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

Early graft-infiltrating lymphocytes are not associated with graft rejection in a mouse model of skin transplantation

Graft-infiltrating lymphocytes (GILs) play an important role in promoting rejection after organ transplantation. We recently reported that GILs that accumulated up to 3 days post-transplantation did not promote rejection, whereas GILs present 3-5 days post-transplantation promoted rejection in a mouse heart transplantation model. However, the immunological behaviour of GILs in murine skin transplantation remains unclear. GILs were isolated on days 3, 5 or 7 post-transplantation from C57BL/6 (B6) allogeneic skin grafts transplanted onto BALB/c mice. BALB/c Rag2-/- γc-/- mice (BRGs) underwent B6 skin graft transplantation 10 weeks after adoptive transfer of day 3, 5, or 7 GILs. BRGs reconstituted with day 5 or 7 GILs completely rejected B6 grafts. However, when B6 grafts harvested from recipient BALB/c mice on day 5 or 7 were re-transplanted into BRGs, half of the re-transplanted day 5 grafts established long-term survival, although all re-transplanted day 7 grafts were rejected. BRGs reconstituted with day 3 GILs did not reject B6 grafts. Consistently, re-transplantation using day 3 skin grafts resulted in no rejection. Administration of anti-CD25 antibodies did not prevent the phenomenon observed for the day 3 skin grafts. Furthermore, BRGs reconstituted with splenocytes from naïve BALB/c mice immediately rejected the naïve B6 skin grafts and the re-transplanted day 3 B6 grafts, suggesting that day 3 GILs were unable to induce allograft rejection during the rejection process. In conclusion, the immunological role of GILs depends on the time since transplantation. Day 3 GILs had neither protective nor alloreactive effects in the skin transplant model.

Noninvasive Monitoring of Allograft Rejection Using a Novel Epidermal Sampling Technique

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Despite promising short- and long-term results to date in vascularized composite allotransplantation (VCA), acute rejection remains the most common major complication in recipients. Currently, diagnosis of acute rejection relies on clinical inspection correlated with histopathological analysis. However, disagreement exists regarding the value of full-thickness skin and mucosal biopsies and histopathology remains semiquantitative, subject to sampling bias, and prone to intra- and inter-observer variabilities. Additionally, biopsies may cause infection, scarring, and/or potentially incite rejection through immune activation after injury. Noninvasive methods to diagnose rejection represent a critical unmet need for the emerging field of VCA. Here, we propose a novel technique utilizing skin stripping of the epidermis and subsequent molecular analysis to detect known markers of acute rejection. Using a small animal VCA model, we sought to validate our epidermal sampling technique as a noninvasive diagnostic test for acute rejection.

Markers of inflammation in recipients of continuous-flow left ventricular assist devices

Although the newer continuous-flow left ventricular assist devices (CF-LVADs) provide clinical advantages over the pulsatile pumps, the effects of low pulsatility on inflammation are incompletely understood. The objective of our study was to examine the levels of inflammatory mediators in CF-LVAD recipients compared with both healthy control subjects and heart failure patients who were candidates for CF-LVAD support. Plasma levels of chemokines, cytokines, and inflammatory markers were measured in 18 CF-LVAD recipients and compared with those of 14 healthy control subjects and 14 heart failure patients who were candidates for CF-LVADs. The levels of granulocyte macrophage-colony stimulating factor, macrophage inflammatory proteins-1β, and macrophage-derived chemokine were significantly higher in the CF-LVAD group compared with both the heart failure and the healthy control groups, whereas no significant differences were observed between the healthy control subjects and the heart failure groups. Compared with the healthy controls, C-reactive protein, interferon gamma-induced protein-10, monocyte chemotactic protein-1, and interleukin-8 levels were significantly higher in both the CF-LVAD and heart failure groups, but no significant differences were observed between the CF-LVAD recipients and the heart failure patients. Inflammatory markers were elevated in CF-LVAD recipients compared with healthy control subjects and the heart failure patients. Further studies should investigate the clinical implications of elevated levels of inflammation in CF-LVAD recipients.

