CD4+ and CD8+ regulatory T cell characterization in the rat using a unique transgenic Foxp3-EGFP model

BACKGROUND

Regulatory T cells (Treg) in diverse species include CD4⁺ and CD8⁺ T cells. In all species, CD8⁺ Treg have been only partially characterized and there is no rat model in which CD4⁺ and CD8⁺ FOXP3⁺ Treg are genetically tagged.

RESULTS

We generated a Foxp3-EGFP rat transgenic line in which FOXP3 gene was expressed and controlled EGFP. CD4⁺ and CD8⁺ T cells were the only cells that expressed EGFP, in similar proportion as observed with anti-FOXP3 antibodies and co-labeled in the same cells. CD4⁺EGFP⁺ Treg were 5-10 times more frequent than CD8⁺EGFP⁺ Treg. The suppressive activity of CD4⁺ and CD8⁺ Treg was largely confined to EGFP⁺ cells. RNAseq analyses showed similarities but also differences among CD4⁺ and CD8⁺ EGFP⁺ cells and provided the first description of the natural FOXP3⁺CD8⁺ Treg transcriptome. In vitro culture of CD4⁺ and CD8⁺ EGFP^- cells with TGFbeta and IL-2 generated induced EGFP⁺ Treg. CD4⁺ and CD8⁺ EGFP⁺ Treg were expanded upon in vivo administration of a low dose of IL-2.

CONCLUSIONS

This new and unique rat line constitutes a useful model to identify and isolate viable CD4⁺ and CD8⁺ FOXP3⁺ Treg. Additionally, it allows to identify molecules expressed in CD8⁺ Treg that may allow to better define their phenotype and function not only in rats but also in other species.

IL-34 deficiency impairs FOXP3+ Treg function in a model of autoimmune colitis and decreases immune tolerance homeostasis

Background

Immune homeostasis requires fully functional Tregs with a stable phenotype to control autoimmunity. Although IL‐34 is a cytokine first described as mainly involved in monocyte cell survival and differentiation, we recently described its expression by CD8⁺ Tregs in a rat model of transplantation tolerance and by activated FOXP3⁺ CD4⁺ and CD8⁺ Tregs in human healthy individuals. However, its role in autoimmunity and potential in human diseases remains to be determined.

Methods

We generated Il34^−/− rats and using both Il34^−/− rats and mice, we investigated their phenotype under inflammatory conditions. Using Il34^−/− rats, we further analyzed the impact of the absence of expression of IL‐34 for CD4⁺ Tregs suppressive function. We investigated the potential of IL‐34 in human disease to prevent xenogeneic GVHD and human skin allograft rejection in immune humanized immunodeficient NSG mice. Finally, taking advantage of a biocollection, we investigated the correlation between presence of IL‐34 in the serum and kidney transplant rejection.

Results

Here we report that the absence of expression of IL‐34 in Il34^−/− rats and mice leads to an unstable immune phenotype, with production of multiple auto‐antibodies, exacerbated under inflammatory conditions with increased susceptibility to DSS‐ and TNBS‐colitis in Il34^−/− animals. Moreover, we revealed the striking inability of Il34^−/− CD4⁺ Tregs to protect Il2rg^−/− rats from a wasting disease induced by transfer of pathogenic cells, in contrast to Il34^+/+ CD4⁺ Tregs. We also showed that IL‐34 treatment delayed EAE in mice as well as GVHD and human skin allograft rejection in immune humanized immunodeficient NSG mice. Finally, we show that presence of IL‐34 in the serum is associated with a longer rejection‐free period in kidney transplanted patients.

Conclusion

Altogether, our data emphasize on the crucial necessity of IL‐34 for immune homeostasis and for CD4⁺ Tregs suppressive function. Our data also shows the therapeutic potential of IL‐34 in human transplantation and auto‐immunity.

Highlights

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Absence of expression of IL‐34 in Il34^−/− rats and mice leads to an unstable immune phenotype, with a production of multiple auto‐antibodies and exacerbated immune pathology under inflammatory conditions.

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Il34^−/− CD4⁺ Tregs are unable to protect Il2rg^−/− rats from colitis induced by transfer of pathogenic cells.

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IL‐34 treatment delayed EAE in mice, as well as acute GVHD and human skin allograft rejection in immune‐humanized immunodeficient NSG mice.

Anti-CD45RC antibody immunotherapy prevents and treats experimental Autoimmune PolyEndocrinopathy Candidiasis Ectodermal Dystrophy syndrome

Targeted monoclonal antibody (mAb) therapies show great promise for the treatment of transplant rejection and autoimmune diseases by inducing more specific immunomodulatory effects than broadly immunosuppressive drugs routinely used. We recently described the therapeutic advantage of targeting CD45RC, expressed at high levels by conventional T cells (Tconv, CD45RChigh), their precursors and terminally differentiated T (TEMRA) cells, but not by regulatory T cells (Tregs, CD45RClow/-). We demonstrated efficacy of anti-CD45RC mAb treatment in transplantation but its potential has not been examined in autoimmune diseases. APECED is a rare genetic syndrome caused by loss-of-function mutations of the key central tolerance mediator, autoimmune regulator (AIRE) leading to abnormal auto-reactive T cell responses and autoantibodies production. Herein, we showed that, in a rat model of APECED syndrome, anti-CD45RC mAb was effective both as prevention and treatment of autoimmune manifestations and inhibited autoantibody development. Anti-CD45RC mAb intervention depleted CD45RChigh T cells, inhibited CD45RChigh B cells, and restored the Treg/Tconv ratio and the altered Tregs transcriptomic profile. In APECED patients, CD45RC was significantly increased in peripheral blood T cells and lesioned organs from APECED patients were infiltrated by CD45RChigh cells. Our observations highlight the potential role for CD45RChigh cells in the pathogenesis of experimental and human APECED syndrome and the potential of anti-CD45RC antibody treatment.

Cross-Reactive Donor-Specific CD8+ Tregs Efficiently Prevent Transplant Rejection

To reduce the use of non-specific immunosuppressive drugs detrimental to transplant patient health, therapies in development aim to achieve antigen-specific tolerance by promoting antigen-specific regulatory T cells (Tregs). However, identification of the natural antigens recognized by Tregs and the contribution of their dominance in transplantation has been challenging. We identify epitopes derived from distinct major histocompatibility complex (MHC) class II molecules, sharing a 7-amino acid consensus sequence positioned in a central mobile section in complex with MHC class I, recognized by cross-reactive CD8⁺ Tregs, enriched in the graft. Antigen-specific CD8⁺ Tregs can be induced in vivo with a 16-amino acid-long peptide to trigger transplant tolerance. Peptides derived from human HLA class II molecules, harboring the rat consensus sequence, also activate and expand human CD8⁺ Tregs, suggesting its potential in human transplantation. Altogether, this work should facilitate the development of therapies with peptide epitopes for transplantation and improve our understanding of CD8⁺ Treg recognition.

