RANTES/CCL5 polymorphisms as a risk factor for recurrent acute rejection

Circulating Donor-Specific Anti-HLA Antibodies Associate With Immune Activation Independent of Kidney Transplant Histopathological Findings

Despite the critical role of cytokines in allograft rejection, the relation of peripheral blood cytokine profiles to clinical kidney transplant rejection has not been fully elucidated. We assessed 28 cytokines through multiplex assay in 293 blood samples from kidney transplant recipients at time of graft dysfunction. Unsupervised hierarchical clustering identified a subset of patients with increased pro-inflammatory cytokine levels. This patient subset was hallmarked by a high prevalence (75%) of donor-specific anti-human leukocyte antigen antibodies (HLA-DSA) and histological rejection (70%) and had worse graft survival compared to the group with low cytokine levels (HLA-DSA in 1.7% and rejection in 33.7%). Thirty percent of patients with high pro-inflammatory cytokine levels and HLA-DSA did not have histological rejection. Exploring the cellular origin of these cytokines, we found a corresponding expression in endothelial cells, monocytes, and natural killer cells in single-cell RNASeq data from kidney transplant biopsies. Finally, we confirmed secretion of these cytokines in HLA-DSA-mediated cross talk between endothelial cells, NK cells, and monocytes. In conclusion, blood pro-inflammatory cytokines are increased in kidney transplant patients with HLA-DSA, even in the absence of histology of rejection. These observations challenge the concept that histology is the gold standard for identification of ongoing allo-immune activation after transplantation.

Analysis of 75 Candidate SNPs Associated With Acute Rejection in Kidney Transplant Recipients: Validation of rs2910164 in MicroRNA MIR146A

BACKGROUND

Identifying kidney allograft recipients who are predisposed to acute rejection (AR) could allow for optimization of clinical treatment to avoid rejection and prolong graft survival. It has been hypothesized that a part of this predisposition is caused by the inheritance of specific genetic variants. There are many publications reporting a statistically significant association between a genetic variant, usually in the form of a single-nucleotide polymorphism (SNP), and AR. However, there are additional publications reporting a lack of this association when a different cohort of recipients is analyzed for the same single-nucleotide polymorphism.

METHODS

In this report, we attempted to validate 75 common genetic variants, which have been previously reported to be associated with AR, using a large kidney allograft recipient cohort of 2390 European Americans and 482 African Americans.

RESULTS

Of those variants tested, only 1 variant, rs2910164, which alters the expression of the microRNA MIR146A, was found to exhibit a significant association within the African American cohort. Suggestive variants were found in the genes CTLA and TLR4.

CONCLUSIONS

Our results show that most variants previously reported to be associated with AR were not validated in our cohort. This shows the importance of validation when reporting the associations with complex clinical outcomes such as AR. Additional work will need to be done to understand the role of MIR146A in the risk of AR in kidney allograft recipients.

An in vitro model of antibody-mediated injury to glomerular endothelial cells: Upregulation of MHC class II and adhesion molecules

Chronic active antibody-mediated rejection is a major cause of allograft failure in kidney transplantation. Microvascular inflammation and transplant glomerulopathy are defining pathologic features of chronic active antibody-mediated rejection and are associated with allograft failure. However, the mechanisms of leukocyte infiltration and glomerular endothelial cell injury remain unclear. We hypothesized MHC class II ligation on glomerular endothelial cells (GEnC) would result in upregulation of adhesion molecules and production of chemoattractants. A model of endothelial cell activation in the presence of antibodies to MHC classes I and II was used to determine the expression of adhesion molecules and chemokines. Murine GEnC were activated with IFNγ, which upregulated gene expression of β2-microglobulin (MHC class I), ICAM1, VCAM1, CCL2, CCL5, and IL-6. IFNγ stimulation of GEnC increased surface expression of MHC class I, MHC class II, ICAM1, and VCAM1. Incubation with antibodies directed at MHC class I or class II did not further enhance adhesion molecule expression. Multispectral imaging flow cytometry and confocal microscopy demonstrated MHC molecules co-localized with the adhesion molecules ICAM1 and VCAM1 on the GEnC surface. GEnC secretion of chemoattractants, CCL2 and CCL5, was increased by IFNγ stimulation. CCL2 production was further enhanced by incubation with sensitized plasma. Endothelial activation induces de novo expression of MHC class II molecules and increases surface expression of MHC class I, ICAM1 and VCAM1, which are all co-localized together. Maintaining the integrity and functionality of the glomerular endothelium is necessary to ensure survival of the allograft. IFNγ stimulation of GEnC propagates an inflammatory response with production of chemokines and co-localization of MHC and adhesion molecules on the GEnC surface, contributing to endothelial cell function as antigen presenting cells and an active player in allograft injury.

