Human dendritic cells and transplant outcome

Overexpression of miR-223 Promotes Tolerogenic Properties of Dendritic Cells Involved in Heart Transplantation Tolerance by Targeting Irak1

Dendritic cells (DCs) are key mediators of transplant rejection. Numerous factors have been identified that regulate transplant immunopathology by modulating the function of DCs. Among these, microRNAs (miRNAs), small non-coding RNA molecules, have received much attention. The miRNA miR-223 is very highly expressed and tightly regulated in hematopoietic cells. It plays an important role in modulating the immune response by regulating neutrophils and macrophages, and its dysregulation contributes to multiple types of immune diseases. However, the role of miR-223 in immune rejection is unclear. Here, we observed expression of miR-223 in patients and mice who had undergone heart transplantation and found that it increased in the serum of both, and also in DCs from the spleens of recipient mice, although it was unchanged in splenic T cells. We also found that miR-223 expression decreased in lipopolysaccharide-stimulated DCs. Increasing the level of miR-223 in DCs promoted polarization of DCs toward a tolerogenic phenotype, which indicates that miR-223 can attenuate activation and maturation of DCs. MiR-223 effectively induced regulatory T cells (Tregs) by inhibiting the function of antigen-presenting DCs. In addition, we identified Irak1 as a miR-223 target gene and an essential regulator of DC maturation. In mouse allogeneic heterotopic heart transplantation models, grafts survived longer and suffered less immune cell infiltration in mice with miR-223-overexpressing immature (im)DCs. In the miR-223-overexpressing imDC recipients, T cells from spleen differentiated into Tregs, and the level of IL-10 in heart grafts was markedly higher than that in the control group. In conclusion, miR-223 regulates the function of DCs via Irak1, differentiation of T cells into Tregs, and secretion of IL-10, thereby suppressing allogeneic heart graft rejection.

Chimerism, Transplant Tolerance, and Beyond

The present review discusses current developments in tolerance induction for solid organ transplantation with a particular emphasis on chimerism-based approaches. It explains the basic mechanisms of chimerism-based tolerance and provides an update on ongoing clinical tolerance trials. The concept of "delayed tolerance" is presented, and ongoing preclinical studies in the nonhuman primate setting-including current limitations and hurdles regarding this approach-are illustrated. In addition, a brief overview and update on cell-based tolerogenic clinical trials is provided. In a critical approach, advantages, limitations, and potential implications for the future of these different regimens are discussed.

Standardisation of flow cytometry for whole blood immunophenotyping of islet transplant and transplant clinical trial recipients

Understanding the immunological phenotype of transplant recipients is important to improve outcomes and develop new therapies. Immunophenotyping of whole peripheral blood (WPB) by flow cytometry is a rapid method to obtain large amounts of data relating to the outcomes of different transplant treatments with limited patient impact. Healthy individuals and patients with type 1 diabetes (T1D) enrolled in islet transplantation were recruited and WPB was collected. 46 fluorochrome-conjugated mouse-anti-human antibodies were used (43 of 46 antibodies were titrated). BD cytometer setup and tracking beads were used to characterize and adjust for cytometer performance. Antibody cocktails were pre-mixed <60 minutes before staining. Multicolour panels were designed based on fluorochrome brightness, antigen density, co-expression, and fluorochrome spillover into non-primary detectors in each panel on a 5 laser flow cytometer. WPB sample staining used 50–300 μl WPB for each panel and was performed within 2 hours of blood sample collection. Samples were acquired on a BD-LSRFortessa. The operating procedures, including specimen collection, antibody cocktails, staining protocol, flow-cytometer setup and data analysis, were standardized. The staining index of 43 antibodies and the spillover spreading matrix for each panel was calculated. The final concentrations for the 46 antibodies used was determined for staining of WPB samples. Absolute cell-count and 7 leukocyte profiling panels consisting of subsets and/or status of granulocytes, monocytes, dendritic, B, NK, and T cells including regulatory T cells (Tregs) and NKT were designed and established on a 5 laser BD-LSR Fortessa. 13 T1D patients, including 4 islet transplant recipients and 8 healthy controls, were evaluated. The ability to reproducibly measure immune subsets and immune-profiles of islet transplant patients up to 18 months post transplantation has been established as a tool to measure immune cell reconstitution after transplantation.

