Enforced c-REL deficiency prolongs survival of islet allografts1

Peptide Tk-PQ induces immunosuppression in skin allogeneic transplantation via increasing Foxp3+ Treg and impeding nuclear translocation of NF-κB

Solid organ transplantation is used as the last resort for patients with end-stage disease, but allograft rejection is an unsolved problem. Here, we showed that Tk-PQ, a peptide derived from trichosanthin, had an immune-suppressive effect without obvious cytotoxicity in vitro and in a mouse skin allo-transplantation model. In vitro, treatment of Tk-PQ administrated type 2 T helper cell (Th2)/regulatory T-cell (Treg) cytokines, and increased the ratio of CD4⁺CD25⁺Foxp3⁺ Treg by repressing the PI3K/mTOR pathway. In addition, Tk-PQ decreased NF-κB activation to downregulate pro-inflammatory cytokines. Tk-PQ treatment in the mouse skin transplantation model also caused the similar molecular and cellular phenotypes. Furthermore, Tk-PQ enhanced the suppressive function of Treg by increasing Foxp3 expression, and substantially improved allograft survival. These finding demonstrate that Tk-PQ has the potential to be used in clinical allogeneic transplantation.

Ablation of Transcription Factor IRF4 Promotes Transplant Acceptance by Driving Allogenic CD4+ T Cell Dysfunction

CD4⁺ T cells orchestrate immune responses and destruction of allogeneic organ transplants, but how this process is regulated on a transcriptional level remains unclear. Here, we demonstrated that interferon regulatory factor 4 (IRF4) was a key transcriptional determinant controlling T cell responses during transplantation. IRF4 deletion in mice resulted in progressive establishment of CD4⁺ T cell dysfunction and long-term allograft survival. Mechanistically, IRF4 repressed PD-1, Helios, and other molecules associated with T cell dysfunction. In the absence of IRF4, chromatin accessibility and binding of Helios at PD-1 cis-regulatory elements were increased, resulting in enhanced PD-1 expression and CD4⁺ T cell dysfunction. The dysfunctional state of Irf4-deficient T cells was initially reversible by PD-1 ligand blockade, but it progressively developed into an irreversible state. Hence, IRF4 controls a core regulatory circuit of CD4⁺ T cell dysfunction, and targeting IRF4 represents a potential therapeutic strategy for achieving transplant acceptance.

A small-molecule c-Rel inhibitor reduces alloactivation of T cells without compromising antitumor activity

Preventing unfavorable GVHD without inducing broad suppression of the immune system presents a major challenge of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We developed a novel strategy to ameliorate GVHD while preserving graft-versus-tumor (GVT) activity by small molecule-based inhibition of the NF-κB family member c-Rel. Underlying mechanisms included reduced alloactivation, defective gut homing, and impaired negative feedback on interleukin (IL)-2 production, resulting in optimal IL-2 levels, which, in the absence of competition by effector T cells, translated into expansion of regulatory T cells. c-Rel activity was dispensable for antigen-specific T-cell receptor (TCR) activation, allowing c-Rel-deficient T cells to display normal GVT activity. In addition, inhibition of c-Rel activity reduced alloactivation without compromising antigen-specific cytotoxicity of human T cells. Finally, we were able to demonstrate the feasibility and efficacy of systemic c-Rel inhibitor administration. Our findings validate c-Rel as a promising target for immunomodulatory therapy and demonstrate the feasibility and efficacy of pharmaceutical inhibition of c-Rel activity.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Inhibition of nuclear factor-κB activation in pancreatic β-cells has a protective effect on allogeneic pancreatic islet graft survival

Pancreatic islet transplantation, a treatment for type 1 diabetes, has met significant challenges, as a substantial fraction of the islet mass fails to engraft, partly due to death by apoptosis in the peri- and post-transplantation periods. Previous evidence has suggested that NF-κB activation is involved in cytokine-mediated β-cell apoptosis and regulates the expression of pro-inflammatory and chemokine genes. We therefore sought to explore the effects of β-cell-specific inhibition of NF-κB activation as a means of cytoprotection in an allogeneic model of islet transplantation. To this end, we used islets isolated from the ToI-β transgenic mouse, where NF-κB signalling can specifically and conditionally be inhibited in β-cells by expressing an inducible and non-degradable form of IκBα regulated by the tet-on system. Our results show that β-cell-specific blockade of NF-κB led to a prolonged islet graft survival, with a relative higher preservation of the engrafted endocrine tissue and reduced inflammation. Importantly, a longer delay in allograft rejection was achieved when mice were systemically treated with the proteasome inhibitor, Bortezomib. Our findings emphasize the contribution of NF-κB activation in the allograft rejection process, and suggest an involvement of the CXCL10/IP-10 chemokine. Furthermore, we suggest a potential, readily available therapeutic agent that may temper this process.