SIRPα/CD47 axis controls the maintenance of transplant tolerance sustained by myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses. Interaction of SIRP alpha (SIRPα), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response regulating macrophages and dendritic cells functions. We previously described that MDSC expressing SIRPα accumulated after transplantation and maintained kidney allograft tolerance. However, the role of the SIRPα/CD47 axis on MDSC function remained unknown. Here, we found that blocking SIRPα or CD47 with monoclonal antibodies (mAbs) induced differentiation of MDSC into myeloid cells overexpressing MHC class II, CD86 costimulatory molecule and increased secretion of macrophage-recruiting chemokines (eg, MCP-1). Using a model of long-term kidney allograft tolerance sustained by MDSC, we observed that administration of blocking anti-SIRPα or CD47 mAbs induced graft dysfunction and rejection. Loss of tolerance came along with significant decrease of MDSC and increase in MCP-1 concentration in the periphery. Graft histological and transcriptomic analyses revealed an inflammatory (M1) macrophagic signature at rejection associated with overexpression of MCP-1 mRNA and protein in the graft. These findings indicate that the SIRPα-CD47 axis regulates the immature phenotype and chemokine secretion of MDSC and contributes to the induction and the active maintenance of peripheral acquired immune tolerance.

Characterization of two rat models of cystic fibrosis-KO and F508del CFTR-Generated by Crispr-Cas9

BACKGROUND

Genetically engineered animals are essential for gaining a proper understanding of the disease mechanisms of cystic fibrosis (CF). The rat is a relevant laboratory model for CF because of its zootechnical capacity, size, and airway characteristics, including the presence of submucosal glands.

METHODS

We describe the generation of a CF rat model (F508del) homozygous for the p.Phe508del mutation in the transmembrane conductance regulator (Cftr) gene. This model was compared to new Cftr -/- rats (CFTR KO). Target organs in CF were examined by histological staining of tissue sections and tooth enamel was quantified by micro-computed tomography. The activity of CFTR was evaluated by nasal potential difference (NPD) and short-circuit current measurements. The effect of VX-809 and VX-770 was analyzed on nasal epithelial primary cell cultures from F508del rats.

RESULTS

Both newborn F508del and Knock out (KO) animals developed intestinal obstruction that could be partly compensated by special diet combined with an osmotic laxative. The two rat models exhibited CF phenotypic anomalies such as vas deferens agenesis and tooth enamel defects. Histology of the intestine, pancreas, liver, and lungs was normal. Absence of CFTR function in KO rats was confirmed ex vivo by short-circuit current measurements on colon mucosae and in vivo by NPD, whereas residual CFTR activity was observed in F508del rats. Exposure of F508del CFTR nasal primary cultures to a combination of VX-809 and VX-770 improved CFTR-mediated Cl- transport.

CONCLUSIONS

The F508del rats reproduce the phenotypes observed in CFTR KO animals and represent a novel resource to advance the development of CF therapeutics.

Generation of gene-edited rats by delivery of CRISPR/Cas9 protein and donor DNA into intact zygotes using electroporation

The generation of gene-edited animals using the CRISPRs/Cas9 system is based on microinjection into zygotes which is inefficient, time consuming and demands high technical skills. We report the optimization of an electroporation method for intact rat zygotes using sgRNAs and Cas9 protein in combination or not with ssODNs (~100 nt). This resulted in high frequency of knockouts, between 15 and 50% of analyzed animals. Importantly, using ssODNs as donor template resulted in precise knock-in mutations in 25–100% of analyzed animals, comparable to microinjection. Electroporation of long ssDNA or dsDNA donors successfully used in microinjection in the past did not allow generation of genome-edited animals despite dsDNA visualization within zygotes. Thus, simultaneous electroporation of a large number of intact rat zygotes is a rapid, simple, and efficient method for the generation of a variety of genome-edited rats.

In Vitro and In Vivo Assessment of T, B and Myeloid Cells Suppressive Activity and Humoral Responses from Transplant Recipients

The main concern in transplantation is to achieve specific tolerance through induction of regulatory cells. The understanding of tolerance mechanisms requires reliable models. Here, we describe models of tolerance to cardiac allograft in rat, induced by blockade of costimulation signals or by upregulation of immunoregulatory molecules through gene transfer. Each of these models allowed in vivo generation of regulatory cells such as regulatory T cells (Tregs), regulatory B cells (Bregs) or regulatory myeloid cells (RegMCs). In this manuscript, we describe two complementary protocols that have been used to identify and define in vitro and in vivo regulatory cell activity to determine their responsibility in tolerance induction and maintenance. First, an in vitro suppressive assay allowed rapid identification of cells with suppressive capacity on effector immune responses in a dose dependent manner, and can be used for further analysis such as cytokine measurement or cytotoxicity. Second, the adoptive transfer of cells from a tolerant treated recipient to a newly irradiated grafted recipient, highlighted the tolerogenic properties of these cells in controlling graft directed immune responses and/or converting new regulatory cells (termed infectious tolerance). These methods are not restricted to cells with known phenotypic markers and can be extended to any cell population. Furthermore, donor directed allospecificity of regulatory cells (an important goal in the field) can be assessed by using third party donor cells or graft either in vitro or in vivo. Finally, to determine the specific tolerogenic capacity of these regulatory cells, we provide protocols to assess the humoral anti-donor antibody responses and the capacity of the recipient to develop humoral responses against new or former known antigens. The models of tolerance described can be used to further characterize regulatory cells, to identify new biomarkers, and immunoregulatory molecules, and are adaptable to other transplantation models or autoimmune diseases in rodent or human.

Advances in transgenic animal models and techniques

On May 11th and 12th 2017 was held in Nantes, France, the international meeting "Advances in transgenic animal models and techniques" ( http://www.trm.univ-nantes.fr/ ). This biennial meeting is the fifth one of its kind to be organized by the Transgenic Rats ImmunoPhenomic (TRIP) Nantes facility ( http://www.tgr.nantes.inserm.fr/ ). The meeting was supported by private companies (SONIDEL, Scionics computer innovation, New England Biolabs, MERCK, genOway, Journal Disease Models and Mechanisms) and by public institutions (International Society for Transgenic Technology, University of Nantes, INSERM UMR 1064, SFR François Bonamy, CNRS, Région Pays de la Loire, Biogenouest, TEFOR infrastructure, ITUN, IHU-CESTI and DHU-Oncogeffe and Labex IGO). Around 100 participants, from France but also from different European countries, Japan and USA, attended the meeting.

Comparative Analysis of piggyBac, CRISPR/Cas9 and TALEN Mediated BAC Transgenesis in the Zygote for the Generation of Humanized SIRPA Rats

BAC transgenic mammalian systems offer an important platform for recapitulating human gene expression and disease modeling. While the larger body mass, and greater genetic and physiologic similarity to humans render rats well suited for reproducing human immune diseases and evaluating therapeutic strategies, difficulties of generating BAC transgenic rats have hindered progress. Thus, an efficient method for BAC transgenesis in rats would be valuable. Immunodeficient mice carrying a human SIRPA transgene have previously been shown to support improved human cell hematopoiesis. Here, we have generated for the first time, human SIRPA BAC transgenic rats, for which the gene is faithfully expressed, functionally active, and germline transmissible. To do this, human SIRPA BAC was modified with elements to work in coordination with genome engineering technologies-piggyBac, CRISPR/Cas9 or TALEN. Our findings show that piggyBac transposition is a more efficient approach than the classical BAC transgenesis, resulting in complete BAC integration with predictable end sequences, thereby permitting precise assessment of the integration site. Neither CRISPR/Cas9 nor TALEN increased BAC transgenesis. Therefore, an efficient generation of human SIRPA transgenic rats using piggyBac opens opportunities for expansion of humanized transgenic rat models in the future to advance biomedical research and therapeutic applications.