Graft-derived CCL2 increases graft injury during antibody-mediated rejection of cardiac allografts

The pathogenic role of macrophages in antibody-mediated rejection (AMR) remains unclear. Monocyte chemoattractant protein-1 (MCP-1/CCL2) is a potent chemotactic factor for monocytes and macrophages. The current studies used a murine model of AMR to investigate the role of graft-derived CCL2 in AMR and how macrophages may participate in antibody-mediated allograft injury. B6.CCR5−/−/CD8−/− recipients rejected MHC-mismatched WT A/J allografts with high donor-reactive antibody titers and diffuse C4d deposition in the large vessels and myocardial capillaries, features consistent with AMR. In contrast, A/J.CCL2−/− allografts induced low donor-reactive antibody titers and C4d deposition at Day 7 posttransplant. Decreased donor-reactive CD4 T cells producing interferon gamma were induced in response to A/J.CCL2−/− versus WT allografts. Consequently, A/J.CCL2−/− allograft survival was modestly but significantly longer than A/J allografts. Macrophages purified from WT allografts expressed high levels of IL-1β and IL-12p40 and this expression and the numbers of classically activated macrophages were markedly reduced in CCL2-deficient allografts on Day 7. The results indicate that allograft-derived CCL2 plays an important role in directing classically activated macrophages into allografts during AMR and that macrophages are important contributors to the inflammatory environment mediating graft tissue injury in this pathology, suggesting CCL2 as a therapeutic target for AMR.

Anti-CD45RB/anti-TIM-1-induced tolerance requires regulatory B cells

The role of B cells in transplant tolerance remains unclear. Although B-cell depletion often prolongs graft survival, sometimes it results in more rapid rejection, suggesting that B cells may have regulatory activity. We previously demonstrated that tolerance induction by anti-CD45RB antibody requires recipient B cells. Here, we show that anti-CD45RB in combination with anti-TIM-1 antibody has a synergistic effect, inducing tolerance in all recipients in a mouse islet allograft model. This effect depends on the presence of recipient B cells, requires B-cell IL-10 activity, and is antigen-specific. These data suggest the existence of a regulatory B-cell population that promotes tolerance via an IL-10-dependent pathway.

CXCL10: a candidate biomarker in transplantation

Interferon (IFN) γ-induced protein 10 kDa (IP-10) or C-X-C motif chemokine 10 (CXCL10) is a small cytokine belonging to the CXC chemokine family. This family of signaling molecules is known to control several biological functions and to also play pivotal roles in disease initiation and progression. By binding to its specific cognate receptor CXCR3, CXCL10 critically regulates chemotaxis during several immune-inflammatory processes. In particular, this chemokine controls chemotaxis during the inflammatory response resulting from allograft rejection after transplantation. Interestingly, a strong association has been described between CXCL10 production, immune response and the fate of the graft following allotransplantation. Enhanced CXCL10 production has been observed in recipients of transplants of different organs. This enhanced production likely comes from either the graft or the immune cells and is correlated with an increase in the concentration of circulating CXCL10. Because CXCL10 can be easily measured in the serum and plasma from a patient, the detection and quantitation of circulating CXCL10 could be used to reveal a transplant recipient's immune status. The purpose of this review is to examine the critical role of CXCL10 in the pathogenesis of allograft rejection following organ transplantation. This important role highlights the potential utilization of CXCL10 not only as a therapeutic target but also as a biomarker to predict the severity of rejection, to monitor the inflammatory status of organ recipients and, hopefully, to fine-tune patient therapy in transplantation.

Gene expression profiling in acute allograft rejection: challenging the immunologic constant of rejection hypothesis

