Characterization of transfusion-elicited acute antibody-mediated rejection in a rat model of kidney transplantation

Exploration of the shared gene signatures and biological mechanisms between ischemia-reperfusion injury and antibody-mediated rejection in renal transplantation

BACKGROUND

Antibody-mediated rejection (ABMR) plays a crucial role in graft loss during allogeneic renal transplantation. In renal transplantation, ischemia-reperfusion injury (IRI) is unavoidable, serves as a major contributor to acute rejection, and is linked to graft loss. However, the mechanisms underlying IRI and ABMR are unclear. Therefore, this study aimed to investigate the shared genetic characteristics and biological mechanisms between IRI and ABMR.

METHODS

Gene expressions for IRI (GSE43974) and ABMR (GSE129166 and GSE36059) were retrieved from the Gene Expression Omnibus database. The shared differentially expressed genes (DEGs) of IRI and ABMR were identified, and subsequent functional enrichment analysis was performed. Immune cell infiltration in ABMR and its relationship with the shared DEGs were investigated using the CIBERSORT method. Random forest analysis, a protein-protein interaction network, and Cytoscape were used to screen hub genes, which were subsequently subjected to gene set enrichment analysis, miRNA prediction, and transcription factors analysis. The survival analysis was performed through Kaplan-Meier curves. Finally, drug compound prediction was performed on the shared DEGs using the Drug Signature Database.

RESULTS

Overall, 27 shared DEGs were identified between the renal IRI and ABMR groups. Among these, 24 genes exhibited increased co-expression, whereas none showed decreased co-expression. The shared DEGs were primarily enriched in the inflammation signaling pathways. Notably, CD4 memory T cells were identified as potential critical mediators of IRI, leading to ABMR. Tumor necrosis factor alpha-induced protein 3 (TNFAIP3), interferon regulatory factor 1 (IRF1), and early growth response 2 (EGR2) were identified as key components in the potential mechanism that link IRI and ABMR. Patients undergoing renal transplantation with higher expression levels of TNFAIP3, IRF1, and EGR2 exhibited decreased survival rates compared to those with lower expression levels.

CONCLUSION

Inflammation is a key mechanism that links IRI and ABMR, with a potential role played by CD4 memory T cells. Furthermore, TNFAIP3, IRF1, and EGR2 are implicated in the underlying mechanism between IRI and ABMR.

APRIL/BLyS deficient rats prevent donor specific antibody (DSA) production and cell proliferation in rodent kidney transplant model

APRIL (A proliferation inducing ligand) and BLyS (B Lymphocyte Stimulator) are two critical survival factors for B lymphocytes and plasma cells, the main source of alloantibody. We sought to characterize the specific effects of these cytokines in a kidney transplant model of antibody mediated rejection (AMR). We engineered APRIL-/- and BLyS-/- Lewis rats using CRISPR/Cas9. APRIL-/- and BLyS-/- rats were sensitized with Brown Norway (BN) blood (complete MHC mismatch). Twenty-one days following sensitization, animals were harvested and collected tissues were analyzed using flow cytometry, ELISPOT, and immunohistochemistry. Flow cross match and a 3 day mixed lymphocyte reaction (MLR) was performed to assess donor specific antibody (DSA) production and T-cell proliferation, respectively. Sensitized dual knock out Lewis rats (APRIL-/-/BLyS-/-) underwent kidney transplantation and were sacrificed on day 7 post-transplant. Sensitized BLyS-/- had significant decreases in DSA and cell proliferation compared to WT and APRIL-/- (p<0.02). Additionally, BLyS-/- rats had a significant reduction in IgG secreting cells in splenic marginal zone B lymphocytes, and in cell proliferation when challenged with alloantigen compared to WT and APRIL-/-. Transplanted APRIL-/-/BLyS-/- rodents had significantly less DSA and antibody secreting cells compared to WT (p<0.05); however, this did not translate into a significant difference in AMR seen between groups. In summary, our studies suggest that APRIL and BLyS play a greater role in DSA generation rather than AMR, highlighting the role of cellular pathways that regulate AMR.

C4d Deposition after Allogeneic Renal Transplantation in Rats Is Involved in Initial Apoptotic Cell Clearance

In the context of transplantation, complement activation is associated with poor prognosis and outcome. While complement activation in antibody-mediated rejection is well-known, less is known about complement activation in acute T cell-mediated rejection (TCMR). There is increasing evidence that complement contributes to the clearance of apoptotic debris and tissue repair. In this regard, we have analysed published human kidney biopsy transcriptome data clearly showing upregulated expression of complement factors in TCMR. To clarify whether and how the complement system is activated early during acute TCMR, experimental syngeneic and allogeneic renal transplantations were performed. Using an allogeneic rat renal transplant model, we also observed upregulation of complement factors in TCMR in contrast to healthy kidneys and isograft controls. While staining for C4d was positive, staining with a C3d antibody showed no C3d deposition. FACS analysis of blood showed the absence of alloantibodies that could have explained the C4d deposition. Gene expression pathway analysis showed upregulation of pro-apoptotic factors in TCMR, and apoptotic endothelial cells were detected by ultrastructural analysis. Monocytes/macrophages were found to bind to and phagocytise these apoptotic cells. Therefore, we conclude that early C4d deposition in TCMR may be relevant to the clearance of apoptotic cells.

