Chronic cardiac rejection in the LEW to F344 rat model. Blockade of CD28-B7 costimulation by CTLA4Ig modulates T cell and macrophage activation and attenuates arteriosclerosis

Interleukin-5 (IL-5) Therapy Prevents Allograft Rejection by Promoting CD4+CD25+ Ts2 Regulatory Cells That Are Antigen-Specific and Express IL-5 Receptor

CD4⁺CD25⁺Foxp3⁺T cell population is heterogenous and contains three major sub-groups. First, thymus derived T regulatory cells (tTreg) that are naïve/resting. Second, activated/memory Treg that are produced by activation of tTreg by antigen and cytokines. Third, effector lineage CD4⁺CD25⁺T cells generated from CD4⁺CD25^- T cells' activation by antigen to transiently express CD25 and Foxp3. We have shown that freshly isolated CD4⁺CD25⁺T cells are activated by specific alloantigen and IL-4, not IL-2, to Ts2 cells that express the IL-5 receptor alpha. Ts2 cells are more potent than naïve/resting tTreg in suppressing specific alloimmunity. Here, we showed rIL-5 promoted further activation of Ts2 cells to Th2-like Treg, that expressed foxp3, irf4, gata3 and il5. In vivo, we studied the effects of rIL-5 treatment on Lewis heart allograft survival in F344 rats. Host CD4⁺CD25⁺T cells were assessed by FACS, in mixed lymphocyte culture and by RT-PCR to examine mRNA of Ts2 or Th2-like Treg markers. rIL-5 treatment given 7 days after transplantation reduced the severity of rejection and all grafts survived ≥60d whereas sham treated rats fully rejected by day 31 (p<0.01). Treatment with anti-CD25 or anti-IL-4 monoclonal antibody abolished the benefits of treatment with rIL-5 and accelerated rejection. After 10d treatment with rIL-5, hosts' CD4⁺CD25⁺ cells expressed more Il5ra and responded to specific donor Lewis but not self. Enriched CD4⁺CD25⁺ cells from rIL-5 treated rats with allografts surviving >60 days proliferated to specific donor only when rIL-5 was present and did not proliferate to self or third party. These cells had more mRNA for molecules expressed by Th2-like Treg including Irf4, gata3 and Il5. These findings were consistent with IL-5 treatment preventing rejection by activation of Ts2 cells and Th2-like Treg.

T cell co-stimulation and co-inhibition in cardiovascular disease: a double-edged sword

The role of inflammation in cardiovascular disease (CVD) is now widely accepted. Immune cells, including T cells, are influenced by inflammatory signals and contribute to the onset and progression of CVD. T cell activation is modulated by T cell co-stimulation and co-inhibition pathways. Immune checkpoint inhibitors (ICIs) targeting T cell inhibition pathways have revolutionized cancer treatment and improved survival in patients with cancer. However, ICIs might induce cardiovascular toxicity via T cell re-invigoration. With the rising use of ICIs for cancer treatment, a timely overview of the role of T cell co-stimulation and inhibition molecules in CVD is desirable. In this Review, the importance of these molecules in the pathogenesis of CVD is highlighted in preclinical studies on models of CVD such as vein graft disease, myocarditis, graft arterial disease, post-ischaemic neovascularization and atherosclerosis. This Review also discusses the therapeutic potential of targeting T cell co-stimulation and inhibition pathways to treat CVD, as well as the possible cardiovascular benefits and adverse events after treatment. Finally, the Review emphasizes that patients with cancer who are treated with ICIs should be monitored for CVD given the reported association between the use of ICIs and the risk of cardiovascular toxicity.

Effect of Conversion to CTLA4Ig on Tacrolimus-Induced Diabetic Rats

BACKGROUND

The effect of conversion to cytotoxic T lymphocyte-associated protein 4 immunoglobulin (CTLA4Ig) treatment on tacrolimus (TAC)-induced renal dysfunction is well known, but its effect on TAC-induced diabetes mellitus (DM) is still undetermined. In the present study, we tested the diabetogenicity of CTLA4Ig and evaluated the effect of conversion to CTLA4Ig treatment on TAC-induced diabetic rats.

