Tolerance induction of alloreactive T cells via ex vivo blockade of the CD40:CD40L costimulatory pathway results in the generation of a potent immune regulatory cell

Differential induction of donor-reactive Foxp3+ regulatory T cell via blockade of CD154 vs CD40

Recently published studies in both murine models and a meta-analysis of non-human primate renal transplant studies showed that anti-CD154 reagents conferred a significant survival advantage over CD40 blockers in both animal models and across multiple organs. Here we sought to compare the induction of donor-reactive forkhead box P3+-induced regulatory T cells (Foxp3+ iTreg) in mice treated with anti-CD154 versus anti-CD40 monoclonal antibodies (mAbs). Results indicated that while treatment with anti-CD154 mAb resulted in a significant increase in the frequency of donor-reactive CD4+ Foxp3+ iTreg following transplantation, treatment with anti-CD40 or Cd40 deficiency failed to recapitulate this result. Because we recently identified CD11b as an alternate receptor for CD154 during alloimmunity, we interrogated the role of CD154:CD11b interactions in the generation of Foxp3+ iTreg and found that blockade of CD11b in Cd40-/- recipients resulted in increased donor-reactive Foxp3+ iTreg as compared with CD40 deficiency alone. Mechanistically, CD154:CD11b inhibition decreased interleukin (IL)-1β from CD11b+ and CD11c+ dendritic cells, and blockade of IL-1β synergized with CD40 deficiency to promote Foxp3+ iTreg induction and prolong allograft survival. Taken together, these data provide a mechanistic basis for the observed inferiority of anti-CD40 blockers as compared with anti-CD154 mAb and illuminate an IL-1β-dependent mechanism by which CD154:CD11b interactions prevent the generation of donor-reactive Foxp3+ iTreg during transplantation.

In or out of control: Modulating regulatory T cell homeostasis and function with immune checkpoint pathways

Regulatory T cells (Tregs) are the master regulators of immunity and they have been implicated in different disease states such as infection, autoimmunity and cancer. Since their discovery, many studies have focused on understanding Treg development, differentiation, and function. While there are many players in the generation and function of truly suppressive Tregs, the role of checkpoint pathways in these processes have been studied extensively. In this paper, we systematically review the role of different checkpoint pathways in Treg homeostasis and function. We describe how co-stimulatory and co-inhibitory pathways modulate Treg homeostasis and function and highlight data from mouse and human studies. Multiple checkpoint pathways are being targeted in cancer and autoimmunity; therefore, we share insights from the clinic and discuss the effect of experimental and approved therapeutics on Treg biology.

Regulatory T cells and transplantation tolerance: Emerging from the darkness?

The field of tissue transplantation has revolutionized the treatment of patients with failing organs. Its success, thus far, has depended on combinations of immunosuppressive drugs that damp host immunity, while also imposing numerous unwanted side-effects. There is a longstanding recognition that better treatment outcomes, will come from replacing these drugs, fully or in part, by taking advantage of tractable physiological mechanisms of self-tolerance. The past 50 years have seen many advances in the field of self-tolerance, but perhaps, the most tractable of these has been the more recent discovery of a subset T-cells (Treg) whose role is to regulate or damp immunity. This article is intended to first provide the reader with some historical background to explain why we have been slow to identify these cells, despite numerous clues to their existence, and also to indicate how little we know about how they achieve their regulatory function in averting transplant rejection. However, as is often the case in immunology, the therapeutic needs often dictate that our advances move to translation even before detailed explanations of the science are available. The final part of the article will briefly summarize how Treg are being harnessed as agents to interface with or perhaps, replace current drug combinations.

Phase II Trial of Costimulation Blockade With Abatacept for Prevention of Acute GVHD

PURPOSE

Severe (grade 3-4) acute graft-versus-host disease (AGVHD) is a major cause of death after unrelated-donor (URD) hematopoietic cell transplant (HCT), resulting in particularly high mortality after HLA-mismatched transplantation. There are no approved agents for AGVHD prevention, underscoring the critical unmet need for novel therapeutics. ABA2 was a phase II trial to rigorously assess safety, efficacy, and immunologic effects of adding T-cell costimulation blockade with abatacept to calcineurin inhibitor (CNI)/methotrexate (MTX)-based GVHD prophylaxis, to test whether abatacept could decrease AGVHD.

METHODS

ABA2 enrolled adults and children with hematologic malignancies under two strata: a randomized, double-blind, placebo-controlled stratum (8/8-HLA-matched URD), comparing CNI/MTX plus abatacept with CNI/MTX plus placebo, and a single-arm stratum (7/8-HLA-mismatched URD) comparing CNI/MTX plus abatacept versus CNI/MTX CIBMTR controls. The primary end point was day +100 grade 3-4 AGVHD, with day +180 severe-AGVHD-free-survival (SGFS) a key secondary end point. Sample sizes were calculated using a higher type-1 error (0.2) as recommended for phase II trials, and were based on predicting that abatacept would reduce grade 3-4 AGVHD from 20% to 10% (8/8s) and 30% to 10% (7/8s). ABA2 enrolled 142 recipients (8/8s, median follow-up = 716 days) and 43 recipients (7/8s, median follow-up = 708 days).

RESULTS

In 8/8s, grade 3-4 AGVHD was 6.8% (abatacept) versus 14.8% (placebo) (P = .13, hazard ratio = 0.45). SGFS was 93.2% (CNI/MTX plus abatacept) versus 82% (CNI/MTX plus placebo, P = .05). In the smaller 7/8 cohort, grade 3-4 AGVHD was 2.3% (CNI/MTX plus abatacept, intention-to-treat population), which compared favorably with a nonrandomized matched cohort of CNI/MTX (30.2%, P < .001), and the SGFS was better (97.7% v 58.7%, P < .001). Immunologic analysis revealed control of T-cell activation in abatacept-treated patients.

CONCLUSION

Adding abatacept to URD HCT was safe, reduced AGVHD, and improved SGFS. These results suggest that abatacept may substantially improve AGVHD-related transplant outcomes, with a particularly beneficial impact on HLA-mismatched HCT.

CD11b is a novel alternate receptor for CD154 during alloimmunity

Antagonism of the CD154/CD40 pathway is a highly effective means of inducing long-term graft survival in preclinical models. Using a fully allogeneic murine transplant model, we found that CD154 blockade was more effective in prolonging graft survival than was CD40 blockade, raising the possibility that CD154 binds a second receptor. To test this, we queried the impact of CD154 antagonism in the absence of CD40. Data indicated that anti-CD154 functioned to reduce graft-infiltrating CD8+ T cells in both WT and CD40-/- hosts. Because it has recently been reported that CD154 can ligate CD11b, we addressed the impact of blocking CD154-CD11b interactions during transplantation. We utilized a specific peptide antagonist that prevents CD154 binding of CD11b but has no effect on CD154-CD40 interactions. CD154:CD11b antagonism significantly increased the efficacy of anti-CD40 in prolonging allograft survival as compared to anti-CD40 plus control peptide. Mechanistically, CD154:CD11b antagonism functioned to reduce the frequency of graft-infiltrating CD8+ T cells and innate immune cells. These data therefore demonstrate that blocking CD154 interactions with both CD40 and CD11b is required for optimal inhibition of alloimmunity and provide an explanation for why CD40 blockers may be less efficacious than anti-CD154 reagents for the inhibition of allograft rejection.