Modulation of Synthetic Tracheal Grafts with Extracellular Matrix Coatings

Synthetic scaffolds for the repair of long-segment tracheal defects are hindered by insufficient biocompatibility and poor graft epithelialization. In this study, we determined if extracellular matrix (ECM) coatings improved the biocompatibility and epithelialization of synthetic tracheal grafts (syn-TG). Porcine and human ECM substrates (pECM and hECM) were created through the decellularization and lyophilization of lung tissue. Four concentrations of pECM and hECM coatings on syn-TG were characterized for their effects on scaffold morphologies and on in vitro cell viability and growth. Uncoated and ECM-coated syn-TG were subsequently evaluated in vivo through the orthotopic implantation of segmental grafts or patches. These studies demonstrated that ECM coatings were not cytotoxic and, enhanced the in vitro cell viability and growth on syn-TG in a dose-dependent manner. Mass spectrometry demonstrated that fibrillin, collagen, laminin, and nephronectin were the predominant ECM components transferred onto scaffolds. The in vivo results exhibited similar robust epithelialization of uncoated and coated syn-TG patches; however, the epithelialization remained poor with either uncoated or coated scaffolds in the segmental replacement models. Overall, these findings demonstrated that ECM coatings improve the seeded cell biocompatibility of synthetic scaffolds in vitro; however, they do not improve graft epithelialization in vivo.

Suppression of Inflammation-Associated Kidney Damage Post-Transplant Using the New PrC-210 Free Radical Scavenger in Rats

Allograft kidney transplantation, which triggers host cellular- and antibody-mediated rejection of the kidney, is a major contributor to kidney damage during transplant. Here, we asked whether PrC-210 would suppress damage seen in allograft kidney transplant. Brown Norway (BN) rat kidneys were perfused in situ (UW Solution) with or without added 30 mM PrC-210, and then immediately transplanted into Lewis (LEW) rats. 20 h later, the transplanted BN kidneys and LEW rat plasma were analyzed. Kidney histology, and kidney/serum levels of several inflammation-associated cytokines, were measured to assess mismatch-related kidney pathology, and PrC-210 protective efficacy. Twenty hours after the allograft transplants: (i) significant histologic kidney tubule damage and mononuclear inflammatory cell infiltration were seen in allograft kidneys; (ii) kidney function metrics (creatinine and BUN) were significantly elevated; (iii) significant changes in key cytokines, i.e., TIMP-1, TNF-alpha and MIP-3A/CCL20, and kidney activated caspase levels were seen. In PrC-210-treated kidneys and recipient rats, (i) kidney histologic damage (Banff Scores) and mononuclear infiltration were reduced to untreated background levels; (ii) creatinine and BUN were significantly reduced; and (iii) activated caspase and cytokine changes were significantly reduced, some to background. In conclusion, the results suggest that PrC-210 could provide broadly applicable organ protection for many allograft transplantation conditions; it could protect transplanted kidneys during and after all stages of the transplantation process-from organ donation, through transportation, re-implantation and the post-operative inflammation-to minimize acute and chronic rejection.

B-cell Deficiency Attenuates Transplant Glomerulopathy in a Rat Model of Chronic Active Antibody-mediated Rejection

BACKGROUND

Transplant glomerulopathy (TG) is a pathological feature of chronic active antibody-mediated rejection (cAMR) and is associated with renal allograft failure. The specific role of B cells in the pathogenesis of TG is unclear.

METHODS

We used a minor mismatched rat kidney transplant model with B cell-deficient recipients, generated by clustered regularly interspaced short palindromic repeats/Cas9 technology, to investigate the impact of B-cell depletion on the pathogenesis of TG. We hypothesized that B-cell deficiency would prevent TG in the rat kidney transplant model of cAMR. Treatment groups included syngeneic, allogeneic, sensitized allogeneic, and B cell-deficient allogeneic transplant recipients.

RESULTS

B cell-deficient recipients demonstrated reduced TG lesions, decreased microvascular inflammation, reduced allograft infiltrating macrophages, and reduced interferon gamma transcripts within the allograft. Allograft transcript levels of interferon gamma, monocyte chemoattractant protein-1, and interleukin-1β correlated with numbers of intragraft macrophages. B cell-deficient recipients lacked circulating donor-specific antibodies and had an increased splenic regulatory T-cell population.

CONCLUSIONS

In this model of cAMR, B-cell depletion attenuated the development of TG with effects on T cell and innate immunity.

