Nadia Azzollini

Pretransplant Infusion of Mesenchymal Stem Cells Prolongs the Survival of a Semiallogeneic Heart Transplant through the Generation of Regulatory T Cells

In this study, we investigated whether mesenchymal stem cells (MSC) had immunomodulatory properties in solid organ allotransplantation, using a semiallogeneic heart transplant mouse model, and studied the mechanism(s) underlying MSC tolerogenic effects. Either single (portal vein, day −7) or double (portal vein, day −7 and tail vein, day −1) pretransplant infusions of donor-derived B6C3 MSC in B6 recipients induced a profound T cell hyporesponsiveness and prolonged B6C3 cardiac allograft survival. The protolerogenic effect was abrogated when donor-derived MSC were injected together with B6C3 hematopoietic stem cells (HSC), suggesting that HSC negatively impact MSC immunomodulatory properties. Both the induction (pretransplant) and the maintenance phase (>100 days posttransplant) of donor-derived MSC-induced tolerance were associated with CD4+CD25+Foxp3+ Treg expansion and impaired anti-donor Th1 activity. MSC-induced regulatory T cells (Treg) were donor-specific since adoptive transfer of splenocytes from tolerant mice prevented the rejection of fully MHC-mismatched donor-specific secondary allografts but not of third-party grafts. In addition, infusion of recipient-derived B6 MSC tolerized a semiallogeneic B6C3 cardiac allograft, but not a fully MHC-mismatched BALB/c graft, and expanded Treg. A double i.v. pretransplant infusion of recipient-derived MSC had the same tolerogenic effect as the combined intraportal/i.v. MSC infusions, which makes the tolerogenic protocol applicable in a clinical setting. In contrast, single MSC infusions given either peritransplant or 1 day after transplant were less effective. Altogether these findings indicate that MSC immunomodulatory properties require HSC removal, partial sharing of MHC Ags between the donor and the recipient and pretransplant infusion, and are associated with expansion of donor-specific Treg.

In Vivo Maturation of Functional Renal Organoids Formed from Embryonic Cell Suspensions

The shortage of transplantable organs provides an impetus to develop tissue-engineered alternatives. Producing tissues similar to immature kidneys from simple suspensions of fully dissociated embryonic renal cells is possible in vitro, but glomeruli do not form in the avascular environment. Here, we constructed renal organoids from single-cell suspensions derived from E11.5 kidneys and then implanted these organoids below the kidney capsule of a living rat host. This implantation resulted in further maturation of kidney tissue, formation of vascularized glomeruli with fully differentiated capillary walls, including the slit diaphragm, and appearance of erythropoietin-producing cells. The implanted tissue exhibited physiologic functions, including tubular reabsorption of macromolecules, that gained access to the tubular lumen on glomerular filtration. The ability to generate vascularized nephrons from single-cell suspensions marks a significant step to the long-term goal of replacing renal function by a tissue-engineered kidney.

Localization of Mesenchymal Stromal Cells Dictates Their Immune or Proinflammatory Effects in Kidney Transplantation

Multipotent mesenchymal stromal cells (MSC) have recently emerged as promising candidates for cell‐based immunotherapy in solid‐organ transplantation. However, optimal conditions and settings for fully harnessing MSC tolerogenic properties need to be defined. We recently reported that autologous MSC given posttransplant in kidney transplant patients was associated with transient renal insufficiency associated with intragraft recruitment of neutrophils and complement C3 deposition. Here, we moved back to a murine kidney transplant model with the aim to define the best timing of MSC infusion capable of promoting immune tolerance without negative effects on early graft function. We also investigated the mechanisms of the immunomodulatory and/or proinflammatory activities of MSC according to whether cells were given before or after transplant. Posttransplant MSC infusion in mice caused premature graft dysfunction and failed to prolong graft survival. In this setting, infused MSC localized mainly into the graft and associated with neutrophils and complement C3 deposition. By contrast, pretransplant MSC infusion induced a significant prolongation of kidney graft survival by a Treg‐dependent mechanism. MSC‐infused pretransplant localized into lymphoid organs where they promoted early expansion of Tregs. Thus, pretransplant MSC infusion may be a useful approach to fully exploit their immunomodulatory properties in kidney transplantation.