METHODS

We tested diabetogenicity of CTLA4Ig by escalating doses (0.25, 0.5, 1, 2, and 4 mg/kg weekly) for 4 weeks. In the conversion study, we administered TAC (1.5 mg/kg) for 3 weeks and confirmed TAC-induced DM by intraperitoneal glucose tolerance test. Thereafter, TAC administration was continued, withdrawn, or replaced by CTLA4Ig treatment (1 or 2 mg/kg) for additional 3 weeks. The effect of CTLA4Ig on TAC-induced DM in vivo and in vitro was evaluated by assessing pancreatic islet function, histopathology, oxidative stress, apoptosis, and macrophage infiltration.

RESULTS

Intraperitoneal glucose tolerance test in the CTLA4Ig groups did not differ from the control group. In addition, plasma insulin level, glucose-induced insulin secretion, and islet viability were not different between the CTLA4Ig and control groups. In the conversion study, TAC withdrawal ameliorated pancreatic islet dysfunction compared with the TAC group, and conversion to CTLA4Ig further improved pancreatic islet function compared with the TAC withdrawal group. TAC-induced oxidative stress, apoptotic cell death, and infiltration of macrophages decreased with TAC withdrawal, and CTLA4Ig conversion further reduced those values. In the in vitro study, CTLA4Ig decreased TAC-induced pancreatic islet cell death and reactive oxygen species production.

CONCLUSIONS

CTLA4Ig was not diabetogenic, and conversion to CTLA4Ig reduced TAC-induced pancreatic islet injury.

Histone/protein deacetylase 11 targeting promotes Foxp3+ Treg function

Current interest in Foxp3+ T-regulatory (Treg) cells as therapeutic targets in transplantation is largely focused on their harvesting pre-transplant, expansion and infusion post-transplantation. An alternate strategy of pharmacologic modulation of Treg function using histone/protein deacetylase inhibitors (HDACi) may allow more titratable and longer-term dosing. However, the effects of broadly acting HDACi vary, such that HDAC isoform-selective targeting is likely required. We report data from mice with constitutive or conditional deletion of HDAC11 within Foxp3+ Treg cells, and their use, along with small molecule HDAC11 inhibitors, in allograft models. Global HDAC11 deletion had no effect on health or development, and compared to WT controls, Foxp3+ Tregs lacking HDAC11 showed increased suppressive function, and increased expression of Foxp3 and TGF-β. Likewise, compared to WT recipients, conditional deletion of HDAC11 within Tregs led to long-term survival of fully MHC-mismatched cardiac allografts, and prevented development of transplant arteriosclerosis in an MHC class II-mismatched allograft model. The translational significance of HDAC11 targeting was shown by the ability of an HDAC11i to promote long-term allograft allografts in fully MHC-disparate strains. These data are powerful stimuli for the further development and testing of HDAC11-selective pharmacologic inhibitors, and may ultimately provide new therapies for transplantation and autoimmune diseases.

Flt3-L Augments the Engraftment of Donor-Derived Bone Marrow Cells When Combined with Sublethal Irradiation and Costimulatory (CD28/B7 and CD40/CD40L) Blockade

