Targeting of the chemokine receptor CCR1 suppresses development of acute and chronic cardiac allograft rejection

Role of chemokine receptors in transplant rejection and graft-versus-host disease

Organ transplantation increases life expectancy and improves the quality of life of patients experiencing specific conditions such as terminal organ failure. Despite matching efforts between donor and recipient, immune activation can interfere with allograft survival after transplantation if immunosuppression is not used. With both innate and adaptive responses, this is a complicated immunological process. This can lead to organ rejection, or graft-versus-host disease (GVHD), depending on the origin of the immune response. Inflammatory factors, such as chemokine receptors and their ligands, are involved in a wide variety of immunological processes, including modulating transplant rejection or GVHD, therefore, chemokine biology has been a major focus of transplantation studies. These molecules attract circulating peripheral leukocytes to infiltrate into the allograft and facilitate dendritic and T cell trafficking between lymph nodes and the graft during the allogeneic response. In this chapter, we will review the most relevant chemokine receptors such as CXCR3 and CCR5, among others, and their ligands involved in the process of allograft rejection for solid organ transplantation and graft-versus-host disease in the context of hematopoietic cell transplantation.

Immune characteristics of kidney transplant recipients with acute respiratory distress syndrome induced by COVID-19 at single-cell resolution

BACKGROUND

COVID-19-induced acute respiratory distress syndrome (ARDS) can result in tissue damage and multiple organ dysfunction, especially in kidney transplant recipients (KTRs) receiving immunosuppressive drugs. Presently, single-cell research on COVID-19-induced ARDS is considerably advanced, yet knowledge about ARDS in KTRs is still constrained.

METHODS

Single-cell RNA sequencing (scRNA-seq) analysis was performed to construct a comprehensive single-cell immune landscape of the peripheral blood mononuclear cells (PBMCs) of eight patients with COVID-19-induced ARDS, five KTRs with COVID-19-induced ARDS, and five healthy individuals. Subsequently, we conducted a comprehensive bioinformatics analysis, including cell clustering, enrichment analysis, trajectory analysis, gene regulatory network analysis, and cell-cell interaction analysis, to investigate the heterogeneity of the immune microenvironment in KTRs with ARDS.

RESULT

Our study revealed that KTRs exhibit significant heterogeneity with COVID-19-induced ARDS compared with those of other individuals, with significant reductions in T cells, as well as an abnormal proliferation of B cells and monocytes. In the context of dual influences from immunosuppression and viral infection, KTRs exhibited more specific plasma cells, along with significant enrichment of dysfunctional GZMB and XAF1 double-positive effector T cells and IFI27-positive monocytes. Additionally, robust communication existed among T cells and monocytes in cytokine signaling. These effects impede the process of immune reconstitution in KTR patients.

CONCLUSION

Our findings suggest that KTRs with COVID-19-induced ARDS show elevated antibody levels, impaired T cell differentiation, and dysregulation of innate immunity. In summary, this study provides a theoretical foundation for a comprehensive understanding of COVID-19-induced ARDS in KTRs.

The role of macrophages in thermal injury

Macrophages, first discovered for their phagocytic ability, are a complicated and heterogeneous cell type. The unique properties of macrophages allow them to perform a vast array of functions, including phagocytosis, cytokine production, antigen presentation, and wound healing. Some macrophage populations are derived from monocytes and are induced into specific phenotypes by the local tissue microenvironment, while other macrophages form during early embryonic development. The exposure of the host to local pathogens and/or traumatic injury alters the tissue microenvironment and, in turn, influences changes in macrophage phenotype and function. Perhaps the most significant change in the local tissue microenvironment and subsequent macrophage phenotype occurs after thermal injury, which causes localized tissue damage and a massive systemic inflammatory response. However, few studies have explored the influence of burn injury on the host macrophages and macrophage function in burn wounds. Furthermore, the literature is scant regarding the impact macrophage function has on outcomes in thermal injury. This review will focus on the current knowledge of macrophage function in burn wounds and the phenotypic changes in macrophages during thermal injury while identifying knowledge gaps.

Vascular Signaling in Allogenic Solid Organ Transplantation - The Role of Endothelial Cells

Graft rejection remains the major obstacle after vascularized solid organ transplantation. Endothelial cells, which form the interface between the transplanted graft and the host’s immunity, are the first target for host immune cells. During acute cellular rejection endothelial cells are directly attacked by HLA I and II-recognizing NK cells, macrophages, and T cells, and activation of the complement system leads to endothelial cell lysis. The established forms of immunosuppressive therapy provide effective treatment options, but the treatment of chronic rejection of solid organs remains challenging. Chronic rejection is mainly based on production of donor-specific antibodies that induce endothelial cell activation—a condition which phenotypically resembles chronic inflammation. Activated endothelial cells produce chemokines, and expression of adhesion molecules increases. Due to this pro-inflammatory microenvironment, leukocytes are recruited and transmigrate from the bloodstream across the endothelial monolayer into the vessel wall. This mononuclear infiltrate is a hallmark of transplant vasculopathy. Furthermore, expression profiles of different cytokines serve as clinical markers for the patient’s outcome. Besides their effects on immune cells, activated endothelial cells support the migration and proliferation of vascular smooth muscle cells. In turn, muscle cell recruitment leads to neointima formation followed by reduction in organ perfusion and eventually results in tissue injury. Activation of endothelial cells involves antibody ligation to the surface of endothelial cells. Subsequently, intracellular signaling pathways are initiated. These signaling cascades may serve as targets to prevent or treat adverse effects in antibody-activated endothelial cells. Preventive or therapeutic strategies for chronic rejection can be investigated in sophisticated mouse models of transplant vasculopathy, mimicking interactions between immune cells and endothelium.