Role of T-cell-specific nuclear factor κB in islet allograft rejection

BACKGROUND

Pancreatic islet transplantation has the potential to cure type 1 diabetes, a chronic lifelong disease, but its clinical applicability is limited by allograft rejection. Nuclear factor κB (NF-κB) is a transcription factor important for survival and differentiation of T cells. In this study, we tested whether NF-κB in T cells is required for the rejection of islet allografts.

METHODS

Mice expressing a superrepressor form of NF-κB selectively in T cells (IκBαΔN-Tg mice) with or without the antiapoptotic factor Bcl-xL, or mice with impaired T-cell receptor (TCR)- and B cell receptor-driven NF-κB activity (CARMA1-KO mice) were rendered diabetic and transplanted with islet allografts. Secondary skin transplantation in long-term acceptors of islet allografts was used to test for the development of donor-specific tolerance. Immune infiltration of the transplanted islets was examined by immunofluorescence. TCR-transgenic CD4 T cells were used to follow T-cell priming and differentiation.

RESULTS

Islet allograft survival was prolonged in IκBαΔN-Tg mice, although the animals did not develop donor-specific tolerance. Reduced NF-κB activity did not prevent T-cell priming or differentiation but reduced survival of activated T cells, as transgenic expression of Bcl-xL restored islet allograft rejection in IκBαΔN-Tg mice. Abolishing TCR- and B cell receptor-driven activation of NF-κB selectively by CARMA1 deficiency prevented T-cell priming and islet allograft rejection.

CONCLUSIONS

Our data suggest that T cell-NF-κB plays an important role in the rejection of islet allografts. Targeting NF-κB selectively in lymphocytes seems a promising approach to facilitate acceptance of transplanted islets.

Dendritic cells with TGF-β1 and IL-2 differentiate naive CD4+ T cells into alloantigen-specific and allograft protective Foxp3+ regulatory T cells

BACKGROUND

Naturally occurring, thymic-derived Foxp3+CD25+CD4+ regulatory T cells (nTregs) are pivotal for the maintenance of self-tolerance. nTregs, however, are sparse and lack alloantigen specificity, and these properties pose challenges for their use in clinical transplantation.

METHODS

We established mixed leukocyte reaction (MLR) with dendritic cells (DCs) as stimulators and CD4+ T cells as responders and supplemented the MLR with IL-2 and TGF-β1 and investigated whether DCs+IL-2+TGF-β1 differentiate the polyclonal CD4+ cells into alloantigen-specific and allograft protective Tregs.

RESULTS

We found a greater than a 10-fold increase in Foxp3+CD25+ subpopulation (P<0.01) following stimulation of BALB/c CD4+ cells with C57BL/6 (B6) CD11c+ DCs+IL-2+TGF-β1 in the MLR. Levels of TGF-β1 messenger RNA (mRNA) (P=0.01) and the ratios of TGF-β1 mRNA to granzyme B mRNA (P=0.0003) and Foxp3 mRNA to granzyme B mRNA (P<0.01) were higher in alloantigen-induced Tregs (alloTregs) compared with nTregs. alloTregs suppressed MLR at a 16:1 responder to suppressor ratio, whereas nTregs suppressed at 4:1. Suppression by alloTregs was alloantigen specific and was observed at the level of responder cells and at the level of stimulator cells. In a fully H-2-mismatched, nonlymphopenic, immunocompetent mouse islet transplantation model, alloTregs but not nTregs prolonged survival of islet allografts without any other immunosuppressive therapy (P=0.0003), and the protection was alloantigen specific.

CONCLUSIONS

A combination of CD11c+ DCs, IL-2, and TGF-β1 may help differentiate naive, high abundant CD4+ T into alloantigen-specific and allograft protective Foxp3+Tregs.

Nuclear factor-κB in immunity and inflammation: the Treg and Th17 connection

Although nuclear factor-kB (NF-kB) is generally considered to be a pro-inflammatory transcription factor, recent studies indicate that it also plays a critical role in the development of an anti-inflammatory T cell subset called regulatory T (Treg) cells. Two NF-kB proteins, c-Rel and p65, drive the development of Treg cells by promoting the formation of a Foxp3-specific enhanceosome. Consequently, c-Rel-deficient mice have marked reductions in Treg cells, and c-Rel-deficient T cells are compromised in Treg cell differentiation. However, with the exception of Foxp3, most NF-kB target genes in immune cells are pro-inflammatory. These include several Th17-related cytokine genes and the retinoid-related orphan receptor-g (Rorg or Rorc) that specifies Th17 differentiation and lineage-specific function. T cells deficient in c-Rel or p65 are significantly compromised in Th17 differentiation, and c-Rel -deficient mice are defective in Th17 responses. Thus, NF-kB is required for the development of both anti-inflammatory Treg and pro-inflammatory Th17 cells.

