Predominance of intraglomerular T-bet or GATA3 may determine mechanism of transplant rejection

Programmed T cell differentiation: Implications for transplantation

While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.

Characterization of eomesodermin and T-bet expression by allostimulated CD8+ T cells of healthy volunteers and kidney transplant patients in relation to graft outcome

Memory T cell (Tmem) responses play a critical role in the outcome of allo-transplantation. While the role of the T-box transcription factor Eomesodermin (Eomes) in the maintenance of antigen-specific Tmem is well studied, little is known about Eomes⁺ CD8⁺ T cell responses after transplantation. We evaluated the phenotype and function of allo-reactive Eomes⁺ CD8⁺ T cells in healthy volunteers and kidney transplant patients and their relation to transplant outcome. High Eomes expression by steady-state CD8⁺ T cells correlated with effector and memory phenotype. Following allo-stimulation, the expression of both the T-box proteins Eomes and T-bet by proliferating cells increased significantly, where high expression of Eomes and T-bet correlated with higher incidence of allo-stimulated IFNγ⁺ TNFα⁺ CD8⁺ T cells. In patients with no subsequent rejection, Eomes but not T-bet expression by donor-stimulated CD8⁺ T cells, increased significantly after transplantation. This was characterized by increased Eomes^hi T-bet^-/lo and decreased Eomes^-/lo T-bet^hi CD8⁺ T cell subsets, with no significant changes in the Eomes^hi T-bet^hi CD8⁺ T cell subset. No upregulation of exhaustion markers programmed-death-1 (PD-1) and cytotoxic-T-lymphocyte-associated-antigen-4 (CTLA4) by donor-stimulated Eomes⁺ CD8⁺ T cells was observed. Before transplantation, in patients without rejection, there were higher incidences of Eomes^hi T-bet^-/lo , and lower incidences of Eomes^hi T-bet^hi and Eomes^-/lo T-bet^hi donor-stimulated CD8⁺ T cell subsets, compared to those with subsequent rejection. Overall, our findings indicate that high Eomes expression by allo-stimulated T-bet⁺ CD8⁺ T cells is associated with enhanced effector function, and that an elevated incidence of donor-stimulated CD8⁺ T cells co-expressing high levels of Eomes and T-bet before transplantation, may correlate with an increased incidence of acute cellular rejection.

Triptolide inhibits donor-specific antibody production and attenuates mixed antibody-mediated renal allograft injury

Donor-specific antibodies (DSAs) are major mediators of renal allograft injury, and strategies to inhibit DSAs are important in promoting long-term graft survival. Triptolide exhibits a wide spectrum of antiinflammatory and immunosuppressive activities, and in autoimmune diseases it inhibits autoantibody levels. In this study, we investigated the suppressive role of triptolide in the generation of DSAs in transplant recipients. We found that triptolide treatment of skin allograft recipients in mice significantly suppressed the development of circulating anti-donor-specific IgG and effectively alleviated DSA-mediated renal allograft injury, which led to prolonged allograft survival. In vitro studies revealed that triptolide inhibited the differentiation of B cells into CD138⁺ CD27⁺⁺ plasma cells; reduced the levels of IgA, IgG, and IgM secreted by plasma cells; and repressed somatic hypermutation and class switch recombination of B cells. Moreover, triptolide-treated recipients showed reduced numbers of B cells, plasma cells, and memory B cells in spleens and decreased numbers of T, B, natural killer (NK) cells, and macrophages infiltrating grafts. These findings highlight the importance of triptolide in suppressing DSAs and establish triptolide as a novel therapeutic agent for antibody-mediated allograft rejection.

Transplant glomerulopathy

In the renal allograft, transplant glomerulopathy represents a morphologic lesion and not a specific diagnosis. The hallmark pathologic feature is glomerular basement membrane reduplication by light microscopy or electron microscopy in the absence of immune complex deposits. Transplant glomerulopathy results from chronic, recurring endothelial cell injury that can be mediated by HLA alloantibodies (donor-specific antibodies), various autoantibodies, cell-mediated immune injury, thrombotic microangiopathy, or chronic hepatitis C. Clinically, transplant glomerulopathy may be silent, detectable on protocol biopsy, or present with overt manifestations, including up to nephrotic range proteinuria, hypertension, and declining glomerular filtration rate. In either case, transplant glomerulopathy is associated with reduced graft survival. This review details the morphologic features of transplant glomerulopathy found on light microscopy, immunofluorescence microscopy, and electron microscopy. The pathophysiology of the causes and risk factors are discussed. Clinical manifestations are emphasized and potential therapeutic modalities are examined.

