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.

Compensatory renal hypertrophy following nephrectomy: When and how?

Following surgical removal of one kidney, the other enlarges and increases its function. The mechanism for the sensing of this change and the growth is incompletely understood but begins within days and compensatory renal hypertrophy (CRH) is the dominant contributor to the growth. In many individuals undergoing nephrectomy for cancer or kidney donation this produces a substantial and helpful increase in renal function. Two main mechanisms have been proposed, one in which increased activity by the remaining kidney leads to hypertrophy, the second in which there is release of a kidney specific factor in response to a unilateral nephrectomy that initiates CRH. Whilst multiple growth factors and pathways such as the mTORC pathway have been implicated in experimental studies, their roles and the precise mechanism of CRH are not defined. Unrestrained hypoxia inducible factor activation in renal cancer promotes growth and may play an important role in driving CRH.

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.

Oxygen-permeable microwell device maintains islet mass and integrity during shipping

Islet transplantation is currently the only minimally invasive therapy available for patients with type 1 diabetes that can lead to insulin independence; however, it is limited to only a small number of patients. Although clinical procedures have improved in the isolation and culture of islets, a large number of islets are still lost in the pre-transplant period, limiting the success of this treatment. Moreover, current practice includes islets being prepared at specialized centers, which are sometimes remote to the transplant location. Thus, a critical point of intervention to maintain the quality and quantity of isolated islets is during transportation between isolation centers and the transplanting hospitals, during which 20-40% of functional islets can be lost. The current study investigated the use of an oxygen-permeable PDMS microwell device for long-distance transportation of isolated islets. We demonstrate that the microwell device protected islets from aggregation during transport, maintaining viability and average islet size during shipping.

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.

A Combinatorial Protein Microarray for Probing Materials Interaction with Pancreatic Islet Cell Populations

Pancreatic islet transplantation has become a recognized therapy for insulin-dependent diabetes mellitus. During isolation from pancreatic tissue, the islet microenvironment is disrupted. The extracellular matrix (ECM) within this space not only provides structural support, but also actively signals to regulate islet survival and function. In addition, the ECM is responsible for growth factor presentation and sequestration. By designing biomaterials that recapture elements of the native islet environment, losses in islet function and number can potentially be reduced. Cell microarrays are a high throughput screening tool able to recreate a multitude of cellular niches on a single chip. Here, we present a screening methodology for identifying components that might promote islet survival. Automated fluorescence microscopy is used to rapidly identify islet derived cell interaction with ECM proteins and immobilized growth factors printed on arrays. MIN6 mouse insulinoma cells, mouse islets and, finally, human islets are progressively screened. We demonstrate the capability of the platform to identify ECM and growth factor protein candidates that support islet viability and function and reveal synergies in cell response.

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.

Interleukin-17A-Induced Human Mesenchymal Stem Cells Are Superior Modulators of Immunological Function

Interferon-γ (IFN-γ)-preactivated mesenchymal stem cells (MSC-γ) are highly immunosuppressive but immunogenic in vivo due to their inherent expression of major histocompatibility (MHC) molecules. Here, we present an improved approach where we modified human bone marrow-derived MSC with interleukin-17A (MSC-17) to enhance T cell immunosuppression but not their immunogenicity. MSC-17, unlike MSC-γ, showed no induction or upregulation of MHC class I, MHC class II, and T cell costimulatory molecule CD40, but maintained normal MSC morphology and phenotypic marker expression. When cocultured with phytohemagglutinin (PHA)-activated human T cells, MSCs-17 were potent suppressors of T cell proliferation. Furthermore, MSC-17 inhibited surface CD25 expression and suppressed the elaboration of Th1 cytokines, IFN-γ, tumor necrosis factor-α (TNF-α), and IL-2 when compared with untreated MSCs (UT-MSCs). T cell suppression by MSC-17 correlated with increased IL-6 but not with indoleamine 2,3-dioxygenase 1, cyclooxygenase 1, and transforming growth factor β-1. MSC-17 but not MSC-γ consistently induced CD4(+) CD25(high) CD127(low) FoxP3(+) regulatory T cells (iTregs) from PHA-activated CD4(+) CD25(-) T cells. MSC-induced iTregs expressed CD39, CD73, CD69, OX40, cytotoxic T-lymphocyte associated antigen-4 (CTLA-4), and glucocorticoid-induced TNFR-related protein (GITR). These suppressive MSCs-17 can engender Tregs to potently suppress T cell activation with minimal immunogenicity and thus represent a superior T cell immunomodulator for clinical application.