Role of T cell-nuclear factor κB in transplantation

Nuclear factor (NF) κB is a pleiotropic transcription factor that is ubiquitously expressed. After transplantation of solid organs, NF-κB in the graft is activated within a few hours as a consequence of ischemia/reperfusion and then again after a few days in intragraft infiltrating cells during the process of acute allograft rejection. In the present article, we review the components of the NF-κB pathway, their mechanisms of activation, and their role in T cell and antigen-presenting cell activation and differentiation and in solid organ allograft rejection. Targeted inhibition of NF-κB in selected cell types may promote graft survival with fewer adverse effects compared with global immunosuppressive therapies.

The NF-κB transcription factor c-Rel is required for Th17 effector cell development in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease involving effector Th subsets such as Th1 and Th17. In this study, we demonstrate that mice lacking the NF-κB transcription factor family member c-Rel (rel(-/-)), which are known to be resistant to EAE, show impaired Th17 development. Mixed bone marrow chimeras and EAE adoptive transfer experiments show that the deficiency of effector Th17 cells in rel(-/-) mice is T cell intrinsic. Consistent with this finding, c-Rel was activated in response to TCR signaling in the early stages of Th17 development and controlled the expression of Rorc, which encodes the Th17 transcription factor retinoic acid-related orphan receptor γt. CD28, but not IL-2, repression of Th17 development was dependent on c-Rel, implicating a dual role for c-Rel in modulating Th17 development. Adoptive transfer experiments also suggested that c-Rel control of regulatory T cell differentiation and homeostasis influences EAE development and severity by influencing the balance between Th17 and regulatory T cells. Collectively, our findings indicate that in addition to promoting Th1 differentiation, c-Rel regulates the development and severity of EAE via multiple mechanisms that impact on the generation of Th17 cells.

Direct Rel/NF-κB inhibitors: structural basis for mechanism of action

The Rel/NF-κB transcription factors have emerged as novel therapeutic targets for a variety of human diseases and pathological conditions, including inflammation, autoimmune diseases, cancer, ischemic injury, osteoporosis, transplant rejection and neurodegeneration. Several US FDA-approved drugs may, in part, attribute their therapeutic effects to the inhibition of the Rel/NF-κB pathway. Strategies for blocking the Rel/NF-κB signaling pathway have inspired the pharmaceutical industry to develop inhibitors for I-κB kinase, however, this article focuses instead on identifying natural compounds that directly target and inhibit DNA binding and transcription activity of Rel/NF-κB. These include compounds containing a quinone core, an α,β unsaturated carbonyl and a benzene diamine. By investigating the mechanisms of action of existing natural inhibitors, novel strategies and synthetic approaches can be devised that will facilitate the development of novel and selective Rel/NF-κB inhibitors with better safety profiles.

Improved intraportal islet transplantation outcome by systemic IKK-beta inhibition: NF-κB activity in pancreatic islets depends on oxygen availability

Intraportal islet transplantation suffers from low efficiency caused by substantial islet mass loss after transplantation. How this process is regulated is still unclear. Here, we show that NF-κB activation was detectable in islet grafts shortly after transplantation of porcine islets to diabetic NMRI nu/nu mice, and systemic NF-κB inhibition in transplanted animals significantly prolonged islet graft survival. Proinflammatory cytokines alone did not cause evident cell death in pancreatic islet within 24 h, while the combination of cytokines with hypoxia resulted in a strong induction of cell death that could be blocked dose-dependently by a selective IKK-β inhibitor. Under hypoxia, NF-κB activity impaired expression of antiapoptotic gene BCL-xL, c-FLIP and survivin. NF-κB activation in isolated islets was reduced by hypoxia in a time-dependent manner, accordingly, NF-κB activation in transplanted islets diminished by time. Our data indicate that, while NF-κB has an antiapoptotic role under normoxia, low oxygen conditions decrease its activity and transform it to a proapoptotic transcription factor in pancreatic islets. We conclude that NF-κB inhibition represents a potential strategy to improve islet transplantation efficiency.

Diannexin decreases inflammatory cell infiltration into the islet graft, reduces β-cell apoptosis, and improves early graft function

BACKGROUND

A major unmet challenge is to reduce the islet mass needed for insulin independence in type 1 diabetic recipients after islet transplantation. The recombinant homodimer of human annexin V, diannexin, has completed a Phase II Clinical Trial in Kidney Transplantation (NCT00615966).

METHODS

We developed a marginal islet mass transplantation model (10-12 islets per gram of recipient body weight) and investigated whether diannexin prevents β-cell apoptosis and improves islet graft function. Diannexin was administered to islet cell donors shortly before pancreas harvest, added to isolation reagents, and infused into recipients at the time of transplantation and repeated daily until day 4.