Disruption of Tfh:B Cell Interactions Prevents Antibody-Mediated Rejection in a Kidney Transplant Model in Rats: Impact of Calcineurin Inhibitor Dose

We aimed to investigate the mechanisms of humoral immune activation in ABMR using a MHC-mismatched rat kidney transplant model. We applied low dose cyclosporine A (loCNI) to allow donor-specific antibody (DSA) formation and rejection and high dose cyclosporine A (hiCNI) for non-rejection. DSA and leukocyte subsets were measured by flow cytometry. Germinal centers (GC), T follicular helper cells (Tfh), plasma cells and interleukin-21 (IL-21) expression were analyzed by immunofluorescence microscopy. Expression of important costimulatory molecules and cytokines was measured by qRT-PCR. Allograft rejection was evaluated by a nephropathologist. We found that DSA formation correlated with GC frequency and expansion, and that GC size was linked to the number of activated Tfh. In hiCNI, GC and activated Tfh were virtually absent, resulting in fewer plasma cells and no DSA or ABMR. Expression of B cell activating T cell cytokine IL-21 was substantially inhibited in hiCNI, but not in loCNI. In addition, hiCNI showed lower expression of ICOS ligand and IL-6, which stimulate Tfh differentiation and maintenance. Overall, Tfh:B cell crosstalk was controlled only by hiCNI treatment, preventing the development of DSA and ABMR. Additional strategies targeting Tfh:B cell interactions are needed for preventing alloantibody formation and ABMR.

Combined Immunotherapy With Belatacept and BTLA Overexpression Attenuates Acute Rejection Following Kidney Transplantation

Background

Costimulatory blockade provides new therapeutic opportunities for ensuring the long-term survival of kidney grafts. The adoption of the novel immunosuppressant Belatacept has been limited, partly due to concerns regarding higher rates and grades of acute rejection in clinical trials. In this study, we hypothesized that a combined therapy, Belatacept combined with BTLA overexpression, may effectively attenuate acute rejection after kidney transplantation.

Materials and Methods

The rat kidney transplantation model was used to investigate graft rejection in single and combined therapy. Graft function was analyzed by detecting serum creatinine. Pathological staining was used to observe histological changes in grafts. The expression of T cells was observed by immunohistochemistry and flow cytometry. In vitro, we constructed an antigen-stimulated immune response by mixed lymphocyte culture, treated with or without Belatacept and BTLA-overexpression adenovirus, to observe the proliferation of receptor cells and the expression of cytokines. In addition, western blot and qRT-PCR analyses were performed to evaluate the expression of CTLA-4 and BTLA at various time points during the immune response.

Results

In rat models, combined therapy reduced the serum creatinine levels and prolonged graft survival compared to single therapy and control groups. Mixed acute rejection was shown in the allogeneic group and inhibited by combination treatment. Belatacept reduced the production of DSA and the deposition of C4d in grafts. Belatacept combined with BTLA overexpression downregulated the secretion of IL-2 and IFN-γ, as well as increasing IL-4 and IL-10 expression. We also found that Belatacept combined with BTLA overexpression inhibited the proliferation of spleen lymphocytes. The duration of the elevated expression levels of CTLA-4 and BTLA differentially affected the immune response.

Conclusion

Belatacept combined with BTLA overexpression attenuated acute rejection after kidney transplantation and prolonged kidney graft survival, which suggests a new approach for the optimization of early immunosuppression after kidney transplantation.

Precise treatment of acute antibody-mediated cardiac allograft rejection in rats using C4d-targeted microbubbles loaded with nitric oxide

BACKGROUND

Antibody-mediated rejection (AMR) constitutes an important cause of cardiac allograft loss; however, all current therapeutic strategies represent systemic applications with unsatisfactory efficacy. Previously, we successfully non-invasively detected C4d, a specific marker for AMR diagnosis, in allografts using C4d-targeted microbubbles (MB_C4d). In this study, we extended this approach by incorporating nitric oxide (NO), as high NO levels manifest immunosuppressive and anti-thrombotic effects.

METHODS

We designed novel MB_C4d loaded with NO (NO-MB_C4d). A rat model of AMR was established by pre-sensitization with skin transplantation. Contrast-enhanced ultrasound (CEUS) images were obtained and quantitatively analyzed following NO-MB_C4d injection. Allograft survival and histologic features were analyzed to evaluate the therapeutic effect and underlying mechanism of NO-MB_C4d toward AMR.

RESULTS

We successfully obtained CEUS images following NO-MB_C4d injection and demonstrated that the ultrasound signal intensity of the myocardial area and clearance time of NO-MB_C4d both increased with increased C4d grade, thereby realizing non-invasive diagnosis of AMR. Furthermore, allograft survival was significantly prolonged, and rejection was obviously attenuated following NO-MB_C4d injection through significant suppression of thrombosis and reduction of inflammatory cell infiltrates. Overall, the therapeutic efficacy was significantly improved in the NO-MB_C4d group compared with the control NO-MB group, demonstrating that precise treatment could significantly improve the therapeutic efficacy compared with that afforded by systemic applications.

CONCLUSIONS

This study presented a novel tool to provide simultaneous non-invasive diagnosis and precise treatment of AMR using NO-MB_C4d CEUS imaging, which may be expected to provide a better option for recipients with AMR in clinic.

