Donor-derived Cell-free DNA Identifies Antibody-mediated Rejection in Donor Specific Antibody Positive Kidney Transplant Recipients

BACKGROUND

Elevated levels of donor-derived cell-free DNA (dd-cfDNA) in the plasma of renal allograft recipients indicates organ injury and an increased probability of active rejection. Donor-specific antibodies (DSA) to HLA antigens are associated with risk of antibody-mediated rejection (ABMR). This study assessed the combined use of dd-cfDNA and DSA testing to diagnose active ABMR.

METHODS

Donor-derived cell-free DNA was assayed in 90 blood samples with paired DSA and clinically indicated biopsies from 87 kidney transplant patients. Sixteen cases met criteria for active ABMR. Performance characteristics of dd-cfDNA for diagnosis of active ABMR were determined for samples with prior or current positive DSA (DSA+, n = 33).

RESULTS

The median level of dd-cfDNA (2.9%) in DSA+ patients with active ABMR was significantly higher than the median level (0.34%) in DSA+ patients without ABMR (P < 0.001). The median level of dd-cfDNA in DSA- patients was 0.29%. The positive predictive value of dd-cfDNA (at 1%) to detect active ABMR in DSA+ patients was 81%, whereas the negative predictive value was 83%. The positive predictive value for DSA+ alone was 48%.

CONCLUSIONS

The combined use of dd-cfDNA and DSA testing may improve the noninvasive diagnosis of active ABMR in kidney transplant patients. Patients with dd-cfDNA+/ DSA+ results have a high probability of active ABMR.

Repetitive ischemic injuries to the kidneys result in lymph node fibrosis and impaired healing

The contribution of the kidney-draining lymph node (KLN) to the pathogenesis of ischemia-reperfusion injury (IRI) of the kidney and its subsequent recovery has not been explored in depth. In addition, the mechanism by which repetitive IRI contributes to renal fibrosis remains poorly understood. Herein, we have found that IRI of the kidney is associated with expansion of high endothelial venules (HEVs) and activation of fibroblastic reticular cells (FRCs) in the KLN, as demonstrated by significant expansion in the extracellular matrix. The lymphotoxin α signaling pathway mediates activation of FRCs, and chronic treatment with lymphotoxin β receptor-immunoglobulin fusion protein (LTβr-Ig) resulted in marked alteration of the KLN as well as augmentation of renal fibrosis. Depletion of FRCs reduced T cell activation in the KLN and ameliorated renal injury in acute IRI. Repetitive renal IRI was associated with senescence of FRCs, fibrosis of the KLN, and renal scarring, which were ameliorated by FRC administration. Therefore, our study emphasizes the critical role of FRCs in both the initiation and repair phases of injury following IRI of the kidney.

Designing natural and synthetic immune tissues

Vaccines and immunotherapies have provided enormous improvements for public health, but there are fundamental disconnects between where most studies are performed-in cell culture and animal models-and the ultimate application in humans. Engineering immune tissues and organs, such as bone marrow, thymus, lymph nodes and spleen, could be instrumental in overcoming these hurdles. Fundamentally, designed immune tissues could serve as in vitro tools to more accurately study human immune function and disease, while immune tissues engineered for implantation as next-generation vaccines or immunotherapies could enable direct, on-demand control over generation and regulation of immune function. In this Review, we discuss recent interdisciplinary strategies that are merging materials science and immunology to create engineered immune tissues in vitro and in vivo. We also highlight the hurdles facing these approaches and the need for comparison to existing clinical options, relevant animal models, and other emerging technologies.