HLA-DQ alloantibodies directly activate the endothelium and compromise differentiation of FoxP3high regulatory T lymphocytes

Development of donor-specific antibodies is associated with reduced allograft survival in renal transplantation. Recent clinical studies highlight the prevalence of human leukocyte antigen (HLA)-DQ antibodies amongst de novo donor-specific antibodies (DSAs), yet the specific contribution of these DSAs to rejection has not been examined. Antibody-mediated rejection primarily targets the microvasculature, so this study explored how patient HLA-DQ alloantibodies can modulate endothelial activation and so immunoregulation. HLA-DQ antibodies phosphorylated Akt and S6 kinase in microvascular endothelial cells. This activation prior to culture with alloreactive lymphocytes increased IL-6 and RANTES secretion. The antibody-mediated upregulation of IL-6 was indeed Akt-dependent. The binding of HLA-DQ antibodies to endothelial cells selectively reduced T cell alloproliferation and FoxP3^high Treg differentiation. In clinical studies, detection of HLA-DQ DSAs with other DSAs is associated with worse graft survival than either alone. Endothelial cells stimulated with HLA-DR and HLA-DQ antibodies showed a synergistic increase in pro-inflammatory cytokine secretion and a decrease in Treg expansion. HLA-DQ antibodies strongly promote pro-inflammatory responses in isolation and in combination with other HLA antibodies. Thus, our data give new insights into the pathogenicity of HLA-DQ DSAs.

Genetics of acute rejection after kidney transplantation

Treatment of acute rejection (AR) following kidney transplantation has improved in recent years, but there are still limitations to successful outcomes. This review article covers literature in regard to recipient and donor genetics of AR kidney and secondarily of liver allografts. Many candidate gene and some genome-wide association studies (GWASs) have been conducted for AR in kidney transplantation. Genetic associations with AR in kidney and liver are mostly weak, and in most cases, the associations have not been reproducible. A limitation in the study of AR is the lack of sufficiently large populations that account for population stratification to study the AR phenotype which in this era occurs in <10% of transplants. Furthermore, the AR phenotype has been difficult to define and the definitions of classifications have evolved over time. Literature related to the pharmacogenomics of tacrolimus is robust and has been validated in many studies. Associations between gene expression and AR are emerging as markers of outcomes and AR classification. In the future, combinations of pretransplant genotype for AR risk prediction, genotype-based immune suppressant dosing, and pharmacogenomic markers to select AR maintenance or treatment and expression markers from biopsies may provide valuable clinical tools for guiding treatment.

Impact of genetic variations in C-C chemokine receptors and ligands on infectious diseases

Chemokine receptors and ligands are crucial for extensive immune response against infectious diseases such as malaria, leishmaniasis, HIV and tuberculosis and a wide variety of other diseases. Role of chemokines are evidenced in the activation and regulation of immune cell migration which is important for immune response against diseases. Outcome of disease is determined by complex interaction among pathogen, host genetic variability and surrounding milieu. Variation in expression or function of chemokines caused by genetic polymorphisms could be associated with attenuated immune responses. Exploration of chemokine genetic polymorphisms in therapeutic response, gene regulation and disease outcome is important. Infectious agents in human host alter the expression of chemokines via epigenetic alterations and thus contribute to disease pathogenesis. Although some fragmentary data are available on chemokine genetic variations and their contribution in diseases, no unequivocal conclusion has been arrived as yet. We therefore, aim to investigate the association of CCR5-CCL5 and CCR2-CCL2 genetic polymorphisms with different infectious diseases, transcriptional regulation of gene, disease severity and response to therapy. Furthermore, the role of epigenetics in genes related to chemokines and infectious disease are also discussed.