Oxidized-ATP Attenuates Kidney Allograft Rejection By Inhibiting T-Cell, B-Cell, and Macrophage Activity

Background

Extracellular ATP binds to purinergic receptors and promotes inflammatory responses. We tested whether oxidized ATP (oATP), P2X7 receptor antagonist can attenuate acute kidney allograft rejection.

Methods

Brown Norway kidney allografts were transplanted into Lewis recipients. Three groups were defined: oATP (n=8), cyclosporine A (n=6), and no treatment (n=8). On day 7, we assessed kidney allograft survival, function, and rejection characteristics. We further determined T-cell, B-cell, and macrophage response to oATP in vivo and in vitro and examined intragraft inflammatory gene transcripts.

Results

Kaplan–Meier survival analyses demonstrated significantly better graft survival rates in oATP and CsA groups compared with no treatment (P<0.05). Similarly, serum creatinine (Scr) and BUN levels were significantly lower in oATP and CsA groups (P<0.05). oATP reduced both T cell–mediated rejection and antibody-mediated rejection, inhibited B-cell and T-cell activation, and downregulated intragraft IL-6 mRNA levels (P<0.0001). In vitro, oATP prevented proliferation in mixed lymphocyte reaction assays, and inhibited macrophage P2X7R activity in a dose-dependent manner.

Conclusions

Our findings suggest that oATP mitigates kidney allograft rejection by inhibiting T-cell, B-cell, and macrophage activity and indicate a potential role for the purinergic system and oATP in solid organ transplantation.

Unilateral nephrectomy versus renal arterial embolization and technique survival in peritoneal dialysis patients with autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder associated with progressive enlargement of the kidneys and liver. ADPKD patients may require renal volume reduction, especially before renal transplantation. The standard treatment is unilateral nephrectomy. However, surgery incurs a risk of blood transfusion and alloimmunization. Furthermore, when patients are treated with peritoneal dialysis (PD), surgery is associated with an increased risk of temporary or definitive switch to haemodialysis (HD). Unilateral renal arterial embolization can be used as an alternative approach to nephrectomy.

METHODS

We performed a multicentre retrospective study to compare the technique of survival of PD after transcatheter renal artery embolization with that of nephrectomy in an ADPKD population. We included ADPKD patients treated with PD submitted to renal volume reduction by either surgery or arterial embolization. Secondary objectives were to compare the frequency and duration of a temporary switch to HD in both groups and the impact of the procedure on PD adequacy parameters.

RESULTS

More than 700 patient files from 12 centres were screened. Only 37 patients met the inclusion criteria (i.e. treated with PD at the time of renal volume reduction) and were included in the study (21 embolized and 16 nephrectomized). Permanent switch to HD was observed in 6 embolized patients (28.6%) versus 11 nephrectomized patients (68.8%) (P = 0.0001). Renal artery embolization was associated with better technique survival: subdistribution hazard ratio (SHR) 0.29 [95% confidence interval (CI) 0.12-0.75; P = 0.01]. By multivariate analysis, renal volume reduction by embolization and male gender were associated with a decreased risk of switching to HD. After embolization, a decrease in PD adequacy parameters was observed but no embolized patients required temporary HD; the duration of hospitalization was significantly lower [5 days [interquartile range (IQR) 4.0-6.0] in the embolization group versus 8.5 days (IQR 6.0-11.0) in the surgery group.

CONCLUSIONS

Transcatheter renal artery embolization yields better technique survival of PD in ADPKD patients requiring renal volume reduction.

APRIL/BLyS Blockade Reduces Donor-specific Antibodies in Allosensitized Mice

BACKGROUND

Highly sensitized candidates on the transplant waitlist remain a significant challenge, as current desensitization protocols have variable success rates of donor-specific antibody (DSA) reduction. Therefore, improved therapies are needed. A proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS) are critical survival factors for B-lymphocytes and plasma cells, which are the primary sources of alloantibody production. We examined the effect of APRIL/BLyS blockade on DSA in a murine kidney transplant model as a possible novel desensitization strategy.

METHODS

C57BL/6 mice were sensitized with intraperitoneal (IP) injections of 2 × 10 BALB/c splenocytes. Twenty-one days following sensitization, animals were treated with 100 μg of BLyS blockade (B-cell activating factor receptor-immunoglobulin) or APRIL/BLyS blockade (transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin), administered thrice weekly for an additional 21 days. Animals were then euthanized or randomized to kidney transplant with Control Ig, BLyS blockade, or APRIL/BLyS blockade. Animals were euthanized 7 days posttransplant. B-lymphocytes and DSA of BLyS blockade only or APRIL/BLyS blockade-treated mice were assessed by flow cytometry, immunohistochemistry, and enzyme-linked immunospot.