CD83 Antibody Inhibits Human B Cell Responses to Antigen as well as Dendritic Cell-Mediated CD4 T Cell Responses

Anti-CD83 Ab capable of Ab-dependent cellular cytotoxicity can deplete activated CD83+ human dendritic cells, thereby inhibiting CD4 T cell-mediated acute graft-versus-host disease. As CD83 is also expressed on the surface of activated B lymphocytes, we hypothesized that anti-CD83 would also inhibit B cell responses to stimulation. We found that anti-CD83 inhibited total IgM and IgG production in vitro by allostimulated human PBMC. Also, Ag-specific Ab responses to immunization of SCID mice xenografted with human PBMC were inhibited by anti-CD83 treatment. This inhibition occurred without depletion of all human B cells because anti-CD83 lysed activated CD83+ B cells by Ab-dependent cellular cytotoxicity and spared resting (CD83-) B cells. In cultured human PBMC, anti-CD83 inhibited tetanus toxoid-stimulated B cell proliferation and concomitant dendritic cell-mediated CD4 T cell proliferation and expression of IFN-γ and IL-17A, with minimal losses of B cells (<20%). In contrast, the anti-CD20 mAb rituximab depleted >80% of B cells but had no effect on CD4 T cell proliferation and cytokine expression. By virtue of the ability of anti-CD83 to selectively deplete activated, but not resting, B cells and dendritic cells, with the latter reducing CD4 T cell responses, anti-CD83 may be clinically useful in autoimmunity and transplantation. Advantages might include inhibited expansion of autoantigen- or alloantigen-specific B cells and CD4 T cells, thus preventing further production of pathogenic Abs and inflammatory cytokines while preserving protective memory and regulatory cells.

Hyaluronan in the lymphatics: The key role of the hyaluronan receptor LYVE-1 in leucocyte trafficking

LYVE-1, a close relative of the leucocyte receptor, CD44, is the main receptor for hyaluronan (HA) in lymphatic vessel endothelium and a widely used marker for distinguishing between blood and lymphatic vessels. Enigmatic for many years because of its anomalous HA-binding characteristics, the function of LYVE-1 has just recently been identified as that of a lymphatic docking receptor for dendritic cells, selectively engaging with their surface HA glycocalyx to regulate entry to peripheral lymphatics and migration to downstream lymph nodes for immune activation. Furthermore, LYVE-1 mediates the trafficking of macrophages, and is also exploited by HA-encapsulated Group A streptococci for lymphatic invasion and host dissemination. Consistent with a role in lymphatic trafficking, the interaction of LYVE-1 with HA and its degradation products can also activate intracellular signalling pathways for endothelial junctional retraction and lymphatic endothelial proliferation. Here we outline the latest findings on the receptor in the context of its peculiar biochemical properties and speculate on how the interaction of LYVE-1 with different HA sizes and conformations might variably influence cell function as a consequence of avidity and receptor crosslinking. Finally, we evaluate evidence that LYVE-1 can also bind growth factors and associate with kinase-linked growth factor receptors and conclude on how the LYVE-1·HA axis may be exploited as a target to either block inflammation or tissue allograft rejection, or potentiate vaccine and drug delivery.

Pre-transplant infusion of donor-derived dendritic cells maintained at the immature stage by sinomenine increases splenic Foxp3+ Tregs in recipient rats after renal allotransplantation

OBJECTIVE

The immunosuppressive mechanism of sinomenine in organ allotransplantation was investigated, especially its effect of blocking dendritic cell (DC) maturation, which might influence the frequency of regulatory T cells (Tregs).

METHODS

Bone marrow cells from male donor Wistar rats were induced to differentiate into DCs in vitro in the presence or absence of sinomenine, and characterized by flow cytometry. These two groups of DCs were respectively injected into male recipient Sprague-Dawley rats via the tail vein, at both high and low doses. Sprague-Dawley rats receiving saline injection were used as controls. Seven days later, renal transplantation was performed from donor Wistar rats to the recipient Sprague-Dawley rats. Seven days after transplantation, spleens were collected from the recipients. The proportions of Tregs and Foxp3⁺ Tregs to CD4⁺ T cells were determined using flow cytometry.

RESULTS

With sinomenine treatment, the frequency of mature DCs was reduced, as indicated by lower expression of the surface markers CD80, CD86, and RT1B. In recipient Sprague-Dawley rats that received sinomenine-treated DCs before renal allotransplantation, the proportions of splenic Tregs and Foxp3⁺ Tregs were significantly higher than in control recipients receiving saline or DCs without sinomenine treatment (all p<0.05). A high dose of sinomenine-treated DCs (10⁶ cells) had a more obvious effect in increasing Tregs than the low dose (10⁵ cells) (p<0.05).

CONCLUSION

Pre-transplant infusion of donor-derived sinomenine-induced maturation arrested DCs could result in the increase of Foxp3⁺ Tregs in the spleens of recipients after renal allotransplantation.

