T-cell mediated induction of allogeneic endothelial cell chemokine expression

Failure of Costimulatory Blockade-induced Regulatory T Cells to Sustain Long-term Survival of High Ischemic Allografts

BACKGROUND

Costimulatory blockade-induced allograft tolerance has been achieved in rodent models, but these strategies do not translate well to nonhuman primate and clinical transplants. One confounder that may underlie this discrepancy is the greater ischemic inflammation imposed on the transplants. In mice, cardiac allografts subjected to prolonged cold ischemic storage (CIS) before transplant have increased ischemia-reperfusion injury, which amplifies infiltrating endogenous memory CD8 T-cell activation within hours after transplantation to mediate acute graft inflammation and cytotoxic lymphocyte-associated molecule-4 immunoglobulin-resistant rejection. This study tested strategies inhibiting memory CD8 T-cell activation within such high ischemic allografts to achieve long-term survival.

METHODS

A/J (H-2 a ) hearts subjected to 0.5 or 8 h of CIS were transplanted to C57BL/6 (H-2 b ) recipients and treatment with peritransplant costimulatory blockade. At 60 d posttransplant, regulatory T cells (Treg) were depleted in recipients of high ischemic allografts with anti-CD25 monoclonal antibody (mAb) or diphtheria toxin.

RESULTS

Whereas peritransplant (days 0 and +1) anti-lymphocyte function-associated antigen-1 mAb and anti-CD154 mAb prolonged survival of >60% allografts subjected to minimal CIS for >100 d, only 20% of allografts subjected to prolonged CIS survived beyond day 80 posttransplant and rejection was accompanied by high titers of donor-specific antibody. Peritransplant anti-lymphocyte function-associated antigen-1, anti-tumor necrosis factor-α, and anti-CD154 mAb plus additional anti-CD154 mAb on days 14 and 16 obviated this donor-specific antibody and promoted Treg-mediated tolerance and survival of 60% of high ischemic allografts beyond day 100 posttransplant, but all allografts failed by day 120.

CONCLUSIONS

These studies indicate a strategy inducing prolonged high ischemic allograft survival through Treg-mediated tolerance that is not sustained indefinitely.

Development and nationwide validation of kidney graft injury markers using urinary exosomes and microvesicles (complete English translation of the Japanese version)

BACKGROUND

Non-invasive, prompt, and proper detection tools for kidney graft injuries (KGIs) are awaited to ensure graft longevity. We screened diagnostic biomarkers for KGIs following kidney transplantation using extracellular vesicles (EVs; exosomes and microvesicles) from the urine samples of patients.

METHODS

One hundred and twenty-seven kidney recipients at 11 Japanese institutions were enrolled in this study; urine samples were obtained prior to protocol/episode biopsies. EVs were isolated from urine samples, and EV RNA markers were assayed using quantitative reverse transcription polymerase chain reaction. Diagnostic performance of EV RNA markers and diagnostic formulas comprising these markers were evaluated by comparison with the corresponding pathological diagnoses.

RESULTS

EV CXCL9, CXCL10, and UMOD were elevated in T-cell-mediated rejection samples compared with other KGI samples, while SPNS2 was elevated in chronic antibody-mediated rejection (cABMR) samples. A diagnostic formula developed through Sparse Logistic Regression analysis using EV RNA markers allowed us to accurately (with an area under the receiver operator characteristic curve [AUC] of 0.875) distinguish cABMR from other KGI samples. EV B4GALT1 and SPNS2 were also elevated in cABMR, and a diagnostic formula using these markers was able to distinguish between cABMR and chronic calcineurin toxicity accurately (AUC 0.886). In interstitial fibrosis and tubular atrophy (IFTA) urine samples and those with high Banff chronicity score sums (BChS), POTEM levels may reflect disease severity, and diagnostic formulas using POTEM detected IFTA (AUC 0.830) and high BChS (AUC 0.850).

CONCLUSIONS

KGIs could be diagnosed with urinary EV mRNA analysis with relatively high accuracy.

Early coupled up-regulation of interleukin-12 receptor beta-1 in CD8+ central memory and effector T cells for better clinical outcomes in liver transplant recipients

This study aimed to investigate the role of initial priming of interleukin (IL)-12 receptor beta-1 in CD8(+) central memory T cells (initial IL-12RTCM priming) and CCR7-negative subsets (CNS) in effector cell expansion and clinical outcome after living donor liver transplantation (LDLT). One hundred and six patients who underwent LDLT were classified into the following three groups according to hierarchical clustering of CD8(+) CD45 isoforms before LDLT: I, naive-dominant; II, effector memory-dominant; and III, effector-dominant. The pre-existing CD8(+) effector cells (TE ) and activated immune status increased progressively from group I to group II to group III. Groups I, II and III received tacrolimus (Tac)/glucocorticoid (GC) regimens. Eighteen group III recipients received Tac/mycophenolate mofetil (MMF) and were defined as group IV. Initial IL-12RTCM priming was slightly, moderately and markedly decreased in droups I, II, and III, respectively. Initial priming of IL-12Rβ1 in CNS was decreased markedly in the three groups with marked decreases of TE , perforin and interferon (IFN)-γ; all parameters were restored by up-regulation of IL-12Rβ1(+) TCM through the self-renewal of TCM . The lag time required until coupled up-regulation of IL-12Rβ1 of TCM and CNS to above baseline was 12, 20 and 32 days in groups I, II and III, respectively. Inferior clinical outcomes were associated with increasing lag time. In contrast, the initial priming of IL-12Rβ1 in TCM and CNS remained above baseline in group IV due to MMF-mediated increase of IL-12Rβ1. Early coupled up-regulation of TCM and CNS leads to efficient TE differentiation and optimal clinical outcomes.