Glibenclamide ameliorates transplant-induced arteriosclerosis and inhibits macrophage migration and MCP-1 expression

AIMS

Glibenclamide, a diabetes mellitus type 2 medication, has anti-inflammatory and autoimmune properties. This study investigated the effects of glibenclamide on transplant-induced arteriosclerosis as well as the underlying molecular events.

METHODS

Male C57Bl/6 (H-2b) and BALB/c (H-2d) mice were used for aorta transplantation. We used hematoxylin and eosin (HE) and Elastic Van Gieson (EVG) staining for histological assessment, and qRT-PCR and ELISA to measure mRNA and protein levels. Mouse peritoneal macrophages were isolated for lipopolysaccharide (LPS) stimulation and glibenclamide treatment followed by ELISA, Western blot, and Transwell assays.

RESULTS

Glibenclamide inhibited transplant-induced arteriosclerosis in vivo. Morphologically, glibenclamide reduced inflammatory cell accumulation and collagen deposition in the aortas. At the gene level, glibenclamide suppressed aortic cytokine mRNA levels, including interleukin-1β (IL-1β; 10.64 ± 3.19 vs. 23.77 ± 5.72; P < .05), tumor necrosis factor-α (TNF-α; 4.59 ± 0.78 vs. 13.89 ± 5.42; P < .05), and monocyte chemoattractant protein-1 (MCP-1; 202.66 ± 23.44 vs. 1172.73 ± 208.80; P < .01), while IL-1β, TNF-α, and MCP-1 levels were also reduced in the mouse sera two weeks after glibenclamide treatment (IL-1β, 39.40 ± 13.56 ng/ml vs. 78.96 ± 9.39 ng/ml; P < .01; TNF-α, 52.60 ± 13.00 ng/ml vs. 159.73 ± 6.76 ng/ml; P < .01; and MCP-1, 56.60 ± 9.07 ng/ml vs. 223.07 ± 36.28 ng/ml; P < .001). Furthermore, glibenclamide inhibited macrophage expression and secretion of inflammatory factors in vitro through suppressing activation of the nuclear factor-κB (NF-κB) pathway and MCP-1 production.

CONCLUSION

Glibenclamide protected against aorta transplantation-induced arteriosclerosis by reducing inflammatory factors in vivo and inhibited macrophage migration and MCP-1 production in vitro.

Potent and selective CC chemokine receptor 1 antagonists labeled with carbon-13, carbon-14, and tritium

1-(4-Fluorophenyl)-1H-pyrazolo[3,4-c]pyridine-4-carboxylic acid (2-methanesulfonyl-pyridin-4-ylmethyl)-amide (1) and its analogs (2) and (3) are potent CCR1 antagonists intended for the treatment of rheumatoid arthritis. The detailed syntheses of these 3 compounds labeled with carbon-13 as well as the preparation of (1) and (2) labeled with carbon-14, and (1) labeled with tritium, are described.

Histone/protein deacetylase 11 targeting promotes Foxp3+ Treg function

Current interest in Foxp3+ T-regulatory (Treg) cells as therapeutic targets in transplantation is largely focused on their harvesting pre-transplant, expansion and infusion post-transplantation. An alternate strategy of pharmacologic modulation of Treg function using histone/protein deacetylase inhibitors (HDACi) may allow more titratable and longer-term dosing. However, the effects of broadly acting HDACi vary, such that HDAC isoform-selective targeting is likely required. We report data from mice with constitutive or conditional deletion of HDAC11 within Foxp3+ Treg cells, and their use, along with small molecule HDAC11 inhibitors, in allograft models. Global HDAC11 deletion had no effect on health or development, and compared to WT controls, Foxp3+ Tregs lacking HDAC11 showed increased suppressive function, and increased expression of Foxp3 and TGF-β. Likewise, compared to WT recipients, conditional deletion of HDAC11 within Tregs led to long-term survival of fully MHC-mismatched cardiac allografts, and prevented development of transplant arteriosclerosis in an MHC class II-mismatched allograft model. The translational significance of HDAC11 targeting was shown by the ability of an HDAC11i to promote long-term allograft allografts in fully MHC-disparate strains. These data are powerful stimuli for the further development and testing of HDAC11-selective pharmacologic inhibitors, and may ultimately provide new therapies for transplantation and autoimmune diseases.

Comparative transcriptomic analysis of porcine peripheral blood reveals differentially expressed genes from the cytokine-cytokine receptor interaction pathway related to health status

While some research has looked into the host genetic response in pigs challenged with specific viruses or bacteria, few studies have explored the expression changes of transcripts in the peripheral blood of sick pigs that may be infected with multiple pathogens on farms. In this study, the architecture of the peripheral blood transcriptome of 64 Duroc sired commercial pigs, including 18 healthy animals at entry to a growing facility (set as a control) and 23 pairs of samples from healthy and sick pen mates, was generated using RNA-Seq technology. In total, 246 differentially expressed genes were identified to be specific to the sick animals. Functional enrichment analysis for those genes revealed that the over-represented gene ontology terms for the biological processes category were exclusively immune activity related. The cytokine-cytokine receptor interaction pathway was significantly enriched. Nine functional genes from this pathway encoding members (as well as their receptors) of the interleukins, chemokines, tumor necrosis factors, colony stimulating factors, activins, and interferons exhibited significant transcriptional alteration in sick animals. Our results suggest a subset of novel marker genes that may be useful candidate genes in the evaluation and prediction of health status in pigs under commercial production conditions.