In humans, the role and relationship between molecular pathways that lead to tissue destruction during acute allograft rejection are not fully understood. Based on studies conducted in humans, we recently hypothesized that different immune-mediated tissue destruction processes (i.e. cancer, infection, autoimmunity) share common convergent final mechanisms. We called this phenomenon the "Immunologic Constant of Rejection (ICR)." The elements of the ICR include molecular pathways that are consistently described through different immune-mediated tissue destruction processes and demonstrate the activation of interferon-stimulated genes (ISGs), the recruitment of cytotoxic immune cells (primarily through CXCR3/CCR5 ligand pathways), and the activation of immune effector function genes (IEF genes; granzymes A/B, perforin, etc.). Here, we challenge the ICR hypothesis by using a meta-analytical approach and systematically reviewing microarray studies evaluating gene expression on tissue biopsies during acute allograft rejection. We found the pillars of the ICR consistently present among the studies reviewed, despite implicit heterogeneity. Additionally, we provide a descriptive mechanistic overview of acute allograft rejection by describing those molecular pathways most frequently encountered and thereby thought to be most significant. The biological role of the following molecular pathways is described: IFN-γ, CXCR3/CCR5 ligand, IEF genes, TNF-α, IL-10, IRF-1/STAT-1, and complement pathways. The role of NK cell, B cell and T-regulatory cell signatures are also addressed.

Memory T cells migrate to and reject vascularized cardiac allografts independent of the chemokine receptor CXCR3

BACKGROUND

Memory T cells migrate to and reject transplanted organs without the need for priming in secondary lymphoid tissues, but the mechanisms by which they do so are not known. Here, we tested whether CXCR3, implicated in the homing of effector T cells to sites of infection, is critical for memory T-cell migration to vascularized allografts.

METHODS

CD4 and CD8 memory T cells were sorted from alloimmunized CXCR3 and wildtype B6 mice and cotransferred to congenic B6 recipients of BALB/c heart allografts. Graft-infiltrating T cells were quantitated 20 and 72 hr later by flow cytometry. Migration and allograft survival were also studied in splenectomized alymphoplastic (aly/aly) recipients, which lack secondary lymphoid tissues.

RESULTS

We found that polyclonal and antigen-specific memory T cells express high levels of CXCR3. No difference in migration of wildtype versus CXCR3 CD4 and CD8 memory T cells to allografts could be detected in wildtype or aly/aly hosts. In the latter, wildtype and CXCR3 memory T cells precipitated acute rejection at similar rates. Blocking CCR5, a chemokine receptor also upregulated on memory T cells, did not delay graft rejection mediated by CXCR3 memory T cells.

CONCLUSIONS

CXCR3 is not critical for the migration of memory T cells to vascularized organ allografts. Blocking CXCR3 or CXCR3 and CCR5 does not delay acute rejection mediated by memory T cells. These findings suggest that the mechanisms of memory T cell-homing to transplanted organs may be distinct from those required for their migration to sites of infection.

High pretransplant serum levels of CXCL9 are associated with increased risk of acute rejection and graft failure in kidney graft recipients

Several clinical and experimental models have underlined the role of the CXCR3-binding chemokines in the immune-mediated kidney diseases. This study aimed to investigate the predictive value of measuring pretransplant CXCL9 levels for acute rejection (AR) onset and kidney transplantation outcome. Pretransplantation serum levels of CXCL9 were tested retrospectively in 252 kidney graft recipients, whose stratification in two groups according to CXCL9 levels (<272.1 pg/ml vs. >272.1 pg/ml) showed highly significant differences in 5-year survival rates (97.7% vs. 73.3%; P < 0.001). Multivariate analysis demonstrated that among the analysed variables, CXCL9 [relative risk (RR) 11.708] and AR (RR 3.604) had the highest predictive power of graft loss. Accordingly, patients with AR (254.4 + or - 22.1; P < 0.05) and, even more, those with anti-thymoglobulin (ATG)-treated AR also showed increased pretransplant serum CXCL9 levels (319.3 + or - 28.1, P < 0.001). Moreover, CXCL9 expression and distribution were investigated in tissue specimens obtained from 10 patients affected by AR, and wide CXCL9 expression was detected not only in infiltrating inflammatory cells but also in vascular and tubular structures. Measurement of pretransplant serum CXCL9 levels might represent the tracking of a clinically useful parameter to identify subjects at high risk of AR and graft failure. These findings might be used for the individualization of immunosuppressive therapies.