HIV Interferes with the Dendritic Cell-T Cell Axis of Macrophage Activation by Shifting Mycobacterium tuberculosis-Specific CD4 T Cells into a Dysfunctional Phenotype

HIV coinfection is the greatest risk factor for transition of latent Mycobacterium tuberculosis infection into active tuberculosis (TB). Epidemiological data reveal both the reduction and the impairment of M. tuberculosis-specific CD4 T cells, although the cellular link and actual mechanisms resulting in immune impairment/suppression need further characterization. M. tuberculosis-specific CD4 T cells play a central role in development of protective immunity against TB, in which they participate in the activation of macrophages through the dendritic cell (DC)-T cell axis. Using an in vitro priming system for generating Ag-specific T cells, we explored if HIV-M. tuberculosis-infected (coinfected) human DCs can dysregulate the M. tuberculosis-specific CD4 T cell phenotype and functionality and subsequently mediate the failure to control M. tuberculosis infection in macrophages. After coculture with coinfected DCs, M. tuberculosis Ag-specific CD4 T cells lost their ability to enhance control of M. tuberculosis infection in infected macrophages. Coinfection of DCs reduced proliferation of M. tuberculosis Ag-specific CD4 T cells without affecting their viability, led to increased expression of coinhibitory factors CTLA-4, PD-1, and Blimp-1, and decreased expression of costimulatory molecules CD40L, CD28, and ICOS on the T cells. Expression of the regulatory T cell markers FOXP3 and CD25, together with the immunosuppressive cytokines TGF-β and IL-10, was also significantly increased by coinfection compared with M. tuberculosis single infection. Our data suggest a pattern in which HIV, through its effect on DCs, impairs the ability of M. tuberculosis-specific CD4 T cells to maintain a latent TB within human macrophages, which could play an early role in the subsequent development of TB.

Cell Therapy in Organ Transplantation: Our Experience on the Clinical Translation of Regulatory T Cells

Solid organ transplantation is the treatment of choice for patients with end-stage organ dysfunction. Despite improvements in short-term outcome, long-term outcome is suboptimal due to the increased morbidity and mortality associated with the toxicity of immunosuppressive regimens and chronic rejection (1–5). As such, the attention of the transplant community has focused on the development of novel therapeutic strategies to achieve allograft tolerance, a state whereby the immune system of the recipient can be re-educated to accept the allograft, averting the need for long-term immunosuppression. Indeed, reports of “operational” tolerance, whereby the recipient is off all immunosuppressive drugs and maintaining good graft function, is well documented in the literature for both liver and kidney transplantations (6–8). However, this phenomenon is rare and in the setting of liver transplantation has been shown to occur late after transplantation, with the majority of patients maintained on life-long immunosupression to prevent allograft rejection (9). As such, significant research has focused on immune regulation in the context of organ transplantation with regulatory T cells (Tregs) identified as cells holding considerable promise in this endeavor. This review will provide a brief introduction to human Tregs, their phenotypic and functional characterization and focuses on our experience to date at the clinical translation of Treg immunotherapy in the setting of solid organ transplantation.

iNKT cell activation plus T-cell transfer establishes complete chimerism in a murine sublethal bone marrow transplant model

Transplant tolerance induction makes it possible to preserve functional grafts for a lifetime without immunosuppressants. One powerful method is to generate mixed hematopoietic chimeras in recipients by adoptive transfer of donor-derived bone marrow cells (BMCs). In our murine transplantation model, we established a novel method for mixed chimera generation using sublethal irradiation, CD40-CD40L blockade, and invariant natural killer T-cell activation. However, numerous BMCs that are required to achieve stable chimerism makes it difficult to apply this model for human transplantation. Here, we show that donor-derived splenic T cells could contribute to not only the reduction of BMC usage but also the establishment of complete chimerism in model mice. By cotransfer of T cells together even with one-fourth of the BMCs used in our original method, the recipient mice yielded complete chimerism and could acquire donor-specific skin-allograft tolerance. The complete chimeric mice did not show any remarks of graft versus host reaction in vivo and in vitro. Inhibition of the apoptotic signal resulted in increase in host-derived CD8⁺ T cells and chimerism brake. These results suggest that donor-derived splenic T cells having veto activity play a role in the depletion of host-derived CD8⁺ T cells and the facilitation of complete chimerism.

Challenges and opportunities in targeting the CD28/CTLA-4 pathway in transplantation and autoimmunity

INTRODUCTION

T cell activation is a complex process that requires multiple cell signaling pathways, including a primary recognition signal and additional costimulatory signals. One of the best-characterized costimulatory pathways includes the Ig superfamily members CD28 and CTLA-4 and their ligands CD80 and CD86. Areas covered: This review discusses past, current and future biological therapies that have been utilized to block the CD28/CTLA-4 cosignaling pathway in the settings of autoimmunity and transplantation, as well the challenges facing successful implementation of these therapies. Expert opinion: The development of CD28 blockers Abatacept and Belatacept provided a more targeted therapy approach for transplant rejection and autoimmune disease relative to calcineurin inhibitors and anti-proliferatives, but overall efficacy may be limited due to their collateral effect of simultaneously blocking CTLA-4 coinhibitory signals. As such, current investigations into the potential of selective CD28 blockade to block the costimulatory potential of CD28 while exploiting the coinhibitory effects of CTLA-4 are promising. However, as selective CD28 blockade inhibits the activity of both effector and regulatory T cells, an important goal for the future is the design of therapies that will maximize the attenuation of effector responses while preserving the suppressive function of T regulatory cells.

The Role of Animal Models in the Study of Hematopoietic Stem Cell Transplantation and GvHD: A Historical Overview

Bone marrow transplantation (BMT) is the only therapeutic option for many hematological malignancies, but its applicability is limited by life-threatening complications, such as graft-versus-host disease (GvHD). The last decades have seen great advances in the understanding of BMT and its related complications; in particular GvHD. Animal models are beneficial to study complex diseases, as they allow dissecting the contribution of single components in the development of the disease. Most of the current knowledge on the therapeutic mechanisms of BMT derives from studies in animal models. Parallel to BMT, the understanding of the pathophysiology of GvHD, as well as the development of new treatment regimens, has also been supported by studies in animal models. Pre-clinical experimentation is the basis for deep understanding and successful improvements of clinical applications. In this review, we retrace the history of BMT and GvHD by describing how the studies in animal models have paved the way to the many advances in the field. We also describe how animal models contributed to the understanding of GvHD pathophysiology and how they are fundamental for the discovery of new treatments.