Frequency of RANTES gene polymorphisms and their association with incidence of malaria: a longitudinal study on children in Iganga district, Uganda

BACKGROUND

The severity and outcome of malaria is influenced by host immunity in which chemokines such as Regulated upon Activation, Normal T cell Expressed and Secreted (RANTES) play an important role. Previous studies show that variations in the RANTES gene affect RANTES protein production, hence altering host immunity. In this study, the relationship between presence of mutations in RANTES and incidence of malaria in a cohort of children living in a malaria-endemic area of Uganda was determined.

METHODS

This was a longitudinal study comprising of 423 children aged between 6 months and 9 years, who were actively followed up for 1 year. Malaria episodes occurring in the cohort children were detected and the affected children treated with national policy drug regimen. Mutations in the RANTES gene were determined by PCR-RFLP method and their frequencies were calculated. A multivariate negative binomial regression model was used to estimate the impact of RANTES mutations on malaria incidence. In all statistical tests, a P-value of <0.05 was considered as significant.

RESULTS

The frequencies of the -403A and In1.1C allele were 53.7 and 19.2 %, respectively. No mutations were found at the -28 locus. After adjustment of incidence rates for age, blood group, insecticide-treated bed net (ITN) use, malaria history and the sickle cell trait, 1n1.1T/C heterozygotes and homozygotes showed a non-significant trend towards higher incidence rates compared to wild-type individuals (IRR = 1.10; P = 0.55 and IRR = 1.25; P = 0.60, respectively). Similarly, there was no significant difference in malaria incidence rates between RANTES -403G/A heterozygotes or homozygotes and those without mutations (IRR = 1.09; P = 0.66 and IRR = 1.16; P = 0.50, respectively). No relation was seen between RANTES polymorphisms, baseline parasite densities and the time to first re-infection after administration of anti-malaria drugs.

CONCLUSIONS

This study showed that the -403A mutation occurs in nearly half of the study population and the In1.1C allele occurs in one in every four children. Despite the high frequency of these mutations, there was no clear association with malaria incidence. Other studies evaluating more markers, that could potentially modulate RANTES gene transcription alongside other genetic modifiers of malaria susceptibility, may provide further explanations to these less dramatic findings.

Gene transfer of the S24F regulated on activation normal T-cell expressed and secreted-chemokine ligand 5 variant attenuates cardiac allograft rejection

BACKGROUND

Regulated on activation normal T-cell expressed and secreted (RANTES)-chemokine ligand 5 plays a key role in mediating heart transplant rejection. Suppression of RANTES-mediated signals can reduce leukocyte recruitment and mitigate transplant rejection severity. The present study describes the construction of an adenovirus overexpression vector encoding a natural S24F RANTES variant as a means of reducing leukocyte recruitment, resulting in the prevention of allograft rejection.

METHODS

The in vitro transendothelial chemotaxis assay was used to compare RANTES-induced transmigration of peripheral blood mononuclear cells across human umbilical vein endothelial cells cultured on the upper Transwell chamber. Intracoronary delivery of Ad-S24F, Ad-Null, or phosphate-buffered saline was performed in BALB/c donor hearts that were transplanted into the abdominal cavity of C57BL/6 recipients as a measure of allograft survival. Intragraft inflammatory cell infiltrates and associated proinflammatory cytokine expression profiles were detected by immunohistochemistry and quantitative real-time polymerase chain reaction on day 6 after transplantation, respectively.