Genome Editing in Rats Using TALE Nucleases

The rat is an important animal model to understand gene function and model human diseases. Since recent years, the development of gene-specific nucleases has become important for generating new rat models of human diseases, to analyze the role of genes and to generate human antibodies. Transcription activator-like (TALE) nucleases efficiently create gene-specific knockout rats and lead to the possibility of gene targeting by homology-directed recombination (HDR) and generating knock-in rats. We describe a detailed protocol for generating knockout and knock-in rats via microinjection of TALE nucleases into fertilized eggs. This technology is an efficient, cost- and time-effective method for creating new rat models.

Homology-directed repair in rodent zygotes using Cas9 and TALEN engineered proteins

The generation of genetically-modified organisms has been revolutionized by the development of new genome editing technologies based on the use of gene-specific nucleases, such as meganucleases, ZFNs, TALENs and CRISPRs-Cas9 systems. The most rapid and cost-effective way to generate genetically-modified animals is by microinjection of the nucleic acids encoding gene-specific nucleases into zygotes. However, the efficiency of the procedure can still be improved. In this work we aim to increase the efficiency of CRISPRs-Cas9 and TALENs homology-directed repair by using TALENs and Cas9 proteins, instead of mRNA, microinjected into rat and mouse zygotes along with long or short donor DNAs. We observed that Cas9 protein was more efficient at homology-directed repair than mRNA, while TALEN protein was less efficient than mRNA at inducing homology-directed repair. Our results indicate that the use of Cas9 protein could represent a simple and practical methodological alternative to Cas9 mRNA in the generation of genetically-modified rats and mice as well as probably some other mammals.

Regulatory B Cells with a Partial Defect in CD40 Signaling and Overexpressing Granzyme B Transfer Allograft Tolerance in Rodents

Emerging knowledge regarding B cells in organ transplantation has demonstrated that these cells can no longer be taken as mere generators of deleterious Abs but can also act as beneficial players. We previously demonstrated in a rat model of cardiac allograft tolerance induced by short-term immunosuppression an accumulation in the blood of B cells overexpressing inhibitory molecules, a phenotype also observed in the blood of patients that spontaneously develop graft tolerance. In this study, we demonstrated the presence in the spleen of regulatory B cells enriched in the CD24(int)CD38(+)CD27(+)IgD(-)IgM(+/low) subpopulation, which are able to transfer donor-specific tolerance via IL-10 and TGF-β1-dependent mechanisms and to suppress in vitro TNF-α secretion. Following anti-CD40 stimulation, IgD(-)IgM(+/low) B cells were blocked in their plasma cell differentiation pathway, maintained high expression of the inhibitory molecules CD23 and Bank1, and upregulated Granzyme B and Irf4, two molecules described as highly expressed by regulatory B cells. Interestingly, these B cells recognized specifically a dominant donor Ag, suggesting restricted specificity that could lead to a particular B cell response. Regulatory B cells were not required for induction of tolerance and appeared following Foxp3(+)CD4(+)CD25(+) regulatory T cells, suggesting cooperation with regulatory T cells for their expansion. Nevertheless, following transfer to new recipients, these B cells migrated to the allograft, kept their regulatory profile, and promoted local accumulation of Foxp3(+)CD4(+)CD25(+) regulatory T cells. Mechanisms of regulatory B cells and their cell therapy potential are important to decipher in experimental models to pave the way for future developments in the clinic.

IL-34 is a Treg-specific cytokine and mediates transplant tolerance

Cytokines and metabolic pathway-controlling enzymes regulate immune responses and have potential as powerful tools to mediate immune tolerance. Blockade of the interaction between CD40 and CD40L induces long-term cardiac allograft survival in rats through a CD8+CD45RClo Treg potentiation. Here, we have shown that the cytokine IL-34, the immunoregulatory properties of which have not been previously studied in transplantation or T cell biology, is expressed by rodent CD8+CD45RClo Tregs and human FOXP3+CD45RCloCD8+ and CD4+ Tregs. IL-34 was involved in the suppressive function of both CD8+ and CD4+ Tregs and markedly inhibited alloreactive immune responses. Additionally, in a rat cardiac allograft model, IL-34 potently induced transplant tolerance that was associated with a total inhibition of alloantibody production. Treatment of rats with IL-34 promoted allograft tolerance that was mediated by induction of CD8+ and CD4+ Tregs. Moreover, these Tregs were capable of serial tolerance induction through modulation of macrophages that migrate early to the graft. Finally, we demonstrated that human macrophages cultured in the presence of IL-34 greatly expanded CD8+ and CD4+ FOXP3+ Tregs, with a superior suppressive potential of antidonor immune responses compared with non-IL-34-expanded Tregs. In conclusion, we reveal that IL-34 serves as a suppressive Treg-specific cytokine and as a tolerogenic cytokine that efficiently inhibits alloreactive immune responses and mediates transplant tolerance.

Efficient gene targeting by homology-directed repair in rat zygotes using TALE nucleases

The generation of genetically modified animals is important for both research and commercial purposes. The rat is an important model organism that until recently lacked efficient genetic engineering tools. Sequence-specific nucleases, such as ZFNs, TALE nucleases, and CRISPR/Cas9 have allowed the creation of rat knockout models. Genetic engineering by homology-directed repair (HDR) is utilized to create animals expressing transgenes in a controlled way and to introduce precise genetic modifications. We applied TALE nucleases and donor DNA microinjection into zygotes to generate HDR-modified rats with large new sequences introduced into three different loci with high efficiency (0.62%–5.13% of microinjected zygotes). Two of these loci (Rosa26 and Hprt1) are known to allow robust and reproducible transgene expression and were targeted for integration of a GFP expression cassette driven by the CAG promoter. GFP-expressing embryos and four Rosa26 GFP rat lines analyzed showed strong and widespread GFP expression in most cells of all analyzed tissues. The third targeted locus was Ighm, where we performed successful exon exchange of rat exon 2 for the human one. At all three loci we observed HDR only when using linear and not circular donor DNA. Mild hypothermic (30°C) culture of zygotes after microinjection increased HDR efficiency for some loci. Our study demonstrates that TALE nuclease and donor DNA microinjection into rat zygotes results in efficient and reproducible targeted donor integration by HDR. This allowed creation of genetically modified rats in a work-, cost-, and time-effective manner.

Gene targeting in rats using transcription activator-like effector nucleases

The rat is a model of choice to understanding gene function and modeling human diseases. Since recent years, successful engineering technologies using gene-specific nucleases have been developed to gene edit the genome of different species, including the rat. This development has become important for the creation of new rat animals models of human diseases, analyze the role of genes and express recombinant proteins. Transcription activator-like (TALE) nucleases are designed nucleases consist of a DNA binding domain fused to a nuclease domain capable of cleaving the targeted DNA. We describe a detailed protocol for generating knockout rats via microinjection of TALE nucleases into fertilized eggs. This technology is an efficient, cost- and time-effective method for creating new rat models.