SiRNA In Vivo-Targeted Delivery to Murine Dendritic Cells by Oral Administration of Recombinant Yeast

SiRNA therapeutics promise a future where any target in the transcriptome could be potentially addressed. However, the delivery of SiRNAs and targeting of particular cell types or organs are major challenges. A novel, efficient, and safe delivery system for promising the introduction of SiRNAs into particular cell types within living organisms is of great significance. Our previous studies have proved that recombinant protein (MSTN) and exogenous gene (EGFP) as vaccines, and furthermore functional CD40 shRNA expression can be delivered into dendritic cells (DCs) in mouse by oral administration of recombinant yeast (Saccharomyces cerevisiae). Here, we describe the details of the promising and innovative approach based on oral administration of recombinant yeast that allows in vivo-targeted delivery of functional SiRNA to murine intestinal DCs.

Distinctive Expression of Bcl-2 Factors in Regulatory T Cells Determines a Pharmacological Target to Induce Immunological Tolerance

Distinctive molecular characteristics of functionally diverse lymphocyte populations may represent novel pharmacological targets for immunotherapy. The intrinsic apoptosis pathway is differently regulated among conventional and regulatory T cells (Tregs). Targeted pharmacological modulation of this pathway with a small molecule Bcl-2/Bcl-xL inhibitor (ABT-737) caused a selective depletion of effector T cells and a relative enrichment of Tregs in vivo. Treatment with ABT-737 resulted in a tolerogenic milieu, which was exploited to alleviate graft-versus-host disease, to prevent allograft rejection in a stringent fully MHC-mismatched skin transplantation model and to induce immunological tolerance in combination with bone marrow transplantation. This concept has the potential to find various applications for immunotherapy, since it allows pharmacologic exploitation of the immunomodulatory properties of Tregs without the need for cell manipulation ex vivo.

In vivo targeted delivery of CD40 shRNA to mouse intestinal dendritic cells by oral administration of recombinant Sacchromyces cerevisiae

Short hairpin RNA (shRNA)-mediated gene regulation is a commonly used technique for gene manipulation. An efficient and safe delivery system is indispensable when shRNA is delivered into living organisms for gene therapy. Previous studies have proved that DNA and protein can be delivered into dendritic cells (DCs) by non-pathogenic Saccharomyces cerevisiae without being degraded. CD40 is closely related to apoptosis of tumor cells and some immune mechanisms. In this study, we demonstrated that recombinant yeast S. cerevisiae efficiently delivered the shRNA of immune-associated gene (CD40) into mouse intestinal DCs via oral administration. Western blot analysis of isolated intestinal DCs indicated that the inhibition of CD40 gene expression reached up to 56-91%. The secretion of cytokines such as interleukin-2 (IL-2), IL-6, IL-10, IL-12, tumor necrosis factor-α and interferon-γ in intestinal DCs had varying degrees of changes. In conclusion, we found that orally administered recombinant yeast can be used as an efficient shRNA delivery system for intestinal DC-specific gene silencing and immunomodulation in vivo.

Synergic silencing of costimulatory molecules prevents cardiac allograft rejection

BACKGROUND

While substantial progress has been made in blocking acute transplant rejection with the advent of immune suppressive drugs, chronic rejection, mediated primarily by recipient antigen presentation, remains a formidable problem in clinical transplantation. We hypothesized that blocking co-stimulatory pathways in the recipient by induction of RNA interference using small interference RNA (siRNA) expression vectors can prolong allogeneic heart graft survival.

METHOD

Vectors expressing siRNA specifically targeting CD40 and CD80 were prepared. Recipients (BALB/c mice) were treated with CD40 and/or CD80 siRNA expression vectors via hydrodynamic injection. Control groups were injected with a scrambled siRNA vector and sham treatment (PBS). After treatment, a fully MHC-mismatched (BALB/c to C57/BL6) heart transplantation was performed.

RESULT

Allogeneic heart graft survival (>100 days) was approximately 70% in the mice treated simultaneously with CD40 and CD80 siRNA expression vectors with overall reduction in lymphocyte interstitium infiltration, vascular obstruction, and edema. Hearts transplanted into CD40 or CD80 siRNA vector-treated recipients had an increased graft survival time compared to negative control groups, but did not survive longer than 40 days. In contrast, allogenic hearts transplanted into recipients treated with scrambled siRNA vector and PBS stopped beating within 10-16 days. Real-time PCR (RT-PCR) and flow cytometric analysis showed an upregulation of FoxP3 expression in spleen lymphocytes and a concurrent downregulation of CD40 and CD80 expression in splenic dendritic cells of siRNA-treated mice. Functional suppressive activity of splenic dendritic cells (DCs) isolated from tolerant recipients was demonstrated in a mixed lymphocyte reaction (MLR). Furthermore, DCs isolated from CD40- and CD80-treated recipients promoted CD4+CD25+FoxP3+ regulatory T cell differentiation in vitro.

CONCLUSION

This study demonstrates that the simultaneous silencing of CD40 and CD80 genes has synergistic effects in preventing allograft rejection, and may therefore have therapeutic potential in clinical transplantation.

Alloanergization of human T cells results in expansion of alloantigen-specific CD8(+) CD28(-) suppressor cells

Allostimulation with concurrent costimulatory blockade induces alloantigen-specific hyporesponsiveness in responder T cells ("alloanergization"). Alloanergized responder cells also acquire alloantigen-specific suppressive activity, suggesting this strategy induces active immune tolerance. While this acquired suppressive activity is mediated primarily by CD4(+) FOXP3(+) cells, other cells, most notably CD8(+) suppressor cells, have also been shown to ameliorate human alloresponses. To determine whether alloanergization expands CD8(+) cells with allosuppressive phenotype and function, we used mixed lymphocyte cultures in which costimulatory blockade was provided by belatacept, an FDA-approved, second-generation CTLA-4-immunoglobulin fusion protein that blocks CD28-mediated costimulation, as an in vitro model of HLA-mismatched transplantation. This strategy resulted in an eightfold expansion of CD8(+) CD28(-) T cells which potently and specifically suppressed alloresponses of both CD4(+) and CD8(+) T cells without reducing the frequency of a range of functional pathogen-specific T cells. This CD8-mediated allosuppression primarily required cell-cell contact. In addition, we observed expansion of CD8(+) CD28(-) T cells in vivo in patients undergoing alloanergized HLA-mismatched bone marrow transplantation. Use of costimulatory blockade-mediated alloanergization to expand allospecific CD8(+) CD28(-) suppressor cells merits exploration as an approach to inducing or supporting immune tolerance to alloantigens after allogeneic transplantation.

Targeting co-stimulatory pathways: transplantation and autoimmunity

The myriad of co-stimulatory signals expressed, or induced, upon T-cell activation suggests that these signalling pathways shape the character and magnitude of the resulting autoreactive or alloreactive T-cell responses during autoimmunity or transplantation, respectively. Reducing pathological T-cell responses by targeting T-cell co-stimulatory pathways has met with therapeutic success in many instances, but challenges remain. In this Review, we discuss the T-cell co-stimulatory molecules that are known to have critical roles during T-cell activation, expansion, and differentiation. We also outline the functional importance of T-cell co-stimulatory molecules in transplantation, tolerance and autoimmunity, and we describe how therapeutic blockade of these pathways might be harnessed to manipulate the immune response to prevent or attenuate pathological immune responses. Ultimately, understanding the interplay between individual co-stimulatory and co-inhibitory pathways engaged during T-cell activation and differentiation will lead to rational and targeted therapeutic interventions to manipulate T-cell responses and improve clinical outcomes.