Chemokines and Their Receptors in Islet Allograft Rejection and as Targets for Tolerance Induction

Graft rejection is a major barrier to successful outcome of transplantation surgery. Islet transplantation introduces insulin secreting tissue into type 1 diabetes mellitus recipients, relieving patients from exogenous insulin injection. However, insulitis of grafted tissue and allograft rejection prevent long-term insulin independence. Leukocyte trafficking is necessary for the launch of successful immune responses to pathogen or allograft. Chemokines, small chemotactic cytokines, direct the migration of leukocytes through their interaction with chemokine receptors found on cell surfaces of immune cells. Unique receptor expression of leukocytes, and the specificity of chemokine secretion during various states of immune response, suggest that the extracellular chemokine milieu specifically homes certain leukocyte subsets. Thus, only those leukocytes required for the current immune task are attracted to the inflammatory site. Chemokine blockade, using antagonists and monoclonal antibodies directed against chemokine receptors, is an emerging and specific immunosuppressive strategy. Importantly, chemokine blockade may potentiate tolerance induction regimens to be used following transplantation surgery, and prevent the need for life-long immunosuppression of islet transplant recipients. Here, the role for chemokine blockade in islet transplant rejection and tolerance is reviewed.

Association between Monocyte Count and Risk of Incident CKD and Progression to ESRD

BACKGROUND AND OBJECTIVES

Experimental evidence suggests a role for monocytes in the biology of kidney disease progression; however, whether monocyte count is associated with risk of incident CKD, CKD progression, and ESRD has not been examined in large epidemiologic studies.

DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS

We built a longitudinal observational cohort of 1,594,700 United States veterans with at least one eGFR during fiscal year 2004 (date of last eGFR during this period designated time zero) and no prior history of ESRD, dialysis, or kidney transplant. Cohort participants were followed until September 30, 2013 or death. Monocyte count closest to and before time zero was categorized in quartiles: quartile 1, >0.00 to ≤0.40 thousand cells per cubic millimeter (k/cmm); quartile 2, >0.40 to ≤0.55 k/cmm; quartile 3, >0.55 to ≤0.70 k/cmm; and quartile 4, >0.70 k/cmm. Survival models were built to examine the association between monocyte count and risk of incident eGFR<60 ml/min per 1.73 m2, risk of incident CKD, and risk of CKD progression defined as doubling of serum creatinine, eGFR decline ≥30%, or the composite outcome of ESRD, dialysis, or renal transplantation.

RESULTS

Over a median follow-up of 9.2 years (interquartile range, 8.3-9.4); in adjusted survival models, there was a graded association between monocyte counts and risk of renal outcomes. Compared with quartile 1, quartile 4 was associated with higher risk of incident eGFR<60 ml/min per 1.73 m2 (hazard ratio, 1.13; 95% confidence interval, 1.12 to 1.14) and risk of incident CKD (hazard ratio, 1.15; 95% confidence interval, 1.13 to 1.16). Quartile 4 was associated with higher risk of doubling of serum creatinine (hazard ratio, 1.22; 95% confidence interval, 1.20 to 1.24), ≥30% eGFR decline (hazard ratio, 1.18; 95% confidence interval, 1.17 to 1.19), and the composite renal end point (hazard ratio, 1.19; 95% confidence interval, 1.16 to 1.22). Cubic spline analyses of the relationship between monocyte count levels and renal outcomes showed a linear relationship, in which risk was higher with higher monocyte count. Results were robust to changes in sensitivity analyses.

CONCLUSIONS

Our results show a significant association between higher monocyte count and risks of incident CKD and CKD progression to ESRD.

Chemokines and Chemokine Receptors in the Development of Lupus Nephritis

Lupus nephritis (LN) is a major cause of morbidity and mortality in the patients with systemic lupus erythematosus (SLE), an autoimmune disease with damage to multiple organs. Leukocyte recruitment into the inflamed kidney is a critical step to promote LN progression, and the chemokine/chemokine receptor system is necessary for leukocyte recruitment. In this review, we summarize recent studies on the roles of chemokines and chemokine receptors in the development of LN and discuss the potential and hurdles of developing novel, chemokine-based drugs to treat LN.

Increased levels of CD4(+) and CD8(+) T cells expressing CCR1 in patients developing allograft dysfunction; a cohort study

BACKGROUND

Leukocyte infiltration into the graft has pivotal effects on kidney transplantation outcome. The present study sought to determine whether the expression of sequential chemokine receptors on CD4(+) and CD8(+) T cells in human renal allograft can predict clinical episodes.

METHODS

Blood samples from 52 consecutive renal transplant patients were evaluated at the time of transplantation and at three times (2, 90 and 180days) after transplantation to analyze the expression of CCR1 and CXCR3 on CD4(+) and CD8(+) T cells by flowcytometry. A total of 30 biopsies, including protocol biopsy (n=24) and cause biopsy (n=6), were investigated according to the Banff criteria.

RESULTS

The mean percentage of CD4(+) and CD8(+) T cells expressing CCR1 was significantly increased in patients with allograft dysfunction (n=25) (p=0.006, p=0.004). The mean fluorescence intensity of CXCR3 on CD4(+) and CD8(+) T cells were found to be significantly higher in graft dysfunction than that in well-functioning grafts. (p<0.001, p=0.007). Receiver Operating Characteristic (ROC) Curve Analysis showed that the calculated AUC was 0.86 at the third month for CD4(+)CCR1(+) and CD8(+)CCR1(+) (p<0.001). Multiple logistic regression analysis showed that an increase in CD4(+) expressing CXCR3 leads to a lower risk of graft dysfunction (OR=0.37), while an increase in CD8(+) expressing CCR1 results in a higher risk of graft dysfunction (OR=3.66).

CONCLUSION

During renal transplantation, CD4(+) and CD8(+) T cells expressing CCR1 were increased in patients who developed graft dysfunction. These findings may prospectively predict allograft dysfunction, and help elucidate the underlying pathogenic mechanisms.