Defective CD8 Signaling Pathways Delay Rejection in Older Recipients

CD8+ T cells play a cardinal feature in response to alloantigens and are able to generate effector/memory T cells independently from CD4+ T cells. To investigate the impact of aging on CD8 T cells, we used a fully mismatched mouse skin transplant model. Our findings showed a prolonged allograft survival in older recipients associated with a significant increase of CD4+ and CD8+ CD44high CD62Llow effector/memory T cells and a reduced systemic IFNγ production. When reconstituting young CBA Rag-1 mice that lack mature T and B cells with old CD8+ T cells expressing clonal anti-H2K T cell receptor (TCR) alloreactive for MHC I, graft survival was significantly prolonged and comparable to those receiving young CD8+ T cells. Moreover, our data showed that reduced systemic IFNγ levels observed in old recipients had been linked to a compromised expression of the IL-2R β subunit (CD122) by old CD8+ T cells. In addition, we observed an impaired IFNγ production on IL-2 receptor activation. At the same time, gene profiling analysis of old CD8 T cells demonstrated reduced chemokine ligand-3 and CD40L expression that resulted in compromised CD8+ T cell/dendritic cell communication, leading to impaired migratory and phagocytic activity of CD11c cells.Collectively, our study demonstrated that aging delays allograft rejection. CD8 T cells play a critical role in this process linked to a compromised production of IFNγ, in addition to a defective IL-2 receptor signaling machinery and a defective communication between CD8 T cells and dendritic cells.

Blockade of CCR7 leads to decreased dendritic cell migration to draining lymph nodes and promotes graft survival in low-risk corneal transplantation

The chemokine receptor CCR7 is essential for migration of mature dendritic cells (DCs) to the regional lymph nodes, and it has been shown that blocking of CCR7 improves graft survival after high-risk corneal transplantation in vascularized recipient corneas. However, it is so far unknown whether blocking of CCR7 reduces migration of DCs from the avascular cornea to the draining lymph nodes and whether this leads to improved graft survival also in the low-risk setting of corneal transplantation, which accounts for the majority of perforating transplantations performed. Therefore, in this study, pellets containing Freund's adjuvant and bovine serum albumin (BSA) conjugated to Alexa488 fluorescent dye were implanted into the corneal stroma of BALB/c mice to analyze antigen uptake by corneal DCs and their migration to the regional lymph nodes. After pellet implantation, mice were either treated by local administration of a CCR7 blocking fusion protein that consisted of CCL19 fused to the Fc part of human IgG1 or a control-IgG. In vivo fluorescence microscopy showed uptake of Alexa488-conjugated BSA by corneal DCs within 8 h. Furthermore, analysis of single cell suspensions of draining lymph nodes prepared after 48 h revealed that 2.1 ± 0.3% of CD11c(+) cells were also Alexa488(+). Importantly, DC migration was significantly reduced after topical administration of CCL19-IgG (1.2 ± 0.2%; p < 0.05). To test the effect of CCR7 blockade on graft rejection after allogeneic low-risk keratoplasty, corneal transplantations were performed using C57BL/6-mice as donors and BALB/c-mice as recipients. Treatment mice received two intraperitoneal loading doses of CCL19-IgG prior to transplantation, followed by local treatment with CCL19-IgG containing eye drops for the first two weeks after transplantation. Control mice received same amounts of control-IgG. Kaplan-Meier survival analysis showed that in the CCL19-IgG treated group, 76% of the grafts survived through the end of the 8 week observation period, whereas 38% of the grafts survived in the control group (p < 0.05). Taken together, our study shows that blockade of CCR7 reduces the migration of mature corneal DCs to the draining lymph nodes and leads to improved graft survival in low-risk corneal transplantation.

Disease Recurrence and Acute Cellular Rejection Episodes During the First Year After Lung Transplantation Among Patients With Sarcoidosis

INTRODUCTION

Sarcoidosis is reported to recur after lung transplantation (LT). We sought to determine the frequency of recurrent disease after LT and predictors of recurrence. We also evaluated the incidence and severity of acute cellular rejection (ACR) episodes among these patients.

METHODS

The database of LT patients at Cleveland Clinic was interrogated for sarcoidosis patients who underwent LT between May 1993 and 2011. Charts were reviewed for demographics, type of transplant, posttransplant biopsy findings, and outcomes.

RESULTS

Data were available for 30 patients (mean age, 50 ± 9.3 years; range, 30-65 years; M-to-F ratio, 17:13; single-to-double-to-heart lung ratio, 5:24:1). Recurrence of sarcoidosis was noted among 7 patients (pathological recurrence in all and radiological findings suggesting recurrence in 1 patient) with no impact on overall outcomes. Presence of granulomas on explanted lungs was the only predictor of recurrence (85.7% vs 30.4%, odds ratio, 13.7; 1.4-136.2; P = 0.02).Overall burden of ACR episodes on all bronchoscopies was significantly lower in patients with disease recurrence (7.6 % vs 21.3% of biopsies, P = 0.038). Among patients with recurrent disease, ACR did not develop once disease recurrence had been seen on transbronchial biopsy.

CONCLUSIONS

A significant proportion of sarcoidosis patients have disease recurrence after LT and presence of active granulomas on explant is associated with subsequent recurrence. There may be an association of recurrence with lower frequency of ACR episodes. There does not appear to be any impact of sarcoidosis recurrence on 1-, 3-, or 5-year survivals.