Anti-CD20 monoclonal antibodies: beyond B-cells

Anti-CD20 monoclonal antibodies (MoAbs), employed in treating CD20⁺ lymphomas and autoimmune diseases, appear to have broader functions than just eradicating malignant B-cells and decreasing autoantibody production. Rituximab-induced T-cell inactivation, reported both in-vitro and in-vivo, may contribute to the increased risk of T-cell-dependent infections, observed in patients receiving this therapy. T-cell polarization into a suppressive phenotype, often observed in patients receiving rituximab for autoimmune disorders, was reported to be associated with prolonged remissions. Elimination of B-cells serving as antigen-presenting cells, thereby causing impaired T-cell activation, could play a significant role in induction of these changes. Direct binding of rituximab to a CD20dim T-cell population, inducing its depletion, may contribute to the decreased T-cell activation following rituximab therapy. Further investigation of the complex network through which rituximab and new anti-CD20 MoAbs act, would advance the employment of these agents in different clinical settings.

Regulatory T cells and the control of the allergic response

The study of immune regulation and tolerance has been traditionally associated with self/nonself-discrimination. However, the finding that dominant tolerance, a model that puts in evidence the active role of regulatory T cells, can develop to nonself-antigens suggests that the imposition of tolerance can be context dependent. This paper reviews the emerging field of acquired immune tolerance to non-self antigens, with an emphasis on the different subsets of induced regulatory T cells that appear to specialize in specific functional niches. Such regulatory mechanisms are important in preventing the onset of allergic diseases in healthy individuals. In addition, it may be possible to take advantage of these immune regulatory mechanisms for the induction of tolerance in cases where pathological immune responses are generated to allergens occurring in nature, but also to other immunogens such as biological drugs developed for medical therapies.

Ex Vivo Alloanergization with Belatacept: A Strategy to Selectively Modulate Alloresponses after Transplantation

Ex vivo alloanergization of human immune cells, via allostimulation in the presence of costimulatory blockade with either a combination of anti-B7.1 and anti-B7.2 antibodies or first-generation cytotoxic T-lymphocyte antigen 4-immunoglobulin (CTLA4-Ig), induces alloantigen-specific hyporesponsiveness and expands alloantigen-specific regulatory T cells (Treg). We have successfully used this approach in the clinical setting of haploidentical hematopoietic stem cell transplantation. Recently, the in vivo use of a new second-generation CTLA4-Ig, belatacept, has shown promise in controlling alloresponses after transplantation of both human kidneys and islet cells. We therefore compared the efficiency of first- and second-generation CTLA4-Ig in alloanergizing human peripheral blood mononuclear cells (PBMCs) and investigated whether ex vivo alloanergization with belatacept could be used to engineer an alloantigen-specific immunoregulatory population of autologous cells suitable for administration to recipients of cellular or solid organ transplant recipients. Alloanergization of HLA-mismatched human PBMCs with belatacept resulted in a greater reduction in subsequent alloresponses than alloanergization with first generation CTLA4-Ig. Moreover, subsequent ex vivo re-exposure of alloanergized cells to alloantigen in the absence of belatacept resulted in a significant expansion of Tregs with enhanced alloantigen-specific suppressive function. Alloanergized PBMCs retained functional Epstein-Barr virus (EBV)-specific T-cell responses, and expanded Tregs did not suppress EBV-specific proliferation of autologous cells. These results suggest that ex vivo alloanergization with belatacept provides a platform to engineer populations of recipient Treg with specificity for donor alloantigens but without nonspecific suppressive capacity. The potential advantages of such cells for solid organ transplantation include ( 1 ) reduction of the need for nonspecific immunosuppression, ( 2 ) retention of pathogen-specific immunity, and ( 3 ) control of graft rejection, if used as an intervention.

Long-term hepatic allograft acceptance based on CD40 blockade by ASKP1240 in nonhuman primates

Blockade of the CD40-CD154 costimulatory signal is an attractive strategy for immunosuppression and tolerance induction in organ transplantation. Treatment with anti-CD154 monoclonal antibodies (mAbs) results in potent immunosuppression in nonhuman primates (NHPs). Despite plans for future clinical use, further development of these treatments was halted by complications. As an alternative approach, we have been focusing on the inhibition of the counter receptor, CD40 and have shown that a novel human anti-CD40 mAb, ASKP1240, markedly prolongs renal allograft survival in NHPs, although allografts eventually underwent chronic allograft nephropathy. On the basis of our previous findings that a CD40-CD154 costimulation blockade induces tolerance to hepatic, but not cardiac, allografts in rodents, we tested here our hypothesis that a blockade of CD40 by ASKP1240 allows acceptance of hepatic allografts in NHPs. A 2-week ASKP1240 induction treatment prolonged liver allograft survival in NHPs; however, the graft function deteriorated due to chronic rejection. In contrast, a 6-month ASKP1240 maintenance monotherapy efficiently suppressed both cellular and humoral alloimmune responses and prevented rejection on the hepatic allograft. No serious side effects, including thromboembolic complications, were noted in the ASKP1240-treated monkeys. We conclude that CD40 blockade by ASKP1240 would be a desirable immunosuppressant for clinical liver transplantation.

Biological functions of regulatory T cells

The subpopulation of CD4(+) T lymphocytes that co-express the transcription factor Foxp3 plays a unique role as regulatory T lymphocytes (Tregs) that modulate many aspects of the immune response. Multiple mechanisms have been proposed for the suppressor function of CD4(+)Foxp3(+) T cells based on in vitro studies, but much less is known about how Tregs suppress immune responses in vivo. Both polyclonal Tregs and antigen-specific Tregs are capable of exerting potent suppressive effects in vivo, and it is likely that they mediate their biologic functions using different mechanisms. Antigen-specific Tregs primarily target dendritic cells and inhibit dendritic cell functions including the expression of costimulatory molecules and the presentation of antigen early during the generation of the immune response. The end result is a complete inhibition of both the expansion and the differentiation of T effector cells. Polyclonal Tregs also act on dendritic cells, but at a later phase, and do not inhibit expansion of T effector cells, but appear to modulate differentiation and cell trafficking. The cell surface molecules involved in the interaction of Tregs with dendritic cells, as well as the biochemical pathways modified by this interaction remain to be fully elucidated. A complete understand of the biological functions of Tregs in vivo should facilitate the development of pharmacologic and biologic agents that can be used to modulate Treg function in a therapeutic setting.

Early treatment of NOD mice with B7-H4 reduces the incidence of autoimmune diabetes

OBJECTIVE

Autoimmune diabetes is a T cell-mediated disease in which insulin-producing β-cells are destroyed. Autoreactive T cells play a central role in mediating β-cell destruction. B7-H4 is a negative cosignaling molecule that downregulates T-cell responses. In this study, we aim to determine the role of B7-H4 on regulation of β-cell-specific autoimmune responses.

RESEARCH DESIGN AND METHODS

Prediabetic (aged 3 weeks) female NOD mice (group 1, n = 21) were treated with intraperitoneal injections of B7-H4.Ig at 7.5 mg/kg, with the same amount of mouse IgG (group 2, n = 24), or with no protein injections (group 3, n = 24), every 3 days for 12 weeks.