Complement-Mediated Dysfunction of Glomerular Filtration Barrier Accelerates Progressive Renal Injury

Intrarenal complement activation leads to chronic tubulointerstitial injury in animal models of proteinuric nephropathies, making this process a potential target for therapy. This study investigated whether a C3-mediated pathway promotes renal injury in the protein overload model and whether the abnormal exposure of proximal tubular cells to filtered complement could trigger the resulting inflammatory response. Mice with C3 deficiency were protected to a significant degree against the protein overload-induced interstitial inflammatory response and tissue damage, and they had less severe podocyte injury and less proteinuria. When the same injury was induced in wild-type (WT) mice, antiproteinuric treatment with the angiotensin-converting enzyme inhibitor lisinopril reduced the amount of plasma protein filtered, decreased the accumulation of C3 by proximal tubular cells, and protected against interstitial inflammation and damage. For determination of the injurious role of plasma-derived C3, as opposed to tubular cell-derived C3, C3-deficient kidneys were transplanted into WT mice. Protein overload led to the development of glomerular injury, accumulation of C3 in podocytes and proximal tubules, and tubulointerstitial changes. Conversely, when WT kidneys were transplanted into C3-deficient mice, protein overload led to a more mild disease and abnormal C3 deposition was not observed. These data suggest that the presence of C3 increases the glomerular filtration barriers susceptibility to injury, ultrafiltered C3 contributes more to tubulointerstitial damage induced by protein overload than locally synthesized C3, and local C3 synthesis is irrelevant to the development of proteinuria. It is speculated that therapies targeting complement combined with interventions to minimize proteinuria would more effectively prevent the progression of renal disease.

The Toll-IL-1R Member Tir8/SIGIRR Negatively Regulates Adaptive Immunity against Kidney Grafts

Members of the TLR/IL-1R superfamily mediate ischemia/reperfusion injury and initiate immune response in transplanted organs. In this study, we tested the hypothesis that Toll-IL-1R8 (TIR8), a negative regulator of TLR/IL-1R highly expressed in the kidney, modulates immune cell activation underlying kidney rejection. In a mouse model of fully mismatched kidney allotransplantation in which the graft is spontaneously accepted, intragraft Tir8 expression was enhanced compared with naive kidneys. Targeted deletion of Tir8 in the graft exerted a powerful antitolerogenic action leading to acute rejection. Similarly, in a mouse model of kidney graft acceptance induced by costimulation blockade, most Tir8−/− grafts were acutely rejected. Despite similar levels of TLR4, IL-1R, and their ligands, the posttransplant ischemia/reperfusion-induced inflammatory response was more severe in Tir8−/− than in Tir8+/+ grafts and was followed by expansion and maturation of resident dendritic cell precursors. In vitro, Tir8−/− dendritic cell precursors acquired higher allostimulatory activity and released more IL-6 upon stimulation with a TLR4 ligand and TNF-α than Tir8+/+ cells, which may explain the increased frequency of antidonor-reactive T cells and the block of regulatory T cell formation in recipients of a Tir8−/− kidney. Thus, TIR8 acts locally as a key regulator of allogeneic immune response in the kidney. Tir8 expression and/or signaling in donor tissue are envisaged as a novel target for control of innate immunity and amelioration of graft survival.

Dendritic cells genetically engineered with adenoviral vector encoding dnIKK2 induce the formation of potent CD4+ T-regulatory cells.