Predictive biomarkers of renal allograft failure

BACKGROUND

Survival of renal allografts is limited by chronic allograft deterioration resulting from processes that are difficult to detect in their early stages, when therapeutic interventions would be most effective. Predictive biomarkers from easily accessible specimens, such as blood or urine, might improve early diagnosis of smoldering graft-damaging processes and help with the identification of patients at particularly high risk of sustained injury, thereby helping to tailor therapy and appropriate follow-up screening.

OBJECTIVE

This article reviews recently investigated biomarkers for the prediction of renal allograft failure, outlines the new '-omic' technologies as a potential source for the identification of new predictive biomarkers and judges the practical value of predictive biomarkers at the present timepoint.

METHODS

A literature search was performed using the medical database PubMed. No general restrictions (e.g., year of publication) were applied, but the focus was set on more recently published articles.

CONCLUSION

Despite a large number of interesting studies, none of the investigated candidate biomarkers is robustly established for widespread clinical use or able to replace biopsies for graft assessment.

Targeted complement inhibitors protect against posttransplant cardiac ischemia and reperfusion injury and reveal an important role for the alternative pathway of complement activation

Ischemia reperfusion injury (IRI) is an unavoidable event during solid organ transplantation and is a major contributor to early graft dysfunction and subsequent graft immunogenicity. In a therapeutic paradigm using targeted complement inhibitors, we investigated the role of complement, and specifically the alternative pathway of complement, in IRI to heart isografts. Mouse heterotopic isograft heart transplants were performed in C57BL/6 mice treated with a single injection of either CR2-Crry (inhibits all complement pathways) or CR2-fH (inhibits alternative complement pathway) immediately posttransplantation. Transplanted hearts were harvested at 12 and 48 h for analysis. Both inhibitors resulted in a significant reduction in myocardial IRI, as measured by histology and serum cardiac troponin I levels. Furthermore, compared with untreated controls, both inhibitors reduced graft complement deposition, neutrophil and macrophage infiltration, adhesion molecule expression (P-selectin, E-selectin, and I-CAM-1), and proinflammatory cytokine expression (TNF-α, IL-1β, KC, and MCP-1). The reduction in myocardial damage and cellular infiltration was not significantly different between CR2-Crry- and CR2-fH-treated mice, although adhesion molecule and cytokine levels were significantly lower in CR2-Crry-treated mice compared with CR2-fH-treated mice. In conclusion, the alternative complement pathway plays a major contributing role in myocardial IRI after heart transplantation, and local (targeted) complement inhibition has the potential to provide an effective and safe therapeutic strategy to reduce graft injury. Although total complement blockade may be somewhat more efficacious in terms of reducing inflammation, specific blockade of the alternative pathway is likely to be less immunosuppressive in an already immunocompromised recipient.

Coupled regulation of interleukin-12 receptor beta-1 of CD8+ central memory and CCR7-negative memory T cells in an early alloimmunity in liver transplant recipients

This study investigated how CD8(+) T cell subsets respond to allo- and infectious immunity after living donor liver transplantation (LDLT). Early alloimmunity: 56 recipients were classified into three types according to the post-transplant course; type I demonstrated uneventful post-transplant course, type II developed severe sepsis leading to multiple organ dysfunction syndrome or retransplantation and type III with acute rejection. In 23 type I recipients, the interleukin (IL)-12 receptor beta-1 (R beta 1)(+) cells of central memory T cells (Il-12R beta 1(+) T(CM)) were increased above the pretransplant level. In 16 type II recipients, IL-12R beta 1(+) T(CM) was decreased markedly below the pretransplant level on postoperative day (POD) 5. In 17 type III recipients, IL-12R beta 1(+) T(CM) was decreased for a more prolonged period until POD 10. Along with down-regulation of IL-12R beta 1(+) T(CM), the IL-12R beta 1(+) cells of CCR7-negative subsets (CNS) as well as perforin, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha decreased gradually, resulting in the down-regulation of effectors and cytotoxicity. The down-regulation of IL-12R beta 1(+) T(CM) was suggested to be due to the recruitment of alloantigen-primed T cells into the graft, and then their entry into the secondary lymphoid organ, resulting in graft destruction. Infectious immunity: immunocompetent memory T cells with the capacity to enhance effectors and cytotoxicity were generated in response to post-transplant infection along with both up-regulation of the IL-12R beta 1(+) T(CM) and an increase in the CNS showing the highest level of IL-12R beta 1(+) cells. In conclusion, this work demonstrated that the IL-12R beta 1(+) cells of T(CM) and CNS are regulated in a tightly coupled manner and that expression levels of IL-12R beta 1(+) T(CM) play a crucial role in controlling allo- and infectious immunity.