RESULTS

B7-H4.Ig reduced the incidence of autoimmune diabetes, compared with the control groups (diabetic mice 28.6% of group 1, 66.7% of group 2 [P = 0.0081], and 70.8% of group 3 [group 1 vs. 3, P = 0.0035]). Histological analysis revealed that B7-H4 treatment did not block islet infiltration but rather suppressed further infiltrates after 9 weeks of treatment (group 1 vs. 2, P = 0.0003). B7-H4 treatment also reduced T-cell proliferation in response to GAD65 stimulation ex vivo. The reduction of diabetes is not due to inhibition of activated T cells in the periphery but rather to a transient increase of Foxp3(+) CD4(+) T-cell population at one week posttreatment (12.88 ± 1.29 vs. 11.58 ± 1.46%; n = 8; P = 0.03).

CONCLUSIONS

Our data demonstrate the protective role of B7-H4 in the development of autoimmune diabetes, suggesting a potential means of preventing type 1 diabetes by targeting the B7-H4 pathway.

CD154 blockade abrogates allospecific responses and enhances CD4(+) regulatory T-cells in mouse orthotopic lung transplant

Acute cellular rejection (ACR) is a common and important clinical complication following lung transplantation. While there is a clinical need for the development of novel therapies to prevent ACR, the regulation of allospecific effector T-cells in this process remains incompletely understood. Using the MHC-mismatched mouse orthotopic lung transplant model, we investigated the short-term role of anti-CD154 mAb therapy alone on allograft pathology and alloimmune T-cell effector responses. Untreated C57BL/6 recipients of BALB/c left lung allografts had high-grade rejection and diminished CD4(+) : CD8(+) graft ratios, marked by predominantly CD8(+) >CD4(+) IFN-γ(+) allospecific effector responses at day 10, compared to isograft controls. Anti-CD154 mAb therapy strikingly abrogated both CD8(+) and CD4(+) alloeffector responses and significantly increased lung allograft CD4(+) : CD8(+) ratios. Examination of graft CD4(+) T-cells revealed significantly increased frequencies of CD4(+) CD25(+) Foxp3(+) regulatory T-cells in the lung allografts of anti-CD154-treated mice and was associated with significant attenuation of ACR compared to untreated controls. Together, these data show that CD154/CD40 costimulation blockade alone is sufficient to abrogate allospecific effector T-cell responses and significantly shifts the lung allograft toward an environment predominated by CD4(+) T regulatory cells in association with an attenuation of ACR.

Intervention with costimulatory pathways as a therapeutic approach for graft-versus-host disease

Graft-versus-host disease (GVHD) is mediated by mature donor T cells contained in the hematopoietic stem cell graft. During the development of GVHD, signaling through a variety of costimulatory receptors plays an important role in allogeneic T cell responses. Even though delivery of costimulatory signals is a prerequisite for full activation of donor T cells in the phase of their interactions with host APCs, their involvement with GVHD might occur over multiple stages. Like many other aspects of GVHD, promise of therapeutic interventions with costimulatory pathways has been gleaned from preclinical models. In this review, I summarize some of the advances in roles of costimulatory molecules in GVHD pathophysiology and discuss preclinical approaches that warrant further exploration in the clinic, focusing on novel strategies to delete pathogenic T cells.

Topical inhibition of T cell costimulatory pathways in draining lymph nodes may suppress allograft rejection

Topical immune suppression is an attractive and practical therapeutic option to prolong survival time of allografts, before the appearance of new agent with higher immunosuppressive efficacy and lower undesirable side effects. The initiation of rejection and outcome of allografts is principally mediated by alloantigen reactive T cells. The activation of T cells requires at least two signals, first is T-cell receptor signal and second is costimulatory signal. T cells that encounter antigen without the appropriate costimulatory signal become anergy or tolerance. Migration of alloantigen-bearing dendritic cells into the T-cell zone of secondary lymphoid tissues, which are essential for primary alloimmune responses, effectively induces T-cell activation and expansion with the presence of two signals. Draining lymph nodes are the promising targets for topical immune suppression, as disrupting lymphatic drainage from the transplanted graft to lymph nodes prevented rejection of skin allografts and lymphadenectomy prolong the survival time of skin and corneal allografts in experimental animals. Therefore, we hypothesize that inhibition of T cell costimulatory pathways in draining lymph nodes could impair the alloantigen-specific immune response and reduce systemic immunosuppressive drugs dose for allografts survival. Further investigations are required to identify most efficient way for draining lymph nodes transfer of costimulatory molecule gene or topical drug administration of costimulatory inhibitors to draining lymph nodes.

T-cell costimulatory molecules in acute-graft-versus host disease: therapeutic implications

Acute Graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation. Although this process is thought to consist of several phases, T-cell activation plays a critical role in the pathogenesis of acute GVHD. To become efficient effectors, T-cells require additional costimulation after T-cell receptor signaling. A number of molecules are involved in costimulation of T-cells such as CD28, CD40L, CD30, OX40, 4-1BB, ICOS, and LIGHT. The system is regulated by inhibitory molecules, CTLA-4, and PD-1. There is experimental evidence that those molecules are implicated in the pathogenesis of GHVD. We describe how these molecules are involved in acute GVHD and how the blockade of costimulatory molecules may have potential implications for the treatment of patients with acute GVHD.

GVHD after haploidentical transplantation: a novel, MHC-defined rhesus macaque model identifies CD28- CD8+ T cells as a reservoir of breakthrough T-cell proliferation during costimulation blockade and sirolimus-based immunosuppression

We have developed a major histocompatibility complex-defined primate model of graft-versus-host disease (GVHD) and have determined the effect that CD28/CD40-directed costimulation blockade and sirolimus have on this disease. Severe GVHD developed after haploidentical transplantation without prophylaxis, characterized by rapid clinical decline and widespread T-cell infiltration and organ damage. Mechanistic analysis showed activation and possible counter-regulation, with rapid T-cell expansion and accumulation of CD8(+) and CD4(+) granzyme B(+) effector cells and FoxP3(pos)/CD27(high)/CD25(pos)/CD127(low) CD4(+) T cells. CD8(+) cells down-regulated CD127 and BCl-2 and up-regulated Ki-67, consistent with a highly activated, proliferative profile. A cytokine storm also occurred, with GVHD-specific secretion of interleukin-1 receptor antagonist (IL-1Ra), IL-18, and CCL4. Costimulation Blockade and Sirolimus (CoBS) resulted in striking protection against GVHD. At the 30-day primary endpoint, CoBS-treated recipients showed 100% survival compared with no survival in untreated recipients. CoBS treatment resulted in survival, increasing from 11.6 to 62 days (P < .01) with blunting of T-cell expansion and activation. Some CoBS-treated animals did eventually develop GVHD, with both clinical and histopathologic evidence of smoldering disease. The reservoir of CoBS-resistant breakthrough immune activation included secretion of interferon-γ, IL-2, monocyte chemotactic protein-1, and IL-12/IL-23 and proliferation of cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin-resistant CD28(-) CD8(+) T cells, suggesting adjuvant treatments targeting this subpopulation will be needed for full disease control.