RESULTS

In the syngeneic marginal islet mass transplantation model, the median time needed to achieve normoglycemia was reduced from 17.0 days among untreated controls to 3.5 days among diannexin-treated recipients (P=0.004). Histologic analysis of islet grafts harvested on day 3 posttransplantation revealed decreased macrophage (44.7%±9.8% vs. 19.2%±3.2%, P=0.007) and T-cell infiltration (25.9%±5.5% vs. 9.1%±1.1%, P=0.004), and a lower rate of islet cell apoptosis (20.5%±2.8% vs. 7.6%±2.3%, P=0.01) with diannexin treatment. Expression profiling of the islet grafts showed significantly lower levels of mRNA for the proapoptotic molecule Bid, but higher levels of interleukin-6, interferon-γ, and immunosuppressive cytokine interleukin-10.

CONCLUSIONS

Our findings demonstrate that diannexin improves the early function of marginal mass islet grafts, and its effects are associated with reductions in inflammatory cell infiltration and β-cell death by apoptosis after islet transplantation.

Immunological synapse: a multi-protein signalling cellular apparatus for controlling gene expression

The interaction of T cells with antigen-presenting cells is the hallmark of adaptive immunity. In vitro studies have described the formation of an immunological synapse between these cells, and intra-vital imaging has described in great detail the dynamics of these interactions. The immunological synapse has become a paradigm to study signals exchanged between the two cells. A wealth of information has been amassed regarding the localization of signalling molecules, their kinetics and the transcription factors they activate. We continue to discover mechanisms that cause receptors and signalling molecules to compartmentalize in the cell; however, the emerging challenge lies in understanding how the immunological synapse contributes to differentiation. Here, we review some of the transcription factors activated downstream of T-cell receptor signalling and discuss mechanisms by which antigen dose and affinity may influence differentiation. Antigen affinity might change the kind of transcription factors that are activated whereas antigen dose is likely to influence the temporal dynamics of the transcription factors. The immunological synapse is therefore likely to influence differentiation by modulating the trafficking of transcription factors and by promoting asymmetric cell division, an emerging concept.

RNAi-mediated c-Rel silencing leads to apoptosis of B cell tumor cells and suppresses antigenic immune response in vivo

c-Rel is a member of the Rel/NF-κB transcription factor family and is predominantly expressed in lymphoid and myeloid cells, playing a critical role in lymphocyte proliferation and survival. Persistent activation of the c-Rel signal transduction pathway is associated with allergies, inflammation, autoimmune diseases, and a variety of human malignancies. To explore the potential of targeting c-Rel as a therapeutic agent for these disorders, we designed a small interfering RNA (siRNA) to silence c-Rel expression in vitro and in vivo. C-Rel-siRNA expression via a retroviral vector in a B cell tumor cell line leads to growth arrest and apoptosis of the tumor cells. Silencing c-Rel in primary B cells in vitro compromises their proliferative and survival response to CD40 activation signals, similar to the impaired response of c-Rel knockout B cells. Most important, in vivo silencing of c-Rel results in significant impairment in T cell-mediated immune responses to antigenic stimulation. Our study thus validates the efficacy of c-Rel-siRNA, and suggests the development of siRNA-based therapy, as well as small molecular inhibitors for the treatment of B cell tumors as well as autoimmune diseases.

Hyperexpression of Foxp3 and IDO During Acute Rejection of Islet Allografts

BACKGROUND

We investigated the hypothesis that Foxp3+ cells are an integral component of antiallograft immunity but are dominated by pathogenic effectors.

METHODS

Wild-type H-2b C57BL/6 (B6) mice or B6 mice with a targeted disruption of c-Rel gene (c-Rel-/-) were used as recipients of islet grafts from allogeneic DBA/2 (H-2d) mice or syngeneic B6 mice. We developed kinetic quantitative polymerase chain reaction assays and measured intragraft expression of mRNA for Foxp3, IDO, cytolytic molecules, proinflammatory cytokines, and chemokines/receptors.

RESULTS

Intraislet levels of mRNA for Foxp3, IDO, CD3, CD25, tumor necrosis factor-alpha, RANTES, IP-10, and CXCR3 were highest in DBA/2 islet allografts from WT B6 recipients compared to DBA/2 islet allografts from c-Rel-/- B6 recipients or syngeneic B6 islet grafts from WT B6 mice. The ratio of granzyme B or IFN-gamma to Foxp3 was higher with the DBA/2 islet allografts from the WT B6 recipients compared to DBA/2 islet allografts from c-Rel-/- B6 recipients or B6 islet grafts from WT B6 recipients.

CONCLUSIONS

Foxp3+ cells are an integral component of acute rejection of allografts but may be dominated by pathogenic effectors.