Silk fibroin preserves beta cell function under inflammatory stress while stimulating islet cell surface GLUT2 expression

Silk fibroin is a novel biomaterial for enhancing transplanted islet cell function and survival. This study investigated whether silk fibroin may have unique properties that improve islet function in the face of inflammatory-mediated stress during transplantation. Murine islet function was tested in vitro with either silk fibroin or alginate and challenged with inflammatory cytokines. The glucose-stimulated insulin secretion index for all conditions decreased with inflammatory cytokines, but was better preserved for islets exposed to silk compared to those exposed to alginate or medium. GLUT2 transporter expression on the cell surface of islets exposed to silk was increased compared to alginate or medium alone. Upon cytokine stress, a greater percentage of islet cells exposed to silk expressed GLUT2 on their surface. We conclude that preconditioning islets with silk fibroin stimulates islet cell surface GLUT2 expression, an increase, which persists under inflammatory stress, and may improve islet engraftment and function after transplantation.

Improving Vaccine and Immunotherapy Design Using Biomaterials

Polymers, lipids, scaffolds, microneedles, and other biomaterials are rapidly emerging as technologies to improve the efficacy of vaccines against infectious disease and immunotherapies for cancer, autoimmunity, and transplantation. New studies are also providing insight into the interactions between these materials and the immune system. This insight can be exploited for more efficient design of vaccines and immunotherapies. Here, we describe recent advances made possible through the unique features of biomaterials, as well as the important questions for further study.

Reprogramming the Local Lymph Node Microenvironment Promotes Tolerance that Is Systemic and Antigen Specific

Many experimental therapies for autoimmune diseases, such as multiple sclerosis (MS), aim to bias T cells toward tolerogenic phenotypes without broad suppression. However, the link between local signal integration in lymph nodes (LNs) and the specificity of systemic tolerance is not well understood. We used intra-LN injection of polymer particles to study tolerance as a function of signals in the LN microenvironment. In a mouse MS model, intra-LN introduction of encapsulated myelin self-antigen and a regulatory signal (rapamycin) permanently reversed paralysis after one treatment during peak disease. Therapeutic effects were myelin specific, required antigen encapsulation, and were less potent without rapamycin. This efficacy was accompanied by local LN reorganization, reduced inflammation, systemic expansion of regulatory T cells, and reduced T cell infiltration to the CNS. Our findings suggest that local control over signaling in distinct LNs can promote cell types and functions that drive tolerance that is systemic but antigen specific.

BTLA+ Dendritic Cells: The Regulatory T Cell Force Awakens

The role of dendritic cells (DCs) in the induction of antigen-specific tolerance mediated by extrathymic regulatory T (Treg) cells remains incompletely defined. In this issue of Immunity, Jones et al. (2016) show that BTLA⁺DEC205⁺CD8⁺CD11c⁺ DCs efficiently induce peripheral Treg cells via the engagement of HVEM, a receptor for BTLA.

Surgical complications of laparoendoscopic single-site donor nephrectomy: a retrospective study

The single-port approach has been associated with an unacceptably high rate of umbilical port hernias in large series of patients undergoing single-port cholecystectomy and colectomy and with additional surgical risks thought secondary to technical and ergonomic limitations. A retrospective review of 378 consecutive laparoendoscopic single-site(LESS) donor nephrectomies performed between 04/15/2009 and 04/09/2014 was conducted. Twelve patients (3%) developed an umbilical hernia. Eleven (92%) were female and eight (73%) of these patients had a prior pregnancy. Hernias were reported 13.5 ± 6.9 months after donation, and the mean size was 5.1 ± 3.7 cm. Seven additional cases (1.9%) required a return to the operating room for internal hernia (2), evisceration (1), bleeding (1), enterotomy (1), and wound infection (2). The original incision was utilized for reexploration. One patient required emergent conversion to an open procedure for bleeding during the initial donation. There were no mortalities. Recipient patient and graft survival were 99% and 99% at 1 year, respectively. Although reports associated with earlier experiences with single-site procedures suggested an unacceptably high rate of hernias at the surgical site, this does not seem to be the case at our center. This technique is a reliable surgical technique for left donor nephrectomy at this institution.