RESULTS

Regulated on activation normal T-cell expressed and secreted-induced peripheral blood mononuclear cell transendothelial chemotaxis is inhibited by S24F (Ad-S24F, 9.2%±0.02%; Ad-Null, 17.7%±0.02%; medium control, 15.1%±0.01%; P<0.05). Cardiac allograft survival was prolonged after delivery of 1×10 plaque-forming units of Ad-S24F (13.00±0.33 days compared with 9.38±0.60 and 9.00±0.38 days after Ad-Null or phosphate-buffered saline treatment, respectively, P<0.05). S24F gene transfer reduced the number of intragraft CD8 T lymphocytes, monocyte-macrophages, and T-cell receptor αβ cell infiltrates (P<0.05) and decreased transcripts for RANTES and interferon-γ (P<0.05).

CONCLUSION

S24F is an important component of the chemokine network involved in regulating the biologic activity of RANTES, and its expression can be used in the prevention and treatment of cardiac allograft rejection.

Role of regulated upon activation normal T-cell expressed and secreted in a model of retransplantation acute rejection mediated by alloreactive memory CD4+ T cells

BACKGROUND

It is unknown what role Regulated Upon Activation Normal T-Cell Exposed and Secreted may play in retransplantation or T-cell memory-transfer models. The experiment observed the influence of the chemokine RANTES in a mouse model of acute cardiac allograft rejection induced by adoptive transfer of alloreactive CD4(+) memory T (Tm) cells.

METHODS

Alloreactive CD4(+) Tm cells from spleens of skin-grafted C57BL/6 were adoptively transferred to naïve C57BL/6 recipients prior to heterotopic heart transplantation. We measured the median survival time of cardiac grafts and performed some tests.

RESULTS

Spleens from skin-grafted C57BL/6 contained 26.83% CD4(+) Tm cells. The median graft survival time of heterotopic heart transplantations (n = 6) was 5.17 ± 0.17 days for hosts receiving CD4(+) Tm cells compared with 7.76 ± 0.21 days among controls (n = 6; P < .001). The mean rejection activity in histological sections of cardiac allografts at day 5 postgrafting was 3.92 ± 0.08 in the CD4(+) Tm cell recipient group (n = 6) compared with 2.67 ± 0.14 in the controls (n = 6; P < .001). Gene expression of Ccl5, interferon (IFN)-γ and interleukin2 was significantly higher among CD4(+) Tm recipients compared with controls. Serum concentrations of RANTES and IFN-γ were higher in the heterotopic heart transplantation group receiving CD4(+) Tm compared with controls.

CONCLUSIONS

Alloreactive CD4(+) Tm cells contribute to increased expression and secretion of RANTES, and to the Tm and other inflammatory cells migration into the graft.

Toll-like receptor 4 in experimental kidney transplantation: early mediator of endogenous danger signals

The role of toll-like receptors (TLRs) has been described in the pathogenesis of renal ischemia/reperfusion injury, but data on the expression and function of TLR4 during renal allograft damage are still scarce. We analyzed the expression of TLR4 in an experimental rat model 6 and 28 days after allogeneic kidney transplantation in comparison to control rats and rats after syngeneic transplantation. On day 6, a significant induction in TLR4 expression--restricted to the glomerular compartment--was found in acute rejecting allografts only. TLR4 expression strongly correlated with renal function, and TLR4 induction was accompanied by a significant increase in CC chemokine expression within the graft as well as in urinary CC chemokine excretion. TLR4 induction may be caused by an influx of macrophages as well as TLR4-expressing intrinsic renal cells. Fibrinogen deposition in renal allografts correlated with renal TLR4 expression and may act as a potent stimulator of chemokine release via TLR4 activation. This study provides, for the first time, data about the precise intrarenal localization and TLR4 induction after experimental kidney transplantation. It supports the hypothesis that local TLR4 activation by endogenous ligands may be one pathological link from unspecific primary allograft damage to subsequent chemokine release, infiltration and activation of immune cells leading to deterioration of renal function and induction of renal fibrosis.