Role of MCP-1 in cardiovascular disease: molecular mechanisms and clinical implications

Many of the major diseases, including cardiovascular disease, are widely recognized as inflammatory diseases. MCP-1 (monocyte chemotactic protein-1) plays a critical role in the development of cardiovascular diseases. MCP-1, by its chemotactic activity, causes diapedesis of monocytes from the lumen to the subendothelial space where they become foam cells, initiating fatty streak formation that leads to atherosclerotic plaque formation. Inflammatory macrophages probably play a role in plaque rupture and the resulting ischaemic episode as well as restenosis after angioplasty. There is strong evidence that MCP-1 plays a major role in myocarditis, ischaemia/reperfusion injury in the heart and in transplant rejection. MCP-1 also plays a role in cardiac repair and manifests protective effects under certain conditions. Such protective effects may be due to the induction of protective ER (endoplasmic reticulum) stress chaperones by MCP-1. Under sustained ER stress caused by chronic exposure to MCP-1, the protection would break down resulting in the development of heart failure. MCP-1 is also involved in ischaemic angiogenesis. The recent advances in our understanding of the molecular mechanisms that might be involved in the roles that MCP-1 plays in cardiovascular disease are reviewed. The gene expression changes induced by the signalling events triggered by MCP-1 binding to its receptor include the induction of a novel zinc-finger protein called MCPIP (MCP-1-induced protein), which plays critical roles in the development of the pathophysiology caused by MCP-1 production. The role of the MCP-1/CCR2 (CC chemokine receptor 2) system in diabetes, which is a major risk factor for cardiovascular diseases, is also reviewed briefly. MCP-1/CCR2- and/or MCPIP-targeted therapeutic approaches to intervene in inflammatory diseases, including cardiovascular diseases, may be feasible.

Chemokine-directed strategies to attenuate allograft rejection

A key event during T cell-mediated rejection of allografts is the trafficking of donor antigen-primed effector T cells from the lymphoid tissue to the graft. This trafficking is mediated in part by chemokine produced in the graftengaging receptors on the T cells and other graftinfiltrating leukocytes. The presence of specific sets of chemokines and chemokine receptors is detectable in rejecting allografts. In animal models, allograft rejection is delayed when chemokine-chemokine receptor function is absent or antagonized but cellular infiltration and graft survival eventually occur, suggesting that T cells and other leukocytes use several trafficking mechanisms during rejection. The use of chemokines as footprints of rejection may be of considerable value as noninvasive biomarkers in transplantation.

Predictive role of pretransplant serum CXCL10 for cardiac acute rejection

BACKGROUND

The detection of acute rejection in heart transplantation remains an important feature of transplant management, especially in the early phase. Frequent surveillance with endomyocardial biopsy is necessary, even though it is an invasive procedure and carries a certain risk. Hence, noninvasive biomarkers able to predict acute rejection could be a further helpful tool in patient management. The interferon-gamma-inducible chemokine CXCL10 is required for initiation and development of graft failure caused by acute or chronic rejection. It has been reported that CXCL10 serum level is predictive of graft loss in kidney graft recipients. In the present study, we investigated whether pretransplant CXCL10 serum level may be a predictive noninvasive biomarker in heart transplant (HTx) recipients, as well.

METHODS

Sera from 143 patients undergoing orthotopic heart transplantation were collected before surgery and tested for CXCL10 and CCL22 and compared with serum samples from healthy subjects.

RESULTS

We found that basal CXCL10 serum levels in HTx recipients were significantly higher than in healthy subjects, whereas no difference was seen in CCL22 levels. Among HTx recipients, CXCL10 serum levels of rejectors were significantly higher than in nonrejectors. Our results showed that CXCL10 was a significant independent risk factor of several variables and had the highest predictive value for early acute heart rejection, with 160 pg/mL cutoff value.

CONCLUSIONS

In HTx recipients, measurement of pretransplant CXCL10 serum levels could be a clinically useful tool for predicting cardiac acute rejection, especially in the early posttransplant period.