Regulation of the Immune System by Laminins

Laminins are trimeric proteins that are major components of the basement membranes that separate endothelia and epithelia from the underlying tissue. Sixteen laminin isoforms have been described, each with distinct tissue expression patterns and functions. While laminins have a critical structural role, recent evidence also indicates that they also impact the migration and functions of immune cells. Laminins are differentially expressed upon immunity or tolerance and orientate the immune response. This review will summarize the structure of laminins, the modulation of their expression, and their interactions with the immune system. Finally, the role of the laminins in autoimmune diseases and transplantation will be discussed.

A robust in vitro model for trans-lymphatic endothelial migration

Trans-endothelial migration (TEM) is essential for leukocyte circulation. While much is known about trans-blood endothelial migration, far less is known about trans-lymphatic endothelial migration. We established an in vitro system to evaluate lymphatic TEM for various cell types across primary mouse and human lymphatic endothelial cells (LEC), and validated the model for the murine LEC cell line SVEC4-10. T cells exhibited enhanced unidirectional migration from the basal (abluminal) to the apical (luminal) surface across LEC, whereas for blood endothelial cells (BEC) they migrated similarly in both directions. This preferential, vectorial migration was chemotactic toward many different chemoattractants and dose-dependent. Stromal protein fibers, interstitial type fluid flow, distribution of chemokines in the stromal layer, and inflammatory cytokines influenced LEC phenotype and leukocyte TEM. Activated and memory CD4 T cells, macrophages, and dendritic cell (DC) showed chemoattractantΔdriven vectorial migration, while CD8 T cell migration across LEC was not. The system was further validated for studying cancer cell transmigration across lymphatic endothelium. This model for lymphatic TEM for various migrating and endothelial cell types possesses the capacity to be high-throughput, highly reproducible and integrate the complexities of lymphatic biology, stromal variability, chemoattractant distribution, and fluid flow.

Cell-Free DNA and Active Rejection in Kidney Allografts

Histologic analysis of the allograft biopsy specimen is the standard method used to differentiate rejection from other injury in kidney transplants. Donor-derived cell-free DNA (dd-cfDNA) is a noninvasive test of allograft injury that may enable more frequent, quantitative, and safer assessment of allograft rejection and injury status. To investigate this possibility, we prospectively collected blood specimens at scheduled intervals and at the time of clinically indicated biopsies. In 102 kidney recipients, we measured plasma levels of dd-cfDNA and correlated the levels with allograft rejection status ascertained by histology in 107 biopsy specimens. The dd-cfDNA level discriminated between biopsy specimens showing any rejection (T cell-mediated rejection or antibody-mediated rejection [ABMR]) and controls (no rejection histologically), P<0.001 (receiver operating characteristic area under the curve [AUC], 0.74; 95% confidence interval [95% CI], 0.61 to 0.86). Positive and negative predictive values for active rejection at a cutoff of 1.0% dd-cfDNA were 61% and 84%, respectively. The AUC for discriminating ABMR from samples without ABMR was 0.87 (95% CI, 0.75 to 0.97). Positive and negative predictive values for ABMR at a cutoff of 1.0% dd-cfDNA were 44% and 96%, respectively. Median dd-cfDNA was 2.9% (ABMR), 1.2% (T cell-mediated types ≥IB), 0.2% (T cell-mediated type IA), and 0.3% in controls (P=0.05 for T cell-mediated rejection types ≥IB versus controls). Thus, dd-cfDNA may be used to assess allograft rejection and injury; dd-cfDNA levels <1% reflect the absence of active rejection (T cell-mediated type ≥IB or ABMR) and levels >1% indicate a probability of active rejection.