RESULTS

APRIL/BLyS inhibition resulted in a significant reduction of DSA by flow crossmatch compared with controls (P < 0.01). APRIL/BLyS blockade also significantly depleted IgM- and IgG-secreting cells and B-lymphocyte populations compared to controls (P < 0.0001). APRIL/BLyS blockade in transplanted mice also resulted in decreased B-lymphocyte populations; however, no difference in rejection rates were seen between groups.

CONCLUSIONS

APRIL/BLyS blockade with transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin significantly depleted B-lymphocytes and reduced DSA in this sensitized murine model. APRIL/BLyS inhibition may be a clinically useful desensitization strategy for sensitized transplant candidates.

Desensitization and treatment with APRIL/BLyS blockade in rodent kidney transplant model

Alloantibody represents a significant barrier in kidney transplant through the sensitization of patients prior to transplant through antibody mediated rejection (ABMR). APRIL BLyS are critical survival factors for mature B lymphocytes plasma cells, the primary source of alloantibody. We examined the effect of APRIL/BLyS blockade via TACI-Ig (Transmembrane activator calcium modulator cyclophilin lig interactor-Immunoglobulin) in a preclinical rodent model as treatment for both desensitization ABMR. Lewis rats were sensitized with Brown Norway (BN) blood for 21 days. Following sensitization, animals were then sacrificed or romized into kidney transplant (G4, sensitized transplant control); desensitization with TACI-Ig followed by kidney transplant (G5, sensitized + pre-transplant TACI-Ig); kidney transplant with post-transplant TACI-Ig for 21 days (G6, sensitized + post-transplant TACI-Ig); desensitization with TACI-Ig followed by kidney transplant post-transplant TACI-Ig for 21 days (G7, sensitized + pre- post-transplant TACI-Ig). Animals were sacrificed on day 21 post-transplant tissues were analyzed using flow cytometry, IHC, ELISPOT, RT-PCR. Sensitized animals treated with APRIL/BLyS blockade demonstrated a significant decrease in marginal zone non-switched B lymphocyte populations (p<0.01). Antibody secreting cells were also significantly reduced in the sensitized APRIL/BLyS blockade treated group. Post-transplant APRIL/BLyS blockade treated animals were found to have significantly less C4d deposition less ABMR as defined by Banff classification when compared to groups receiving APRIL/BLyS blockade before transplant or both before after transplant (p<0.0001). The finding of worse ABMR in groups receiving APRIL/BLyS blockade before both before after transplant may indicate that B lymphocyte depletion in this setting also resulted in regulatory lymphocyte depletion resulting in a worse rejection. Data presented here demonstrates that the targeting of APRIL BLyS can significantly deplete mature B lymphocytes, antibody secreting cells, effectively decrease ABMR when given post-transplant in a sensitized animal model.

Immunoproteasome inhibition induces plasma cell apoptosis and preserves kidney allografts by activating the unfolded protein response and suppressing plasma cell survival factors

Chronic antibody-mediated rejection is the leading cause of allograft dysfunction and loss after kidney transplantation, and current immunosuppressive regimens fail to target the plasma cells that produce alloantibodies. We previously showed that treatment with the immunoproteasome inhibitor ONX 0914 prevented the expansion of plasma cells and prevented chronic allograft nephropathy and organ failure after kidney transplantation in rats, but the mechanism has remained elusive. In the current study, we confirmed a long-term reduction in alloantibody production and improvements in allograft histology in rats treated with ONX 0914 or with the broad-spectrum proteasome inhibitor bortezomib. Plasma cells from allotransplanted rats expressed immunoproteasomes at high levels. Immunoproteasome inhibition with ONX 0914 led to ubiquitin-conjugate accumulation, activation of the unfolded protein response, and induction of apoptosis in plasma cells. In addition, ONX 0914 suppressed the expression of adhesion molecules (VLA-4 and LFA-1), plasma cell survival factors (APRIL and IL-6), and IFN-γ-inducible chemokines in bone marrow, while the APRIL receptor BCMA, the IL-6 receptor, and the chemokine receptors CXCR4 and CXCR3 were down-regulated on plasma cells. Taken together, immunoproteasome inhibition blocked alloantibody production by inducing apoptosis of plasma cells through activating the unfolded protein response and suppressing plasma cell survival factors in the bone marrow.

Complete B Cell Deficiency Reduces Allograft Inflammation and Intragraft Macrophages in a Rat Kidney Transplant Model

BACKGROUND

Increasingly, it is being appreciated that B cells have broad roles beyond the humoral response and are able to contribute to and regulate inflammation. The specific role of B cells in the pathogenesis of early allograft inflammation remains unclear.

METHODS

To address this question, we generated B cell-deficient (B) Lewis rats via clustered regularly interspaced short palindromic repeats (CRISPR) technology. In a full mismatch transplant model, kidneys from Brown Norway donors were transplanted into B Lewis recipients or wild type Lewis recipients. T cell-mediated rejection was attenuated with cyclosporine.