Background. Immature dendritic cells (DC), characterized by low expression of both major histocompatibility complex class II antigens and co-stimulatory molecules, can be instrumental in the induction of peripheral tolerance. Because nuclear factor (NF)-&kgr;B is central to DC maturation, the authors engineered DC with an adenoviral vector (Adv) encoding for a kinase-defective dominant negative form of IKK2 (dnIKK2) to block NF-&kgr;B activation and inhibit DC maturation. Methods. DC were obtained by culturing bone marrow from Brown Norway (BN) rats with granulocyte-macrophage colony-stimulating factor and interleukin-4 for 11 days. To block NF-&kgr;B activation, at day 9, cells were transfected with AdV-dnIKK2. At day 11, cells were used as stimulators in primary mixed leukocyte reaction (MLR) with naive Lewis rat lymphocytes as responders. CD4+ T cells were purified from primary MLR and tested in secondary MLR with allogeneic mature DC and in co-culture MLR with naive lymphocytes. The tolerogenic potential of dnIKK2-DC was evaluated in vivo in a model of rat kidney allotransplantation. Results. DnIKK2-DC were immature and lacked any allostimulatory activity. T cells preexposed to allogeneic dnIKK2-DC were hyporesponsive to a secondary stimulation with mature DC and acquired potent regulatory properties, inhibiting naive T-cell proliferation toward allogeneic stimuli. Pretransplant infusion of allogeneic donor dnIKK2-DC prolonged the survival of a kidney allograft from the same allogeneic donor, without the need for immunosuppressive therapy. Conclusions. Allogeneic DC, rendered immature by dnIKK2 transfection, induce in vitro differentiation of naive T cells into CD4+ T-regulatory cells, effective at low ratios with target cells, rendering them applicable for cellular therapy of immune-mediated abnormalities and for preventing transplant rejection.

Pretransplant donor peripheral blood mononuclear cells infusion induces transplantation tolerance by generating regulatory T cells.

Background. It was suggested that maintenance of tolerance to organ transplantation may depend on the formation of T regulatory cells. Methods. Lewis (LW) rats were made tolerant to a Brown Norway kidney by pretransplant donor peripheral blood mononuclear cells (PBMC) infusion. At greater than 90 days after transplantation, lymph node cells (LN) and graft-infiltrating leukocytes (GIL) alloreactivity was tested in mixed lymphocyte reaction (MLR), coculture, and transwell experiments. GIL phenotype was analyzed by FACS. mRNA expression of cytokines and other markers was analyzed on CD4+ T cells from LN. The tolerogenic potential of tolerant cells in vivo was evaluated by adoptive transfer. Results. Tolerant LN cells showed a reduced proliferation against donor stimulators but a normal anti–third-party alloreactivity. In coculture, these cells inhibited antidonor but not antithird-party reactivity of naïve LN cells. Interleukin (IL)-10 and FasL mRNA expression was up-regulated in tolerant CD4+ T cells, but an anti–IL-10 monoclonal antibody (mAb) only partially reversed their inhibitory effect. Immunoregulatory activity was concentrated in the CD4+CD25+ T-cell subset. In a transwell system, tolerant T cells inhibited a naïve MLR to a lesser extent than in a standard coculture. Regulatory cells transferred tolerance after infusion into naïve LW recipients. CD4+ T cells isolated from tolerized grafts were hyporesponsive to donor stimulators and suppressed a naïve MLR against donor antigens. Conclusions. Donor-specific regulatory T cells play a role in tolerance induction by donor PBMC infusion. Regulatory activity is concentrated in the CD4+CD25+ subset and requires cell-to-cell contact. Regulatory CD4+ T cells accumulate in tolerized kidney grafts where they could exert a protective function against host immune response.

Adeno-Associated Virus–Mediated CTLA4Ig Gene Transfer Protects MHC-Mismatched Renal Allografts from Chronic Rejection

Short-term results of renal transplantation have improved considerably in the past 20 yr; however, similar improvements in long-term outcome have not been achieved. The primary cause of late graft loss is chronic rejection that might be treated by gene therapeutic approaches. Ideally, one would like to impair locally the contact between transplant antigen and the host immune system without compromising the generalized immune competence of the recipient. This can be achieved by local expression of the therapeutic protein in the site of interest using gene therapy. Here it is shown that chronic allograft rejection can be prevented effectively by local delivery of recombinant adeno-associated virus (AAV) vectors that encode the CTLA4Ig immunosuppressant protein to the donor kidney in a fully MHC-mismatched rat strain combination. AAV CTLA4Ig prevented progressive proteinuria and protected transplant kidneys from renal structural injury. A population of anergic T cells with regulatory activity, which eventually were responsible for the induction of tolerance, were found in recipient lymph nodes and in the graft as long as 120 d after transplantation. These data indicate that AAV-mediated CTLA4Ig gene transfer to donor graft represents a promising tool to prevent the onset of chronic rejection and circumvent the unwanted systemic adverse effects of the administration of immunomodulatory protein.