CXC chemokine ligand (CXCL) 9 and CXCL10 are antagonistic costimulation molecules during the priming of alloreactive T cell effectors

Donor Ag-reactive CD4 and CD8 T cell production of IFN-gamma is a principal effector mechanism promoting tissue injury during allograft rejection. The CXCR3-binding chemokines CXCL9 and CXCL10 recruit donor-reactive T cells to the allograft, but their role during the priming of donor-reactive T cells to effector function is unknown. Using a murine model of MHC-mismatched cardiac transplantation, we investigated the influence of CXCL9 and CXCL10 during donor-reactive T cell priming. In allograft recipient spleens, CXCL9 and CXCL10 were expressed as early as 24 h posttransplant and increased with similar kinetics, concurrently with CXCR3 expression on T cells. CXCL9, but not CXCL10, expression required NK cell production of IFN-gamma. The absence of CXCL9 in donor allografts, recipients, or both significantly decreased the frequency of donor-reactive CD8 T cells producing IFN-gamma and increased the frequency of donor-reactive CD8 T cells producing IL-17A. In contrast, the absence of CXCL10 increased the frequency of IFN-gamma-producing CD8 T cells in a CXCL9-dependent manner. These data provide novel evidence that donor-reactive CD8 T cells use the CXCR3 chemokine axis as a costimulation pathway during priming to allografts where CXCL9 promotes the development of IFN-gamma-producing CD8 T cells, and CXCL10 antagonizes this skewing.

Regulation of CCL2 and CCL3 expression in human brain endothelial cells by cytokines and lipopolysaccharide

BACKGROUND

Chemokines are emerging as important mediators of CNS inflammation capable of activating leukocyte integrins and directing the migration of leukocyte subsets to sites of antigenic challenge. In this study we investigated the expression, release and binding of CCL2 (MCP-1) and CCL3 (MIP-1alpha) in an in vitro model of the human blood-brain barrier.

METHODS

The kinetics of expression and cytokine upregulation and release of the beta-chemokines CCL2 and CCL3 were studied by immunocytochemistry and enzyme-linked immunosorbent assay in primary cultures of human brain microvessel endothelial cells (HBMEC). In addition, the differential binding of these chemokines to the basal and apical endothelial cell surfaces was assessed by immunoelectron microscopy.

RESULTS

Untreated HBMEC synthesize and release low levels of CCL2. CCL3 is minimally expressed, but not released by resting HBMEC. Treatment with TNF-alpha, IL-1beta, LPS and a combination of TNF-alpha and IFN-gamma, but not IFN-gamma alone, significantly upregulated the expression and release of both chemokines in a time-dependent manner. The released CCL2 and CCL3 bound to the apical and basal endothelial surfaces, respectively. This distribution was reversed in cytokine-activated HBMEC resulting in a predominantly basal localization of CCL2 and apical distribution of CCL3.

CONCLUSIONS

Since cerebral endothelial cells are the first resident CNS cells to contact circulating leukocytes, expression, release and presentation of CCL2 and CCL3 on cerebral endothelium suggests an important role for these chemokines in regulating the trafficking of inflammatory cells across the BBB in CNS inflammation.

The early course of kidney allograft rejection: defining the time when rejection begins

We studied the early events in mouse kidney allografts and isografts to define when allorecognition begins and when alloimmune tissue injury begins. Allografts but not isografts showed T-cell infiltration in perivascular areas from day 1, but tubulitis and arteritis did not develop until day 7. Flow cytometry confirmed the early allospecific CD3(+)CD8(+) T-cell infiltrate. At day 1, both allografts and isografts showed extensive transcriptome changes, reflecting the response to surgery, but only allografts showed expression of interferon-gamma (IFN-gamma)-inducible transcripts and T-cell-associated transcripts. Although the number of CD68(+) myeloid cell numbers did not increase in day 1 isografts or allografts, mRNA expression for myeloid markers was increased in isografts and allografts, suggesting activation of resident cells of the macrophage-dendritic cell series (MMDCs) in response to injury, followed by increased CD68(+) cell numbers from day 2. By day 3, an interstitial T-cell and MMDC infiltrate was established in allografts, corresponding with the emergence of allospecific tissue injury, as reflected by decreased parenchymal transcripts. Thus, in renal allografts, allorecognition by T cells occurs in perivascular sites by day 1, but alloimmune parenchymal damage begins at day 3, coinciding with the emergence of the interstitial T-cell-MMDC infiltrate.