In Vivo Attenuation of Antibody-Mediated Acute Renal Allograft Rejection by Ex Vivo TGF-β-Induced CD4+Foxp3+ Regulatory T Cells

Antibody-mediated rejection (AMR) has emerged as the major cause of renal allograft dysfunction, and more effective strategies need to be explored for improving transplant outcomes. Regulatory T cells (Tregs), consisting of at least natural and induced Treg subsets, suppress effector responses at multiple levels and play a key role in transplantation tolerance. In this study, we investigated the effect of induced Tregs (iTregs) on preventing antibody-mediated renal injury and rejection in a mouse model. We observed that infusion of iTregs markedly attenuated histological graft injury and rejection and significantly improved renal allograft survival. iTregs exhibited a comprehensive ability to regulate immunological disorders in AMR. First, iTreg treatment decreased the levels of circulating antidonor antibody and the antibody deposition within allografts. Second, iTregs significantly reduced cell infiltration including CD4⁺ T cells (including Th1, Th17, and Tfh), CD8⁺IFN-γ⁺ cells, natural killer cells, B cells, and plasma cells, which are involved in the process of AMR. Our results also highlight a predominance of M1 macrophage infiltration in grafts with acute AMR, and M1 macrophage could be reduced by iTreg treatment. Collectively, our data demonstrate, for the first time, that TGF-β-induced Tregs can attenuate antibody-mediated acute renal allograft injury through targeting multiple effectors. Thus, use of iTregs in prevention of AMR in clinical practice could be expected.

Unusual Proliferative Glomerulonephritis in a Patient Diagnosed to Have Hypoparathyroidism, Sensorineural Deafness, and Renal Dysplasia (HDR) Syndrome with a Novel Mutation in the GATA3 Gene

Hypoparathyroidism, sensorineural deafness, and renal dysplasia (HDR) syndrome is a rare autosomal dominant disease caused by GATA3 mutations. Although several cases with variable renal features have been reported, the presence of histological changes within the glomeruli in adult patients is unclear. We herein report an adult case of HDR syndrome with a novel p.C288W (TGC>TGG) missense mutation in GATA3. His renal histology showed a membranoproliferative glomerulonephritis-like glomerular lesion. Additional renal histological analyses of HDR syndrome patients will be needed to clarify the role of GATA3 in both the developing and adult kidney.

Predominant Tubular Interleukin-18 Expression in Polyomavirus-Associated Nephropathy

Polyomavirus-associated nephropathy (PVAN) occurs in a significant percentage of renal transplant recipients, with BK virus reactivation as the main causative agent. PVAN leads to tubular damage and may result in allograft loss. In this study, we analyzed the antiviral immune response in PVAN. Transcription of the proinflammatory cytokine interleukin-18 (IL-18) was significantly higher in PVAN biopsies compared with T cell-mediated rejection (TCMR) (1.42 ± 0.20 and 0.69 ± 0.10, respectively; *P = 0.0021). Tubular expression of IL-18 was significantly increased in PVAN compared with TCMR (2.00 ± 0.24 and 1.333 ± 0.13, respectively; *P = 0.028). In contrast, in TCMR, IL-18 was expressed predominantly by CD163-positive macrophages. These data suggest that the antiviral immune response in PVAN is partly coordinated by the tubular epithelium, whereas in TCMR, this may be controlled by inflammatory cells.

IL-6 Trans-Signaling Drives Murine Crescentic GN

The role of IL-6 signaling in renal diseases remains controversial, with data describing both anti-inflammatory and proinflammatory effects. IL-6 can act via classic signaling, engaging its two membrane receptors gp130 and IL-6 receptor (IL-6R). Alternatively, IL-6 trans-signaling requires soluble IL-6R (sIL-6R) to act on IL-6R-negative cells that express gp130. Here, we characterize the role of both pathways in crescentic nephritis. Patients with crescentic nephritis had significantly elevated levels of IL-6 in both serum and urine. Similarly, nephrotoxic serum-induced nephritis (NTN) in BALB/c mice was associated with elevated serum IL-6 levels. Levels of serum sIL-6R and renal downstream signals of IL-6 (phosphorylated signal transducer and activator of transcription 3, suppressor of cytokine signaling 3) increased over time in this model. Simultaneous inhibition of both IL-6 signaling pathways using anti-IL-6 antibody did not have a significant impact on NTN severity. In contrast, specific inhibition of trans-signaling using recombinant sgp130Fc resulted in milder disease. Vice versa, specific activation of trans-signaling using a recombinant IL-6-sIL-6R fusion molecule (Hyper-IL-6) significantly aggravated NTN and led to increased systolic BP in NTN mice. This correlated with increased renal mRNA synthesis of the Th17 cell cytokine IL-17A and decreased synthesis of resistin-like alpha (RELMalpha)-encoding mRNA, a surrogate marker of lesion-mitigating M2 macrophage subtypes. Collectively, our data suggest a central role for IL-6 trans-signaling in crescentic nephritis and offer options for more effective and specific therapeutic interventions in the IL-6 system.