T-cell costimulatory blockade as a constituent for recipient conditioning prior to bone marrow transplantation has led to the development of less toxic protocols for the establishment of donor cell chimerism. We therefore hypothesized that the addition of the hematopoietic growth factor, Flt3-ligand (Flt3-L), to the perioperative inhibition of the CD28/B7 and CD40/CD40 ligand costimulatory pathways would enhance the engraftment of allogeneic bone marrow. Recipient BALB/c ByJ (H-2d, Mlsc, Vβ6+/Vβ8+ TCR) received a single sublethal dose of total body irradiation (300 rad) 6 h prior to transplantation IV with unfractionated donor CBA/J (H-2k, Mlsd, Vβ6-/Vβ8+ TCR) bone marrow cells. CTLA4-Ig and/or MR1 were administered at 500 μg IP on days 0, 2, 4, and 6 posttransplantation. Flt3-L was administered at 10 μg IP on days 0–6. Donor cell chimerism was determined on days 30–90 by flow cytometric analysis. Donor-specific tolerance was assessed by skin grafting. In vitro TCR cross-linking assays and flow cytometry were utilized to explore the deletion of donor-reactive T cells. Recipients receiving CTLA4-Ig and MR1 engrafted allogeneic bone marrow cells in the peripheral blood (3/6; 50%) with chimerism being detected at 2–31%. Addition of Flt3-L to this preconditioning regimen enhanced the incidence of engraftment of donor bone marrow cells (10/13; 3–70%). Long-term survival of donor but not third-party-specific skin grafts demonstrated that donor-specific tolerance had been achieved in the chimeric recipients. Deletion of the donor-reactive T cells within the chimeric recipients was also observed. The addition of hematopoietic growth factors and cytokines to the nonmyeloablative regimen of sublethal irradiation and T-cell costimulatory blockade provides a novel strategy for the establishment of donor cell chimerism and for the induction of stable and robust donor-specific tolerance. The deletion of donor-reactive T cells using this protocol suggests the reliability and feasibility of this protocol for clinical transplantation.

Immune-mediated vascular injury and dysfunction in transplant arteriosclerosis

Solid organ transplantation is the only treatment for end-stage organ failure but this life-saving procedure is limited by immune-mediated rejection of most grafts. Blood vessels within transplanted organs are targeted by the immune system and the resultant vascular damage is a main contributor to acute and chronic graft failure. The vasculature is a unique tissue with specific immunological properties. This review discusses the interactions of the immune system with blood vessels in transplanted organs and how these interactions lead to the development of transplant arteriosclerosis, a leading cause of heart transplant failure.

Both rejection and tolerance of allografts can occur in the absence of secondary lymphoid tissues

In this study, we showed that aly/aly mice, which are devoid of lymph nodes and Peyer's patches, acutely rejected fully allogeneic skin and heart grafts. They mounted potent inflammatory direct alloresponses but failed to develop indirect alloreactivity after transplantation. Remarkably, skin allografts also were rejected acutely by splenectomized aly/aly (aly/aly-spl(-)) mice devoid of all secondary lymphoid organs. In these recipients, the rejection was mediated by alloreactive CD8(+) T cells presumably primed in the bone marrow. In contrast, cardiac transplants were not rejected by aly/aly-spl(-) mice. Actually, aly/aly-spl(-) mice that spontaneously accepted a heart allotransplant and displayed donor-specific tolerance also accepted skin grafts from the same, but not a third-party, donor via a mechanism involving CD4(+) regulatory T cells producing IL-10 cytokine. Therefore, direct priming of alloreactive T cells, as well as rejection and regulatory tolerance of allogeneic transplants, can occur in recipient mice lacking secondary lymphoid organs.

Systemic minor histocompatibility antigen expression in blood endothelial cells prevents T cell-mediated vascular immunopathology