Regulatory myeloid cells in transplantation

Regulatory myeloid cells (RMC) are emerging as novel targets for immunosuppressive (IS) agents and hold considerable promise as cellular therapeutic agents. Herein, we discuss the ability of regulatory macrophages, regulatory dendritic cells, and myeloid-derived suppressor cells to regulate alloimmunity, their potential as cellular therapeutic agents, and the IS agents that target their function. We consider protocols for the generation of RMC and the selection of donor- or recipient-derived cells for adoptive cell therapy. Additionally, the issues of cell trafficking and antigen (Ag) specificity after RMC transfer are discussed. Improved understanding of the immunobiology of these cells has increased the possibility of moving RMC into the clinic to reduce the burden of current IS agents and to promote Ag-specific tolerance. In the second half of this review, we discuss the influence of established and experimental IS agents on myeloid cell populations. IS agents believed historically to act primarily on T cell activation and proliferation are emerging as important regulators of RMC function. Better insights into the influence of IS agents on RMC will enhance our ability to develop cell therapy protocols to promote the function of these cells. Moreover, novel IS agents may be designed to target RMC in situ to promote Ag-specific immune regulation in transplantation and to usher in a new era of immune modulation exploiting cells of myeloid origin.

Tolerance induction: hematopoietic chimerism

PURPOSE OF REVIEW

Although numerous experimental models to induce allograft tolerance have been reported, it has been difficult to translate these basic studies to clinical transplantation. However, successful induction of tolerance in HLA-mismatched kidney transplantation has recently been reported. In this review, recent progress in tolerance induction in preclinical (nonhuman primates) and clinical transplantation is summarized.

RECENT FINDINGS

Among many clinical trials to induce renal allograft tolerance, success has so far been achieved only by combining donor bone marrow with organ transplantation. Induction of renal allograft tolerance by transient or durable mixed chimerism has been reported in HLA-matched or mismatched kidney transplant recipients. More recently, renal allograft tolerance by induction of full donor chimerism has also been reported using a more intensified preparative conditioning regimen.

SUMMARY

Durable allograft tolerance has been achieved by induction of hematopoietic chimerism in clinical kidney transplantation, with outstanding long-term results in successful cases. However, these approaches have been associated with higher early complications than are seen following transplantation with conventional immunosuppression. Improvements in the consistency and safety of tolerance induction and extension of successful protocols to other organs will be the next steps in bringing tolerance to a wider range of clinical applications.

Roles of dendritic cells in murine hepatic warm and liver transplantation-induced cold ischemia/reperfusion injury

Dendritic cells (DCs) induce and regulate both innate and adaptive immune responses; however, their in vivo functional importance in hepatic ischemia/reperfusion (IR) injury is perplexing. We hypothesized that liver-resident DC and locally recruited blood-borne DC might have distinctive roles in hepatic IR injury. We tested this hypothesis by using DC-deficient, fms-like tyrosine kinase 3 ligand (Flt3L) knockout (KO) mice in hepatic warm (70% partial clamping for 60 minutes) and cold IR injury (liver transplant [LTx] with 24-hour cold storage). Flt3L KO liver and lymphoid organs contained virtually no CD11c+ F4/80- DC. Hepatic warm IR injury was significantly lower in Flt3L KO than in wildtype (WT) mice with lower alanine aminotransferase (ALT) levels, reduced hepatic necrosis, and lower neutrophil infiltration. Hepatic messenger RNA (mRNA) and protein levels for inflammatory cytokines (tumor necrosis factor alpha [TNFα], interleukin [IL]-6) and chemokines (CCL2, CXCL2) were also significantly lower in Flt3L KO than in WT mice, indicating that lack of both liver-resident and blood-borne DC ameliorated hepatic warm IR injury. Adoptive transfer of splenic or hepatic WT DC into Flt3L KO or WT mice increased hepatic warm IR injury, suggesting injurious roles of DC infusion. When Flt3L KO liver was transplanted into WT mice, ALT levels were significantly higher than in WT to WT LTx, with enhanced hepatic necrosis and neutrophil infiltration, indicating a protective role of liver-resident DC.

CONCLUSION

Using both warm and cold hepatic IR models, this study suggests differential roles of liver-resident versus blood-borne DC, and points to the importance of the local microenvironment in determining DC function during hepatic IR injury.

Dendritic cell populations with different concentrations of lipid regulate tolerance and immunity in mouse and human liver

BACKGROUND & AIMS

Immune cells of the liver must be able to recognize and react to pathogens yet remain tolerant to food molecules and other nonpathogens. Dendritic cells (DCs) are believed to contribute to hepatic tolerance. Lipids have been implicated in dysfunction of DCs in cancer. Therefore, we investigated whether high lipid content in liver DCs affects induction of tolerance.

METHODS

Mouse and human hepatic nonparenchymal cells were isolated by mechanical and enzymatic digestion. DCs were purified by fluorescence-activated cell sorting or with immunomagnetic beads. DC lipid content was assessed by flow cytometry, immune fluorescence, and electron microscopy and by measuring intracellular component lipids. DC activation was determined from surface phenotype and cytokine profile. DC function was assessed in T-cell, natural killer (NK) cell, and NKT cell coculture assays as well as in vivo.