Spiegelmer Inhibition of MCP-1/CCR2--Potential as an Adjunct Immunosuppressive Therapy in Transplantation

The rejection process remains the key unsolved issue after transplantation of disparate tissue. The CC chemokine monocyte chemoattractant protein-1 (MCP-1/CCL2) has been reported to be involved in the process of alloimmune interaction. Spiegelmers are l-oligonucleotides that can be designed to bind to pharmacologically relevant target molecules. Here, we tested a high-affinity Spiegelmer-based MCP-1 inhibitor (mNOX-E36) in an allogeneic heart transplant model. Fully vascularized allogeneic heterotopic heart transplantations from BALB/c to C57BL/6 mice were performed. Mice were either treated with the anti-MCP-1-Spiegelmer (mNOX-E36) in monotherapy or in combination with subtherapeutic doses of cyclosporine A (CsA) (10 mg/kgBW/day) for 10 days. Controls received equivalent doses of a non-functional Spiegelmer (revmNOX-E36). Graft survival of allogeneic heart transplants was slightly but significantly prolonged under mNOX-E36 monotherapy (median graft survival 10 day ± 0.7) compared to revmNOX-E36 (median graft survival 7 day ± 0.3; P = 0.001). A synergistic beneficial effect could be seen when mNOX-E36 was administered in combination with subtherapeutic doses of CsA (18 day ± 2.8 versus 7 day ± 0.3; P < 0.0001). Levels of inflammatory cytokines and 'alarmins' were significantly reduced, and the number of F4/80(+) cells was lower under combination therapy (1.8% ± 1.3%; versus 14.6% ± 4.4%; P = 0.0002). This novel inhibitor of the MCP-1/CCR2 axis (mNOX-E36), which has already proven efficacy and tolerability in early clinical trials, alleviates acute rejection processes in allogeneic transplantation especially when combined with subtherapeutic doses of CsA. Thus, mNOX-E36 may have potential as an adjunct immunomodulatory agent.

The chemokine receptor CCR1 is constitutively active, which leads to G protein-independent, β-arrestin-mediated internalization

Activation of G protein-coupled receptors by their associated ligands has been extensively studied, and increasing structural information about the molecular mechanisms underlying ligand-dependent receptor activation is beginning to emerge with the recent expansion in GPCR crystal structures. However, some GPCRs are also able to adopt active conformations in the absence of agonist binding that result in the initiation of signal transduction and receptor down-modulation. In this report, we show that the CC-type chemokine receptor 1 (CCR1) exhibits significant constitutive activity leading to a variety of cellular responses. CCR1 expression is sufficient to induce inhibition of cAMP formation, increased F-actin content, and basal migration of human and murine leukocytes. The constitutive activity leads to basal phosphorylation of the receptor, recruitment of β-arrestin-2, and subsequent receptor internalization. CCR1 concurrently engages Gαi and β-arrestin-2 in a multiprotein complex, which may be accommodated by homo-oligomerization or receptor clustering. The data suggest the presence of two functional states for CCR1; whereas receptor coupled to Gαi functions as a canonical GPCR, albeit with high constitutive activity, the CCR1·β-arrestin-2 complex is required for G protein-independent constitutive receptor internalization. The pertussis toxin-insensitive uptake of chemokine by the receptor suggests that the CCR1·β-arrestin-2 complex may be related to a potential scavenging function of the receptor, which may be important for maintenance of chemokine gradients and receptor responsiveness in complex fields of chemokines during inflammation.

Macrophages: contributors to allograft dysfunction, repair, or innocent bystanders?

PURPOSE OF REVIEW

Macrophages are members of the innate immune response. However, their role in the adaptive immune response is not known. The purpose of this review is to highlight our current understanding of macrophage structure and function and how they may participate in allograft injury.

RECENT FINDINGS

Studies in acute kidney injury models identify macrophages as key mediators of inflammatory injury, while more recent studies indicate that they may play a reparative role, depending on phenotype - M1 or M2 type macrophages. Mregs, generated in vitro, appear to have immune suppressive abilities and a unique phenotype. In solid-organ transplant, the emphasis of studies has been on acute or chronic injury. These data are derived from animal models using depletion of macrophages or antagonizing their activation and inflammatory responses. The relative contribution of macrophage phenotype in transplantation has not been explored.

SUMMARY

These studies suggest that macrophages play an injurious role in acute cellular allograft rejection, as well as in chronic injury. Infiltration of an allograft with macrophages is also associated with worse graft function and poor prognosis. Further studies are needed to understand the mechanisms of macrophage-mediated injury, explore their potential reparative role, and determine if they or their functional products are biomarkers of poor graft outcomes.

Chemokines in innate and adaptive granuloma formation

Granulomas are cellular inflammations that vary widely in histologic appearance depending upon the inciting agent and immunologic status of the responding host. Despite their heterogeneity, granulomas are at their core an ancient innate sequestration response characterized by the accumulation of mononuclear phagocytes. In fact, this innate cellular response was first observed by Metchnikov in simple invertebrates. Among higher vertebrates, environmental pressures have resulted in the evolution of more sophisticated adaptive immune responses which can be superimposed upon and modify the character of granulomatous inflammation. Compared to immune responses that rapidly neutralize and eliminate infectious agents, the granuloma represents a less desirable "fall back" response which still has value to the host but can be co-opted by certain infectious agents and contribute to bystander organ damage. Understanding granulomas requires an analysis of the complex interplay of innate and adaptive molecular signals that govern the focal accumulation and activity of their cellular components. Among these signals, small molecular weight chemoattractant proteins known as chemokines are potentially important contributors as they participate in both directing leukocyte migration and function. This tract will discuss the contribution of chemokines to the development of innate and adaptive granuloma formation, as well as describe their relationship to more recently evolved cytokines generated during adaptive immune responses.