Attenuation of T cell-mediated damage of blood endothelial cells (BECs) in transplanted organs is important to prevent transplant vasculopathy (TV) and chronic rejection. Here, we assessed the importance of minor histocompatibility antigen (mHA) distribution and different coinhibitory molecules for T cell-BEC interaction. A transgenic mHA was directed specifically to BECs using the Tie2 promoter and cellular interactions were assessed in graft-versus-host disease-like and heterotopic heart transplantation settings. We found that cognate CD4(+) T-cell help was critical for the activation of BEC-specific CD8(+) T cells. However, systemic mHA expression on BECs efficiently attenuated adoptively transferred, BEC-specific CD4(+) and CD8(+) T cells and hence prevented tissue damage, whereas restriction of mHA expression to heart BECs precipitated the development of TV. Importantly, the lack of the coinhibitory molecules programmed death-1 (PD-1) and B and T lymphocyte attenuator fostered the initial activation of BEC-specific CD4(+) T cells, but did not affect development of TV. In contrast, TV was significantly augmented in the absence of PD-1 on BEC-specific CD8(+) T cells. Taken together, these results indicate that antigen distribution in the vascular bed determines the impact of coinhibition and, as a consequence, critically impinges on T cell-mediated vascular immunopathology.

Natural killer cells in rejection and tolerance of solid organ allografts

PURPOSE OF REVIEW

A series of recent studies defy conventional wisdom by showing that natural killer (NK) cells exert a powerful and long-lasting influence on the immune response to whole organ allografts. The early activation of NK cells following transplantation is associated with killing of allogeneic target cells and release of immunomodulatory chemokines and cytokines, which can contribute to either rejection or tolerance. Here, we review findings describing NK cell receptors, potential mediators and mechanisms underlying the dual influence of NK cells in solid organ transplantation.

RECENT FINDINGS

New studies show that NK cells can discriminate between self and foreign tissues and play a key role in the initiation and regulation of adaptive immune responses after solid organ transplantation. Depending upon the types of NK cell receptors engaged and the nature of cytokines released, early NK cell activation can promote either rejection or tolerance.

SUMMARY

Solid organ transplantation is associated with the early activation of NK cells, which are then licensed to kill allogeneic target cells directly or via antibody-dependent cellular cytotoxicity and release various chemokines and immunomodulatory cytokines. Depending upon the nature of NK cell subsets activated and their ability to kill allogeneic target cells and release certain types of cytokines, NK cells can promote the activation/expansion of pro-inflammatory Th1 cells or regulatory Th2/Treg cells thus tilting the balance of alloimmunity towards rejection or tolerance. An in-depth understanding of these mechanisms will be necessary in order to design therapies targeting NK cells in human transplantation.

Effects of immunoglobulin to prevent coronary allograft vasculopathy in heart transplantation

INTRODUCTION

Although 100,000 cardiac transplants have been performed, coronary allograft vasculopathy (CAV), which is a phenomenon of chronic rejection, is still a serious problem.

AREAS COVERED

Several adhesion molecules, cytokines, and chemokines play a critical role in the process. Recent investigations have proved some promising methodologies for preventing or treating rejection. Although immunoglobulins are known to be an effective treatment in many diseases, their effect on cardiac transplantation or CAV is to be elucidated.

EXPERT OPINION

In this review article, we described some promising methodologies that use immunoglobulins to prevent CAV. Immunoglobulins may be used to prevent CAV.

The role of coinhibitory signaling pathways in transplantation and tolerance

Negative costimulatory molecules, acting through so-called inhibitory pathways, play a crucial role in the control of T cell responses. This negative “second signal” opposes T cell receptor activation and leads to downregulation of T cell proliferation and promotes antigen specific tolerance. Much interest has focused upon these pathways in recent years as a method to control detrimental alloresponses and promote allograft tolerance. However, recent experimental data highlights the complexity of negative costimulatory pathways in alloimmunity. Varying effects are observed from molecules expressed on donor and recipient tissues and also depending upon the activation status of immune cells involved. There appears to be significant overlap and redundancy within these systems, rendering this a challenging area to understand and exploit therapeutically. In this article, we will review the literature at the current time regarding the major negative costimulation pathways including CTLA-4:B7, PD-1:PD-L1/PD-L2 and PD-L1:B7-1, B7-H3, B7-H4, HVEM:BTLA/CD160, and TIM-3:Galectin-9. We aim to outline the role of these pathways in alloimmunity and discuss their potential applications for tolerance induction in transplantation.