Generation of Rag1-knockout immunodeficient rats and mice using engineered meganucleases

Despite the recent availability of gene-specific nucleases, such as zinc-finger nucleases (ZFNs) and transcription activator-like nucleases (TALENs), there is still a need for new tools to modify the genome of different species in an efficient, rapid, and less costly manner. One aim of this study was to apply, for the first time, engineered meganucleases to mutate an endogenous gene in animal zygotes. The second aim was to target the mouse and rat recombination activating gene 1 (Rag1) to describe, for the first time, Rag1 knockout immunodeficient rats. We microinjected a plasmid encoding a meganuclease for Rag1 into the pronucleus of mouse and rat zygotes. Mutant animals were detected by PCR sequencing of the targeted sequence. A homozygous RAG1-deficient rat line was generated and immunophenotyped. Meganucleases were efficient, because 3.4 and 0.6% of mouse and rat microinjected zygotes, respectively, generated mutated animals. RAG1-deficient rats showed significantly decreased proportions and numbers of immature and mature T and B lymphocytes and normal NK cells vs. littermate wild-type controls. In summary, we describe the use of engineered meganucleases to inactivate an endogenous gene with efficiencies comparable to those of ZFNs and TALENs. Moreover, we generated an immunodeficient rat line useful for studies in which there is a need for biological parameters to be analyzed in the absence of immune responses.

Control of transplant tolerance and intragraft regulatory T cell localization by myeloid-derived suppressor cells and CCL5

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature cells that are believed to inhibit immune responses in the contexts of cancer and organ transplantation, in association with regulatory T cells (Treg). However, the way in which MDSC cooperate with Treg remains elusive. In this study, we used DNA microarrays to analyze gene expression in blood-derived MDSC from rat recipients of kidney allografts. We found CCL5 (Rantes), a chemotactic C-C motif 5 chemokine, to be strongly downregulated after treatment with a tolerizing regimen. The amount of CCL5 protein was also lower in the plasma of tolerant recipients, whereas intragraft CCL5 was unchanged. Because CCL5 is chemotactic for Treg, we hypothesized that a gradient of CCL5 between the graft and peripheral blood might contribute to the intragraft localization of Treg in tolerant animals. To test this hypothesis, we treated tolerant rat recipients of kidney allografts with recombinant rat CCL5 to restore normal plasma concentrations. This led to a strong reduction in intragraft Treg monitored by immunohistofluorescence and by quantitative real-time PCR measurement of Foxp3 mRNA. Ultimately, this treatment led to an increase in serum creatinine concentrations and to kidney graft rejection after about a month. The kidney function of syngeneic grafts was not affected by a similar administration of CCL5. These data highlight the contribution of MDSC to the establishment of a graft-to-periphery CCL5 gradient in tolerant kidney allograft recipients, which controls recruitment of Treg to the graft where they likely contribute to maintaining tolerance.

Effects of BCL-2 over-expression on B cells in transgenic rats and rat hybridomas

The rat is an important biomedical experimental model that benefited from the recent development of new transgenic and knockout techniques. With the goal to optimize rat mAb production and to analyze the impact of Bcl-2 on B-cell development, we generated bcl-2 transgenic rats. Transgenic rats showed Bcl-2 over-expression in B cells, increased B cell numbers in lymphoid organs, elevated production of immunoglobulins (Igs) and prolonged B-cell survival in vitro. Transgenic rats remained healthy, reproduced normally and did not develop autoimmunity. Fusions with bcl-2 transgenic splenocytes did not result in increased hybridoma generation. A comparison of on- and off-rates of 39 mAbs generated with bcl-2 transgenic and wild-type animals revealed no significant differences. Over-expression of Bcl-2 in hybridomas did not change cell proliferation but resulted in increased Ig production. Bcl-2 transgenic rats will be a useful tool for the generation of rat mAbs, the analysis of B cells in different pathophysiological models, such as autoimmunity, cancer or organ transplantation, and the study of rat B-cell biology.

Effects of Human Alpha-Synuclein A53T-A30P Mutations on SVZ and Local Olfactory Bulb Cell Proliferation in a Transgenic Rat Model of Parkinson Disease

A transgenic Sprague Dawley rat bearing the A30P and A53T α-synuclein (α-syn) human mutations under the control of the tyrosine hydroxylase promoter was generated in order to get a better understanding of the role of the human α-syn mutations on the neuropathological events involved in the progression of the Parkinson's disease (PD). This rat displayed olfactory deficits in the absence of motor impairments as observed in most early PD cases. In order to investigate the role of the mutated α-syn on cell proliferation, we focused on the subventricular zone (SVZ) and the olfactory bulbs (OB) as a change of the proliferation could affect OB function. The effect on OB dopaminergic innervation was investigated. The human α-syn co-localized in TH-positive OB neurons. No human α-syn was visualized in the SVZ. A significant increase in resident cell proliferation in the glomerular but not in the granular layers of the OB and in the SVZ was observed. TH innervation was significantly increased within the glomerular layer without an increase in the size of the glomeruli. Our rat could be a good model to investigate the role of human mutated α-syn on the development of olfactory deficits.

TNF blockade abrogates the induction of T cell-dependent humoral responses in an allotransplantation model

TNF blockade modulates many aspects of the immune response and is commonly used in a wide array of immune-mediated inflammatory diseases. As anti-TNF induces anti-dsDNA IgM antibodies but not other antinuclear reactivities in human arthritis, we investigated here the effect of TNF blockade on the induction of TD humoral responses using cardiac allograft and xenograft models. A single injection of an anti-rat TNF antibody in LEW.1A recipients grafted with congenic LEW.1W hearts almost completely abrogated the induction of IgM and IgG alloantibodies. This was associated with decreased Ig deposition and leukocyte infiltration in the graft at Day 5. TNF blockade did not affect germinal-center formation in the spleen or expression of Th1/Th2 cytokines, costimulatory and regulatory molecules, and TLRs in spleen and graft of the recipient animals. Clinically, the abrogation of the induction of the alloantibodies was associated with a marked prolongation of graft survival. In contrast, anti-TNF did not alter acute xenograft rejection mediated by TI antibodies in a hamster-to-rat model. Taken together, these data indicate that TNF blockade abrogates the induction of TD humoral responses and accordingly, may have a beneficial effect in antibody-mediated inflammatory pathologies.