Capillary dilation and rarefaction are correlated with intracapillary inflammation in antibody-mediated rejection

Antibody-mediated rejection (ABMR) remains one of the major causes of graft loss after renal transplantation. It is dominated by endothelial damage in microcirculation. Clarifying the mechanism of microcirculating damage is obviously a key step to understand the pathogenesis of ABMR. Here we characterized capillary variation in ABMR and its possible mechanisms. Compared with T cell-mediated rejection and stable grafts, there was a significant dilation and rarefaction in peritubular capillaries (PTCs) of the ABMR group; Image-Pro Plus revealed a significantly larger intra-PTC area. Interestingly, the dilation of PTCs was strongly correlated with the intra-PTC cell counting. Moreover, peritubular capillary inflammation is correlated with in situ T-bet expression, and there was a good correlation between the intra-PTC expression of T-bet and the PTC diameter. HIF-1α up-regulation could be observed in ABMR but it was not necessary for capillary dilation. In general, ABMR is characterized with early capillary dilation and rarefaction; our data confirmed that the dilation is strongly correlated with intracapillary inflammation, which in turn is correlated with in situ T-bet expression. T-bet plays an important role in the development of microcirculating injury, and thus it is a potential target for the treatment of ABMR.

The diagnostic value of transcription factors T-bet/GATA3 ratio in predicting antibody-mediated rejection

Background. Previous data showed that the predominance of intraglomerular T-bet or GATA3 is correlated with different mechanisms of rejection, suggesting that the ratio of T-bet/GATA3 might be used to distinguish antibody-mediated rejection (ABMR) and T-cell-mediated rejection (TCMR). Methods. We compared the intraglomerular T-bet/GATA3 ratio in ABMR and TCMR. The intragraft expression of T-bet and GATA3 was studied via immunohistochemistry. The correlation of the diagnosis of AMR with the ratio of T-bet/GATA3 was examined. Results. Both intraglomerular T-bet- and GATA3-expressing cells were increased during acute rejection. T-bet/GATA3>1 was strongly correlated with ABMR (93.3% versus 18.2%). The incidence of positive HLA-I/II antibodies and glomerulitis is significantly higher in T-bet/GATA3>1 group (P < 0.001, 0.013, resp.). The scores of peritubular capillary inflammation and glomerulitis were also higher in T-bet/GATA3>1 group (P = 0.052, P < 0.001, resp.). Nevertheless, T-bet/GATA3>1 is also correlated with C4d-negative ABMR and resistance to steroid treatment. Compared with C4d deposition, T-bet/GATA3>1 had a slight lower (90% versus 100%) specificity but a much higher (87.5% versus 68.8%) sensitivity. Conclusion. Our data suggested that intraglomerular predominance of T-bet over GATA3 might be used as diagnosis maker of ABMR in addition to C4d, especially in C4d-negative cases.

Late and chronic antibody-mediated rejection: main barrier to long term graft survival

Antibody-mediated rejection (AMR) is an important cause of graft loss after organ transplantation. It is caused by anti-donor-specific antibodies especially anti-HLA antibodies. C4d had been regarded as a diagnosis marker for AMR. Although most early AMR episodes can be successfully controlled or reversed, late and chronic AMR remains the leading cause of late graft loss. The strategies which work in early AMR have limited effect on late/chronic episodes. Here, we reviewed the lines of evidence that late/chronic AMR is the leading cause of late graft loss, characteristics of late AMR, and current strategies in managing late/chronic AMR. More effort should be put on the management of late/chronic AMR to make a better long term graft survival.