Ecto-5' nucleotidase (CD73)-mediated adenosine generation and signaling in murine cardiac allograft vasculopathy

Ecto-5'-nucleotidase (CD73) catalyzes the terminal phosphohydrolysis of 5'-adenosine monophosphate and is widely expressed on endothelial cells where it regulates barrier function. Because it is also expressed on lymphocytes, we hypothesized that it modulates vascular immune regulation under homeostatic conditions and dysregulation under stress conditions such as cardiac allotransplantation. In a heterotopic cardiac allotransplantation model, CD73 deficiency in either donors or recipients resulted in decreased graft survival and the development of cardiac allograft vasculopathy, suggesting a contribution of CD73 on both graft-resident and circulating cells in vasculopathy pathogenesis. Vascular perturbations incited by lack of CD73 included loss of graft barrier function and diminished graft expression of the A(2B) adenosine receptor (A(2B)AR), with a concordant exacerbation of the acute inflammatory and immune responses. The importance of CD73 in modulating endothelial-lymphocyte interaction was further demonstrated in allomismatched in vitro coculture experiments. Either genetic deletion or pharmacological blockade of CD73 increased transendothelial lymphocyte migration and inflammatory responses, suggesting that CD73 plays a critical role to suppress transendothelial leukocyte trafficking through its enzymatic activity. In addition, antagonism of A(2B)AR caused a significant increase in vascular leakage, and agonism of A(2B)AR resulted in marked prolongation of graft survival and suppression of cardiac allograft vasculopathy development. These data suggest a new paradigm in which phosphohydrolysis of adenosine monophosphate by CD73 on graft-resident or circulating cells diminishes transendothelial leukocyte trafficking and mitigates inflammatory and immune sequelae of cardiac transplantation via the A(2B)AR.

Donor-reactive CD8 memory T cells infiltrate cardiac allografts within 24-h posttransplant in naive recipients

Normal immune responses stimulated by pathogenic and environmental antigens generate memory T cells that react with donor antigens and no currently used immunosuppressive drug completely inhibits memory T-cell function. While donor-reactive memory T cells clearly compromise graft outcomes, mechanisms utilized by memory T cells to promote rejection are largely unknown. In this study, we investigated how early endogenous memory cells infiltrate and express effector function in cardiac allografts. Endogenous CD8 memory T cells in nonsensitized recipients distinguish syngeneic versus allogeneic cardiac allografts within 24 h of reperfusion. CD8-dependent production of IFN-gamma and CXCL9/Mig was observed 24 to 72 h posttransplant in allografts but not isografts. CXCL9 was produced by donor cells in response to IFN-gamma made by recipient CD8 T cells reactive to donor class I major histocompatibility complex (MHC) molecules. Activated CD8 T cells were detected in allografts at least 3 days before donor-specific effector T cells producing IFN-gamma were detected in the recipient spleen. Early inflammation mediated by donor-reactive CD8 memory T cells greatly enhanced primed effector T-cell infiltration into allografts. These results suggest that strategies for optimal inhibition of alloimmunity should include neutralization of infiltrating CD8 memory T cells within a very narrow window after transplantation.

Adenovirus-mediated interleukin-13 gene therapy attenuates acute kidney allograft injury

BACKGROUND

Kidney transplantation is possible by virtue of systemic immunosuppression, which is in turn accompanied by serious side effects. The search for novel therapeutic agents and strategies is ongoing. Here we investigate the effects of adenovirus-mediated gene therapy with interleukin (IL)-13, which is a cytokine with strong immunomodulatory properties, on acute renal allograft injury. In addition, we compare the effects of local (intrarenal) and systemic (intramuscular) IL-13 gene therapy in kidney transplantation.

METHODS

The experiments were performed in a rat Fisher to Lewis acute rejection model of kidney transplantation. An adenovirus-IL-13 or adenovirus-luciferase was injected either into the donor kidney before transplantation (local treatment) or into the hind leg muscle of recipient rats (systemic treatment). A group with no treatment served as control. No additional immunosuppressive therapy was applied. The rats were sacrificed after 8 days and inflammatory markers and renal pre-fibrosis were assessed.

RESULTS

Efficient gene transfer was confirmed by ELISA, immunohistochemistry and real-time PCR. IL-13 gene therapy diminished graft infiltration with macrophages and cytotoxic T cells and limited up-regulation of mRNA levels of the adhesion molecule E-selectin and pro-inflammatory cytokines TNF-alpha and IFN-gamma. Moreover, reduced renal interstitial pre-fibrosis was found in the rats receiving IL-13 gene therapy. The effects of local and systemic therapy were similar.

CONCLUSIONS

This study demonstrates that IL-13 gene therapy in the graft significantly attenuates acute renal allograft damage, suggesting local therapy with IL-13 as a strategy to reduce the need for systemic immunosuppressive medication and thereby its side effects.

The role of IFN-gamma in regulation of IFN-gamma-inducible protein 10 (IP-10) expression in lung epithelial cell and peripheral blood mononuclear cell co-cultures

Background

Interferons play a critical role in regulating both the innate and adaptive immune responses. Previous reports have shown increased levels of IFN-γ, IFN-γ-inducing IL-12 and IFN-γ-inducible chemokine IP-10 in patients with chronic obstructive pulmonary disease (COPD).

Methods

The present study focuses on the regulation of the IP-10 secretion in co-cultures of lung epithelial cells and peripheral blood mononuclear cells (PBMCs).