Validation of single nucleotide polymorphisms associated with acute rejection in kidney transplant recipients using a large multi-center cohort

There have been numerous reports proposing a statistically significant association between a genetic variant, usually in the form of a single nucleotide polymorphism (SNP), and acute rejection (AR). Unfortunately, there are additional publications reporting a lack of association with AR when a different cohort of recipients was analyzed for the same SNP. The objective of this report was to attempt replication of these published finding in our own kidney allograft recipient cohort. We analyzed 23 genetic variants, previously reported to have a significant association with AR, using a cohort of 969 clinically well-defined kidney transplant recipients. Only one SNP, rs6025 (Leiden mutation), within the coagulation factor V gene, showed a significant association with a P-value of 0.011 in a race-adjusted analysis and a P-value of 0.0003 in multiple variable analysis. An additional SNP, rs11706052 in IMPDH2, gave a modest P-value of 0.044 using multiple variable analysis, which is not significant when multiple testing is taken into consideration. Our results suggest that careful validation of previously reported associations with AR is necessary, and different strategies other than candidate gene studies can help to identify causative genetic variants associated with AR.

A comprehensive genotype-phenotype interaction of different Toll-like receptor variations in a renal transplant cohort

To date, the impact of the TLR (Toll-like receptor) system on early and late kidney transplantation outcome, such as ARE (acute rejection episodes) or cardiovascular morbidity and mortality, has still not been elucidated conclusively. Genetically determined alterations in TLR expression exhibit a possibility to evaluate their role in transplantation. In the present study, we sought to determine a comprehensive genotype-phenotype association with early and late allograft outcomes. We studied 11 SNPs (single nucleotide polymorphisms) in TLR2, TLR3, TLR4, TLR5, TLR9 and within a co-molecule CD14 in 265 patients receiving their first kidney transplant and the association of these with the occurrence of DGF (delayed graft function), ARE or MACE (major adverse cardiovascular events). ARE were significantly more frequent in patients carrying the TLR3 TT/CT allele (43.8 compared with 25.8%; P=0.001) as were rates of DGF (21.4 compared with 12.0%; P=0.030). Furthermore, TLR9 was significantly involved in the occurrence of MACE (TLR9 -1237; P=0.030). Interestingly, there was no significant effect of any TLR polymorphism on graft survival or renal function and the incidence of any infection, including CMV (cytomegalovirus) infection. In conclusion, our present study in renal transplant recipients suggests that the TLR system may be involved in both acute rejection and MACE. Modulation of the TLR system may be a promising target in future therapeutic strategies.

The impact of eNOS, MTR and MTHFR polymorphisms on renal graft survival in children and young adults

BACKGROUND

The main cause of reduced long-term graft survival is chronic allograft injury. Cardiovascular risk factors such as hyperhomocysteinaemia, accumulation of asymmetric dimethylarginine, increased oxidative stress and decreased production of nitric oxide seem to play an important role. Functional polymorphisms of the endothelial isoform of nitric oxide synthase (NOS) gene cause an alteration in nitric oxide production. Nitric oxide levels, and thus oxidative stress, are also influenced by hyperhomocysteinaemia.

METHODS

We carried out a genetic analysis of endothelial nitric oxide synthase (eNOS) 894G>T, methionine synthase (MTR) 2756A>G and methylenetetrahydrofolate reductase (MTHFR) 677C>T/1298A>C in 268 renal allograft recipient/donor (D/R) matches, with respect to long-term graft survival.

RESULTS

While MTHFR 677C>T/1298A>G and MTR 2756A>G polymorphism distribution in both recipients (R) and donors (D) showed no significant difference between matches with loss of graft function and those with long-term graft survival, the frequency of the eNOS 894TT genotype of donors was significantly increased (P = 0.040) in matches with better graft survival. The multivariate analysis identified the eNOS 894 genotype and clinically acute rejection episodes as independent risk factors for graft loss (P = 0.0406 and P = 0.0093, respectively).