Immunophenotyping in BK virus allograft nephropathy distinct from acute rejection

Differentiating BK virus nephropathy (BKVN) from acute rejection (AR) is crucial in clinical practice, as both of them have interstitial inflammation in the grafts. The purpose of the study is to describe the inflammatory cellular constituents of BKVN and to determine the clinical utility of immunophenotyping findings in distinguishing BKVN from AR. In addition, the expression of the HLA-DR was investigated. Sixty-five renal allograft recipients were included in this study, including 22 cases of BKVN, 31 cases of AR, and 12 cases of stable allograft. Immunostaining for infiltrating lymphocytes showed that the number of CD20 cells (P < 0.001) and the percentages of CD3 (P < 0.001), CD4 (P = 0.004), CD8 (P = 0.005), and CD20 (P = 0.002) cells were all significantly different between BKVN and AR. Moreover, there were no statistically significant differences in tubule cell HLA-DR expression (P = 0.156). This observation suggests that the number of CD20 cells and the percentages of CD3, CD4, CD8, and CD20 cells in renal biopsies would aid the distinction between BKVN and AR. On the other hand, the presence of HLA-DR upregulation may not only be specific for acute rejection but also be a response to BKVN.

Intragraft gene expression in positive crossmatch kidney allografts: ongoing inflammation mediates chronic antibody-mediated injury

We studied intragraft gene expression profiles of positive crossmatch (+XM) kidney transplant recipients who develop transplant glomerulopathy (TG) and those who do not. Whole genome microarray analysis and quantitative rt-PCR were performed on RNA from protocol renal allograft biopsies in three groups: (1) +XM/TG+ biopsies before and after TG; (2) +XM/NoTG; and (3) negative crossmatch kidney transplants (control). Microarray comparisons showed few differentially expressed genes between paired biopsies from +XM/TG+ recipients before and after the diagnosis of TG. Comparing +XM/TG+ and control groups, significantly altered expression was seen for 2447 genes (18%) and 3200 genes (24%) at early and late time points, respectively. Canonical pathway analyses of differentially expressed genes showed inflammatory genes associated with innate and adaptive immune responses. Comparing +XM/TG+ and +XM/NoTG groups, 3718 probe sets were differentially expressed but these were over-represented in only four pathways. A classic accommodation phenotype was not identified. Using rt-PCR, the expression of inflammatory genes was significantly increased in +XM/TG+ recipients compared to the +XM/NoTG and control groups. In conclusion, pretransplant donor-specific anti-HLA antibodies results in a gene expression profile characterized by inflammation and cellular infiltration and the majority of +XM grafts are exposed to chronic injury.

A novel role for type 1 angiotensin receptors on T lymphocytes to limit target organ damage in hypertension

RATIONALE

Human clinical trials using type 1 angiotensin (AT(1)) receptor antagonists indicate that angiotensin II is a critical mediator of cardiovascular and renal disease. However, recent studies have suggested that individual tissue pools of AT(1) receptors may have divergent effects on target organ damage in hypertension.

OBJECTIVE

We examined the role of AT(1) receptors on T lymphocytes in the pathogenesis of hypertension and its complications.

METHODS AND RESULTS

Deficiency of AT(1) receptors on T cells potentiated kidney injury during hypertension with exaggerated renal expression of chemokines and enhanced accumulation of T cells in the kidney. Kidneys and purified CD4(+) T cells from "T cell knockout" mice lacking AT(1) receptors on T lymphocytes had augmented expression of Th1-associated cytokines including interferon-γ and tumor necrosis factor-α. Within T lymphocytes, the transcription factors T-bet and GATA-3 promote differentiation toward the Th1 and Th2 lineages, respectively, and AT(1) receptor-deficient CD4(+) T cells had enhanced T-bet/GATA-3 expression ratios favoring induction of the Th1 response. Inversely, mice that were unable to mount a Th1 response due to T-bet deficiency were protected from kidney injury in our hypertension model.

CONCLUSIONS

The current studies identify an unexpected role for AT(1) receptors on T lymphocytes to protect the kidney in the setting of hypertension by favorably modulating CD4(+) T helper cell differentiation.

Dialysis at a crossroads--Part II: A call for action

A previous commentary pointed out that the renal community has led American healthcare in the development and continuous improvement of quality outcomes. However, survival, hospitalization, and quality of life for US dialysis patients is still not optimal. This follow-up commentary examines the obstacles, gaps, and metrics that characterize this unfortunate state of affairs. It posits that current paradigms are essential contributors to quality outcomes but are no longer sufficient to improve quality. New strategies are needed that arise from a preponderance of evidence, in addition to beyond a reasonable doubt standard. This work offers an action plan that consists of new pathways of care that will lead to improved survival, fewer hospitalizations and rehospitalizations, and better quality of life for patients undergoing dialysis therapy. Nephrologists in collaboration with large and small dialysis organizations and other stakeholders, including the Centers for Medicare and Medicaid Services, can implement these proposed new pathways of care and closely monitor their effectiveness. We suggest that our patients deserve nothing less and must receive even more.