RESULTS

Renal inflammation was reduced at 1 week after transplant (Banff scores for interstitial inflammation, microvascular inflammation, glomerulitis, and C4d) in allografts from B recipients. The reduction in interstitial inflammation was predominantly due to a decline in graft infiltrating macrophages. Intragraft T-cell numbers remained unchanged. In addition, B-cell deficiency was associated with increased T regulatory cells and reduced splenic T follicular helper cells at baseline; and significantly increased intragraft and splenic IL-10 mRNA levels after transplant. In vitro, B and wild type splenic T cells produced similar levels of IFN-γ in response to T cell-specific activation.

CONCLUSIONS

B-cell deficiency in this model produced an anti-inflammatory phenotype with a shift toward regulatory T-cell populations, production of anti-inflammatory cytokines (IL-10), and a reduction in allograft inflammation. These findings define a role for B cells to influence the cell populations and mediators involved in the pathogenesis of early allograft inflammation.

Galectin-1-induced tolerogenic dendritic cells combined with apoptotic lymphocytes prolong liver allograft survival

Donor-derived tolerogenic dendritic cells (DCs) and apoptotic lymphocytes (ALs) are practical tools for controlling rejection after transplantation by targeting direct and indirect allorecognition pathways, respectively. To date, few studies have investigated the combination of donor-derived tolerogenic DCs and ALs infusion in organ transplantation protection. In the present study, we generated galectin-1-induced tolerogenic DCs (DC_gal-1s) and ultraviolet irradiation-induced ALs with stable immune characteristics in vitro and potential immune regulatory activity in vivo. A rat model of acute liver transplant rejection was established, and the intrinsic tolerogenic profiles associated with the short-term alleviation of rejection and the long-term maintenance of tolerance in the absence of immunosuppressive drugs were evaluated. The DC_gal-1-AL treatment prolonged allograft survival more significantly than a transfusion of DC_gal-1s or ALs alone. This benefit was associated with CD4⁺ Treg cell expansion and decreased interferon (IFN)-γ⁺ T cell levels. Moreover, DC_gal-1-AL treatment led to different cytokine/chemokine changes in the allograft and peripheral blood, that indicated an alleviation of local and systemic inflammation on day 7 post-transplantation. TGF-β1 and TGF-β2 were significantly increased in the long-term surviving allografts after DC_gal-1-AL treatment. Our results indicate that the combination of DC_gal-1s with ALs effectively prolongs liver allograft survival and represents a novel therapeutic strategy for liver transplant rejection.

Autologous Mesenchymal Stromal Cells Prevent Transfusion-elicited Sensitization and Upregulate Transitional and Regulatory B Cells

BACKGROUND

We hypothesized that immunomodulatory properties of mesenchymal stromal cells (MSC) may be considered for desensitization.

METHODS

Autologous or allogeneic bone marrow derived MSC were infused via tail vein at 0.5 M (0.5 × 106), 1 M, or 2 M cells/dose on days -2, 3, 6, 9, 12 (prevention) or 14, 17, 20, 23, 26 (treatment) relative to transfusion in a Brown Norway to Lewis rat model (10 groups total, n = 6 per group).

RESULTS

At 4 weeks, pooled analyses demonstrated that autologous and allogeneic MSC were equally effective in reducing IgG1 and IgG2a de novo donor-specific antibody (dnDSA, P < 0.001). Dose-response studies indicated that moderate-dose MSC (5 M total) was most effective in reducing IgG1, IgG2a, and IgG2c dnDSA (P ≤ 0.01). Time course studies determined that preventive and treatment strategies were equally effective in reducing IgG1 and IgG2a dnDSA (P ≤ 0.01). However, individual group analyses determined that moderate-dose (5 M) treatment with autologous MSC was most effective in reducing IgG1, IgG2a, and IgG2c dnDSA (P ≤ 0.01). In this group, dnDSA decreased after 1 week of treatment; regulatory B cells increased in the spleen and peripheral blood mononuclear cells; and transitional B cells increased in the spleen, peripheral blood mononuclear cells, and bone marrow (P < 0.05 for all).

CONCLUSIONS

Our findings indicate that autologous MSC prevent transfusion-elicited sensitization and upregulate transitional, and regulatory B cells. Additional studies are needed to determine the biological relevance of these changes after kidney transplantation.

Mouse Model Established by Early Renal Transplantation After Skin Allograft Sensitization Mimics Clinical Antibody-Mediated Rejection