Genome-Wide Analysis of Gene Expression in T Cells to Identify Targets of the NF-κB Transcription Factor c-Rel

It is well established that the NF-kappaB family of transcription factors serves a major role in controlling gene expression in response to T cell activation, but the genome-wide roles of individual family members remain to be determined. c-Rel, a member of the NF-kappaB family, appears to play a specific role in T cell function because T cells from c-Rel(-/-) animals are defective in their response to immune signals. We have used expression profiling to identify sets of genes that are affected by either deletion or overexpression of c-Rel in T cells. Very few of these genes exhibit a strong requirement for c-Rel; rather, c-Rel appears to modulate the expression of a large number of genes in these cells. The sets of c-Rel-affected genes are significantly enriched for genes containing consensus NF-kappaB/Rel sites in their proximal promoter regions. In addition, their promoters contain a higher average density of NF-kappaB/Rel sites compared with all genes represented on the microarrays. A transcriptional module comprised of two closely spaced c-Rel consensus sites is found with higher frequency in the c-Rel-affected gene sets and may represent an important control module for genes regulated by c-Rel or other NF-kappaB family members. We confirmed the importance of these findings on a subgroup of genes by using quantitative PCR to monitor gene expression as well as in vitro c-Rel/DNA binding assays and luciferase reporter assays. The c-Rel-regulated genes identified here support a role for c-Rel in inflammatory responses as well as in the promotion of cell growth and survival.

Mitochondrial Targeting with Antioxidant Peptide SS-31 Prevents Mitochondrial Depolarization, Reduces Islet Cell Apoptosis, Increases Islet Cell Yield, and Improves Posttransplantation Function

Apoptotic cell death is a defined pathway for islet cell demise, and mitochondrial dysfunction contributes to islet cell apoptosis. The hypothesis that the novel peptide D-Arg-2', 6'-dimethyltyrosine-Lys-Phe-NH2 (SS-31), previously shown to target inner mitochondrial membrane and prevent oxidative damage of neuronal cells and other cell types, optimizes pancreatic islet isolation and improves posttransplantation function in recipients with diabetes was investigated. Herein is demonstrated that SS-31 readily penetrates intact mouse islets, preserves mitochondrial polarization, reduces islet cell apoptosis, and increases islet cell yield. Optimization of islet isolation is demonstrable after SS-31 pretreatment of islet (pancreas) donor mice and with the addition of SS-31 to reagents that are used in the isolation of mouse islets. The supplementation of in vitro culture medium with SS-31 reduced islet cell apoptosis and increased the viability of human islets, as ascertained by dual-parameter flow cytometry analysis. In a stringent marginal islet cell mass transplantation model (200 mouse islets transplanted under the renal capsule of syngeneic diabetic mice) and using islets that were derived from old mice (>24 wk), SS-31 treatment was associated with prompt and sustained normoglycemia, whereas the untreated islet graft recipients remained diabetic. Our data suggest a novel strategy to optimize islet isolation and reduce the need for multiple pancreata to achieve insulin independence in the recipient with type 1 diabetes. Because SS-31 was effective with "extended" islet donors, it is hypothesized that the antioxidant SS-31 may serve to increase the pool of eligible organ donors.

Imaging islets labeled with magnetic nanoparticles at 1.5 Tesla

We have developed a magnetic resonance imaging (MRI) technique for imaging Feridex (superparamagnetic iron oxide [SPIO])-labeled islets of Langerhans using a standard clinical 1.5-Tesla (T) scanner and employing steady-state acquisition imaging sequence (3DFIESTA). Both porcine and rat islets were labeled with SPIO by a transfection technique using a combination of poly-l-lysine and electroporation. Electron microscopy demonstrated presence of SPIO particles within the individual islet cells, including beta-cells and particles trapped between cell membranes. Our labeling method produced a transfection rate of 860 pg to 3.4 ng iron per islet, dependent on the size of the islet. The labeling procedure did not disrupt either the function or viability of the islets. In vitro 3DFIESTA magnetic resonance images of single-labeled islets corresponded with their optical images. In vivo T2*-weighted scan using 1.5 T detected as few as 200 SPIO-labeled islets transplanted under rat kidney capsule, which correlated with immunohistochemistry of the transplant for insulin and iron. Ex vivo 3DFIESTA images of kidneys containing 200, 800 or 2,000 SPIO-labeled islet isografts showed good correlation between signal loss and increasing numbers of islets. These data provide evidence that islets can be labeled with SPIO and imaged using clinically available 1.5- T MRI.

Unravelling the complexities of the NF-κB signalling pathway using mouse knockout and transgenic models

The nuclear factor-kappaB (NF-kappaB) signalling pathway serves a crucial role in regulating the transcriptional responses of physiological processes that include cell division, cell survival, differentiation, immunity and inflammation. Here we outline studies using mouse models in which the core components of the NF-kappaB pathway, namely the IkappaB kinase subunits (IKKalpha, IKKbeta and NEMO), the IkappaB proteins (IkappaBalpha, IkappaBbeta, IkappaBvarepsilon and Bcl-3) and the five NF-kappaB transcription factors (NF-kappaB1, NF-kappaB2, c-Rel, RelA and RelB), have been genetically manipulated using transgenic and knockout technology.