Long-term allograft tolerance is characterized by the accumulation of B cells exhibiting an inhibited profile

Numerous reports have highlighted the central role of regulatory T cells in long-term allograft tolerance, but few studies have investigated the B-cell aspect. We analyzed the B-cell response in a rat model of long-term cardiac allograft tolerance induced by a short-term immunosuppression. We observed that tolerated allografts are infiltrated by numerous B cells organized in germinal centers that are strongly regulated in their IgG alloantibody response. Moreover, alloantibodies from tolerant recipients exhibit a deviation toward a Th2 isotype and do not activate in vitro donor-type endothelial cells in a pro-inflammatory way but maintained expression of cytoprotective molecules. Interestingly, this inhibition of the B-cell response is characterized by the progressive accumulation in the graft and in the blood of B cells blocked at the IgM to IgG switch recombination process and overexpressing BANK-1 and the inhibitory receptor Fcgr2b. Importantly, B cells from tolerant recipients are able to transfer allograft tolerance. Taken together, these results demonstrate a strong regulation of the alloantibody response in tolerant recipients and the accumulation of B cells exhibiting an inhibited and regulatory profile. These mechanisms of regulation of the B-cell response could be instrumental to develop new strategies to promote tolerance.

Characterization of immunoglobulin heavy chain knockout rats

The rat is a species frequently used in immunological studies but, until now, there were no models with introduced gene-specific mutations. In a recent study, we described for the first time the generation of novel rat lines with targeted mutations using zinc-finger nucleases. In this study, we compare immune development in two Ig heavy-chain KO lines; one with truncated Cμ and a new line with removed JH segments. Rats homozygous for IgM mutation generate truncated Cμ mRNA with a de novo stop codon and no Cγ mRNA. JH-deletion rats showed undetectable mRNA for all H-chain transcripts. No serum IgM, IgG, IgA and IgE were detected in these rat lines. In both lines, lymphoid B-cell numbers were reduced >95% versus WT animals. In rats homozygous for IgM mutation, no Ab-mediated hyperacute allograft rejection was encountered. Similarities in B-cell differentiation seen in Ig KO rats and ES cell-derived Ig KO mice are discussed. These Ig and B-cell-deficient rats obtained using zinc-finger nucleases-technology should be useful as biomedical research models and a powerful platform for transgenic animals expressing a human Ab repertoire.

Development of initial idiopathic nephrotic syndrome and post-transplantation recurrence: evidence of the same biological entity

BACKGROUND

Buffalo/Mna rats spontaneously develop a nephrotic syndrome (NS). We have demonstrated that this rat nephropathy recurs after renal transplantation. We studied this recurrence by kinetic analysis of graft lesions, infiltrating cells and cytokines.

METHODS

Kidneys from LEW.1 W rats were grafted into proteinuric Buff/Mna or healthy Wistar Furth recipients. Kidney samples were harvested before, during and after the occurrence of proteinuria and analysed for renal histology, cell populations and cytokine transcripts. Results were compared with the evolution of the initial disease studied previously.

RESULTS

Both groups showed normal graft histology at Day 7 and an increasing podocyte swelling at Day 45 was seen only in the Buff/Mna recipients. At Day 80, glomerular atrophy with podocytosis and focal segmental glomerular sclerosis lesions, accompanied by tubular dilatation, appeared in the Buff/Mna group. At Day 122, the intensity of the tubular and glomerular lesions increased in Buff/Mna recipients but not in the control group. An analysis of desmin and Kim-1 (early markers of glomerular and tubular damage, respectively) transcripts expression showed that glomerular lesions precede tubular injury in this model. A monocyte infiltration associated with an increase in TNFα, IL1 and IL12 transcripts appeared before the recurrence. An early increase in Cbeta TCR transcripts with a predominant Th2 profile was observed, highlighting a Th2 polarization in the Buff/Mna recurrence.

CONCLUSIONS

The comparison of profiles of recurrence and initial disease highlighted the same mediators for both events. We propose that initial Buff/Mna idiopathic nephrotic syndrome (INS) and post-transplantation recurrence represent the same entity and a valuable tool for the study of recurring INS.

Lentiviral vectors that express UGT1A1 in liver and contain miR-142 target sequences normalize hyperbilirubinemia in Gunn rats

BACKGROUND & AIMS

Crigler-Najjar type 1 (CN-I) is an inherited liver disease caused by an absence of bilirubin-uridine 5'-diphosphate-glucuronosyltransferase (UGT1A1) activity. It results in life-threatening levels of unconjugated bilirubin, and therapeutic options are limited. We used adult Gunn rats (an animal model of the disease) to evaluate the efficiency of lentiviral-based gene therapy to express UGT1A1 in liver.

METHODS

Gunn rats were given intraportal injections of VSVG-pseudotyped lentiviral vectors that encode UGT1A1 under the control of a liver-specific transthyretin promoter (mTTR.hUGT1A1); this vector does not contain target sequences for miR-142, a microRNA that is expressed specifically in hematopoietic cells. Rats were also injected with the vector mTTR.hUGT1A1.142T, which contains 4 copies of the miR-142 target sequences; its messenger RNA should be degraded in antigen-presenting cells. Bilirubinemia was monitored, and the presence of transduced hepatocytes was analyzed by quantitative polymerase chain reaction. Vector expression was tested in vitro in rat hematopoietic cells.

RESULTS

In Gunn rats, bilirubin levels normalized 2 weeks after administration of mTTR.hUGT1A1. However, hyperbilirubinemia resumed 8 weeks after vector administration, concomitant with the induction of an immune response. In contrast, in rats injected with mTTR-UGT1A1.142T, bilirubin levels normalized for up to 6 months and transduced cells were not eliminated.

CONCLUSIONS

Lentiviral vectors that express UGT1A1 reduce hyperbilirubinemia in immunocompetent Gunn rats for at least 6 months. The immune response against virally expressed UGT1A1 can be circumvented by inclusion of miR-142 target sequences, which reduce vector expression in antigen-presenting cells. This lentiviral-based gene therapy approach might be developed to treat patients with CN-I.

Mechanism and localization of CD8 regulatory T cells in a heart transplant model of tolerance

Despite accumulating evidence for the importance of allospecific CD8(+) regulatory T cells (Tregs) in tolerant rodents and free immunosuppression transplant recipients, mechanisms underlying CD8(+) Treg-mediated tolerance remain unclear. By using a model of transplantation tolerance mediated by CD8(+) Tregs following CD40Ig treatment in rats, in this study, we show that the accumulation of tolerogenic CD8(+) Tregs and plasmacytoid dendritic cells (pDCs) in allograft and spleen but not lymph nodes was associated with tolerance induction in vascularized allograft recipients. pDCs preferentially induced tolerogenic CD8(+) Tregs to suppress CD4(+) effector cells responses to first-donor Ags in vitro. When tolerogenic CD8(+) Tregs were not in contact with CD4(+) effector cells, suppression was mediated by IDO. Contact with CD4(+) effector cells resulted in alternative suppressive mechanisms implicating IFN-gamma and fibroleukin-2. In vivo, both IDO and IFN-gamma were involved in tolerance induction, suggesting that contact with CD4(+) effector cells is crucial to modulate CD8(+) Tregs function in vivo. In conclusion, CD8(+) Tregs and pDCs interactions were necessary for suppression of CD4(+) T cells and involved different mechanisms modulated by the presence of cell contact between CD8(+) Tregs, pDCs, and CD4(+) effector cells.