Results

No IP-10 secretion was detected in cells cultured alone, whereas a significant increase in IP-10 levels was observed in epithelial cell/PBMC co-cultures. Furthermore, the results show that interactions between lung epithelial cells, lymphocytes and monocytes are needed for basal IP-10 secretion. Interestingly, we have also shown that incubation with IL-12 can induce an IFN-γ independent increase in IP-10 levels in co-cultures. Furthermore, inhibition studies supported the suggestion that different intracellular pathways are responsible of IFN-γ and IL-12 mediated IP-10 secretion.

Conclusion

These studies demonstrate a novel diversity in IFN-γ/IL-12 pathways, showing that the IP-10 expression in co-cultures is regulated by multiple factors, such as intercellular interactions in addition to IFN-γ and IL-12 levels. These results may be valuable in designing novel strategies to antagonize IP-10 mediated immunological reactions and chemotactic effects on T cells.

Organ-Specific Differences in the Function of MCP-1 and CXCR3 During Cardiac and Skin Allograft Rejection

BACKGROUND

Chemokines are well-established to function in the recruitment of leukocytes into allografts in the course of rejection. Moreover, some studies have indicated that there are organ-specific differences in chemokine function, but the mechanism accounting for this difference is not known.

METHODS

Fully major histocompatibility complex-mismatched vascularized cardiac transplants or skin transplants were performed using BALB/c (H-2d), C57BL/6 (H-2b), MCP-1-/- (H-2b) and CXCR3-/- (H-2b) mice as donors or recipients. Also, skin grafts (H-2b) were placed onto SCID mice (H-2d) that received BALB/c splenocytes (H-2d) by adoptive transfer either at the time of transplantation, or after a period of 28 days.

RESULTS

Cardiac allografts in MCP-1-/- recipients survived significantly longer (P<0.0005) than wild-type (WT) controls. However, there was no prolongation of survival when MCP-1-/- grafts were used a donors in WT mice. In contrast, the absence of donor but not recipient MCP-1 prolonged skin allograft survival. WT donor cardiac grafts in CXCR3-/- recipients had a modest prolongation of survival (P<0.0005), whereas CXCR3-/- donor cardiac grafts in WT recipients were rejected similar to controls. Also, while recipient CXCR3 had no effect on the rejection of skin, CXCR3-/- donor skin grafts survived significantly longer than WT controls. This survival advantage was lost when vascularized CXCR3-/- skin grafts were used as donors in the SCID model of rejection.

CONCLUSION

Recipient derived MCP-1 and CXCR3 are functional in the rejection of vascularized, but not nonvascularized, allografts. In contrast, donor-derived MCP-1 and CXCR3 are functional in nonvascularized, but not vascularized grafts.

Common Protective and Diverse Smooth Muscle Cell Effects of AAV-Mediated Angiopoietin-1 and -2 Expression in Rat Cardiac Allograft Vasculopathy

Angiopoietin-1 (Ang1) and Ang2 regulate the maintenance of normal vasculature by direct endothelial and indirect smooth muscle cell (SMC) effects. Dysfunction of vascular wall cells is considered central in cardiac allograft vasculopathy (CAV), where inflammation and arterial injury initiate subsequent intimal SMC proliferation. In this study, we investigated the effect of exogenous Ang1 and Ang2 in chronically rejecting rat cardiac allografts by intracoronary adeno-associated virus (AAV)-mediated gene transfer. Bioluminescent imaging of AAV-transfected syngeneic grafts revealed gradual and stable transgene expression in graft cardiomyocytes. In cardiac allografts, both AAV-Ang1 and AAV-Ang2 decreased inflammation and increased antiapoptotic Bcl-2 mRNA and Bcl-2/Bax ratio at 8 weeks. Only AAV-Ang2 decreased the development of CAV, whereas AAV-Ang1 activated arterial SMC and increased PDGF-A mRNA in the allograft. Collectively, our results show that exogenous Ang1 and Ang2 have similar antiinflammatory and antiapoptotic effects in cardiac allografts. Prolonged AAV-mediated Ang1 transgene expression also induced SMC activation, whereas AAV-Ang2 lacked the SMC activating effects and decreased CAV. Our results thus highlight the common protective and diverse SMC effects of Ang1 and Ang2 in cardiac allograft microenvironment and the importance of timing of angiopoietins to achieve therapeutic effects.

The challenge of inhibiting alloreactive T-cell memory

Memory T cells specific for donor antigens present a unique challenge in transplantation. In addition to expressing rapid and robust immune responses to a transplanted organ, memory T cells may be resistant to the effects of currently used graft-prolonging therapies. The increasing recognition that alloreactive memory T cells participate in transplant rejection is driving new lines of research focusing on understanding the immunobiology of alloreactive memory T cells and on designing novel therapies to specifically target memory T cells. The purpose of this review is to summarize the effects of existing immunosuppressive drugs and costimulatory blockade on functions of alloreactive memory T cells that undermine allograft survival.