RESULTS

We observed 2 distinct populations of hepatic DCs in mice and humans based on their lipid content and expression of markers associated with adipogenesis and lipid metabolism. This lipid-based dichotomy in DCs was unique to the liver and specific to DCs compared with other hepatic immune cells. However, rather than mediate tolerance, the liver DC population with high concentrations of lipid was immunogenic in multiple models; they activated T cells, NK cells, and NKT cells. Conversely, liver DCs with low levels of lipid induced regulatory T cells, anergy to cancer, and oral tolerance. The immunogenicity of lipid-rich liver DCs required their secretion of tumor necrosis factor α and was directly related to their high lipid content; blocking DC synthesis of fatty acids or inhibiting adipogenesis (by reducing endoplasmic reticular stress) reduced DC immunogenicity.

CONCLUSIONS

Human and mouse hepatic DCs are composed of distinct populations that contain different concentrations of lipid, which regulates immunogenic versus tolerogenic responses in the liver.

Tolerogenic dendritic cells and their role in transplantation

The pursuit of clinical transplant tolerance has led to enhanced understanding of mechanisms underlying immune regulation, including the characterization of immune regulatory cells, in particular antigen-presenting cells (APC) and regulatory T cells (Treg), that may play key roles in promoting operational tolerance. Dendritic cells (DC) are highly efficient APC that have been studied extensively in rodents and humans, and more recently in non-human primates. Owing to their ability to regulate both innate and adaptive immune responses, DC are considered to play crucial roles in directing the alloimmune response towards transplant tolerance or rejection. Mechanisms via which they can promote central and peripheral tolerance include clonal deletion, the induction of Treg, and inhibition of memory T cell responses. These properties have led to the use of tolerogenic DC as a therapeutic strategy to promote organ transplant tolerance. In rodents, infusion of donor- or recipient-derived tolerogenic DC can extensively prolong donor-specific allograft survival, in association with regulation of the host T cell response. In clinical transplantation, progress has been made in monitoring DC in relation to graft outcome, including studies in operational liver transplant tolerance. Although clinical trials involving immunotherapeutic DC for patients with cancer are ongoing, implementation of human DC therapy in clinical transplantation will require assessment of various critical issues. These include cell isolation and purification techniques, source, route and timing of administration, and combination immunosuppressive therapy. With ongoing non-human primate studies focused on DC therapy, these logistics can be investigated seeking the optimal approaches. The scientific rationale for implementation of tolerogenic DC therapy to promote clinical transplant tolerance is strong. Evaluation of technical and therapeutic logistic issues is an important next step prior to the application of tolerogenic DC in clinical organ transplantation.

HLA-G level on monocytoid dendritic cells correlates with regulatory T-cell Foxp3 expression in liver transplant tolerance

BACKGROUND

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule expressed as membrane-bound and soluble isoforms. Interaction of HLA-G with its receptor, immunoglobulin-like transcript 4 on dendritic cells (DCs) down-regulates their T-cell stimulatory ability.

METHODS

We examined expression of HLA-G, immunoglobulin-like transcript 4, other immune regulatory molecules (inducible costimulator ligand and glucocorticoid-induced tumor necrosis factor-related receptor ligand), and the activation marker CMRF44 on circulating monocytoid dendritic cell (mDC) and plasmacytoid dendritic cell by monoclonal antibody staining and flow cytometry. Three groups of stable liver transplant recipients: operationally tolerant (TOL), prospective immunosuppressive drug weaning, and maintenance immunosuppression (MI) were studied, together with healthy controls (HC). Serum HLA-G levels were measured by enzyme-linked immunosorbent assay.

RESULTS

In TOL patients, monocytoid dendritic cell (mDC) but not plasmacytoid dendritic cell expressed higher HLA-G than in MI patients or HC. In TOL patients, the incidence of CD4(+)CD25(hi)CD127(-) regulatory T cells (Treg) and the intensity of Treg forkhead box p3 (Foxp3) expression were significantly higher than in the MI group. HLA-G expression on circulating mDC correlated significantly with that of Foxp3 in the TOL group. There was no correlation between immunosuppressive drug (tacrolimus) dose or trough level and HLA-G expression or Treg frequency or Foxp3 expression. The incidence of patients with circulating HLA-G levels more than 100 ng/mL was highest in the TOL group, although statistical significance was not achieved.

CONCLUSIONS

Higher HLA-G expression on circulating mDC in TOL recipients compared with MI or HC, suggests a possible role of HLA-G in immune regulation possibly mediated by enhanced host Treg Foxp3 expression.

StrataGraft skin substitute is well-tolerated and is not acutely immunogenic in patients with traumatic wounds: results from a prospective, randomized, controlled dose escalation trial

OBJECTIVE

The goal of this study was to assess the immunogenicity and antigenicity of StrataGraft skin tissue in a randomized phase I/II clinical trial for the temporary management of full-thickness skin loss.

