although it has been widely accepted that LC are the more relevant skin-resident APC, recent experimental evidence challenges this concept and proposes a different role for these important cell populations. In this article we compile recent scientific advances regarding the function of different skin-resident DC and we try to reconcile the new observations with the previously established paradigm.

Genetic immunizations in the presence of a specific neurokinin 1 receptor agonist triggers Th1-Tc1 biased immune responses that protect against B16 melanomas (48.13)

Antigen (Ag) specific Th1-Tc1 cellular immunity induced by genetic immunizations is critical to prevent / eradicate tumors. The high number of resident dendritic cells (DCs) makes the skin an ideal microenvironment for genetic immunizations against tumors. Skin DCs become potent stimulators of Ag specific T cells by signals triggered during acute inflammation in peripheral tissues. The secretion of the pro-inflammatory neuropeptide substance P signaling via the neurokinin 1 receptor (NK1R) represents an early danger signal that stimulates APC functions of DCs. Here we tested whether signaling via the NK1R during skin genetic immunizations favors Th1-Tc1 immunity in C57BL/6 mice injected with B16 melanoma cells. We utilized the gene gun to deliver transgenic (tg) OVA or TRP-2 Ag to mouse skin and the NK1R agonist Sar9Met (O2)11-SP as a potential Th1 adjuvant. Our strategy expressed Ag exclusively in the epidermis and induced substantial migration of activated Langerhans cells (LCs) transporting tg Ag to skin draining lymph nodes, which resulted in generation of Th1-Tc1 immunity. Importantly delivery of tg TRP-2 plus NK1R agonist was able to protect mice against B16 melanoma tumor cell growth. Our data demonstrate that NK1R signaling provides the Th1 adjuvant effect that positively modulates the immunostimulatory functions of LCs during skin genetic immunizations leading to productive immune responses.

Human skin migratory dendritic cells that do not secrete IL-12p70 stimulate both Th17 and Th1 allogeneic responses (36.20)

We analyzed the ability of human skin migratory dendritic cells (smiDC) to stimulate allogeneic (allo)-CD4+ T helper cell responses and to induce differentiation of Th1 and Th17 cells. SmiDCs obtained from cultures of human skin explants consisted of Langerhans cells and dermal DCs, which synthesized IL-8, IL-15, IL-23, IL-10 and TGF-β1, but not IL-12p70, even after exposure to DC1-driving stimuli. Regardless of the lack of IL-12p70 smiLC and DDC induced differentiation of effector memory Th cells that expressed CD45RO, the skin homing molecule CLA, and decreased CD62L and CCR7. SmiDCs stimulated proliferation of allo-CD4+ T cells that differentiated into Th1 and Th17 cells during 5 day-MLCs. T cell proliferation depended on the expression of MHC-II, costimulatory and adhesion molecules by smiDCs. The Th1 biasing function of smiDCs depended on the production of IL-23. The Th17 response was supported by the proinflammatory cytokines IL-8 and IL-15 and was significantly increased by the blockade of IL-6, whereas the blockade of IL-23 did not affect the secretion of IL-17. Levels of IL-17 and IFN-γ secretion reached their maximum at day 4 and 5, respectively. IFN-γ (Th1) and IL-17 (Th17) was produced by two distinct Th cell subsets as demonstrated by flow cytometry. Therefore, human smiDCs support the induction and coexistence of Th1 and Th17 effector T cells by mechanisms distinct from those described in the mouse model.

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.

CD4+ T cell responses elicited by different subsets of human skin migratory dendritic cells

Skin dendritic cells (DC) are professional APC critical for initiation and control of adaptive immunity. In the present work we have analyzed the CD4+ T cell stimulatory function of different subsets of DC that migrate spontaneously from human skin explants, including CD1a+CD14- Langerhans' cells (LC), CD1a-CD14- dermal DC (DDC), and CD1a-CD14+ LC precursors. Skin migratory DC consisted of APC at different stages of maturation-activation that produced IL-10, TGF-beta1, IL-23p19, and IL-12p40, but did not release IL-12p70 even after exposure to DC1-driving stimuli. LC and DDC migrated as mature/activated APC able to stimulate allogeneic naive CD4+ T cells and to induce memory Th1 cells in the absence of IL-12p70. The potent CD4+ T cell stimulatory function of LC and DDC correlated with their high levels of expression of MHC class II, adhesion, and costimulatory molecules. The Th1-biasing function of LC and DDC depended on their ability to produce IL-23. By contrast, CD1a-CD14+ LC precursors migrated as immature-semimature APC and were weak stimulators of allogeneic naive CD4+ T cells. However, and opposite of a potential tolerogenic role of immature DC, the T cell allostimulatory and Th1-biasing function of CD14+ LC precursors increased significantly by augmenting their cell number, prolonging the time of interaction with responding T cells, or addition of recombinant human IL-23 in MLC. The data presented in this study provide insight into the function of the complex network of skin-resident DC that migrate out of the epidermis and dermis after cutaneous immunizations, pathogen infections, or allograft transplantation.