CC chemokine receptors and chronic inflammation--therapeutic opportunities and pharmacological challenges

Chemokines are a family of low molecular weight proteins with an essential role in leukocyte trafficking during both homeostasis and inflammation. The CC class of chemokines consists of at least 28 members (CCL1-28) that signal through 10 known chemokine receptors (CCR1-10). CC chemokine receptors are expressed predominantly by T cells and monocyte-macrophages, cell types associated predominantly with chronic inflammation occurring over weeks or years. Chronic inflammatory diseases including rheumatoid arthritis, atherosclerosis, and metabolic syndrome are characterized by continued leukocyte infiltration into the inflammatory site, driven in large part by excessive chemokine production. Over years or decades, persistent inflammation may lead to loss of tissue architecture and function, causing severe disability or, in the case of atherosclerosis, fatal outcomes such as myocardial infarction or stroke. Despite the existence of several clinical strategies for targeting chronic inflammation, these diseases remain significant causes of morbidity and mortality globally, with a concomitant economic impact. Thus, the development of novel therapeutic agents for the treatment of chronic inflammatory disease continues to be a priority. In this review we introduce CC chemokine receptors as critical mediators of chronic inflammatory responses and explore their potential role as pharmacological targets. We discuss functions of individual CC chemokine receptors based on in vitro pharmacological data as well as transgenic animal studies. Focusing on three key forms of chronic inflammation--rheumatoid arthritis, atherosclerosis, and metabolic syndrome--we describe the pathologic function of CC chemokine receptors and their possible relevance as therapeutic targets.

Mechanisms and mediators of inflammation: potential models for skin rejection and targeted therapy in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an effective treatment option for patients suffering from limb loss or severe disfigurement. However, postoperative courses of VCA recipients have been complicated by skin rejection, and long-term immunosuppression remains a necessity for allograft survival. To widen the scope of this quality-of-life improving procedure minimization of immunosuppression in order to limit risks and side effects is needed. In some aspects, the molecular mechanisms and dynamics of skin allograft rejection seem similar to inflammatory skin conditions. T cells are key players in skin rejection and are recruited to the skin via activation of adhesion molecules, cytokines, and chemokines. Blocking these molecules has not only shown success in the treatment of inflammatory dermatoses, but also prolonged graft survival in various models of solid organ transplantation. In addition to T cell recruitment, ectopic lymphoid structures within the allograft associated with chronic rejection in solid organ transplantation might contribute to the strong alloimmune response towards the skin. Selectively targeting the molecules involved offers exciting novel therapeutic options in the prevention and treatment of skin rejection after VCA.

Cytomegalovirus CC chemokine promotes immune cell migration

Cytomegaloviruses manipulate the host chemokine/receptor axis by altering cellular chemokine expression and by encoding multiple chemokines and chemokine receptors. Similar to human cytomegalovirus (HCMV), rat cytomegalovirus (RCMV) encodes multiple CC chemokine-analogous proteins, including r129 (HCMV UL128 homologue) and r131 (HCMV UL130 and MCMV m129/130 homologues). Although these proteins play a role in CMV entry, their function as chemotactic cytokines remains unknown. In the current study, we examined the role of the RCMV chemokine r129 in promoting cellular migration and in accelerating transplant vascular sclerosis (TVS) in our rat heart transplant model. We determined that r129 protein is released into culture supernatants of infected cells and is expressed with late viral gene kinetics during RCMV infection and highly expressed in heart and salivary glands during in vivo rat infections. Using the recombinant r129 protein, we demonstrated that r129 induces migration of lymphocytes isolated from rat peripheral blood, spleen, and bone marrow and from a rat macrophage cell line. Using antibody-mediated cell sorting of rat splenocytes, we demonstrated that r129 induces migration of naïve/central memory CD4(+) T cells. Through ligand-binding assays, we determined that r129 binds rat CC chemokine receptors CCR3, CCR4, CCR5, and CCR7. In addition, mutational analyses identified functional domains of r129 resulting in recombinant proteins that fail to induce migration (r129-ΔNT and -C31A) or alter the chemotactic ability of the chemokine (r129-F43A). Two of the mutant proteins (r129-C31A and -ΔNT) also act as dominant negatives by inhibiting migration induced by wild-type r129. Furthermore, infection of rat heart transplant recipients with RCMV containing the r129-ΔNT mutation prevented CMV-induced acceleration of TVS. Together our findings indicate that RCMV r129 is highly chemotactic, which has important implications during RCMV infection and reactivation and acceleration of TVS.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

Blocking of CCR5 and CXCR3 suppresses the infiltration of macrophages in acute renal allograft rejection

BACKGROUND

The chemokine receptors CCR5 and CXCR3 are expressed by T cells and macrophages. We examined effects of a CCR5/CXCR3 antagonist (TAK), with a particular focus on the role of macrophages, in a rat kidney transplant model.

METHODS

Dark Agouti rat kidneys were transplanted into Lewis rats. The recipients were treated daily with a 10 mg/kg TAK on posttransplant days 0 to 14 and/or 2 mg/kg of cyclosporine A (CsA) on days 0 to 5. Graft survival, histological changes, and the expression of chemokines and chemokine receptors on T cells and macrophages were studied.