IL-10/TGF-beta-treated dendritic cells, pulsed with insulin, specifically reduce the response to insulin of CD4+ effector/memory T cells from type 1 diabetic individuals

INTRODUCTION

Diabetogenic autoreactive T cells with effector/memory characteristics are described in type 1 diabetes patients (T1D). Alternatively activated dendritic cells (aaDCs) have been regarded as promising tools for clinical application in autoimmune diseases (ADs), although their ability to induce antigen-specific tolerance in T cells derived from ADs has yet to be determined.

METHODS

Monocyte-derived dendritic cells (DCs) were produced utilizing GM-CSF and IL-4, and aaDCs by adding IL-10 and TGF-beta (10/TGF-DC) during differentiation. Both cell groups were insulin-loaded, maturated with lipopolysaccharide, and cocultured with autologous effector/memory T cells derived from T1D individuals, in order to evaluate the induction of insulin-specific tolerance.

RESULTS AND DISCUSSION

In five of eight T1D patients analyzed in vitro, 10/TGF-DC were able to induce insulin-specific tolerance in effector/memory CD4+ T cells (50.4% +/- 13.2 less proliferation), without affecting the proliferative response to an unrelated antigen (candidin). Tolerance induction was dependent on the current activation state of CD4+ T cells in each patient. 10/TGF-DC-stimulated T cells acquired an IL-2(low)IFN-gamma(low)IL-10(high) cytokine profile, and their hyporesponsiveness could be reverted upon exposure to IL-2. This study shows a perspective about the in vitro ability of monocyte-derived 10/TGF-DC to induce antigen-specific tolerance in effector/memory T cells generated during the course of an autoimmune disease.

CD40 expression levels modulate regulatory T cells in Leishmania donovani infection

Dendritic cell (DC)-expressed CD40 is shown to play crucial roles in eliciting effector T cell responses, primarily the proinflammatory CD4(+) Th subsets and cytotoxic CD8(+) T cells that eliminate various infections and tumors, respectively. In contrast, DCs are also implied in the generation of regulatory T cells (Tregs) that counteract the functions of the proinflammatory Th subsets and exacerbate infections. However, the role of DC-expressed CD40 in the generation of Tregs is unknown. In this study, we generated bone marrow-derived DCs from mice (on a BALB/c background) expressing different levels of CD40 and tested their relative efficiency in generating Tregs. We observed that low levels of CD40 expression were required for efficient Treg generation. DCs expressing low levels of CD40 induced Tregs, whereas DCs expressing high levels of CD40 induced effector T cells, possibly CD8(+)CD40(+) T cells with a contraregulatory activity; the adoptive transfer of the former DC exacerbated whereas the latter significantly reduced Leishmania donovani infection in BALB/c mice. Similarly, priming of mice with leishmanial Ag-pulsed DCs expressing high levels of CD40 induced host protection against L. donovani challenge infection. In contrast, priming with the low CD40-expressing DC resulted in aggravated infection as compared with the control mice. The results establish that CD40 can play differential roles in Treg differentiation and determine the course of infection. We demonstrate that the knowledge can be efficiently used in adoptive cell transfer therapy against an infectious disease.

Oligonucleotide based-strategies for allergy with special reference to siRNA

BACKGROUND

Allergic diseases are a significant global health care problem. Current pharmacological approaches address symptoms but do not alter the underlying immune dysregulation. Current allergen-specific immunotherapy has several drawbacks. Therefore, approaches that attenuate allergic responses safely and effectively at the level of upstream causative events are desirable. Oligonuleotide-based therapies [CpG DNA, antisense oligonucleotides, and small interfering RNA (siRNA)] are promising approaches.

OBJECTIVE/METHODS

We review developments in oligonucleotide-based therapies and the potential of siRNA for treating allergy.

RESULTS/CONCLUSIONS

Strategies with oligonucleotides basically aim to reduce T helper type 2 (Th2) responses. It is controversial whether the reduction of Th2 responses does, in fact, attenuate allergic diseases. Increased understanding of allergic mechanisms will enhance the efficacy of oligonucleotide-based therapy.

Mechanism of cellular rejection in transplantation

The explosion of new discoveries in the field of immunology has provided new insights into mechanisms that promote an immune response directed against a transplanted organ. Central to the allograft response are T lymphocytes. This review summarizes the current literature on allorecognition, costimulation, memory T cells, T cell migration, and their role in both acute and chronic graft destruction. An in depth understanding of the cellular mechanisms that result in both acute and chronic allograft rejection will provide new strategies and targeted therapeutics capable of inducing long-lasting, allograft-specific tolerance.

Expansion of allospecific regulatory T cells after anergized, mismatched bone marrow transplantation

Transplantation of hematopoietic stem cells from healthy donors can cure patients with many diseases. Donor T cells can protect against recurrence of infection and disease, but some of these (alloreactive) T cells recognize patient tissues as foreign, causing graft-versus-host disease. Removing T cells from donor grafts before transplantation reduces graft-versus-host disease but increases infection and disease recurrence. Inactivation of alloreactive T cells by inducing tolerance to patient cells (anergization) before transplantation preserves beneficial donor T cell effects while reducing graft-versus-host disease. We show that this approach also results in expansion of regulatory T cells that specifically suppress alloreactive donor T cell responses in the recipient. In addition to reducing graft-versus-host disease, antigen-specific regulatory T cells generated with this strategy could suppress unwanted T cell responses that cause rejection of solid organ transplants and tissue damage in autoimmune disorders.

Depletion of Host Reactive T Cells by Photodynamic Cell Purging and Prevention of Graft Versus Host Disease

Graft versus Host Disease (GVHD) is the principal cause of morbidity and mortality in patients undergoing allogeneic stem cell transplant. T cell depletion has been recognized as a method of reducing the incidence of GVHD in allogeneic transplants. Until recently, most T cell depletion methods were non-selective in reducing lymphocytes. Rhodamine purging is one method, which selectively reduces alloreactive T cells preventing GVHD. We review here the methods of non-selective and selective T cell depletion, particularly the newer method of photodynamic purging utilizing rhodamine.

Inhibition of allergic responses by CD40 gene silencing

BACKGROUND

Gene silencing using small interfering RNA (siRNA) is a potent method of specifically knocking down molecular targets. Small interfering RNA is therapeutically promising, however, treatment of allergic diseases with siRNA has not been explored in vivo. The aim of this study was to evaluate therapeutic effects of CD40 siRNA on inhibition of allergic responses.

METHODS

Mice sensitized with ovalbumin (OVA) and alum were treated with CD40 siRNA, scrambled siRNA, or phosphate buffer saline (PBS) alone, and then challenged intranasally with OVA.