Transplantation tolerance to a single noninherited MHC class I maternal alloantigen studied in a TCR-transgenic mouse model

The mechanisms underlying tolerance to noninherited maternal Ags (NIMA) are not fully understood. In this study, we designed a double-transgenic model in which all the offspring's CD8(+) T cells corresponded to a single clone recognizing the K(b) MHC class I protein. In contrast, the mother and the father of the offspring differed by the expression of a single Ag, K(b), that served as NIMA. We investigated the influence of NIMA exposure on the offspring thymic T cell selection during ontogeny and on its peripheral T cell response during adulthood. We observed that anti-K(b) thymocytes were exposed to NIMA and became activated during fetal life but were not deleted. Strikingly, adult mice exposed to NIMA accepted permanently K(b+) heart allografts despite the presence of normal levels of anti-K(b) TCR transgenic T cells. Transplant tolerance was associated with a lack of a proinflammatory alloreactive T cell response and an activation/expansion of T cells producing IL-4 and IL-10. In addition, we observed that tolerance to NIMA K(b) was abrogated via depletion of CD4(+) but not CD8(+) T cells and could be transferred to naive nonexposed mice via adoptive transfer of CD4(+)CD25(high) T cell expressing Foxp3 isolated from NIMA mice.

Alternatives to calcineurin inhibition in renal transplantation: belatacept, the first co-stimulation blocker

In the early 1990s, Linsley and colleagues produced a soluble fusion protein, comprising of the extracellular domain of cytotoxic T lymphocyte antigen (CTLA)4 and the human IgG1 Fc domain. Since then, several hundreds of scientific publications have demonstrated that CTLA4–Ig blocks CD28-mediated co-stimulation and suppresses unwanted T cell-mediated responses in animal models of transplantation, autoimmunity and inflammation. In the past two decades, Bristol-Myers Squibb Co. has developed abatacept, a CTLA4–Ig molecule for treating psoriasis and rheumatoid arthritis, and belatacept, a second-generation, higher affinity CTLA4–Ig molecule for use in kidney transplantation. Belatacept represents a new class of transplantation immunosuppressants and potentially offers clinicians a breakthrough therapy to preserve kidney function in the long term and reduce the side effects of current immunosuppressive therapies.

Dual effects of the alloresponse by Th1 and Th2 cells on acute and chronic rejection of allotransplants

The contribution of direct and indirect alloresponses by CD4(+) Th1 and Th2 cells in acute and chronic rejection of allogeneic transplants remains unclear. In the present study, we addressed this question using a transplant model in a single MHC class I-disparate donor-recipient mouse combination. BALB/c-dm2 (dm2) mutant mice do not express MHC class I L(d) molecules and reject acutely L(d+) skin grafts from BALB/c mice. In contrast, BALB/c hearts placed in dm2 mice are permanently accepted in the absence of chronic allograft vasculopathy. In this model, CD4(+) T cells are activated following recognition of a donor MHC class I determinant, L(d) 61-80, presented by MHC Class II A(d) molecules on donor and recipient APC. Pre-transplantation of recipients with L(d) 61-80 peptide emulsified in complete Freund's adjuvant induced a Th1 response, which accelerated the rejection of skin allografts, but it had no effect on cardiac transplants. In contrast, induction of a Th2 response to the same peptide abrogated the CD8(+) cytotoxic T cells response and markedly delayed the rejection of skin allografts while it induced de novo chronic rejection of heart transplants. This shows that Th2 cells activated via indirect allorecognition can exert dual effects on acute and chronic rejection of allogeneic transplants.