BACKGROUND

StrataGraft skin tissue consists of a dermal equivalent containing human dermal fibroblasts and a fully stratified, biologically active epidermis derived from Near-diploid Immortalized Keratinocyte S (NIKS) cells, a pathogen-free, long-lived, consistent, human keratinocyte progenitor.

METHODS

Traumatic skin wounds often require temporary allograft coverage to stabilize the wound bed until autografting is possible. StrataGraft and cadaveric allograft were placed side by side on 15 patients with full-thickness skin defects for 1 week before autografting. Allografts were removed from the wound bed and examined for allogeneic immune responses. Immunohistochemistry and indirect immunofluorescence were used to assess tissue structure and cellular composition of allografts. In vitro lymphocyte proliferation assays, chromium-release assays, and development of antibodies were used to examine allogeneic responses.

RESULTS

One week after patient exposure to allografts, there were no differences in the numbers of T or B lymphocytes or Langerhans cells present in StrataGraft skin substitute compared to cadaver allograft, the standard of care. Importantly, exposure to StrataGraft skin substitute did not induce the proliferation of patient peripheral blood mononuclear cells to NIKS keratinocytes or enhance cell-mediated lysis of NIKS keratinocytes in vitro. Similarly, no evidence of antibody generation targeted to the NIKS keratinocytes was seen.

CONCLUSIONS

These findings indicate that StrataGraft tissue is well-tolerated and not acutely immunogenic in patients with traumatic skin wounds. Notably, exposure to StrataGraft did not increase patient sensitivity toward or elicit immune responses against the NIKS keratinocytes. We envision that this novel skin tissue technology will be widely used to facilitate the healing of traumatic cutaneous wounds.This study was registered at www.clinicaltrials.gov (NCT00618839).

Renal transplant recipients have elevated frequencies of circulating myeloid-derived suppressor cells

BACKGROUND

Cancer, particularly cutaneous squamous cell carcinoma (SCC), is a major cause of mortality in renal transplant recipients (RTRs). Myeloid-derived suppressor cells (MDSC) play a central role in suppressing cancer immunosurveillance but their potential mobilisation in RTRs and levels relative to those of other immunoregulatory dendritic cell (DC) populations have not been analysed.

METHODS

The circulating frequencies of MDSC and DC were analysed by multicolour flow cytometry in immunocompetent patients without (n = 13) or with (ICI-SCC(Pos), n = 14) current SCC, normal donors (NDs, n = 34), chronic kidney disease patients (CKD patients, n = 22) and RTRs (n = 31).

RESULTS

Compared to NDs, RTRs had significantly elevated levels of both CD14(Neg) and CD14(Pos) MDSC subsets (P < 0.001), while CKD patients and ICI-SCC(Pos) had significantly elevated levels of only the CD14(Neg)-MDSC subset. DC frequencies were significantly decreased in RTRs and CKD patients but were at normal levels in ICI-SCC(Pos). The MDSC/DC ratio was significantly elevated (P < 0.05) in RTRs (median = 5.7), CKD patients (median = 3.2) and ICI-SCC(Pos) (median = 3.5) relative to NDs (median = 0.7). The use of immunosuppressive drugs in CKD patients and past/current occurrence of SCC in RTRs was associated with significantly increased CD14(Neg)-MDSC frequencies. MDSC enriched from RTRs, when co-cultured with activated NDs T cells significantly suppressed extracellular IL-10 levels and can, when activated with formyl-methionyl-leucyl-phenylalanine, inhibit T-cell proliferation.

CONCLUSIONS

RTRs, CKD patients and ICI-SCC(Pos) have increased MDSC frequencies and MDSC/DC ratios. These changes may impact on cancer immunosurveillance. Therefore, MDSC represent both a potential therapeutic target and prognostic marker in these patients, with respect to the development of SCC and other malignancies.

CD8&alpha;+ plasmacytoid precursor DCs induce antigen-specific regulatory T cells that enhance HSC engraftment in vivo

CD8-positive/T-cell receptor-negative (CD8(+)/TCR(-)) graft facilitating cells (FCs) are a novel cell population in bone marrow that potently enhance engraftment of hemopoietic stem cells (HSCs). Previously, we showed that the CD11c(+)/B220(+)/CD11b(-) plasmacytoid-precursor dendritic cell (p-preDC) FC subpopulation plays a critical but nonredundant role in facilitation. In the present study, we investigated the mechanism of FC function. We report that FCs induce antigen-specific CD4(+)/CD25(+)/FoxP3(+) regulatory T cells (Tregs) in vivo. The majority of chimeric Tregs were recipient derived. Chimeric Tregs harvested at ≥ 4 weeks after transplantation significantly enhanced engraftment of donor- and recipient-derived HSCs, but not third-party HSCs, in conditioned secondary recipients, demonstrating antigen specificity. Although Tregs were present 2 and 3 weeks after transplantation, they did not enhance engraftment. In contrast, week 5 and greater Tregs potently enhanced engraftment. The function of chimeric Tregs was directly correlated with the development of FoxP3 expression. Chimeric Tregs also induced significantly stronger suppression of T-cell proliferation to donor antigen in vitro. Removal of p-preDC FCs resulted in impaired engraftment of allogeneic HSCs and failure to produce chimeric Tregs, suggesting that the CD8α(+) p-preDC subpopulation is critical in the mechanism of facilitation. These data suggest that FCs induce the production of antigen-specific Tregs in vivo, which potently enhance engraftment of allogeneic HSCs. FCs hold clinical potential because of their ability to remain tolerogenic in vivo.