New lines of GFP transgenic rats relevant for regenerative medicine and gene therapy

Adoptive cell transfer studies in regenerative research and identification of genetically modified cells after gene therapy in vivo require unequivocally identifying and tracking the donor cells in the host tissues, ideally over several days or for up to several months. The use of reporter genes allows identifying the transferred cells but unfortunately most are immunogenic to wild-type hosts and thus trigger rejection in few days. The availability of transgenic animals from the same strain that would express either high levels of the transgene to identify the cells or low levels but that would be tolerant to the transgene would allow performing long-term analysis of labelled cells. Herein, using lentiviral vectors we develop two new lines of GFP-expressing transgenic rats displaying different levels and patterns of GFP-expression. The "high-expresser" line (GFP(high)) displayed high expression in most tissues, including adult neurons and neural precursors, mesenchymal stem cells and in all leukocytes subtypes analysed, including myeloid and plasmacytoid dendritic cells, cells that have not or only poorly characterized in previous GFP-transgenic rats. These GFP(high)-transgenic rats could be useful for transplantation and immunological studies using GFP-positive cells/tissue. The "low-expresser" line expressed very low levels of GFP only in the liver and in less than 5% of lymphoid cells. We demonstrate these animals did not develop detectable humoral and cellular immune responses against both transferred GFP-positive splenocytes and lentivirus-mediated GFP gene transfer. Thus, these GFP-transgenic rats represent useful tools for regenerative medicine and gene therapy.

Analysis by quantitative PCR of zygosity in genetically modified organisms

It is extremely useful to define a rapid and accurate method for identifying homozygous and heterozygous transgenic animals prior to setting up breeding programs for transgenic colonies and in experiments in which gene dosage effects could have a functional impact. Southern-blotting is a means of identifying zygosity, but such a method is time consuming and produces a high level of ambiguous results. Some years ago, we described the rapid, precise, non-ambiguous, and high-throughput identification of zygosity in transgenic animals by real-time PCR. This technique allows us to make a clear-cut identification of transgenic rats, transgenic mice, and double-transgenic pigs. Since 2002, however, several authors have made improvements to this method. The following paper describes the ease with which zygosity is determined using real-time PCR.

Generation of gene-specific mutated rats using zinc-finger nucleases

The genetic dissection of physiological and pathological traits in laboratory model organisms is accelerated by the ability to engineer loss-of-function mutations at investigator-specified loci. This chapter describes the use of zinc-finger nucleases (ZFNs) for the targeted disruption of endogenous rat genes directly in the embryo. ZFNs can specifically disrupt target genes in cultured rat cells and in embryos from inbred and outbred strains, leading to permanently genetically modified animals. This technology allows for the rapid, targeted modification of the rat genome.

Generation of transgenic rats by microinjection of short DNA fragments

Here we describe an efficient technique to generate transgenic rats by microinjection of short DNA fragments. We have focused on optimal conditions for superovulation of prepubescent females Sprague-Dawley (CD) strains to have good quality embryos, pseudopregnant females, zygotes preparation, optimal conditions for microinjection and embryo transfer into foster mothers.

The use of lentiviral vectors to obtain transgenic rats

Lentiviral vectors are now well recognized as good vehicles for gene delivery. This is because they can efficiently transduce both dividing and post-mitotic cells, and stably integrate into the host genome allowing for long-term expression of the transgene. Their potential utility for the generation of transgenic animals has been recognized as an attractive and promising alternative to the conventional DNA-microinjection method which lacks efficiency. The initial success of lentiviral transgenesis in mice considerably broadened its use in other species, in which classical transgenic techniques are difficult, such as in the rat.In this chapter, we describe detailed procedures for both the production of human immunodeficiency virus-1 (HIV-1)-derived lentiviral vectors and for the generation of transgenic rats by injection of these vectors into the perivitelline space of fertilized one-cell eggs.

Autoimmune responses against renal tissue proteins in long-term surviving allograft recipients

Major histocompatibility complex antigens (MHC) are classical targets of recipient responses to allotransplants. However, the role of an immune response directed against autologous graft tissue determinants is poorly defined. In this study, we investigated (i) whether autologous kidney tissue extract can induce an immune response to autologous kidney proteins in normal rats, and (ii) if a similar autologous response develops in the long-term surviving LEW.1A recipients of an MHC-mismatched LEW.1W kidney (RT1(u) to RT1(a)). LEW.1A rats immunized with allo- or syngeneic soluble kidney extracts developed a T-cell response to self antigens as shown by the frequency of specific IFN-gamma-producing T cells from LEW.1A rats in the presence of extracts (ELISPOT). In contrast, they responded only marginally to dominant RT1(u) determinants. The ELISPOT against fractions of soluble autologous kidney extracts separated by an FPLC gel-filtration system indicated a preferential response to megalin, a high molecular weight protein that has been shown to be involved in experimental Heymann nephritis. In a model of long-term kidney allograft survival by anti-CD28 administration, recipients also developed humoral but not cellular responses to megalin. Our data suggest that autoimmune processes develop in long-term surviving kidney allograft recipients.

Indirect CD4+ TH1 response, antidonor antibodies and diffuse C4d graft deposits in long-term recipients conditioned by donor antigens priming

Priming of recipients by DST induces long-term survival of mismatched allografts in adult rats. Despite these recipients developing inducible T regulatory cells able to transfer long-term graft survival to a secondary host, a state of chronic rejection is also observed. We revisited the molecular donor MHC targets of the cellular response in acute rejection and analyzed the cellular and humoral responses in recipients with long-term graft survival following transplantation. We found three immunodominant peptides, all derived from LEW.1W RT1.D(u) molecules to be involved in acute rejection of grafts from unmodified LEW.1A recipients. Although the direct pathway of allorecognition was reduced in DST-treated recipients, the early CD4+ indirect pathway response to dominant peptides was almost unimpaired. We also detected early and sustained antidonor class I and II antibody subtypes with diffuse C4d deposits on graft vessels. Finally, long-term accepted grafts displayed leukocyte infiltration, endarteritis and fibrosis, which evolved toward vascular narrowing at day 100. Altogether, these data suggest that the chronic graft lesions developed in long-term graft recipients are the result of progressive humoral injury associated with a persisting indirect T helper response. These features may represent a useful model for understanding and manipulating chronic active antibody-mediated rejection in human.

Induction of T regulatory cells attenuates idiopathic nephrotic syndrome

Buffalo/Mna rats spontaneously develop FSGS and nephrotic syndrome as a result of an immune disorder. Similar to some humans with FSGS, the disease recurs after renal transplantation, suggesting the involvement of a circulating factor. Here, we tested the effect of several immunosuppressive treatments on these rats. Although corticosteroids, cyclosporin A, and anti-T cell receptor treatment reduced proteinuria, only the deoxyspergualin derivative LF15-0195 led to a rapid and complete normalization of proteinuria. Furthermore, this compound led to the regression of renal lesions during both the initial disease and posttransplantation recurrence. The frequency of splenic and peripheral CD4+CD25+FoxP3+ T lymphocytes significantly increased with remission. Moreover, the transfer of purified LF15-0195-induced CD4+CD25+ T cells to irradiated Buff/Mna rats significantly reduced their proteinuria compared with the transfer of untreated control cells, suggesting that LF15-0195 induces regulatory T cells that are able to induce regression of rat nephropathy. These data suggest that idiopathic nephrotic syndrome/FSGS disease can be regulated by cellular transfer, but how this regulation leads to the reorganization of the podocyte cytoskeleton remains to be determined.