Blockade of the 4-1BB pathway attenuates graft arterial disease in cardiac allografts

4-1BB, a member of the tumor necrosis factor (TNF) receptor superfamily, binds the 4-1BB ligand (4-1BBL) and works as a costimulatory molecule and regulates T cell-mediated immune responses. Because T cell-mediated immunity is associated with graft arterial disease (GAD), we investigated the role of the 4-1BB pathway in the progression of GAD. Hearts from C57BL/6 mice were transplanted into Bm12 mice (class II mismatch). 4-1BB expression was induced on CD4(+) and CD8(+) splenocytes in allografts after cardiac transplantation. 4-1BBL was detected in the vessel wall of the rejecting cardiac allograft and in cultured smooth muscle cells (SMCs) stimulated with fetal calf serum. Recipients were injected intraperitoneally with 4-1BBIg every 7 days for 8 weeks. GAD was significantly attenuated by 4-1BBIg treatment (luminal occlusion, 15.4 +/- 3.1% versus control IgG treatment, 75.6 +/- 4.6%, P < 0.001). T-cell infiltration of cardiac allografts and expression of interferon-g , interleukin-6, and interleukin-15 in cardiac allografts were suppressed by 4-1BBIg treatment. Coculture of SMCs with sensitized splenocytes after transplantation induced SMC proliferation, and this was inhibited by addition of 4-1BBIg. The 4-1BB pathway regulates not only T-cell activation but also SMC proliferation. Blockade of the 4-1BB pathway is a promising strategy to prevent progression of GAD.

Critical role of donor tissue expression of programmed death ligand-1 in regulating cardiac allograft rejection and vasculopathy

BACKGROUND

Allograft vasculopathy is a major limiting factor in the long-term success of cardiac transplantation. T cells play a critical role in initiation of cardiac allograft rejection and allograft vasculopathy. The negative T-cell costimulatory pathway PD-1:PDL1/PDL2 (programmed death-1:programmed death ligand-1/2) plays an important role in regulating alloimmune responses. We investigated the role of recipient versus donor PD-1 ligands in the pathogenesis of allograft rejection with emphasis on the role of tissue expression in regulating this alloimmune response in vivo.

METHODS AND RESULTS

We used established major histocompatibility complex class II- and class I-mismatched models of vascularized cardiac allograft rejection, blocking anti-PDL1 and anti-PDL2 antibodies, and PDL1- and PDL2-deficient mice (as donors or recipients) to study the role of the PD-1:PDL1/PDL2 pathway in chronic rejection. We also used PDL1-deficient and wild-type mice and bone marrow transplantation to generate chimeric animals that express PDL1 exclusively on either hematopoietic or parenchymal cells. PDL1 but not PDL2 blockade significantly accelerated cardiac allograft rejection in the bm12-into-B6 and B6-into-bm12 models. Although wild-type cardiac allografts survived long term, PDL1-/- donor hearts transplanted into wild-type bm12 mice exhibited accelerated rejection and vasculopathy associated with enhanced recipient T-cell alloreactivity. Interestingly, PDL1-/- recipients did not exhibit an accelerated tempo of cardiac allograft rejection. Using chimeric animals as donors, we show that PDL1 expression on cardiac tissue alone significantly prolonged graft survival compared with full PDL1-/- donor grafts in transplanted wild-type recipients.

CONCLUSIONS

This is the first report to demonstrate that expression of the negative costimulatory molecule PDL1 on donor cardiac tissue regulates recipient alloimmune responses, allograft rejection, and vasculopathy.