Review of human DC subtypes

Dendritic cells (DC) are critical to the induction and regulation of the innate and adaptive immune responses. They have been implicated in the pathogenesis of many autoimmune and chronic inflammatory diseases as well as contributing to the development of tumours by their lack of appropriate function. As such, understanding human DC biology provides the insight needed to develop applications for their use in the treatment of diseases. Currently, studies on mouse DC outnumber those on human cells; however, the comparison between mouse and human models has been somewhat misleading due to the basic biological and practical differences between the two models. In this review, we summarise the current understanding of human DC subtypes by describing the phenotype of the populations and how this relates to function. We also hope to clarify the differences in nomenclature between the human and mouse models that have arisen by way of the different experimental models.

Distinct populations of metastases-enabling myeloid cells expand in the liver of mice harboring invasive and preinvasive intra-abdominal tumor

The liver is the most common site of adenocarcinoma metastases, even in patients who initially present with early disease. We postulated that immune-suppressive cells in the liver of tumor-bearing hosts inhibit anti-tumor T cells, thereby accelerating the growth of liver metastases. Using models of early preinvasive pancreatic neoplasia and advanced colorectal cancer, aims of this study were to determine immune phenotype, stimulus for recruitment, inhibitory effects, and tumor-enabling function of immune-suppressive cells in the liver of tumor-bearing hosts. We found that in mice with intra-abdominal malignancies, two distinct CD11b(+)Gr1(+) populations with divergent phenotypic and functional properties accumulate in the liver, becoming the dominant hepatic leukocytes. Their expansion is contingent on tumor expression of KC. These cells are distinct from CD11b(+)Gr1(+) populations in other tissues of tumor-bearing hosts in terms of cellular phenotype and cytokine and chemokine profile. Liver CD11b(+)Gr1(+) cells are highly suppressive of T cell activation, proliferation, and cytotoxicity and induce the development of Tregs. Moreover, liver myeloid-derived suppressor cells accelerate the development of hepatic metastases by inactivation of cytotoxic T cells. These findings may explain the propensity of patients with intra-abdominal cancers to develop liver metastases and suggest a promising target for experimental therapeutics.

Elevated myeloid: plasmacytoid dendritic cell ratio associates with late, but not early, liver rejection in children induced with rabbit anti-human thymocyte globulin

BACKGROUND

Dendritic cells (DC) play an important role in the induction and regulation of immune responses.

METHODS

Myeloid CD11c+ DC (MDC), which may have inflammatory functions, and plasmacytoid CD123+ DC (PDC), which may have tolerogenic potential, were measured by flow cytometric analysis, cross-sectionally, once, in 48 children, and longitudinally (pretransplant and at days 1-60, 61-200, and 201-400 posttransplant) in 30 children after liver transplantation (LTx). All children received cadaveric (n=53) or live donor (n=25) liver allografts with rabbit anti-human thymocyte globulin induction and steroid-free tacrolimus therapy. Rejectors in both groups were those children (n=35), who experienced biopsy-proven acute cellular rejection (ACR) within 60 days of DC monitoring.

RESULTS

Among rejectors in the longitudinal and cross-sectional cohorts, the MDC:PDC ratio was higher and was associated with decreased PDC frequencies. Logistic regression analysis, leave-one-out cross-validation, and receiver operating characteristic analysis applied to 30 cross-sectional subjects revealed that an MDC:PDC ratio more than or equal to 1.78 was associated with rejector status with sensitivity and specificity of 76.9% and 88.2%, respectively. Sensitivity and specificity were replicated in the 18 remaining cross-sectional subjects (88.8% and 78.8%, respectively), but not in longitudinally monitored subjects, during the early 60-day period after LTx (30.76% and 62.50%, respectively). A significant negative correlation was observed between tacrolimus whole blood concentrations and PDC frequencies (Spearman r=-0.370, P=0.005) in 48 cross-sectional subjects in whom DC subsets were monitored 1 to 3 years after LTx, but not during the early post-LTx period.

CONCLUSIONS

We conclude that an elevated MDC:PDC ratio associates with liver graft rejection, which occurs after first year in children induced with rabbit anti-human thymocyte globulin.