NF-kappaB and the regulation of hematopoiesis

This review will focus on the role of nuclear factor kappaB (NF-kappaB) signaling in hematopoietic differentiation. We will also discuss several hematopoietic pathologies associated with deregulation of NF-kappaB and their potential therapies.

Deletion of DOCK2, a regulator of the actin cytoskeleton in lymphocytes, suppresses cardiac allograft rejection

Allograft rejection is induced by graft tissue infiltration of alloreactive T cells that are activated mainly in secondary lymphoid organs of the host. DOCK2 plays a critical role in lymphocyte homing and immunological synapse formation by regulating the actin cytoskeleton, yet its role in the in vivo immune response remains unknown. We show here that DOCK2 deficiency enables long-term survival of cardiac allografts across a complete mismatch of the major histocompatibility complex molecules. In DOCK2-deficient mice, alloreactivity and allocytotoxicity were suppressed significantly even after in vivo priming with alloantigens, which resulted in reduced intragraft expression of effector molecules, such as interferon-γ, granzyme B, and perforin. This is mediated, at least in part, by preventing potentially alloreactive T cells from recruiting into secondary lymphoid organs. In addition, we found that DOCK2 is critical for CD28-mediated Rac activation and is required for the full activation of alloreactive T cells. Although DOCK2-deficient, alloreactive T cells were activated in vitro in the presence of exogenous interleukin-2, these T cells, when transferred adoptively, failed to infiltrate into the allografts that were transplanted into RAG1-deficient mice. Thus, DOCK2 deficiency attenuates allograft rejection by simultaneously suppressing multiple and key processes. We propose that DOCK2 could be a novel molecular target for controlling transplant rejection.

Permanent Survival of Fully MHC-Mismatched Islet Allografts by Targeting a Single Chemokine Receptor Pathway

Chemokine receptor blockade can diminish the recruitment of host effector cells and prolong allograft survival, but little is known of the role of chemokine receptors in promoting host sensitization. We engrafted fully allogeneic islets into streptozotocin-treated normal mice or mice with the autosomal recessive paucity of lymph node T cell (plt) mutation; the latter lack secondary lymphoid expression of the CCR7 ligands, secondary lymphoid organ chemokine (CCL21) and EBV-induced molecule-1 ligand chemokine (CCL19). plt mice showed permanent survival of islets engrafted under the kidney capsule, whereas controls rejected islet allografts in 12 days (p < 0.001), and consistent with this, plt mice had normal allogeneic T cell responses, but deficient migration of donor dendritic cell to draining lymph nodes. Peritransplant i.v. injection of donor splenocytes caused plt recipients to reject their allografts by 12 days, and sensitization at 60 days posttransplant of plt mice with well-functioning allografts restored acute rejection. Finally, islet allografts transplanted intrahepatically in plt mice were rejected approximately 12 days posttransplant, like controls, as were primarily revascularized cardiac allografts. These data show that the chemokine-directed homing of donor dendritic cell to secondary lymphoid tissues is essential for host sensitization and allograft rejection. Interruption of such homing can prevent T cell priming and islet allograft rejection despite normal T and B cell functions of the recipient, with potential clinical implications.

Systemic Transforming Growth Factor-??1 Gene Therapy Induces Foxp3+ Regulatory Cells, Restores Self-Tolerance, and Facilitates Regeneration Of Beta Cell Function in Overtly Diabetic Nonobese Diabetic Mice

BACKGROUND

Type 1 diabetes results from auto-aggressive T-cell-mediated destruction of beta cells of the pancreas. Recent data suggest that restoration of self-tolerance may facilitate islet-cell regeneration/recovery. In view of the immunoregulatory activity of transforming growth factor (TGF)-beta1, we investigated whether systemic TGF-beta1 gene therapy blocks islet destructive autoimmunity and facilitates regeneration of beta-cell function in overtly diabetic nonobese diabetic (NOD) mice.

METHODS

We used site-directed mutagenesis to create cysteine to serine mutation at sites 224 and 226 and constructed a replication deficient adenovirus (Ad) vector encoding active form of human TGF-beta1 (Ad-hTGF-beta1). Overtly diabetic NOD mice received intravenous injection of Ad-hTGF-beta1. Seven to 14 days after the injection, the mice received transplants with 500 syngeneic islets under the kidney capsule. Islet-graft survival and regeneration of endogenous beta-cell function were examined.

RESULTS

Syngeneic islet grafts failed by day 17 in all untreated mice, whereas Ad-hTGF-beta1 therapy prolonged survival of islet grafts. Islet grafts from treated mice showed well-preserved islets with a peri-islet infiltrate primarily of CD4+ T cells and expression of CD25 and Foxp3. Systemic TGF-beta1 gene therapy was associated with islet regeneration in the native pancreas. Native pancreas of treated mice revealed islets staining strongly for insulin. Similar to what was found in the syngeneic islet graft, there were well-demarcated peri-islet infiltrates that were positive for CD4, TGF-beta1, and Foxp3.