RESULTS

Treatment with TAK alone suppressed CD4+T cell infiltration and slightly prolonged graft survival. The expressions of both CCR5 and CXCR3, and activated macrophage-associated cytokines and chemokines, were significantly increased on macrophages that had been separated from rejecting kidneys, compared with those from spleens. However, these upregulations were decreased in macrophages from kidneys that had been treated with TAK. Immunohistochemistry also showed that macrophages infiltrating tubules of rejecting kidney expressed both receptors. In the CsA alone group, macrophages were the dominant infiltrating cells, and all allografts were rejected within 10 days. A combined therapy involving CsA and TAK resulted in decreased macrophage infiltration, and graft survival was substantially prolonged. The levels of activated macrophage-associated cytokines and chemokines were also decreased.

CONCLUSION

The dual blocking of CCR5/CXCR3 can be useful in decreasing rejection, with or without CsA. This mechanism acts, not only to block T-cell recruitment to a kidney graft but to suppress the infiltration of macrophages as well.

Macrophages and kidney transplantation

Macrophages are present within the transplanted kidney in varying numbers throughout its lifespan. Because of their prominence during acute rejection episodes, macrophages traditionally have been viewed as contributors to T-cell-directed graft injury. With growing appreciation of macrophage biology, it has become evident that different types of macrophages exist within the kidney, subserving a range of functions that include promotion or attenuation of inflammation, participation in innate and adaptive immune responses, and mediation of tissue injury and fibrosis, as well as tissue repair. A deeper understanding of how macrophages accumulate within the kidney and of what factors control their differentiation and function may identify novel therapeutic targets in transplantation.

Inhibition of chemokine-glycosaminoglycan interactions in donor tissue reduces mouse allograft vasculopathy and transplant rejection

BACKGROUND

Binding of chemokines to glycosaminoglycans (GAGs) is classically described as initiating inflammatory cell migration and creating tissue chemokine gradients that direct local leukocyte chemotaxis into damaged or transplanted tissues. While chemokine-receptor binding has been extensively studied during allograft transplantation, effects of glycosaminoglycan (GAG) interactions with chemokines on transplant longevity are less well known. Here we examine the impact of interrupting chemokine-GAG interactions and chemokine-receptor interactions, both locally and systemically, on vascular disease in allografts.

METHODOLOGY/PRINCIPAL FINDINGS

Analysis of GAG or CC chemokine receptor 2 (CCR2) deficiency were coupled with the infusion of viral chemokine modulating proteins (CMPs) in mouse aortic allograft transplants (n = 239 mice). Inflammatory cell invasion and neointimal hyperplasia were significantly reduced in N-deacetylase-N-sulfotransferase-1 (Ndst1(f/f)TekCre(+)) heparan sulfate (GAG)-deficient (Ndst1(-/-), p<0.044) and CCR2-deficient (Ccr2(-/-), p<0.04) donor transplants. Donor tissue GAG or CCR2 deficiency markedly reduced inflammation and vasculopathy, whereas recipient deficiencies did not. Treatment with three CMPs was also investigated; Poxviral M-T1 blocks CC chemokine receptor binding, M-T7 blocks C, CC, and CXC GAG binding, and herpesviral M3 binds receptor and GAG binding for all classes. M-T7 reduced intimal hyperplasia in wild type (WT) (Ccr2(+/+), p< or =0.003 and Ccr2(-/-), p

CONCLUSIONS/SIGNIFICANCE

Interruption of chemokine-GAG interactions, even in the absence of chemokine-receptor blockade, is a highly effective approach to reduction of allograft rejection, reducing vascular inflammation and prolonging allograft survival. Although chemokines direct both local and systemic cell migration, interruption of inherent chemokine responses in the donor tissue unexpectedly had a greater therapeutic impact on allograft vasculopathy.

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Key Words Collapse

MESH Headings

• Animals
• Aorta/drug effects
• Aorta/pathology
• Aorta/transplantation
• Cell Movement/drug effects
• Cell Proliferation/drug effects
• Chemokines/metabolism
• Chemokines/pharmacology
• Disease Models, Animal
• Glycosaminoglycans/metabolism
• Graft Rejection/complications
• Graft Rejection/enzymology
• Graft Rejection/immunology
• Hyperplasia
• Inflammation/complications
• Inflammation/pathology
• Kidney Transplantation
• Mice
• Mice, Inbred BALB C
• Mice, Inbred C57BL
• Receptors, CCR2/deficiency
• Receptors, CCR2/metabolism
• Sulfotransferases/deficiency
• Sulfotransferases/metabolism
• Survival Analysis
• Tissue Donors
• Transplantation, Homologous
• Tunica Intima/drug effects
• Tunica Intima/pathology
• Vascular Diseases/complications
• Vascular Diseases/enzymology
• Vascular Diseases/immunology
• Vascular Diseases/pathology
• Viral Proteins/pharmacology

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Grants

• RC1 HL100202 NHLBI NIH HHS
• 1RC1HL100202-01 NHLBI NIH HHS
• MOP 577578 CIHR

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Affiliation(s)

Erbin Dai Vascular Biology Research Group, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Li-Ying Liu Vascular Biology Research Group, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Hao Wang Departments of Medicine and Surgery, and Microbiology and Immunology, The University of Western Ontario, London, Ontario, Canada
Dana McIvor Departments of Medicine and Surgery, and Microbiology and Immunology, The University of Western Ontario, London, Ontario, Canada
Yun ming Sun Vascular Biology Research Group, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada Viron Therapeutics, Inc., London, Ontario, Canada
Colin Macaulay Viron Therapeutics, Inc., London, Ontario, Canada
Elaine King Viron Therapeutics, Inc., London, Ontario, Canada
Ganesh Munuswamy-Ramanujam Vascular Biology Research Group, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Mee Yong Bartee Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Jennifer Williams Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Jennifer Davids Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Israel Charo Gladstone Institute, San Francisco, California, United States of America
Grant McFadden Departments of Medicine and Surgery, and Microbiology and Immunology, The University of Western Ontario, London, Ontario, Canada Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America
Jeffrey D. Esko Department of Cellular and Molecular Medicine, University of California San Diego, San Diego, California, United States of America
Alexandra R. Lucas Vascular Biology Research Group, Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada Departments of Medicine and Surgery, and Microbiology and Immunology, The University of Western Ontario, London, Ontario, Canada Division of Cardiovascular Medicine, University of Florida, Gainesville, Florida, United States of America Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, United States of America