RESULTS

A significant reduction in nasal allergic symptoms was observed in the CD40 siRNA treated OVA-allergic mice compared to the controls of scrambled siRNA and PBS alone, which is correlated with the decrease of local eosinophil accumulation. CD40 siRNA treatment knocked down CD40 expression on dendritic cells (DCs) in vivo and impaired their antigen presenting function. Treatment with CD40 siRNA resulted in inhibition of OVA-specific T cell response and decrease of interleukin-4 (IL-4), IL-5, and interferon-gamma production from T cells stimulated with OVA. Administration of CD40 siRNA also suppressed CD40 expression on B cells, resulting in down-regulation of OVA-specific immunoglobulin E (IgE), IgG1, and IgG2a levels. Additionally, increased regulatory T cells were observed in the CD40 siRNA treated mice.

CONCLUSIONS

The present study demonstrates a novel therapeutic use for siRNA in allergy. CD40 siRNA attenuated allergy through inhibition of DC and B cell functions and generation of regulatory T (Treg) cells.

Novel vaccination for allergy through gene silencing of CD40 using small interfering RNA

Small interfering RNA (siRNA) is a potent means of inducing gene-specific silencing. Gene silencing strategies using siRNA have demonstrated therapeutic benefits in animal models of various diseases, and are currently in clinical trials. However, the utility of gene silencing as a treatment for allergic diseases has not yet been reported. In this study, we report a novel therapy for allergy through gene silencing of CD40, a critical costimulatory molecule and a key factor in allergic immune responses. Silencing CD40 resulted in generation of immunoregulatory dendritic cells (DCs). Administration of CD40 siRNA remarkably reduced nasal allergic symptoms and local eosinophil accumulation in the OVA-induced allergic mice. The OVA-specific T cell response was inhibited after the CD40 siRNA treatment. Additionally, anti-OVA specific IgE and production of IL-4 and IL-5 of T cells stimulated by OVA were significantly decreased in CD40 siRNA-treated mice. Furthermore, we demonstrated that the therapeutic effects by CD40 siRNA were associated with impaired Ag-presenting functions of DCs and B cells, and generation of regulatory T cells. The present study highlights a therapeutic potential of siRNA-based treatment for allergic diseases.

Regulatory T cells as therapeutic target in Hodgkin's lymphoma

BACKGROUND

The clinical and pathological features of Hodgkin's lymphoma (HL) reflect an abnormal immune response that results from cytokines and chemokines secreted by Hodgkin/Reed-Sternberg (H/R-S) cells and/or the surrounding tissue.

OBJECTIVE

Increasing evidence indicates that H/R-S cells recruit and/or induce regulatory T (Treg) cells that contribute to an ineffective immune clearance of the malignant cell types and may also impair effects of adaptive cellular immunotherapy applied in HL.

METHODS

In this review we highlight advances in the understanding of immune regulation in HL, and discuss implications for immunotherapy in this disease by targeting Treg cells. However, the origin, development, migration and functional mechanism of these Treg cells are under discussion.

RESULTS/CONCLUSION

As studies demonstrate that the depletion and/or manipulation of Treg cells enhance antitumor immunity, these novel treatment approaches may improve the therapy especially for patients with refractory or relapsed HL.

OX40 controls islet allograft tolerance in CD154 deficient mice by regulating FOXP3+ Tregs

The role of OX40 in the islet allograft tolerance, especially in the absence of CD154 costimulation, remains poorly defined. In the present study, we used CD154 deficient mice to critically examine the role of OX40 in the activation of T effector cells and Foxp3+ Tregs and the effect of blocking OX40 on the induction of islet allograft tolerance. We found that blocking OX40 costimulation in CD154 deficient mice induced donor specific tolerance but stimulating OX40 resulted in prompt islet allograft rejection. We also found that OX40 differentially regulates T effector cells and Foxp3+ Tregs, OX40 signaling mediates proliferation of CD154 deficient T effector cells but blocks the induction and suppressor functions of Foxp3+ Tregs. Our data suggest that the role of OX40 in the induction of islet allograft tolerance involves modifying not only the T effector cells but also the Foxp3+ Tregs in CD154 deficient mice.

Histochemical and molecular overview of the thymus as site for T-cells development

The thymus represents the primary site for T cell lymphopoiesis, providing a coordinated set for critical factors to induce and support lineage commitment, differentiation and survival of thymus-seeding cells. One irrefutable fact is that the presence of non-lymphoid cells through the thymic parenchyma serves to provide coordinated migration and differentiation of T lymphocytes. Moreover, the link between foetal development and normal anatomy has been stressed in this review. Regarding thymic embryology, its epithelium is derived from the embryonic endodermal layer, with possible contributions from the ectoderm. A series of differentiating steps is essential, each of which must be completed in order to provide the optimum environment for thymic development and function. The second part of this article is focused on thymic T-cell development and differentiation, which is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. It depends strongly on the thymic microenvironment, a cellular network formed by epithelial cells, macrophages, dendritic cells and fibroblasts, that provide the combination of cellular interactions, cytokines and chemokines to induce thymocyte precursors for the generation of functional T cells. The mediators of this process are not well defined but it has been demonstrated that some interactions are under neuroendocrine control. Moreover, some studies pointed out that reciprocal signals from developing T cells also are essential for establishment and maintenance of the thymic microenvironment. Finally, we have also highlighted the heterogeneity of the lymphoid, non-lymphoid components and the multi-phasic steps of thymic differentiation. In conclusion, this review contributes to an understanding of the complex mechanisms in which the foetal and postnatal thymus is involved. This could be a prerequisite for developing new therapies specifically aimed to overcome immunological defects, linked or not-linked to aging.

A clinical-scale selective allodepletion approach for the treatment of HLA-mismatched and matched donor-recipient pairs using expanded T lymphocytes as antigen-presenting cells and a TH9402-based photodepletion technique

Selective allodepletion is a strategy to eliminate host-reactive donor T cells from hematopoietic stem cell allografts to prevent graft-versus-host disease while conserving useful donor immune functions. To overcome fluctuations in activation-based surface marker expression and achieve a more consistent and effective allodepletion, we investigated a photodepletion process targeting activation-based changes in p-glycoprotein that result in an altered efflux of the photosensitizer TH9402. Expanded lymphocytes, generated using anti-CD3 and IL-2, were cocultured with responder cells from HLA-matched or -mismatched donors. Optimal results were achieved when cocultured cells were incubated with 7.5 muM TH9402, followed by dye extrusion and exposure to 5 Joule/cm(2) light energy at 5 x 10(6) cells/mL. In mismatched stimulator-responder pairs, the median reduction of alloreactivity was 474-fold (range, 43-fold to 864-fold) compared with the unmanipulated responder. Third-party responses were maintained with a median 1.4-fold (range, 0.9-fold to 3.3-fold) reduction. In matched pairs, alloreactive helper T-lymphocyte precursors were reduced to lower than 1:100 000, while third-party responses remained higher than 1:10 000. This establishes a clinical-scale process capable of highly efficient, reproducible, selective removal of alloreactive lymphocytes from lymphocyte transplant products performed under current Good Manufacturing Practice. This procedure is currently being investigated in a clinical trial of allotransplantation.

In utero environmental tobacco smoke exposure alters gene expression in lungs of adult BALB/c mice

BACKGROUND

In utero environmental tobacco smoke (ETS) exposure exacerbates initial lung responses of adult mice to ovalbumin (OVA), a common allergen in rodent models of allergic asthma.