CXCL9 antagonism further extends prolonged cardiac allograft survival in CCL19/CCL21-deficient mice

CCL19/MIP-3beta and CCL21/SLC are essential for chemotactic recruitment of mature dendritic cells (DC) to T-cell areas of secondary lymphoid tissue. Paucity of lymph node T-cells (plt/plt) mice lack CCL21-serine (ser) and CCL19 expression. We tested plt/plt and wild type (wt) BALB/c (H2d) mice as recipients of heart or skin allografts from C57BL/10J (H2b) donors. Donor DC trafficking to secondary lymphoid tissue was markedly reduced in plt heart but not skin allograft recipients. Heart, but not skin grafts survived significantly longer in plt recipients. Accordingly, T cells from plt heart transplant recipients demonstrated poor anti-donor responses in ex vivo MLR, compared to wt heart or wt and plt skin recipients. Moreover, donor-reactive T cells from plt heart recipients exhibited Th2-skewing in comparison to T cells from wt heart or skin graft recipients. Anti-CXCL9/Mig was administered for 2 weeks post-transplant to determine whether impairment of activated T-cell migration could further prolong cardiac allograft survival in plt recipients. CXCL9-antagonism extended graft survival significantly only in plt mice, likely due, in part, to retention of alloactivated T cells in secondary lymphoid tissue/reduction of graft-infiltrating T cells. Thus, targeting DC and activated T-cell migration concomitantly has additive effects in prolonging heart graft survival with potential for therapeutic application.

Experimental approaches to lymphocyte migration in dermatology in vitro and in vivo

Lymphocyte trafficking through the dermal compartment is part of the physiological surveillance process of the adaptive immune system. On the other hand, persistent or recurrent lymphocyte infiltrates are hallmarks of both types of chronic inflammatory skin diseases, Th1-type such as psoriasis or Th2/allergic-type like atopic dermatitis. A better understanding of the mechanisms underlying lymphocyte movements is one of the key prerequisites for developing more effective therapies. In this review, we introduce a range of simple-to-sophisticated experimental in vitro and in vivo approaches to analyze lymphocyte migration. These methods start from static in vitro adhesion and chemotaxis assays, include dynamic endothelial flow chamber, intravital dual photon, and transcutaneous live-video microscopy, and finally encompass specific genetically deficient or engineered animal models. Discussing pros and cons of these assay systems hopefully generates both state-of-the-art knowledge about the factors involved in most common chronic skin diseases as well as an improved understanding of the limitations and chances of new biologic pharmaceuticals that are currently introduced into clinical practice.

Prediction of Acute Renal Allograft Rejection by Urinary Monokine Induced by IFN-γ (MIG)

Early diagnosis of acute allograft rejection (AR) is still decisive for long-term renal allograft survival. The aim of this study was to define the role of the chemokine monokine induced by IFN-gamma (MIG) (CXCL9) and IFN-gamma-inducible protein 10 (IP-10) (CXCL10) as early markers of AR in renal transplantation (NTX). In a prospective study, 69 de novo renal transplant recipients were monitored and urine samples were collected after NTX for a median of 29 d. In pH-adjusted urine, MIG and IP-10 were determined by modified ELISA. AR was clinically diagnosed in 15 of 69 recipients and confirmed by biopsy in 14 of 15 AR patients (Banff classification). Corresponding to CXCR3-positive infiltrates in renal tissue, urinary MIG was elevated in 14 of 15 AR patients with a median of 2809 pg/ml (quartile 25% and 75% = 870 and 13,000; n = 15), being significantly (P < 0.0001) different from both nonrejecting allograft patients (NO-AR) (median, 25%, and 75%: 96, 1.0, and 161, n = 54) and healthy controls (median, 25%, and 75%: 144, 19, and 208, n = 13). Urinary MIG predicted AR with a sensitivity of 93% and a specificity of 89%. In AR and NO-AR groups, MIG values correlated well with IP-10 (P < 0.001). MIG values indicated both imminent rejection and response to successful antirejection therapy. MIG was not related to intercurrent infections or other causes for impairment of renal function. In a multivariate analysis, MIG correlated best (P < 0.001) with AR from all AR-associated parameters. In conclusion, urinary MIG serves as a very sensitive and specific predictor for AR, mirrors response to antirejection therapy, and thus may contribute to improved long-term renal allograft survival.

E-Selectin Early Overexpression Induced by Allogeneic Activation in Isolated Mouse Lung

BACKGROUND

The interaction between host lymphocytes and graft endothelial cells plays an important role in graft rejection.

METHODS

Using our model of isolated ventilated lung from female mouse perfused with fresh blood from either isogeneic or allogeneic male mouse for 3 hours without noticeable ischemia, we have investigated the kinetics of the early events after endothelial cell triggering by E-selectin engagement.

RESULTS

Isogeneic perfusion induced nonspecific endothelial cell activation, which was characterized by up-regulation of E-selectin, intercellular adhesion molecule (ICAM)-1, and of the pro-inflammatory cytokines tumor necrosis factor (TNF)-alpha, interleukin (IL)-2, and lymphotoxin-alpha (mRNAs by real-time polymerase chain reaction). Allogeneic perfusion was characterized after 3 hours by an additional loose adhesion of lymphocytes mediated by the E-selectin and related to the allogeneic activation of endothelial cells. These in turn expressed the I-A molecule (immunostaining). ICAM-1 and lymphocyte function-associated antigen (LFA)-3 mRNA levels were significantly increased in lung extracts after 2 hours, then vascular cell adhesion molecule (VCAM)-1 and TNF-alpha mRNAs after 3 hours without evidence of TNF-alpha production (enzyme-linked immunoadsorbent assay). The major participation of the E-selectin in early allogeneic activation by way of the protein kinase (PK)C pathway was confirmed by using a neutralizing anti-CD62E monoclonal antibody or the inhibitory PKC 19-31 fragment.