CONCLUSIONS

Our data demonstrate that systemic TGF-beta1 gene therapy blocks islet destructive autoimmunity, facilitates islet regeneration, and cures diabetes in diabetic NOD mice.

Unique gene expression profiles of heart allograft rejection in the interferon regulatory factor-1-deficient mouse

Interferon regulatory factor-1 (IRF1) is a transcription factor for many genes involved in innate and adaptive immune responses. By using DNA array technology, we have previously demonstrated that IRF1 is significantly upregulated during acute rejection in rat heart allografts and is restored to isograft levels when recipients are treated with the immunosuppressants tacrolimus or cyclosporin A (CsA). To understand the precise role of IRF1 in transplant rejection, we investigated the rejection responses of mice completely deficient of IRF1 protein. Heterotopic heart transplantations were performed using C57BL/6J wild-type (WT B6) and IRF1-deficient (IRF1-/-) mice as recipients, and C3H mice as donors. Graft survival was determined by abdominal palpation and rejection was confirmed by histology. On day 6 after transplantation, isografts and allografts were harvested and subjected to gene expression analysis by a commercial nylon array and by real-time RT-PCR. Median survival time of heart allografts was 8 days in the WT B6 mice and 10 days in the IRF1-/- mice. The gene expression profiles of allografts from the WT B6 and IRF1-/- recipients were nearly identical to each other and very different from the profile of the isograft control. Both WT B6 and IRF1-/- profiles showed 13 genes upregulated (IFN-gamma, MCP-2, MIP-1alpha, MIP-1beta, CCR5, MIG, IP-10 and others) and one gene downregulated (SDF2) among the 76 genes detectable on the array. In more detailed analyses, distinct cytokine and chemokine gene expression profiles were identified in the allografts from the WT B6 and IRF1-/- recipients. Whereas IL-4, IL-6, IL-13, MCP-1, MCP-3, and MPIF-2 were upregulated, RANTES, IL-2Rgamma and gp130 were downregulated in allografts from the IRF1-/- recipients when compared to the WT B6 control. Although the inactivation of the IRF1 gene did not sufficiently prevent acute allograft rejection in this model, a unique cytokine and chemokine gene expression profile was found in the absence of IRF1.

Islet transplantation: immunological perspectives

Clinical trials of islet transplantation are showing remarkable success, but they require administration of chronic immunosuppression, and are underscoring the large gap that exists between the number of human donors available and the number of patients that could benefit from the procedure. Recent progress has been made in the definition of key immunological mechanisms that are involved in determining islet transplant outcome. Clinical and preclinical studies, and studies in small animal model systems, will all eventually contribute to the definition of efficient and safe protocols for islet transplantation. If the use of xenografts is successful, it might represent a solution to the shortage of human organs.

Blocking the monocyte chemoattractant protein-1/CCR2 chemokine pathway induces permanent survival of islet allografts through a programmed death-1 ligand-1-dependent mechanism

Islet allografts are subject to rapid rejection through host cellular immune responses involving mononuclear cell recruitment and tissue injury. Interruption of leukocyte recruitment through chemokine receptor targeting is of therapeutic benefit in various experimental models, but little is known about the contribution of chemokine pathways to islet allograft rejection. We found that murine islets produce monocyte chemoattractant protein-1 (MCP-1; CCL2) in vitro and that islet allograft rejection was associated with intragraft expression of MCP-1 and its receptor, CCR2. We therefore investigated whether MCP-1 and CCR2 are required for the rejection of fully MHC-disparate islet allografts. Wild-type mice treated with blocking anti-MCP-1 mAb plus a brief, subtherapeutic course of rapamycin had long-term islet allograft survival, in contrast to the effect of treatment with either mAb or rapamycin alone. CCR2(-/-) mice treated with rapamycin also maintained islet allografts long-term. Both MCP/CCR2- and rapamycin-sensitive signals were required for maximal proliferation of alloreactive T cells, suggesting that MCP-1/CCR2 induce rejection by promoting alloreactive T cell clonal expansion and homing and migration. Prolonged islet allograft survival achieved by blockade of the MCP-1/CCR2 pathway plus rapamycin therapy was accompanied by a mononuclear cell infiltrate expressing the inhibitory receptor, programmed death-1 (PD-1), and its ligand (PD-L1, B7-H1), and prolongation of islet allograft survival was abrogated by anti-PD-L1 mAb therapy. These data show that the blockade of MCP-1 binding to CCR2 in conjunction with subtherapeutic immunosuppression can have profound effects on islet allograft survival and implicate the expression of the PD-1/PD-L1 pathway in the regulation of physiologic responses in vivo.