Immunomodulatory effects of BXL-01-0029, a less hypercalcemic vitamin D analogue, in human cardiomyocytes and T cells

Current immunosuppressive protocols have reduced rejection occurrence in heart transplantation; nevertheless, management of heart transplant recipients is accompanied by major adverse effects, due to drug doses close to toxic range. In allograft rejection, characterized by T-helper 1 (Th1) cell-mediated response, the CXCL10-CXCR3 axis plays a pivotal role in triggering a self-promoting inflammatory loop. Indeed, CXCL10 intragraft production, required for initiation and development of graft failure, supports organ infiltration by Th1 cells. Thus, targeting the CXCL10-CXCR3 axis while avoiding generalized immunosuppression, may be of therapeutic significance. Based on preclinical evidence for immunoregulatory properties of vitamin D receptor agonists, we propose that a less hypercalcemic vitamin D analogue, BXL-01-0029, might have the potential to contribute to rejection management. We investigated the effect of BXL-01-0029 on CXCL10 secretion induced by proinflammatory stimuli, both in human isolated cardiomyocytes (Hfcm) and purified CD4+ T cells. Mycophenolic acid (MPA), the active agent of mycophenolate mofetil, was used for comparison. BXL-01-0029 inhibited IFNgamma and TNFalpha-induced CXCL10 secretion by Hfcm more potently than MPA, impairing cytokine synergy and pathways. BXL-01-0029 reduced also CXCL10 protein secretion and gene expression by CD4+ T cells. Furthermore, BXL-01-0029 did not exert any toxic effect onto both cell types, suggesting its possible use as a dose-reducing agent for conventional immunosuppressive drugs in clinical transplantation.

Prolongation of cardiac and islet allograft survival by a blocking hamster anti-mouse CXCR3 monoclonal antibody

BACKGROUND

Acute allograft rejection requires a multifaceted immune response involving trafficking of immune cells into the transplant and expression of effector cell functions leading to graft destruction. The chemokine receptor CXCR3 and its ligands, CXCL9, CXCL10 and CXCL11, constitute an important pathway for effector cell recruitment posttransplant. However, analysis of CXCR3 expression and function has been hampered by a general lack of availability of a neutralizing anti-CXCR3 monoclonal antibody (mAb) for use in experimental models.

METHODS

We report the generation, characterization, and use of CXCR3-173, a new hamster mAb specific for mouse CXCR3 that recognizes CXCR3 on cells from wild-type but not CXCR3-/- mice.

RESULTS

Using CXCR3-173 mAb, we demonstrate CXCR3 expression on primary memory phenotype CD4+ and CD8+ T cells, naturally occurring CD4+CD25+ Foxp3+ regulatory T cells, natural killer T cells, and approximately 25% of NK cells. CXCR3-173 blocked chemotaxis in vitro in response to CXCL10 or CXCL11 but not CXCL9. When injected into mice, this mAb significantly prolonged both cardiac and islet allograft survival. When combined with a subtherapeutic regimen of rapamycin, CXCR3-173 mAb induced long-term (>100 day) survival of cardiac and islet allografts. The in vivo effects of CXCR3-173 mAb were not associated with effector lymphocyte depletion.

CONCLUSION

These data highlight the utility of CXCR3-173 mAb in developing immunotherapeutic approaches to inhibit transplant rejection and potentially other immune-mediated diseases in murine models.

The role for monocyte chemoattractant protein-1 in the generation and function of memory CD8+ T cells

Memory T cells are resistant to the conventional costimulatory blockade and therefore impede tolerance induction. However, their migratory, survival, and functional requirements for chemokines are not well understood. We herein examine the role for MCP-1 or CCL2 in the generation, migration, and function of memory CD8+ T cells. We found that overall generation of both central memory (TCM) and effector memory (TEM) CD8+ T cells was severely impaired in the absence of MCP-1. Importantly, the survival of TEM, but not TCM, CD8+ cells was reduced without MCP-1, whereas the homeostatic proliferation of TCM, but not TEM, CD8+ cells was weakened in MCP-1-/- mice. However, once they were generated in the absence of MCP-1, in vitro function of both subsets of memory cells remained intact as determined by their proliferation and IFN-gamma production. Interestingly, the migration of TCM, but not TEM, CD8+ cells to inflammatory sites was significantly delayed without MCP-1, whereas both subsets of memory cells underwent comparable expansion and apoptosis with or without MCP-1 during the effector phase. Moreover, the function to eliminate a graft of TCM, but not TEM, CD8+ cells was impaired without MCP-1. Thus, this study demonstrates that MCP-1 plays an important role in not only migration but also generation and survival of memory T cells. This finding provides new insight into the requirement of chemokines for the generation, survival, and function of differential subsets of memory T cells and may have clinic implications for tolerance induction.