CONCLUSIONS

Altogether, our results demonstrate that E-selectin expression (1) is not a consequence of TNF-alpha triggering, (2) up-regulates its own expression and expression of I-A, VCAM-1, TNF-alpha, and lymphotoxin-alpha mRNAs, and (3) down-regulates expression of LFA-3 and ICAM-1 mRNAs. In conclusion, in our physiologic model, the E-selectin highly participates in the loose adhesion of allogeneic lymphocytes and in the early activation of endothelial cell and therefore in structural and functional lung alterations.

Effect of Cognate Human CD4+ T Cell and Endothelial Cell Interactions Upon Chemokine Production

BACKGROUND

In vitro studies have shown that cognate recognition of antigen presented by endothelial cells (EC) causes T cell activation, proliferation, and cytokine release and alters the transmigration of T cells. Here we have investigated chemokine induction caused by cognate interactions between human CD4+ T cells and MHC class II-expressing EC.

METHODS

HLA-DR-restricted CD4+ T cells were cocultured with HLA-DR-expressing allogeneic Eahy.926, aortic, or heart microvascular EC. Chemokine mRNA expression was measured by RTPCR, and chemokine protein secreted was measured by a cytokine array system and ELISA. Molecules involved in chemokine secretion were identified using blocking monoclonal antibodies, and cellular sources of chemokines determined by intracellular chemokine staining. Coculture supernatants were also used in chemotaxis assays.

RESULTS

Nine different chemokine mRNA and proteins were expressed because of noncognate interactions between T cells and EC. Cognate interactions induced de novo expression of four chemokines and upregulation of seven chemokines. Levels of CCL3, CCL8, and CXCL10 secreted into supernatants were in the nanomolar range and were chemotactic for T cells and monocytes. Blocking antibodies to HLA-DR and LFA-3 abrogated production of CCL3, CCL8, and CXCL10. Blocking antibodies to interferon-gamma and tumor necrosis factor-alpha inhibited CCL8 and CXCL10 but not CCL3 production. CCL3 and CXCL10 were produced by both T cells and EC.

CONCLUSIONS

Cognate interactions between alloreactive CD4+ T cells and MHC class II-expressing EC results in a specific pattern of chemokine production. These chemokines could play important roles in recruitment of leukocytes into vascularised allografts.

Therapeutic manipulation of T cell chemotaxis in transplantation

T cell migration and trafficking are regulated by the well defined cellular processes of rolling, activation, tight adhesion, arrest and diapedesis. These processes are, in turn, controlled by molecular events involving integrins, selectins, chemokines and chemokine receptors. Recent studies have shown that sphingosine 1-phosphate receptors and their ligands are also important molecular modulators of migration and trafficking. Many of these molecules are appropriate targets for preventing allograft rejection or for achieving tolerance. Studies of migration and trafficking have also shown that the anatomic choreography of alloantigen presentation and T cell encounter with alloantigen and immunosuppression, are over-riding determinants of T cell priming versus tolerization.

Transmigrated neutrophils down‐regulate the expression of VCAM‐1 on endothelial cells and inhibit the adhesion of flowing lymphocytes

As the first leukocytes recruited during inflammation, neutrophils are ideally situated to regulate the subsequent recruitment of mononuclear leukocytes. Here, we found that human neutrophils recruited by endothelial cells (EC), which had been stimulated with tumor necrosis factor alpha for 4 h, inhibited the adhesion of flowing, mixed mononuclear cells or purified lymphocytes over the subsequent 20 h but did not affect the adhesion of a secondary bolus of neutrophils. The degree of inhibition of lymphocyte adhesion increased with the duration of neutrophil-EC contact and with the number of recruited neutrophils. Antibody-blocking studies showed that lymphocyte adhesion was mediated predominantly by vascular cell adhesion molecule-1 (VCAM-1). Recruited neutrophils reduced the EC expression of VCAM-1 but not intercellular adhesion molecule-1 (ICAM-1) or E-selectin in a manner that mirrored the time- and number-dependent reduction in lymphocyte adhesion. VCAM-1 was not shed into the culture supernatant, and a panel of protease inhibitors was unable to reverse its down-regulation, indicating that it was not proteolytically degraded by neutrophils. In EC that had been in contact with neutrophils, the mRNA message for VCAM-1 but not ICAM-1 was down-regulated, indicating that alterations in transcriptional activity were responsible for the reduction in VCAM-1. Thus, under some inflammatory milieu, neutrophils may delay the recruitment of mononuclear leukocytes by regulating the expression of EC adhesion receptors.