Antibody-mediated rejection (AMR) is the main barrier to renal graft survival, and mouse renal AMR models are important to study this process. Current mouse models are established by priming the recipient to donor skin for over 7 days before kidney transplantation. The robustness of AMR in these cases is too strong to mimic clinical AMR and it is unclear why altering the priming times ranging from 7 to 91 days fails to reduce the AMR potency in these models. In the present study, we found that the donor-recipient combination and skin graft size were determinants of donor-specific antibody (DSA) development patterns after skin transplantation. DSA-IgG was sustained for over 100 days after skin challenge, accounting for an identical AMR robustness upon different skin priming times over 7 days. However, decreasing the skin priming time within 7 days attenuated the robustness of subsequent renal allograft AMR in C3H to Balb/c mice. Four-day skin priming guaranteed that recipients develop acute renal AMR mixed with a high ratio of graft-infiltrating macrophages, renal grafts survived for a mean of 6.4 ± 2.1 days, characterized by typical AMR histological changes, such as glomerulitis, peritubular capillary (PTC) dilation, and capillaritis, deposition of IgG and C3d in PTCs, but less prevalence of microthrombus, whereas the cellular rejection histological change of tubulitis was absent to mild. With this scheme, we also found that the renal AMR model can be developed using common mouse strains such as C57BL/6 and Balb/c, with mean prolonged renal graft survival times of 14.4 ± 5.0 days. Finally, we proved that donor-matched skin challenge after kidney transplantation did not strongly affect DSA development and kidney graft outcome. These findings may facilitate an understanding and establishment of mouse renal allograft AMR models and promote AMR-associated studies.

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.

Renal allograft rejection, lymphocyte infiltration, and de novo donor-specific antibodies in a novel model of non-adherence to immunosuppressive therapy

Background

Non-adherence has been associated with reduced graft survival. The aim of this study was to investigate the immunological mechanisms underlying chronic renal allograft rejection using a model of non-adherence to immunosuppressive therapy. We used a MHC (major histocompatibility complex) -mismatched rat model of renal transplantation (Brown Norway to Lewis), in which rats received daily oral cyclosporine A. In analogy to non-adherence to therapy, one group received cyclosporine A on alternating days only. Rejection was histologically graded according to the Banff classification. We quantified fibrosis by trichrome staining and intra-graft infiltration of T cells, B cells, and monocytes/macrophages by immunohistochemistry. The distribution of B lymphocytes was assessed using immunofluorescence microscopy. Intra-graft chemokine, chemokine receptor, BAFF (B cell activating factor belonging to the TNF family), and immunoglobulin G transcription levels were analysed by RT-PCR. Finally, we evaluated donor-specific antibodies (DSA) and complement-dependent cytotoxicity using flow cytometry.

Results

After 28 days, cellular rejection occurred during non-adherence in 5/6 animals, mixed with humoral rejection in 3/6 animals. After non-adherence, the number of T lymphocytes were elevated compared to daily immunosuppression. Monocyte numbers declined over time. Accordingly, lymphocyte chemokine transcription was significantly increased in the graft, as was the transcription of BAFF, BAFF receptor, and Immunoglobulin G. Donor specific antibodies were elevated in non-adherence, but did not induce complement-dependent cytotoxicity.

Conclusion

Cellular and humoral rejection, lymphocyte infiltration, and de novo DSA are induced in this model of non-adherence.

Electronic supplementary material

The online version of this article (doi: 10.1186/s12865-017-0236-6) contains supplementary material, which is available to authorized users.

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.

Ribonuclease (RNase) Prolongs Survival of Grafts in Experimental Heart Transplantation

BACKGROUND

Cell damage, tissue and vascular injury are associated with the exposure and release of intracellular components such as RNA, which promote inflammatory reactions and thrombosis. Based on the counteracting anti-inflammatory and cardioprotective functions of ribonuclease A (RNase A) in this context, its role in an experimental model of heart transplantation in rats was studied.

METHODS AND RESULTS

Inbred BN/OrlRj rat cardiac allografts were heterotopically transplanted into inbred LEW/OrlRj rats. Recipients were intravenously treated every other day with saline or bovine pancreatic RNase A (50 μg/kg). Toxic side effects were not found (macroscopically and histologically). Heart tissue flow cytometry and quantitative morphological analyses of explanted hearts at postoperative day 1 or postoperative day 4 showed reduced leukocyte infiltration, edema, and thrombus formation in RNase A-treated rats. In allogeneic mixed lymphocyte reactions, RNase A decreased the proliferation of effector T cells. RNase A treatment of rats resulted in prolonged median graft survival up to 10.5 days (interquartile range 1.8) compared to 6.5 days (interquartile range 1.0) in saline treatment (P=0.001). Treatment of rats with a new generated (recombinant) human pancreatic RNase 1 prolonged median graft survival similarly, unlike treatment with (recombinant) inactive human RNase 1 (each 50 μg/kg IV every other day, 11.0 days, interquartile range 0.3, versus 8.0 days, interquartile range 0.5, P=0.007).

CONCLUSIONS

Upon heart transplantation, RNase administration appears to present a promising and safe drug to counteract ischemia/reperfusion injury and graft rejection. Furthermore, RNase treatment may be considered in situations of critical reperfusion after percutaneous coronary interventions or in cardiac surgery using the heart-lung machine.