Cyclin E and Bcl-xL cooperatively induce cell cycle progression in c-Rel−/− B cells

Aberrant overexpression of the c-rel protooncogene is associated with lymphoid malignancy, while c-rel deletion produces severe lymphoproliferative defects and immunodeficiency. To investigate the mechanism of c-rel-induced proliferation and cell cycle progression in B lymphocytes, we have compared signaling events elicited through the BCR in c-rel-/- and wild-type B cells. BCR stimulation of c-rel-/- B cells fails to induce proper cyclin expression, resulting in G1 phase arrest, but it is unclear whether these defects are in fact secondary events of decreased B-cell survival, since c-rel deletion also affects the expression of antiapoptotic genes such as bcl-xL. Here, we use the bcl-xL transgene to correct the viability of c-rel-deficient B cells, and show that the inhibition of apoptosis does not necessarily confer hyperproliferation of B cells activated through the BCR. c-rel-/- B cells still fail to enter the S phase despite improved survival by bcl-xL overexpression, suggesting that c-Rel-associated cell cycle progression is dependent on more than just enhanced cell viability. Overexpression of cyclin E protein, however, can cooperate with Bcl-xL to restore cell cycle progression to c-rel-/- B cells via induction of the cyclin-CDK/Rb-E2F pathway. Furthermore, we show that c-Rel can directly regulate transcription of the e2f3a promoter/enhancer, which is then likely to lead to transcriptional activation of the cyclin E promoter by E2F3a. Hence, these studies provide clear evidence that control of lymphocyte proliferation via c-Rel is linked to a cyclin-dependent process, and suggest that c-Rel not only activates antiapoptotic signaling but also the induction of cell cycle progression.

Distinctions between c-Rel and other NF-kappaB proteins in immunity and disease

c-Rel is a proto-oncogene first identified as the cellular counterpart of the v-Rel oncogene derived from the avian reticuloendotheliosis retrovirus (REV-T). It was subsequently discovered that c-Rel belongs to the NF-kappaB/Rel transcription factor family whose members share a common DNA recognition motif and similar signaling pathways. Despite the similarities, however, each NF-kappaB/Rel member possesses unique properties with regard to tissue expression pattern, response to receptor signals and target gene specificity. These differences are fairly evident from the non-redundant phenotypes exhibited by individual NF-kappaB/Rel knockout mice. Hence the work described in this review will compare and contrast the various physiological functions of c-Rel to those of other NF-kappaB members, particularly with respect to the regulation of proliferation, survival and effector functions in multiple hematopoietic and immunological cell types. The study of c-Rel knockout mice in several disease models will also be discussed as they reveal an important role for c-Rel in response to allergens, auto-antigens, allo-antigens and pathogenic infection.

Selective loss of c-Rel compromises dendritic cell activation of T lymphocytes

Dendritic cells initiate the immune response by presenting antigen in the context of varying levels of costimulation. The maturation state of the dendritic cell determines the quantity and quality (Th1, Th2) of the subsequent T cell response. Members of the NF-kappaB family of transcription factors have previously been implicated in dendritic cell development. Here, we used a mouse with a homozygous c-Rel deletion to investigate the role of c-Rel in the function of bone marrow derived dendritic cells. When direct presentation was evaluated, we found c-Rel(-/-) dendritic cells induce less allogeneic T cell stimulation than c-Rel(+/+) dendritic cells. In addition, T cell encounters with c-Rel(-/-) dendritic cells generate less IFN-gamma and IL-4 when compared to those with c-Rel(+/+) DCs. A similar degree of functional compromise was observed in antigen-specific T cells that were stimulated by c-Rel(-/-) dendritic cells. Functional deficits were not linked to differences in the ability to undergo maturation per se, as LPS exposure induced similar morphologic and cell surface changes in both c-Rel(+/+) and cRel(-/-) DCs. Although LPS induced a compensatory increase in the nuclear activity of fellow NF-kappaB family members, RelB and p65, LPS exposure was unable to negate the deficiencies in autologous T cell proliferation and cytokine production associated with the loss of c-Rel in dendritic cells. Taken together, our study supports a unique and non-redundant role for c-Rel in dendritic cell costimulatory capacity.

Regulation of the immune system by NF-kappaB and IkappaB

NF-kappaB/Rel transcription factor family participates in diverse biological processes including embryo development, hematopoiesis, immune regulation, as well as neuronal functions. In this review, the NF-kappaB/Rel signal transduction pathways and their important roles in the regulation of immune system will be discussed. NF-kappaB/Rel members execute distinct functions in multiple immune cell types via the regulation of target genes essential for cell proliferation, survival, effector functions, cell trafficking and communication, as well as the formation of lymphoid architecture. Consequently, proper activation of NF-kappaB/Rel during immune responses to allergens, auto-antigens, allo-antigens, and pathogenic infection is crucial for the integrity of host innate and adaptive immunity.