Thyroid dysfunction in women with systemic sclerosis

Hypothyroidism has been frequently reported in systemic sclerosis (SSc), but whether SSc itself increases the risk of thyroid dysfunction is still controversial. The aim of the present study was to determine whether routine thyroid function screening in SSc should be warranted. Serum levels of free triiodothyronine, free thyroxine, and thyroid-stimulating hormone, and the presence of thyroid-specific autoantibodies (antithyroid peroxidase and antithyreoglobulin) were measured in 79 women with SSc and 81 age-matched women with osteoarthritis (OA) serving as controls. Hyperthyroidism was found in 2 of 79 (2.5%) SSc and in 4 of 81 (5%) OA cases. Hypothyroidism was found in 16 of 79 (20%) patients with SSc (subclinical in 14/16 cases) and in 9 of 81 (11%) patients with OA (subclinical in all cases; P = 0.131). Antithyreoglobulin antibodies were present in 14% versus 13% patients (SSc versus OA, P = NS), whereas antithyroid peroxidase antibodies were present in 23% versus 11% patients (SSc versus OA, P = 0.057). The risk of hypothyroidism was significantly higher in antithyroid peroxidase-positive patients (P < 0.0001), irrespective of the primary diagnosis, and greater in women with OA (OR = 24.6, 95% CI 4.3-141.9, P < 0.0001) than SSc (OR = 4.2, 95% CI 1.2-14.3, P = 0.035). SSc is not independently associated with an increased risk of thyroid dysfunction, but antithyroid peroxidase antibodies may identify a subset of patients at risk of developing thyroid dysfunction.

Critical role of inducible costimulator signaling in the development of arteriosclerosis

OBJECTIVE

Proliferation and migration of smooth muscle cells (SMCs) and migration and accumulation of monocytes and T cells are landmark events in the development of arteriosclerosis. SMC proliferation in the intima induces interruption of blood flow and results in ischemia and graft rejection. Inducible costimulator (ICOS) is a major costimulator of T cell activation. However, the effect of costimulatory molecules on the formation of neointimal hyperplasia has not been fully elucidated. We examined the role of the ICOS pathway in SMC proliferation.

METHODS AND RESULTS

ICOS ligand (ICOSL) was detected in SMCs stimulated by interleukin (IL)-1beta, and coculture of stimulated SMCs and activated T cells induced SMC proliferation. Inhibition of the ICOS pathway resulted in inhibition of SMC proliferation. In models of transplantation and vascular injury, ICOSL was induced in SMCs in the neointima. Expression of IL-1beta, a key inducer of ICOSL expression, was significantly reduced in mice treated with anti-ICOS antibody or soluble form of ICOS (ICOSIg) and in ICOS-deficient mice. Inhibition of the ICOS pathway significantly suppressed neointimal thickening.

CONCLUSIONS

These results indicate that ICOS on activated T cells contributes to neointimal formation through the regulation of SMC proliferation. These findings provide insights into new therapeutic strategies for arteriosclerosis.

T Cell Costimulation in the Development of Cardiac Allograft Vasculopathy

Cardiac allograft vasculopathy (CAV) is a form of coronary arterial stenosis and a leading cause of death in patients who survive beyond the first year after heart transplantation. Histopathologically, this lesion is concentric diffuse intimal hyperplasia of the arterial wall that is accompanied by extensive infiltration of inflammatory cells, including T cells. Many studies have explored the potential risk factors related to this arterial lesion and its pathogenesis. Continuous minor endothelial cell damage evokes inflammatory processes including T cell activation. Costimulatory molecules play crucial roles in this T cell activation. Many costimulatory pathways have been described, and some are involved in the pathogenesis of CAV, atherogenesis, and subsequent plaque formation. In this review, we summarize the present knowledge of the role of these pathways in CAV development and the possibility of manipulating these pathways as a means to treat heart allograft vascular disease and atherosclerosis.

Quantitative mRNA expression analysis of co-stimulatory molecules in sequential biopsies from heart allografts

Allograft-specific T-cell activation requires two signals, "signal one" via the T-cell receptor and "signal two" via costimulatory pathways. Animal models provide promising data that blockade of costimulatory signals can lead to T-cell anergy and tolerance. We analyzed 72 formalin-fixed and paraffin-embedded sequential heart allograft biopsies from 22 patients by quantitative real-time reverse transcriptase-polymerase chain reaction for the mRNA expression of the costimulatory molecules CD28, CD80, CD86, CD40, and CD154. mRNA expression levels were correlated to histological grade and time-point of rejection. mRNA expression of costimulatory molecules predominantly expressed by antigen-presenting cells (CD80, CD86, CD40), correlated with histological grade of cell-mediated acute rejection. Costimulatory molecules were up-regulated not only during rejection episodes early after transplantation, but also at late occurring rejection. The present results suggest a simultaneous and long-term therapeutical blockade of more than one costimulatory pathway for the prevention of repetitive T-cell mediated acute rejection episodes after heart transplantation.