In remembrance of things past: memory T cells and transplant rejection

A cardinal feature of the adaptive immune response is its ability to generate long-lived populations of memory T lymphocytes. Memory T cells are specific to the antigen encountered during the primary immune response and react rapidly and vigorously upon re-encounter with the same antigen. Memory T cells that recognize microbial antigens provide the organism with long-lasting protection against potentially fatal infections. On the other hand, memory T cells that recognize donor alloantigens can jeopardize the survival of life-saving organ transplants. We review here the immunobiology of memory T cells and describe their role in the rejection of solid organ allografts.

Chemokine Monokine Induced by IFN-γ/CXC Chemokine Ligand 9 Stimulates T Lymphocyte Proliferation and Effector Cytokine Production

Monokine induced by IFN-gamma (MIG; CXC chemokine ligand (CXCL)9) is important in T lymphocyte recruitment in organ transplantation. However, it is not known whether this chemokine, in addition to its chemotactic properties, exerts any effect on T lymphocyte effector functions. For in vivo studies, we used a previously characterized murine model of chronic rejection. The recipient mice were treated with anti-MIG/CXCL9 Ab; graft-infiltrating cells were analyzed for IFN-gamma production. For in vitro studies, exogenous CXCR3 ligands were added to CD4 lymphocytes in MLRs, and the proliferative responses were measured. Separate experiments quantitated the number of IFN-gamma-producing cells in MLRs by ELISPOT. Neutralization of MIG/CXCL9, in the in vivo model, resulted in significant reduction in the percentage of IFN-gamma-producing graft-infiltrating T lymphocytes. In vitro experiments demonstrated that 1) exogenous MIG/CXCL9 stimulated CD4 lymphocyte proliferation in a MHC class II-mismatched MLR, 2) MIG/CXCL9 also increased the number of IFN-gamma-producing CD4 lymphocytes in ELISPOT, 3) neutralization of MIG/CXCL9 in MLR reduced T lymphocyte proliferation, 4) IFN-gamma-inducible protein 10/CXCL10 and IFN-inducible T cell alpha chemoattractant/CXCL11 had similar effects on T lymphocyte proliferation, 5) MIG/CXCL9 stimulated T lymphocyte proliferation in MHC class I- and total MHC-mismatched MLRs, 6) neutralization of CXCR3 reduced MIG/CXCL9-induced T lymphocyte proliferation and the number of IFN-gamma-positive spots on ELISPOT, and 7) the proliferative effects of MIG/CXCL9 were mediated via an IL-2-independent pathway and were controlled by IFN-gamma. This study demonstrates that MIG/CXCL9 stimulates T lymphocyte proliferation and effector cytokine production, in addition to its chemotactic effects. This novel observation expands our current understanding of MIG/CXCL9 biology beyond that of mediating T cell trafficking.

IL-21 induces tumor rejection by specific CTL and IFN-gamma-dependent CXC chemokines in syngeneic mice

IL-21 is an immune-stimulatory four alpha helix cytokine produced by activated T cells. To study the in vivo antitumor activities of IL-21, TS/A murine mammary adenocarcinoma cells were genetically modified to secrete IL-21 (TS/A-IL-21). These cells developed small tumors that were subsequently rejected by 90% of s.c. injected syngeneic mice. Five days after injection, TS/A-IL-21 tumors showed numerous infiltrating granulocytes, NK cells, and to a lesser extent CD8(+) T cells, along with the expression of TNF-alpha, IFN-gamma, and endothelial adhesion molecules ICAM-1 and VCAM-1. At day 7, CD8(+) and CD4(+) T cells increased together with IFN-gamma, and the CXC chemokines IFN-gamma-inducible protein 10, monokine induced by IFN-gamma, and IFN-inducible T cell alpha-chemoattractant. The TS/A-IL-21 tumor displayed a disrupted vascular network with abortive sprouting and signs of endothelial cell damage. In vivo depletion experiments by specific Abs showed that rejection of TS/A-IL-21 cells required CD8(+) T lymphocytes and granulocytes. When injected in IFN-gamma-deficient mice, TS/A-IL-21 cells formed tumors that regressed in only 29% of animals, indicating a role for IFN-gamma in IL-21-mediated antitumor response, but also the existence of IFN-gamma-independent effects. Most immunocompetent mice rejecting TS/A-IL-21 cells developed protective immunity against TS/A-pc (75%) and against the antigenically related C26 colon carcinoma cells (61%), as indicated by rechallenge experiments. A specific CTL response against the gp70-env protein of an endogenous murine retrovirus coexpressed by TS/A and C26 cells was detected in mice rejecting TS/A-IL-21 cells. These data suggest that IL-21 represents a suitable adjuvant in inducing specific CTL responses.

Emerging roles of endothelial cells in transplant rejection

Recent studies of endothelial cell biology have provided numerous original findings relevant to transplantation. The molecular mechanisms utilized by endothelial cells to regulate cell entry into the parenchyma are becoming more clearly defined. Emerging results have additionally elucidated how endothelial cells interact with and respond to T cells and antibodies specific for transplant antigens. Progress made in deciphering the cellular and molecular basis of endothelial cell-mediated inflammation has the potential to help with the identification of novel therapeutic targets for prolonging graft survival.