Implication of matrix metalloproteinase 7 and the noncanonical wingless-type signaling pathway in a model of kidney allograft tolerance induced by the administration of anti-donor class II antibodies

In rats, tolerance to MHC-incompatible renal allografts can be induced by the administration of anti-donor class II Abs on the day of transplantation. In this study we explored the mechanisms involved in the maintenance phase of this tolerance by analyzing intragraft gene expression profiles by microarray in long-term accepted kidneys. Comparison of the gene expression patterns of tolerated to syngeneic kidneys revealed 5,954 differentially expressed genes (p < 0.05). Further analysis of this gene set revealed a key role for the wingless-type (WNT) signaling pathway, one of the pivotal pathways involved in cell regulation that has not yet been implicated in transplantation. Several genes within this pathway were significantly up-regulated in the tolerated grafts, particularly matrix metalloproteinase 7 (MMP7; fold change > 40). Analysis of several other pathway-related molecules indicated that MMP7 overexpression was the result of the noncanonical WNT signaling pathway. MMP7 expression was restricted to vascular smooth muscle cells and was specific to anti-class II Ab-induced tolerance, as it was undetectable in other models of renal and heart transplant tolerance and chronic rejection induced across the same strain combination. These results suggest a novel role for noncanonical WNT signaling in maintaining kidney transplant tolerance in this model, with MMP7 being a key target. Determining the mechanisms whereby MMP7 contributes to transplant tolerance may help in the development of new strategies to improve long-term graft outcome.

Anti-CD28 antibodies modify regulatory mechanisms and reinforce tolerance in CD40Ig-treated heart allograft recipients

Blockade of CD40-CD40 ligand (CD40L) costimulation has been shown to synergize with that of CTLA4/CD28-B7 to promote transplant tolerance. To date, however, CD28-B7 interactions have been prevented using B7-blocking reagents like CTLA4-Ig that inhibit CD28-B7 together with CTLA4-B7 interactions. In this study, we have tested anti-CD28 Abs to prevent selectively CD28-B7 interactions while preserving CTLA4-B7 in addition to CD40-CD40L blockade. In the LEW.1W to LEW.1A rat combination, interfering with CD40-CD40L interactions by CD40Ig administration through gene transfer resulted in indefinite heart allograft survival due to the appearance of clonotypic CD8+CD45RClow regulatory T cells that were capable of transferring the tolerant state to naive animals. However, cardiac transplants in these recipients systematically developed chronic rejection lesions. Whereas anti-CD28 Ab monotherapy only delayed acute rejection and failed to induce tolerance, coadministration of anti-CD28 Abs and CD40Ig resulted in the long-term acceptation of allografts without chronic rejection lesions in 60% of the recipients, reduced the level of intragraft mRNA transcripts for cytokines and immune factors, and fully abrogated alloantibody production. In addition, the nature of regulatory cells was modified: the CD8+CD45RClow clonotypic T cells described in the CD40Ig-treated animals could not be found in cotreated animals, and the other CD8+CD45RClow cells had no regulatory activity and a different cytokine expression profile. Instead, in cotreated recipients we found IDO-dependent non-T cells with regulatory activity in vitro. Thus, the addition of a short-term anti-CD28 treatment with CD40Ig resulted in decreased heart allograft chronic rejection lesions, complete inhibition of Ab production, and modified regulatory mechanisms.

CD40Ig treatment results in allograft acceptance mediated by CD8CD45RC T cells, IFN-gamma, and indoleamine 2,3-dioxygenase

Treatment with CD40Ig results in indefinite allograft survival in a complete MHC-mismatched heart allograft model in the rat. Here we show that serial second, third, and fourth adoptive transfers of total splenocytes from CD40Ig-treated recipients into secondary recipients led to indefinite donor-specific allograft acceptance. Purification of splenocyte subpopulations from CD40Ig-treated recipients demonstrated that only the adoptively transferred CD8(+)CD45RC(low) subset resulted in donor-specific long-term survival, whereas CD8(+)CD45RC(low) T cells from naive animals did not. Accepted grafts displayed increased indoleamine 2,3-dioxygenase (IDO) expression restricted in the graft to ECs. Coculture of donor ECs with CD8(+)CD45RC(low) T cells purified from CD40Ig-treated animals resulted in donor-specific IDO expression dependent on IFN-gamma. Neutralization of IFN-gamma or IDO triggered acute allograft rejection in both CD40Ig-treated and adoptively transferred recipients. This study demonstrates for what we believe to be the first time that interference in CD40-CD40 ligand (CD40-CD40L) interactions induces allospecific CD8(+) Tregs that maintain allograft survival. CD8(+)CD45RC(low) T cells act through IFN-gamma production, which in turn induces IDO expression by graft ECs. Thus, donor alloantigen-specific CD8(+) Tregs may promote local graft immune privilege through IDO expression.

Dominant Tolerance to Kidney Allografts Induced by Anti-Donor MHC Class II Antibodies: Cooperation between T and Non-T CD103+Cells

Allograft acceptance can be induced in the rat by pretransplant infusion of donor blood or spleen cells. Although promoting long-term acceptance, this treatment is also associated with chronic rejection. In this study, we show that a single administration of anti-donor MHC class II alloimmune serum on the day of transplantation results in indefinite survival of a MHC-mismatched kidney graft. Long-term recipients accept a donor-type skin graft and display no histological evidence of chronic rejection. The kidney grafts of tolerant animals display an accumulation of TCR Cbeta, FoxP3, and IDO transcripts. Moreover, as compared with syngeneic recipients, tolerant recipients harbor a large infiltrate of MHC class II(+) cells and CD103(+) cells. In vitro, splenocytes from tolerant recipients exhibit decreased donor-specific proliferation, which is restored by depletion of non-T cells and partially restored by the blockade of IDO. Finally, splenocytes from tolerant recipients, but not purified T cell splenocytes, transfer donor-specific infectious tolerance without chronic rejection, after infusion into naive recipients, over two generations. However, splenocytes depleted of T cells or splenocytes depleted of CD103(+) cells fail to transfer tolerance. Collectively, these data show that a single administration of anti-donor MHC class II alloimmune serum induces a tolerant state characterized by an infiltration of the kidney graft by regulatory T cells and CD103(+) cells. These data also show that the transfer of tolerance requires the presence of both T cells and CD103(+) dendritic cells. The precise mechanism of cooperation of these two cell subsets remains to be defined.

Transgenic modifications of the rat genome

The laboratory rat (R. norvegicus) is a very important experimental animal in several fields of biomedical research. This review describes the various techniques that have been used to generate transgenic rats: classical DNA microinjection and more recently described techniques such as lentiviral vector-mediated DNA transfer into early embryos, sperm-mediated transgenesis, embryo cloning by nuclear transfer and germline mutagenesis. It will also cover techniques associated to transgenesis such as sperm cryopreservation, embryo freezing and determination of zygosity. The availability of several technologies allowing genetic manipulation in the rat coupled to genomic data will allow biomedical research to fully benefit from the rat as an experimental animal.