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CC chemokine receptor-1 activates intimal smooth muscle-like cells in graft arterial disease

BACKGROUND

Graft arterial disease (GAD) limits long-term solid-organ allograft survival. The thickened intima in GAD contains smooth muscle-like cells (SMLCs), leukocytes, and extracellular matrix. The intimal SMLCs in mouse GAD lesions differ from medial smooth muscle cells in their function and phenotype. Although intimal SMLCs may originate by migration and modulation of donor medial cells or by recruitment of host-derived precursors, the mechanisms that underlie their localization within grafts and the factors that drive these processes remain unclear.

METHODS AND RESULTS

This study of aortic transplantation in mice demonstrated an important function for chemokines beyond their traditional role in leukocyte recruitment and activation. Intimal SMLCs, but not medial smooth muscle cells, express functional CC chemokine receptor-1 (CCR1) and respond to RANTES by increased migration and proliferation. Although RANTES infusion in vivo promoted inflammatory cell accumulation in the adventitia of aortic allografts of wild-type and CCR1-deficient recipients, it increased GAD intimal thickening with SMLC proliferation in only the wild-type hosts. Aortic allografts transplanted into CCR1-deficient mice after wild-type bone marrow transplantation did not develop intimal lesions, which indicates that CCR1-bearing inflammatory cells do not contribute to intimal lesion formation. Moreover, RANTES induced SMLC proliferation in vitro but did not promote medial smooth muscle cell growth. Blockade of CCR5 attenuated RANTES-induced T-cell and monocyte/macrophage proliferation but did not affect RANTES-induced SMLC proliferation, consistent with a larger role of CCR1-binding chemokines in SMLC migration and proliferation and GAD development.

CONCLUSIONS

These studies provide a novel mechanistic insight into the formation of vascular intimal hyperplasia and suggest a novel therapeutic strategy for preventing allograft arteriopathy.

Engineering the glycosaminoglycan-binding affinity, kinetics and oligomerization behavior of RANTES: a tool for generating chemokine-based glycosaminoglycan antagonists

Binding to glycosaminoglycans (GAGs) is a necessary prerequisite for the biological activity of the proinflammatory chemokine RANTES in vivo. We have applied protein engineering methods to modulate equilibrium-binding affinity as well as binding kinetics of RANTES towards its GAG ligand which also altered the chemokine's oligomerization behavior. Out of 10 mutants, A22K and H23K were chosen for further in vitro and in vivo characterization because their stability was comparable with wild-type (wt) RANTES. In chemical cross-linking experiments, A22K gave higher and H23K lower molecular weight aggregates compared with wtRANTES as shown on SDS-PAGE. All mutants contained an N-terminal methionine residue, a well-described G-protein-coupled receptor (GPCR) antagonistic modification, which resulted in the mutants' inability to induce monocyte chemotaxis. In surface plasmon resonance experiments using immobilized heparan sulfate (HS) and physiological buffer conditions, Met-RANTES exhibited a significantly longer residual time on the GAG chip compared with the other RANTES variants. In Scatchard plot analysis, RANTES gave a bi-phasic, bell-shaped curve suggesting 'creation' of ligand-binding sites on the protein during HS interaction. This was not observed in the mutants' Scatchard plots which gave K(d) values of 317.5 and 44.5 nM for the A22K and H23K mutants, respectively. The mutants were subsequently tested for their inhibitory effect in a rat model of autoimmune uveitis where only H23K exhibited a transient improvement of the clinical disease score. H23K is therefore proposed to be a GPCR-inactive GAG antagonist which displaces the wt chemokine from its natural HS-proteoglycan co-receptor. The protein engineering approach presented here opens new ways for the treatment of RANTES-related diseases.

Chemokines and transplant vasculopathy

Transplant vasculopathy (TV) remains the leading cause of late death among heart transplant recipients. Transplant vasculopathy is characterized by progressive neointimal proliferation, leading to ischemic failure of the allograft. Multiple experimental and clinical studies have shown that injury to the graft at various stages of transplantation can be a risk factor for development of transplant vasculopathy. The hallmark of cardiac allograft injury is the infiltration of leukocytes. Recruitment of leukocytes requires intercellular communication between infiltrating cells, endothelium, parenchymal cells, and components of extracellular matrix. These events are mediated via the generation of adhesion molecules, cytokines, and chemokines. The chemokines, by virtue of their specific cell receptor expression, can selectively mediate the local recruitment/activation of distinct leukocytes/cells, allowing for migration across the endothelium and beyond the vascular compartment. This report provides a comprehensive review of the chemokines that participate in the development of transplant vasculopathy.

The role of chemokines in transplant graft arterial disease

Despite the development of effective immunosuppressive therapy, transplant graft arterial disease (GAD) remains the major limitation to long-term graft survival. Multiple immune and nonimmune risk factors contribute to this vasculopathic intimal hyperplastic process. Thus, initial interplay between host inflammatory cells and donor endothelial cells triggers alloimmune responses, whereas alloantigen-independent factors such as prolonged ischemia, surgical manipulation, ischemia-reperfusion injury, and hyperlipidemia enhance the antigen-dependent events. Intrinsic to all stages of this process are chemokines, a family of 8- to 10-kDa proteins mediating directional migration of immune cells to sites of inflammation and injury. Beyond their role in immune-cell chemotaxis, chemokines also contribute to cellular activation, vascular remodeling, and angiogenesis. Expression of chemokines and their cognate receptors in allografts correlates with acute organ rejection, as well as GAD. Moreover, chemokine or chemokine receptor blockade prolongs graft survival and attenuates GAD in experimental models. Further studies will likely confirm a substantial utility for antichemokine therapy in human organ transplantation.