The prognostic significance of glomerular infiltrating leukocytes during acute renal allograft rejection

Transplant glomerulitis, observed in T cell-mediated and antibody-mediated rejection, is histologically characterized by intracapillary mononuclear cell infiltration. However, the prognostic value of counting various glomerular inflammatory cells during rejection has not been elucidated, which is a key step for the introduction of novel biomarkers in the clinics. We immunophenotyped glomerulitis during episodes of acute rejection in order to investigate their predictive value for transplant outcomes. To do so, we included 57 transplant biopsies of 57 renal transplant recipients with biopsy-proven acute rejection with a median follow-up of 4.2 years. We determined average glomerular cell counts for T cells, B cells, Tregs, IL-17(+) cells, neutrophils and macrophages. Logistic and Cox regression models were used to investigate the association of glomerular inflammatory cells with response to therapy and graft failure on a population level. We used novel time-dependent ROC curve analyses to investigate the value of glomerular inflammatory cell infiltrates for the prediction of transplant outcomes, applicable to the individual patient. We identified three cell types that were responsible for glomerulitis during rejection: macrophages, T cells and neutrophils. By quantification of glomerular macrophages, an emerging cell type associated with antibody-mediated rejection, we were able to predict the progression towards death-censored graft failure within the first 500 days after the initial episode of rejection. With the use of novel time-dependent ROC analyses, we propose dynamic sensitivities, specificities, and positive and negative predictive values with their corresponding cut-off values for the average amount of glomerular macrophages, depending on what time after rejection death-censored graft failure needs prediction.

The divergent roles of macrophages in solid organ transplantation

PURPOSE OF REVIEW

This review summarizes the phenotype and function of macrophages in the context of solid organ transplantation and will focus on fundamental insights into their paradoxical pro-inflammatory versus suppressive function. We will also discuss the therapeutic potential of regulatory macrophages in tolerance induction.

RECENT FINDINGS

Macrophages are emerging as an essential element of solid organ transplantation. Macrophages are involved in the pathogenesis of ischemia reperfusion injury, as well as both acute and chronic rejection, exacerbating injury through secretion of inflammatory effectors and by amplifying adaptive immune responses. Notably, not all responses associated with macrophages are deleterious to the graft, and graft protection can in fact be conferred by macrophages. This has been attributed to the presence of macrophages with tissue-repair capabilities, as well as the effects of regulatory macrophages.

SUMMARY

The explosion of new information on the role of macrophages in solid organ transplantation has opened up new avenues of research and the possibility of therapeutic intervention. However, the role of myeloid cells in graft rejection, resolution of rejection and tissue repair remains poorly understood. A better understanding of plasticity and regulation of monocyte polarization is vital for the development of new therapies for the treatment of acute and chronic transplant rejection.

Markers of Endothelial-to-Mesenchymal Transition: Evidence for Antibody-Endothelium Interaction during Antibody-Mediated Rejection in Kidney Recipients

Antibody-mediated rejection (ABMR) is a leading cause of allograft loss. Treatment efficacy depends on accurate diagnosis at an early stage. However, sensitive and reliable markers of antibody-endothelium interaction during ABMR are not available for routine use. Using immunohistochemistry, we retrospectively studied the diagnostic value of three markers of endothelial-to-mesenchymal transition (EndMT), fascin1, vimentin, and heat shock protein 47, for ABMR in 53 renal transplant biopsy specimens, including 20 ABMR specimens, 24 cell-mediated rejection specimens, and nine normal grafts. We validated our results in an independent set of 74 unselected biopsy specimens. Endothelial cells of the peritubular capillaries in grafts with ABMR expressed fascin1, vimentin, and heat shock protein 47 strongly, whereas those from normal renal grafts did not. The level of EndMT marker expression was significantly associated with current ABMR criteria, including capillaritis, glomerulitis, peritubular capillary C4d deposition, and donor-specific antibodies. These markers allowed us to identify C4d-negative ABMR and to predict late occurrence of disease. EndMT markers were more specific than capillaritis for the diagnosis and prognosis of ABMR and predicted late (up to 4 years after biopsy) renal graft dysfunction and proteinuria. In the independent set of 74 renal graft biopsy specimens, the EndMT markers for the diagnosis of ABMR had a sensitivity of 100% and a specificity of 85%. Fascin1 expression in peritubular capillaries was also induced in a rat model of ABMR. In conclusion, EndMT markers are a sensitive and reliable diagnostic tool for detecting endothelial activation during ABMR and predicting late loss of allograft function.

Experimental rat models of chronic allograft nephropathy: a review

Chronic allograft nephropathy (CAN) is the leading cause of late allograft loss after renal transplantation (RT), which continues to remain an unresolved problem. A rat model of CAN was first described in 1969 by White et al. Although the rat model of RT can be technically challenging, it is attractive because the pathogenesis of CAN is similar to that following human RT and the pathological features of CAN develop within months as compared with years in human RT. The rat model of RT is considered as a useful investigational tool in the field of experimental transplantation research. We have reviewed the literature on studies of rat RT reporting the donor and recipient strain combinations that have investigated resultant survival and histological outcomes. Several different combinations of inbred and outbred rat combinations have been reported to investigate the multiple aspects of transplantation, including acute rejection, cellular and humoral rejection mechanisms and their treatments, CAN, and potential targets for its prevention.