Renal macrophage activation and Th2 polarization precedes the development of nephrotic syndrome in Buffalo/Mna rats

BACKGROUND

At 8 weeks, Buffalo/Mna rats spontaneously develop a nephrotic syndrome associated with focal segmental glomerulosclerosis (FSGS). We have previously demonstrated that this glomerulopathy recurs after renal transplantation, thus supporting the relevance of this rat model to human idiopathic nephrotic syndrome [1]. In this study, we describe renal immune abnormalities which appear in parallel to the initiation and progression of the spontaneous Buffalo/Mna nephropathy.

METHODS

Buffalo/Mna rat kidney samples were harvested before (4 weeks) and after the occurrence of proteinuria (at 10, 18, and 24 weeks, and at 12, 15, 18, and 24 months). Renal immune cell populations [total lymphocytes, macrophages, T, B, and natural killer (NK) cells] and the expression kinetics of various related cytokine [transforming growth factor-beta (TGF-beta), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin (IL)-1, IL-2, IL-4, IL-6, IL-10, IL-12, and IL-13], chemokine [regulated upon activation, normal T cell expressed and secreted (RANTES) and monocyte chemoattractant protein-l (MCP-1)] and T-cell receptor beta (TCR beta) chain transcripts were studied serially during the course of the disease.

RESULTS

In the Buffalo/Mna kidneys, in parallel to the proteinuria, the focal and segmental glomerular lesions began to develop at 10 weeks (affecting 2.4 +/- 0.8% of glomeruli), increased in number, then in intensity (10.4 +/- 0.8% at 24 weeks, 14.6 +/- 2.3% at 12 months, and 28.9 +/- 7.4% at 18 months). Before the onset of the disease, at a nonproteinuric stage, the transcript expression analysis revealed a strong production of some macrophage-associated cytokines, particularly TNF-alpha (350-fold higher than control levels), which was corroborated by monocyte infiltration. A minor T-cell infiltrate (associated with an increase in Cbeta TCR transcripts), with a predominantly Th2 profile and the down-regulation of Th1 cytokines was also observed. These abnormal macrophage and T-cell patterns remained stable after the onset of the disease. No changes in chemokine and TGF-beta transcripts were observed during the initial stages of the disease.

CONCLUSION

Our data suggest that the Buffalo/Mna rat disease may be the result of an immunologic disorder, involving macrophages and Th2 lymphocytes. We hypothesize that this modified environment could result in the production of a factor deleterious to the glomeruli. Thus, this rat strain could provide a new model for the study of human nephrotic syndrome.

Anti-CD28 antibody-induced kidney allograft tolerance related to tryptophan degradation and TCR class II B7 regulatory cells

B7/CTLA-4 interactions negatively regulate T-cell responses and are necessary for transplant tolerance induction. Tolerance induction may therefore be facilitated by selectively inhibiting the B7/CD28 pathway without blocking that of B7/CTLA-4. In this study, we selectively inhibited CD28/B7 interactions using a monoclonal antibody modulating CD28 in a rat model of acute kidney graft rejection. A short-term treatment abrogated both acute and chronic rejection. Tolerant recipients presented few alloantibodies against donor MHC class II molecules, whereas untreated rejecting controls developed anti-MHC class I and II alloantibodies. PBMC from tolerant animals were unable to proliferate against donor cells but could proliferate against third-party cells. The depletion of B7+, non-T cells fully restored this reactivity whereas purified T cells were fully reactive. Also, NK cells depletion restored PBMC reactivity in 60% of tolerant recipients. Conversely, NK cells from tolerant recipients dose-dependently inhibited alloreactivity. PBMC anti-donor reactivity could be partially restored in vitro by blocking indoleamine-2,3-dioxygenase (IDO) and iNOS. In vivo, pharmacologic inhibition of these enzymes led to the rejection of the otherwise tolerated transplants. This study demonstrates that an initial selective blockade of CD28 generates B7+ non-T regulatory cells and a kidney transplant tolerance sustained by the activity of IDO and iNOS.

Inhibition of chronic rejection and development of tolerogenic T cells after ICOS-ICOSL and CD40-CD40L co-stimulation blockade

BACKGROUND

Blockade of the CD40-CD40L pathway results in long-term allograft survival but does not prevent chronic rejection. ICOS-ICOSL are members of the CD28-B7 family that play an important role in T-cell activation.

METHODS

The authors analyzed the effect of single or combined treatment with an anti-ICOS monoclonal antibody and the fusion molecule CD40 immunoglobulin (Ig) on acute and chronic rejection of heart allografts in rats.

RESULTS

Treatment with anti-ICOS resulted in a modest but significant prolongation of allograft survival. Treatment with CD40Ig resulted in long-term graft survival but the cardiac grafts developed chronic rejection lesions. Combined CD40Ig+anti-ICOS treatment led to indefinite graft survival in all recipients and a significant decrease of chronic rejection lesions compared with CD40Ig alone. Importantly, four of the seven CD40Ig+anti-ICOS-treated recipients showed a complete absence of chronic rejection lesions, whereas all of the CD40Ig-treated recipients showed chronic rejection. The CD40Ig+anti-ICOS group also showed significant decreased graft infiltration, decreased antidonor cytotoxic T-lymphocyte activity, and decreased alloantibodies compared with the CD40Ig-treated group. Adoptive transfer of splenocytes indefinitely prolonged allograft survival, whereas those depleted of T cells did not, suggesting the development of T-regulatory mechanisms. CONCLUSIONS. These data indicate that the chronic rejection mechanisms that are CD40-CD40L independent are ICOS-ICOSL dependent. These results were obtained with conservation of cognate immune responses and development of tolerogenic T cells.

Exhaustive Depletion of Graft Resident Dendritic Cells: Marginally Delayed Rejection but Strong Alteration of Graft Infiltration

BACKGROUND

Donor dendritic cells (DDC) are believed to sustain direct recognition leading to acute allograft rejection. However, DDC are also required for tolerance induction in various models.

METHODS

We studied the effect of DDC depletion on major histocompatibility complex (MHC) mismatched rat heart allografts in a strain combination characterized by a DDC-dependant tolerance induction. Grafts were depleted of DDC either by pretreating donors with cyclophosphamide (CyP) or by being parked in an intermediate recipient treated with cyclosporine A (CsA).

RESULTS

CyP depleted 95% of resident DC and no specific donor MHC class II staining was observed in parked grafts. Parked grafts survived significantly but only moderately longer than untreated grafts (10.8+/-1.9 days vs. 6.5+/-0.5 days; P<0.05). Compared to unmodified grafts, on day 5 after transplantation, the magnitude of the graft infiltrate was dramatically decreased in DDC-depleted grafts, with IgG deposition within the grafts at the time of rejection. In parallel, the cytokine transcript levels were also lower in these grafts on day 5, but reached levels similar to those of unmodified grafts by day 7, indicating a delayed pattern of rejection.

CONCLUSIONS

Taken collectively, these data suggest that DDC depletion has a greater effect on the capacity of tolerance induction than the rejection process.