Mycophenolic acid inhibits maturation and function of human dendritic cells and B cells

Mycophenolic acid (MPA) is considered an immunosuppressive compound mainly because of its inhibitory effects on lymphocyte proliferation. Here we studied specifically the effects of MPA on the ability of dendritic cells (DCs) to activate T cells via the indirect pathway and on the maturation and function of B-lineage cells. We demonstrated that DC cell-surface receptors, associated with antigen uptake and antigen processing and presentation (CD83 and CD205), were differentially downregulated in the presence of MPA, translating into a decreased uptake of alloantigens and reduced stimulation of T cells with decreased cytokine secretion (interleukin (IL)-1Ra and transforming growth factor (TGF)-alpha). Similarly, MPA significantly inhibited B-cell differentiation into memory and plasma cells in vitro and decreased secretion of TNF-alpha, IL-1Ra, and IL-10. We further demonstrated for the first time that not only the amount of antibody secretion was significantly lowered in the presence of MPA but also the total number of antibody-producing cells was reduced. Importantly, we provide direct evidence that HLA-specific antibody secretion was also affected using a newly developed HLA antibody-specific B-cell enzyme-linked immunospot assay. Our data indicate additional pathways by which MPA downregulates the immune system. This in turn may lead to improved conditions for allograft tolerance and control of allograft rejection.

T-cell reactivity during tapering of immunosuppression to low-dose monotherapy prednisolone in HLA-identical living-related renal transplant recipients

BACKGROUND

In many transplant centers, human leukocyte antigen (HLA)-identical living-related (LR) renal transplant recipients receive standard maintenance immunosuppression from 1 year after transplantation. We questioned whether discontinuation of azathioprine (AZA) or mycophenolate mofetil (MMF) influenced T-cell reactivity, circulating dendritic cell (DC) subsets numbers and their maturation status.

METHODS

Twenty-nine HLA-identical LR renal transplant recipients were withdrawn from AZA or MMF. Thereafter, the patients received only prednisolone. T-cell reactivity was determined by interferon-gamma (n=23), interleukin (IL)-10 (n=16), and granzyme B (n=10) Elispot assays. Circulating DC subset numbers and their maturation status determined by CCR2, CCR5, CCR7, and CD83 expression were measured by flow cytometry (n=12).

RESULTS

The number of donor, third-party, and tetanus toxoid-reactive interferon-gamma and granzyme-B producing cells was not affected after withdrawal of immunosuppression. Discontinuation of AZA or MMF resulted in significant increased numbers of third-party (P=0.003) and tetanus toxoid-reactive (P=0.008) IL-10 producing cells, and a trend in higher numbers of donor-reactive IL-10 producing cells (P=0.06). No effect was found on the number of circulating DC subsets, but DC was shifted toward a more mature phenotype.

CONCLUSIONS

In HLA-identical LR renal transplant recipients, therapy with AZA and MMF suppress the IL-10 production and the maturation of DC. This suggests that these immunosuppressants may hinder suppression of immune responses in general, including allogeneic responses.

Bronchiolitis obliterans in lung transplantation: the good, the bad, and the future

Lung transplantation remains the hope for many incurable pulmonary diseases, such as cystic fibrosis, pulmonary fibrosis, and chronic obstructive pulmonary disease. Remarkable progress has been made in improving outcomes, although the incidence of acute rejection remains more than 50% in the 1st year, and the 5-year graft survival is still less than 50% primarily because of the development of chronic rejection and graft dysfunction. Chronic rejection is characterized by the development of obliterative bronchiolitis in allografts and manifests as bronchiolitis obliterans syndrome in humans with no effective treatment. Previous studies support a role for alloreactive T cells in the development of bronchiolitis obliterans syndrome, but the specific mechanisms are unknown. One major stumbling block to research in the field of lung transplantation has been the lack of physiologic models to study the disease in the laboratory. We will review the current understanding of the immunology of the pathogenesis of obliterative bronchiolitis and will discuss exciting new advances from the laboratory as well as the implications for future research in lung transplantation.

Human liver dendritic cells promote T cell hyporesponsiveness

The liver is believed to promote tolerance, which may be beneficial due to its constant exposure to foreign Ags from the portal circulation. Although dendritic cells (DCs) are critical mediators of immune responses, little is known about human liver DCs. We compared freshly purified liver DCs from surgical specimens with autologous blood DCs. Liver and blood DCs were equally immature, but had distinct subset compositions. BDCA-1(+) DCs represented the most prevalent liver DC subset, whereas the majority of peripheral blood DCs were CD16(+). Upon TLR4 ligation, blood DCs secreted multiple proinflammatory cytokines, whereas liver DCs produced substantial amounts of IL-10. Liver DCs induced less proliferation of allogeneic T cells both in a primary MLR and after restimulation. Similarly, Ag-specific CD4(+) T cells were less responsive to restimulation when initially stimulated by autologous liver DCs rather than blood DCs. In addition, liver DCs generated more suppressive CD4(+)CD25(+)FoxP3(+) T regulatory cells and IL-4-producing Th2 cells via an IL-10-dependent mechanism. Our findings are critical to understanding hepatic immunity and demonstrate that human liver DCs promote immunologic hyporesponsiveness that may contribute to hepatic tolerance.