Reepithelialization of Orthotopic Tracheal Allografts Prevents Rejection after Withdrawal of Immunosuppression

Prior work has demonstrated that immunosuppressed orthotopic tracheal allografts undergo progressive reepithelialization over a 48-day period with recipient-derived tracheal epithelium. We hypothesized that reepithelialization of tracheal allografts would prevent rejection after withdrawal of immunosuppression. BALB/c murine tracheal grafts were transplanted orthotopically into either syngeneic or allogeneic C57/BL6 recipients. The recipients were either not immunosuppressed, immunosuppressed with cyclosporine A (10 mg/kg per day) continuously, or immunosuppressed for 48 days and then withdrawn from immunosuppression. The grafts were assessed for acute and chronic rejection 10 days and 50 days after immunosuppression withdrawal. The immunosuppressed allograft recipients maintained a ciliated epithelium acutely and chronically after immunosuppression withdrawal. Ten days after immunosuppression withdrawal, there was a mild cellular infiltrate, which resolved 50 days after withdrawal. Electron microscopy, lymphocyte subpopulation assays, and lamina propria analysis demonstrated that immunosuppression withdrawal did not result in tracheal allograft rejection. In vitro and in vivo assessments did not demonstrate evidence of systemic or local immune tolerance. We conclude that reepithelialization of orthotopic tracheal allografts with recipient-derived mucosa prevents rejection of allograft segments. Tracheal transplantation may require only transient immunosuppression, which can be withdrawn after tracheal reepithelialization.

Th17 and Th1 play distinct roles in obliterative bronchiolitis pathogenesis after transplantation

Development of obliterative bronchiolitis (OB) is the biggest obstacle that limits long-term allograft survival and clinical application of lung transplantation. Mouse orthotopic trachea or lung transplantations were utilized to examine roles of Th17 and Th1 during OB pathogenesis after transplantation. Allografts of wild type recipients displayed elevated levels of Th1 and Th17 cytokines IFNγ, IL-6 and IL-17 expression. Recipients deficient in Th1 key transcriptional factor T-bet resulted in decreased cell infiltration and improved airway integrity in orthotopic transplanted trachea grafts; Lack of Th2 transcriptional factor Stat6 had little effect; While absence of Th17 master transcriptional factor RORγt had striking effects in abolishing airway epithelial injury, a leading factor of OB pathogenesis. Administering anti-IL-6 or anti-IL-17 but not anti-IFNγ mAbs restored normal airway epithelial morphology. Furthermore, we found that anti-CD40L treatment resulted in increased FoxP3 and regulatory T cells, and decreased IFNγ expression; However it had very limited effect on IL-17 suppression and airway epithelial protection. While CTLA4-Ig treatment significantly inhibit IL-17 expression and reduced epithelial injury, and the combination of CTLA4-Ig and anti-CD40L markedly restored airway morphology of grafts. Together, our findings provide new insights for understanding Th17 and Th1 responses during OB pathogenesis and demonstrate the critical importance of suppressing Th17 for OB development after transplantation.

Dipeptidyl peptidase-4 promotes T cell migration

Dipeptidyl peptidase-4 (DPP4) is well known as a post-prandial blood glucose regulating protein by inactivation of incretin hormones. DPP4 also regulates T cell activation by interacting with adenosine deaminase. We investigated the role of hematopoietic DPP4 in T cell-mediated vascular inflammation and atherosclerosis. DPP4 highly expressed on the plasma membrane of T cells especially CD4+ T cells. DPP4 expression increased on circulating T cells in atherosclerotic patients (% DPP4+ CD4+ T cells: 27.46 ± 2.67 vs. 48.06 ± 1.96 for healthy control vs. atherosclerotic patients, p&lt;0.0001). Deficiency of DPP4 on hematopoietic cells protected Ldlr−/− mice from high fat diet-induced atherosclerosis progression and reduced T cell infiltration in aortic plaque. Aorta from Ldlr−/− mice with Dpp4−/− bone marrows showed a much less DPP4 expression, suggesting bone marrow derived cells are the major sources of DPP4 within the aorta. Transwell® migration assay showed T cells with high migratory activity had higher levels of DPP4 expression. Both in vitro and in vivo migration assays suggest T cells deficient for DPP4 displayed a reduced migratory ability. Futher investigation suggests both enzymatic and non-enzymatic actions of DPP4 are involved in the regulation of T cell migration. Taken together, DPP4 increased on T cells in atherosclerosis and is important for T cell migratory activity, which promotes T cell-mediated vascular inflammation and atherosclerotic progression. Our results suggest an essential role for DPP4 in regulating T cell migration.