CONCLUSIONS

The association between eNOS 894G>T polymorphism of donors and graft survival seems to suggest a role for this gene in chronic allograft injury; however, further studies are needed to confirm this hypothesis.

The impact of immune gene polymorphisms in kidney and liver transplantation

Since the completion of the Human Genome Project, it has become clear that genetic variation exists among individuals that can affect functional gene expression. This finding raises the possibility that differences in genetic phenotypes may account for the interindividual responses seen in the context of the alloimmune response. This review highlights studies examining the relative role of immunologic gene polymorphism in the context of renal and liver transplant outcomes (eg, acute rejection and graft survival). Furthermore, it examines the limitations and pitfalls in the study designs and concludes with the potential of single nucleotide polymorphism analysis in the future care of transplant recipients.

Copy number variation in the CCL4L gene is associated with susceptibility to acute rejection in lung transplantation

Lung transplantation (LT) has become an accepted therapy for selected patients with advanced lung disease. One of the main limitations to successful LT is rejection of the transplanted organ where chemokines are pivotal mediators. Here, we test the relationship between copy number variation (CNV) in the CCL4L chemokine gene and rejection risk in LT patients (n=161). Patients with no acute rejection showed a significantly lower mean number of CCL4L copies than patients that showed acute rejection (1.66 vs 1.96, P=0.014), with an even greater number of gene copies seen in patients with more than one episode of acute rejection (1.66 vs 2.30, P=0.001). Additionally, patients with > or =2 CCL4L copies had a significantly higher risk of acute rejection compared with patients that had 0-1 CCL4L copies (odds ratio 2.65; 95% confidence interval, 1.33-5.28; P=0.0046). A combined analysis of CCL4L CNV and the rs4796195 CCL4L single nucleotide polymorphism demonstrated that the effect of CCL4L copy number in acute rejection is mainly because of the number of copies of the CCL4L1 allelic variant. This finding constitutes the first report of CNV as a correlate factor in allograft rejection.

Genetic prediction of renal transplant outcome

PURPOSE OF REVIEW

In the present study, we reviewed recent publications regarding potential genetic predictors of transplant outcome, including acute rejection, metabolism of immunosuppressive medications, long-term transplant outcome, and posttransplant complications.

RECENT FINDINGS

Recent studies are based on the candidate gene analysis; specifically, cytokine genes and innate immune response molecules present popular targets for studies of acute rejection and long-term outcome. Pharmacogenomic studies are mostly focused on the genes of drug targets or the corresponding enzymes metabolizing the drug. Posttransplant complications (i.e. infections, diabetes, and malignancies) are associated with a variety of genes of different pathways. Most of the studies are based on just recipient, but not donor, genotype analysis. Positive results are balanced by reports of no association when evaluating the same genetic polymorphisms. Some of the reports might be affected by insufficient study design, including small sample size, lack of adjustment for potential confounders, and multiple comparisons.

SUMMARY

The field remains controversial because of differences in populations, study design, and statistical methods. Studies are based on candidate gene analysis; however, genome-wide association studies are lacking. Future research should be directed at better designed studies, larger sample size, evaluating both recipients and donors, and implementation of genome-wide association studies.

Genetic polymorphisms and the fate of the transplanted organ

There has been an abundance of publications describing genetic variability in molecules affecting innate and adaptive immunity, pharmacogenetics, and other nonimmunological factors like the renin-angiotensin aldosterone system, coagulation, and fibrosis markers. Studies indicated some associations between polymorphisms in these candidate genes with outcomes in organ transplantation and underlined a potential role of genetic variability in transplantation. To be clinically applicable, large prospective studies must be performed to better define the potential benefits of genotyping on these genetic markers and clinical outcomes. The purposes of this review are to summarize recent data describing associations of polymorphisms in both immunological and nonimmunological molecules with transplant outcomes, with a particular emphasis on renal transplantation, and discuss limitations and clinical implications.