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.

Kidney transplantation: mechanisms of rejection and acceptance

We describe the molecular and cellular mechanisms believed to be responsible for the rejection of renal allografts, including acute T cell-mediated rejection, acute antibody-mediated (humoral) rejection, rejection mediated by the innate immune system, and chronic rejection. We present mechanisms of graft acceptance, including accommodation, regulation, and tolerance. Studies in animals have replicated many pathologic features of acute and chronic rejection. We illuminate the pathogenesis of human pathology by reflection from experimental models.

Inhibition of MCP-1/CCR2 signaling does not inhibit intimal proliferation in a mouse aortic transplant model

BACKGROUND

Transplant arteriopathy is the leading cause of long term morbidity and mortality following heart transplantation. Animal models have demonstrated that monocyte chemoattractant protein (MCP)-1 is induced early after transplant in cardiac and aortic allografts. We have previously reported that deficiency of MCP-1 or its receptor, CC chemokine receptor 2 (CCR2), is associated with a reduction in intimal proliferation in a mouse femoral artery injury model. Using knockout mice, we have now examined the role of MCP-1 and CCR2 in the development of the intimal proliferation of transplant arteriopathy.

METHODS

C57Bl/6 CCR2 and MCP-1 wild-type and knockout mice were used in the studies and aortic transplants were performed between Balb/c mice and C57Bl/6 mice. Aortas from recipient animals were harvested 8 weeks after transplant.

RESULTS

Unlike arterial injury, in an aortic transplant model inhibition of MCP-1/CCR2 signaling did not result in reduced intimal proliferation.

CONCLUSIONS

Despite a pathology that appears similar, the inflammatory mediators that regulate transplant arteriopathy differ from those regulating intimal proliferation secondary to wire injury. Our results suggest that targeting MCP-1/CCR2 signaling is not sufficient to block transplant arteriopathy across a complete MHC-mismatch barrier.

CCR1/CCL5 (RANTES) receptor-ligand interactions modulate allogeneic T-cell responses and graft-versus-host disease following stem-cell transplantation

Acute graft-versus-host disease (GVHD) and leukemic relapse are serious complications of allogeneic stem-cell transplantation (SCT). Recruitment of activated T cells to host target tissues or sites of leukemic infiltration (graft-versus-leukemia [GVL]) is likely mediated by chemokine receptor-ligand interactions. We examined the contribution of donor cell CCR1 expression to the development of GVHD and GVL using a well-established murine SCT model (B6 --> B6D2F1) and CCR1-deficient mice (CCR1(-/-)). Allo-SCT with CCR1(-/-) donor cells significantly reduced systemic and target organ GVHD severity, and CCR1 expression on both T cells and accessory cells contributed to GVHD mortality. Significant GVL activity was preserved following CCR1(-/-) SCT, but the survival advantage diminished with increasing tumor burden. We then explored the effects of CCR1 expression on allo-specific T-cell responses. Although cytolytic effector function was maintained on a per-cell basis, T-cell proliferation and IFNgamma secretion were significantly reduced both in vivo and in vitro. T-cell function was partially dependent on interactions between CCR1 and CCL5. Collectively, these data demonstrate that CCR1 expression on donor cells contributes to the development of both GVHD and GVL, and suggest that CCR1/CCL5 receptor-ligand interactions modulate allo-specific T-cell responses occurring in this context.

CCR5 Blockade Modulates Inflammation and Alloimmunity in Primates

Pharmacologic antagonism of CCR5, a chemokine receptor expressed on macrophages and activated T cells, is an effective antiviral therapy in patients with macrophage-tropic HIV infection, but its efficacy in modulating inflammation and immunity is only just beginning to be investigated. In this regard, the recruitment of CCR5-bearing cells into clinical allografts is a hallmark of acute rejection and may anticipate chronic rejection, whereas conventionally immunosuppressed renal transplant patients homozygous for a nonfunctional Delta32 CCR5 receptor rarely exhibit late graft loss. Therefore, we explored the effects of a potent, highly selective CCR5 antagonist, Merck's compound 167 (CMPD 167), in an established cynomolgus monkey cardiac allograft model. Although perioperative stress responses (fever, diminished activity) and the recruitment of CCR5-bearing leukocytes into the graft were markedly attenuated, anti-CCR5 monotherapy only marginally prolonged allograft survival. In contrast, relative to cyclosporine A monotherapy, CMPD 167 with cyclosporine A delayed alloantibody production, suppressed cardiac allograft vasculopathy, and tended to further prolong graft survival. CCR5 therefore represents an attractive therapeutic target for attenuating postsurgical stress responses and favorably modulating pathogenic alloimmunity in primates, including man.

Structure–activity relationships of novel, highly potent, selective, and orally active CCR1 antagonists

Design and synthesis of a series of 3-amino-4-(2-(2-(4-benzylpiperazin-1-yl)-2-oxoethoxy)phenylamino)cyclobutenedione derivatives as novel CCR1 antagonists are described. Structure-activity relationship studies led to the identification of compound 22, which demonstrated potent binding activity, functional antagonism of CCR1 as well as good species cross-reactivity. In addition, compound 22 also showed desirable pharmacokinetic profiles and was selected for in vivo studies in the mouse collagen-induced arthritis model.