OBJECTIVE

We tested the hypothesis that in utero ETS exposure alters expression of genes (including asthma-related and inflammatory genes) in the lungs of adult mice and that this differential expression is reflected in differential respiratory and immune responses to nontobacco allergens.

METHODS

Using Affymetrix Mouse Genome 430 2.0 arrays, we examined gene expression changes in lungs of BALB/c mice exposed to ETS in utero, OVA, or saline aerosol at weeks 7-8, and OVA sensitization and challenge at weeks 11-15. Data sets were filtered by transcript p-value (< or = 0.05), false discovery rate (< or = 0.05), and fold change (> or = 1.5). Differential expression of selected genes was confirmed by polymerase chain reaction (PCR).

RESULTS

Genes differentially expressed as a result of in utero ETS exposure are involved in regulation of biological processes (immune response, cell proliferation, apoptosis, cell metabolism) through altered cytoskeleton, adhesion, transcription, and enzyme molecules. A number of genes prominent in lung inflammation were differentially expressed on PCR but did not pass selection criteria for microarray, including arginase (Arg1), chitinases (Chia, Chi3l3, Chi3l4), eotaxins (Ccl11, Ccl24), small proline-rich protein 2a (Sprr2a), and cytokines (Il4, Il6, Il10, Il13, Tnfa) .

CONCLUSION

The differential lung gene expression reported here is consistent with previously reported functional changes in lungs of mice exposed in utero to ETS and as adults to the nontobacco allergen OVA.

Dendritic cell expression of OX40 ligand acts as a costimulatory, not polarizing, signal for optimal Th2 priming and memory induction in vivo

Costimulatory cross-talk can occur at multiple cellular levels to potentiate expansion and polarization of Th responses. Although OX40L ligand (OX40L) is thought to play a key role in Th2 development, the critical cellular source of this molecule has yet to be identified. In this study, we demonstrate that OX40L expression by the initiating dendritic cell (DC) is a fundamental requirement for optimal induction of primary and memory Th2 responses in vivo. Analysis of the kinetics of the residual Th2 response primed by OX40L-deficient DC suggested a failure to stimulate appropriate expansion and/or survival of T cells, rather than an inability to polarize per se. The dependence upon OX40L was predominantly due to the provision of signaling through OX40 rather than retrograde signaling to the DC. Mechanistically, impaired Th2 priming in the absence of OX40L was not due to exaggerated regulation because there was no evidence of increased expansion or function of regulatory cell populations, suppression through IL-10 production, or hyporesponsiveness to secondary challenge. These data define a critical role for DC-derived OX40L in the induction and development of Th2 responses in vivo.

Reconstitution of FOXP3+ regulatory T cells (Tregs) after CD25-depleted allotransplantation in elderly patients and association with acute graft-versus-host disease

Selective depletion (SD) of host-reactive donor T cells from allogeneic stem-cell transplants (SCTs) using an anti-CD25 immunotoxin (IT) is a strategy to prevent acute graft-versus-host disease (aGvHD). There is concern that concurrent removal of regulatory T cells (T(regs)) with incomplete removal of alloactivated CD25(+) T cells could increase the risk of aGvHD. We therefore measured T(regs) in the blood of 16 patients receiving a T-cell-depleted allograft together with anti-CD25-IT-treated SD lymphocytes, in 13 of their HLA-identical donors, and in 10 SD products. T(regs) were characterized by intracellular staining for forkhead box protein 3 (FOXP3) and by quantitative reverse-transcription-polymerase chain reaction (qRT-PCR) for FOXP3 gene in CD4(+) cells. Patients received a median of 1.0 x 10(8)/kg SD T cells and a stem cell product containing a median of 0.25 x 10(4)/kg residual T cells. T(regs) reconstituted promptly after SCT and underwent further expansion. Of the CD4(+) T cells in SD products, 1.5% to 4.8% were CD25(-) T(regs). Acute GvHD (>or= grade II) was restricted to 5 patients whose donors had significantly (P = .019) fewer T(regs) compared with those without clinically significant aGvHD. These results suggest that rapid T(reg) reconstitution can occur following SD allografts, either from CD25(-) T(regs) escaping depletion, or from residual CD25(-) and CD25(+) T(regs) contained in the stem-cell product that expand after transplantation and may confer additional protection against GvHD.

Recent Progress in Tolerance Induction through Mixed Chimerism

Organ transplant recipients require life-long treatment with immunosuppressive drugs. Currently available immunosuppression is associated with substantial morbidity and mortality, and is ineffective in inhibiting chronic rejection and graft loss. Therefore, a permanent state of donor-specific tolerance remains a primary goal for transplantation research. The induction of mixed hematopoietic chimerism is an attractive concept in this regard. Hematopoietic chimerism modulates the immunologic repertoire by extending the mechanisms of self-tolerance to donor-specific allotolerance. Despite recent progress in developing nontoxic bone marrow transplantation protocols for rodents, translation to large animals has remained difficult. Here, we outline the concept of tolerance via mixed chimerism, and review recent progress and remaining challenges in bringing this approach to the clinical setting.

Absence of CD4CD25 regulatory T cell expansion in renal transplanted patients treated in vivo with Belatacept mediated CD28–CD80/86 blockade

AIMS

Belatacept is a new recombinant molecule (CTLA4-Ig) that interferes with the second activation signal of T lymphocytes. CTLA4-Ig induced T cell allograft tolerance in rodents but not in primates. We examined the changes in peripheral lymphocyte subsets, including regulatory T cells, in renal transplant patients treated with Belatacept.

METHODS

A cross-sectional immunological study was carried out 6 months after transplantation in 28 patients enrolled in the Belatacept phase II study. Eighteen patients received Belatacept, mycophenolate mofetil and steroids (Belatacept group), while the control group of 10 patients received cyclosporine, mycophenolate mofetil and steroids (CsA group). Lymphocyte subsets were examined by flow cytometry. Foxp3 mRNA expression was measured by quantitative PCR.

RESULTS

The number of T lymphocytes and the percentage of CD3+ T cells were similar in both groups. However, the percentage of CD3+ CD4+ T cells was lower in the Belatacept group than in the control CsA group (B=42.5%+/-13.7 vs CsA=52.9%+/-9, p<0.005), and the percentage of CD3+ CD8+ cells was higher in the Belatacept group than in the control (B=32.9%+/-6.7 vs CsA=19.5%+/-8.2, p<0.0002). The percentage of CD19+ cells was similar in both groups. Among CD56+cells, only the percentage of CD16+ cells was significantly higher in the Belatacept group than in the control (B=82%+/-12 vs CsA=59.7%+/-25, p=0.01). Among CD4 and CD8 T cells the percentage of activated lymphocytes expressing CTLA4, HLA-DR or CD40L was similar in both groups. The percentage of CD4+CD25+ T cells was higher in the CsA group. The percentage of regulatory CD4+CD25+ cells with bright CD25 staining was similar in both groups (B=3.6+/-2.3% vs CsA=4.7+/-1.9%, ns) as was the expression of FoxP3.

CONCLUSION

Our results indicated that Belatacept did not induce regulatory T cell expansion in vivo. We suggest that Belatacept treatment should be maintained after transplantation to allow graft acceptance.