Tumor cell loaded type-1 polarized dendritic cells induce Th1-mediated tumor immunity

Dendritic cells are professional antigen-presenting cells capable of inducing and regulating innate and antigen-specific immune responses. Therapeutic cancer vaccines using ex vivo engineered or in vivo targeted dendritic cells are being evaluated in clinical trials. T-helper type-1 (Th1)-skewed immune responses are characterized by the preferential induction of antigen-specific IFN-gamma-secreting CD4+ T cells and correlate with effector mechanisms important for tumor and viral immunity. Methods to "polarize" human monocyte-derived dendritic cells for the preferential induction of Th1-skewed immune responses have been developed, and polarized dendritic cells (DC1s) are being evaluated in preclinical and clinical studies. Here, we show that stimulation of bone marrow-derived murine dendritic cell populations with poly(I:C) and CpGs results in phenotypic maturation of dendritic cells and synergistic induction of durable, high-level IL-12p70 secretion characteristic of human type-1 polarized dendritic cells. Functionally, these dendritic cells induce antigen-specific Th1-type CD4+ T-cell activation in vitro and in vivo. Dendritic cell maturation and polarization are not inhibited by the presence of live B16 melanoma tumor cells, and tumor-loaded DC1s induce delayed-type hypersensitivity responses in vivo. DC1s loaded with B16 melanoma cells and injected into tumor-bearing mice induce Th1-skewed tumor-specific CD4+ T cells and a significant reduction in tumor growth. Tumor infiltrates in DC1-immunized animals are characterized by the presence of CD4+ T cells and activated macrophages. These results show a murine model of DC1 function and suggest an important role for CD4+ T cells and macrophages in DC1-induced antitumor immune responses. They have implications for the future development of DC1-based immunotherapies and strategies for clinical immune monitoring of their effectiveness.

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.

Highly efficient expression of transgenic proteins by naked DNA-transfected dendritic cells through terminal differentiation

Dendritic cells (DCs) play a key role in the induction and control of immunity. Genetic engineering of DCs is a promising approach for the development of a broad range of immunomodulatory strategies, for purposes ranging from genetic immunization to tolerance induction. The development of DC-based immunotherapies is limited by the inability to efficiently transfect DCs using naked DNA. Here we demonstrate that after plasmid DNA delivery, the transgene expression level controlled by the human immediate-early cytomegalovirus promoter (hIE-CMVp) is higher in mature DCs than in immature DCs and is further increased after terminal differentiation of DCs by agonist anti-CD40 monoclonal antibody (mAb) or after DC interaction with CD4+ T cells. CD40 signaling of DCs resulted in nuclear translocation of the transcription factors nuclear factor-κB (NF-κB), activator of protein-1 (AP-1), and cyclic adenosine monophosphate (cAMP)–responsive element, necessary for the activation of hIE-CMVp. Transgene expression by DCs diminished after the inhibition of these transcription factors or the blockade of adhesion molecules involved in the DC–T-cell synapse. Importantly, CD40 signaling of DCs results in the highly efficient expression and presentation of transgenic antigens and the induction of “in vivo” cytotoxic T-cell (CTL) responses specific for transgenic antigen peptides, demonstrating the functional potential of genetically engineered DCs.

DNA immunisation: altering the cellular localisation of expressed protein and the immunisation route allows manipulation of the immune response

DNA immunisation by intramuscular (IM) injection induces Th1 responses, whereas gene gun (GG) immunisation into the skin stimulates Th2 responses. Three ovalbumin (OVA) cDNA constructs, in which OVA is cytoplasmic (CYT), secreted (SECR), or transmembrane (TM), were compared in immunisation studies using intramuscular injection or biolistic bombardment of the skin. Gene gun immunisation with OVA-CYT or OVA-TM led to strong OVA-specific CTL responses, but not following OVA-SECR immunisation. In contrast, intramuscular immunisation with OVA-SECR or OVA-TM led to potent CTL while immunisation with OVA-CYT was ineffective. OVA-specific antibodies were detected following gene gun immunisation with all three constructs, whereas only the OVA-SECR construct induced antibody production following intramuscular immunisation. These results demonstrate the capacity to manipulate the nature of the immune response by altering the cellular localization of expressed proteins and the route of DNA immunisation.