DnIKK2-transfected dendritic cells induce a novel population of inducible nitric oxide synthase-expressing CD4+CD25- cells with tolerogenic properties

Background. We previously documented that rat bone marrow-derived dendritic cells (DCs), transfected with an adenovirus encoding a dominant negative form of IKK2 (dnIKK2), have impaired allostimulatory capacity and generate CD4+ T cells with regulatory function. Here we investigate the potency, the phenotype, and the mechanism of action of dnIKK2-DC-induced regulatory cells and we evaluated their tolerogenic properties in vivo. Methods. Brown Norway (BN) transfected dnIKK2-DCs were cultured with Lewis (LW) lymphocytes in primary mixed lymphocyte reaction (MLR). CD4+ T cells were purified from primary MLR and incubated in secondary coculture MLR with LW lymphocytes. Phenotypic characterization was performed by fluorescence-activated cell sorting and real-time polymerase chain reaction. The tolerogenic potential of CD4+ T cells pre-exposed to dnIKK2-DCs was evaluated in vivo in a model of kidney allotransplantation. Results. CD4+ T cells pre-exposed to dnIKK2-DCs were CD4+CD25−/dim and expressed interleukin (IL)-10, transforming growth factor-beta, interferon-gamma, IL-2, and inducible nitric oxide synthase (iNOS). These cells (dnIKK2-Treg), cocultured (at up to 1:105 ratio) with a primary MLR, suppressed T-cell proliferation to alloantigens. The regulatory effect was cell-to-cell contact-independent since it was also observed in a transwell system. A nitric oxide synthase inhibitor significantly reverted dnIKK2-Treg-mediated suppression, whereas neutralizing antibodies to IL-10 and TGF-beta had no significant effect. DnIKK2-Treg given in vivo to LW rats prolonged the survival of a kidney allograft from BN rats (the donor rat strain used for generating DCs). Conclusions. DnIKK2-Treg is a unique population of CD4+CD25− T cells expressing high levels of iNOS. These cells potently inhibit T-cell response in vitro and induce prolongation of kidney allograft survival in vivo.

Both darbepoetin alfa and carbamylated erythropoietin prevent kidney graft dysfunction due to ischemia/reperfusion in rats.

Background. Ischemia/reperfusion (I/R) injury is an important cause of renal graft dysfunction. Increases in cold and warm ischemia times lead to a higher risk of early posttransplant complications including delayed graft function and acute rejection. Moreover, prolonged cold ischemia is a predictor of long-term graft loss in kidney transplant patients. Methods. Darbepoetin alfa (DA) and carbamylated nonerythropoietic derivative of erythropoietin (CEPO) protective effects were evaluated in a model of I/R injury after kidney transplantation in both syngeneic and allogeneic combinations. The effects of wortmannin (phosphorylated Akt [p-Akt] inhibitor) administration were also investigated. Serum creatinine was evaluated at 16, 24, 48 hr and at 4 and 7 days posttransplant. Animals were killed 24 hr or 7 days after transplant and kidneys were processed for histological analysis, immunohistochemistry assessment of erythropoietin receptor (EPOR) and &bgr;-common chain receptor expression, granulocyte infiltration, nitrotyrosine staining, p-Akt expression, peritubular capillary (PTC) density, apoptosis, antioxidant, and antiapoptotic gene expression. Results. DA and CEPO significantly reduced serum creatinine, tubular injury, tubular nitrotyrosine staining, and prevented I/R-induced tubular apoptosis, but only when given both to the donor and to the recipient. DA and CEPO cytoprotection was associated with prevention of I/R-induced drop of p-Akt expression in tubuli, and almost complete preservation of capillary density in the tubulointerstitium of the graft. CEPO was more effective than DA in reducing tubular oxidative stress and preserving PTCs. Conclusion. DA and CEPO when given both to the donor and to the recipient, prevented renal graft dysfunction, tubular oxidative stress, and apoptosis after I/R injury in kidney transplantation. Their cytoprotection was mediated by tubular p-Akt activation and PTC density preservation.