The chemokine receptor Cxcr3 is not essential for acute cardiac allograft rejection in mice and rats

Chemokine receptors have gained attention as potential targets for novel therapeutic strategies. We investigated the mechanisms of allograft rejection in chemokine receptor Cxcr3-deficient mice using a model of acute heart allograft rejection in the strain combination BALB/c to C57BL/6. Allograft survival was minimally prolonged in Cxcr3-deficient mice compared to wild-type (wt) animals (8 vs. 7 days) and treatment with a subtherapeutic dose of cyclosporine A (CsA) led to similar survival in Cxcr3-deficient and wt recipients (13 vs. 12 days). At rejection grafts were histologically indistinguishable. Microarray analysis revealed that besides Cxcr3 only few genes were differentially expressed in grafts or in spleens from transplanted or untransplanted animals. Transcript analysis by quantitative RT-PCR of selected cytokines, chemokines, or chemokine receptors or serum levels of selected cytokines and chemokines showed similar levels between the two groups. Furthermore, in a rat heart allograft transplantation model treatment with a small molecule CXCR3 antagonist did not prolong survival despite full blockade of Cxcr3 in vivo. In summary, Cxcr3 deficiency or pharmacologic blockade does not diminish graft infiltration, tempo and severity of rejection. Thus, Cxcr3 does not appear to play a pivotal role in the allograft rejection models described here.

PI3Kgamma (PI3Kgamma) is essential for efficient induction of CXCR3 on activated T cells

The gamma isoform of PI3Kinase (PI3Kgamma) controls leukocyte chemotaxis by participating in GPCR signaling, and by regulating cellular polarization. Here we show that PI3Kgamma is required for efficient induction of CXC chemokine receptor 3 (CXCR3) on T cells upon activation. T cells from PI3Kgamma(-/-) mice up-regulated CXCR3 less efficiently than wild-type controls both upon activation in vitro as well as during Leishmania mexicana infection. Inhibition of PI3Kinases using wortmannin and LY294002 or blockade of PI3Kgamma activity using a selective inhibitor or PI3Kgamma siRNA suppressed induction of CXCR3 on T cells following activation. Levels of CXCR3 and T-bet mRNA were significantly lower in PI3Kgamma inhibitor-treated T cells, indicating that PI3Kgamma may control CXCR3 expression in part through induction of T-bet. These results reveal a novel role for PI3Kgamma in the induction of CXCR3 on T cells and suggest that PI3Kgamma may regulate leukocyte chemotaxis by controlling the expression of chemokine receptors.

Immunosuppression in cardiac graft rejection: a human in vitro model to study the potential use of new immunomodulatory drugs

CXCL10-CXCR3 axis plays a pivotal role in cardiac allograft rejection, so that targeting CXCL10 without inducing generalized immunosuppression may be of therapeutic significance in allotransplantation. Since the role of resident cells in cardiac rejection is still unclear, we aimed to establish reliable human cardiomyocyte cultures to investigate Th1 cytokine-mediated response in allograft rejection. We used human fetal cardiomyocytes (Hfcm) isolated from fetal hearts, obtained after legal abortions. Hfcm expressed specific cardiac lineage markers, specific cardiac structural proteins, typical cardiac currents and generated ventricular action potentials. Thus, Hfcm represent a reliable in vitro tool for allograft rejection research, since they resemble the features of mature cells. Hfcm secreted CXCL10 in response to IFNgamma and TNFalphaalpha; this effect was magnified by cytokine combination. Cytokine synergy was associated to a significant TNFalpha-induced up-regulation of IFNgammaR. The response of Hfcm to some currently used immunosuppressive drugs compared to rosiglitazone, a peroxisome proliferator-activated receptor gamma agonist and Th1-mediated response inhibitor, was also evaluated. Only micophenolic acid and rosiglitazone halved CXCL10 secretion by Hfcm. Given the pivotal role of IFNgamma-induced chemokines in Th1-mediated allograft rejection, these preliminary results suggest that the combined effects of immunosuppressive agents and rosiglitazone could be potentially beneficial to patients receiving heart transplants.