T-bet Regulates Natural Regulatory T Cell Afferent Lymphatic Migration and Suppressive Function

T-bet is essential for natural regulatory T cells (nTreg) to regulate Th1 inflammation, but whether T-bet controls other Treg functions after entering the inflammatory site is unknown. In an islet allograft model, T-bet(-/-) nTreg, but not induced Treg, failed to prolong graft survival as effectively as wild-type Treg. T-bet(-/-) nTreg had no functional deficiency in vitro but failed to home from the graft to draining lymph nodes (dLN) as efficiently as wild type. T-bet regulated expression of adhesion- and migration-related molecules, influencing nTreg distribution in tissues, so that T-bet(-/-) nTreg remained in the grafts rather than migrating to lymphatics and dLN. In contrast, both wild-type and T-bet(-/-) CD4(+) conventional T cells and induced Treg migrated normally toward afferent lymphatics. T-bet(-/-) nTreg displayed instability in the graft, failing to suppress Ag-specific CD4(+) T cells and prevent their infiltration into the graft and dLN. Thus, T-bet regulates nTreg migration into afferent lymphatics and dLN and consequently their suppressive stability in vivo.

IL-10 from marginal zone precursor B cells controls the differentiation of Th17, Tfh and Tfr cells in transplantation tolerance

B cells are known to control CD4T cell differentiation in secondary lymphoid tissues. We hypothesized that IL-10 expression by marginal zone precursor (MZP) regulatory B cells controls the differentiation and positioning of effector and regulatory T cells during tolerization. Costimulatory blockade with donor-specific transfusion (DST) and anti-CD40L mAb in C57BL/6 mice induced tolerance to allogeneic cardiac allograft. B cell depletion or IL-10 deficiency in B cells prevented tolerance, resulting in decreased follicular regulatory CD4(+) T cells (Tfr) and increased IL-21 expression by T follicular helper (Tfh) cells in the B cell and T cell zones. IL-21 acted with IL-6 to induce CCR6(+) Th17 that caused rejection. Deficiency or blockade of IL-6, IL-21, IL-21R, or CCR6 prevented B cell depletion-induced acute cellular rejection; while agonistic mCCL20-Ig induced rejection. Adoptive transfer of IL-10(+/+) MZP in tolerogen treated CD19-Cre(+/-):IL-10(fl/fl) mice rescued the localization of Tfh and Tfr cells in the B cell follicle and prevented allograft rejection. MZP B cell IL-10 is necessary for tolerance and controls the differentiation and position of Th17, Tfh and Tfr cells in secondary lymphoid tissues. This has implications for understanding tolerance induction and how B cell depletion may prevent tolerance.

What's hot, what's new at WTC--basic science

The World Transplant Congress of 2014 presented a broad swath of science that touched on many disparate aspects of cell and organ transplantation, molecular and cellular immunology, systems biology, development, technology and translation into humans. A number of themes emerged this year. B cell biology and antibody chemistry were prominent, as they have been for several years. T cells, co-stimulatory blockade and regulatory T cells continue to dominate many aspects of immune research. Many new aspects of monocyte, macrophage, NK cell and NK T cell development, biology and regulation are now being explored. Diverse aspects of organ injury and the acute and chronic responses to injury are being investigated with new techniques, new targets and a resurgent vigor. Novel advances in xenotransplantation and experimental tolerance garnered much attention. Newer investigations in microbiota and nanotechnology promise significant gains in the near future. Lastly the 'omics of DNA, RNA, proteins, metabolites, bacteria and enzyme actions promise new understanding in biological systems and how to control those systems.