CTLA-4Ig suppresses liver injury by inhibiting acquired immune responses in a mouse model of fulminant hepatitis

Expression of costimulatory molecules is significantly upregulated in various organs in an animal model of severe hepatitis induced by injection of Propionibacterium acnes (P. acnes) and lipopolysaccharide (LPS). In the present study, we examined whether blockade of costimulatory signals by CTLA-4Ig can suppress the liver injury in this model. We injected an adenovirus encoding CTLA-4Ig (AdCTLA-4Ig) into mice 7 days before, on the same day, or 3 days after P. acnes priming. The virus was found to infect the liver preferentially, and CTLA-4Ig was detected in the serum as early as 2 days after viral injection. After injection of LPS, liver injury and survival rates were examined. Most of the mice not injected with AdCTLA-4Ig died within 12 hours after injection of LPS. In contrast, all the AdCTLA-4Ig-injected mice survived when the virus was injected 7 days before or on the same day as P. acnes priming. Importantly, hemorrhagic liver injury and serum alanine aminotransferase levels were significantly reduced after LPS injection even when AdCTLA-4Ig was injected 3 days after P. acnes priming. Immunological analyses showed that CTLA-4Ig inhibited the activation and expansion of P. acnes-specific CD4+ T cells in the hepatic lymph nodes, leading to a reduction in the recruitment of the cells to the liver. The total amounts of interferon-gamma, interleukin-12, and various chemokines in the liver were then decreased, resulting in inhibition of the secondary recruitment of not only T cells but also macrophages. In conclusion, CTLA-4Ig could be useful for treatment of severe liver injury.

Role of the ICOS-B7h Costimulatory Pathway in the Pathophysiology of Chronic Allograft Rejection

BACKGROUND

Inducible costimulator (ICOS) is the third member of the CD28 superfamily and has a unique role in T cell activation and function. Recent studies indicated that the ICOS-B7h pathway plays an important role in alloimmune responses. We further investigated the role of the ICOS pathway in the pathologic process of chronic rejection in vivo.

METHODS

An established major histocompatibility complex class II disparate cardiac transplantation model was used. We treated mice with a blocking anti-B7h monoclonal antibody (mAb) either in the initiation phase (early blockade) or in the progression phase (delayed blockade) of disease. In addition, some mice received mAb in the entire period (whole blockade). At 6 weeks after transplantation, cardiac grafts were evaluated by histopathologic analysis in terms of vasculopathy, fibrosis, and cellular infiltration. The intragraft expressions of cytokines and chemokines were also examined by quantitative real-time polymerase chain reaction analysis.

RESULTS

Early blockade of the ICOS-B7h pathway did not show any protective effect on chronic allograft rejection compared with untreated controls. In contrast, delayed blockade significantly inhibited the development of vasculopathy, fibrosis, and cellular infiltration (P=0.043, P=0.004, and P=0.03 vs. untreated control, respectively). Interestingly, whole blockade did not prevent the chronic rejection process. Furthermore, the inhibitory effect of delayed ICOS blockade on chronic rejection was associated with down-regulation of local intragraft expression of several cytokines and chemokines.

CONCLUSIONS

These data suggest that the ICOS-B7h pathway is critical in the activation of effector/memory T cells that are necessary for the progression of chronic rejection and provide the rationale to develop novel and specific therapies to prevent this process.

Are thyroid peroxidase antibodies associated with cardiovascular disease risk in patients with subclinical hypothyroidism?

OBJECTIVE

Conflicting evidence has been reported about whether subclinical hypothyroidism (SCH) is associated with hyperlipidemia or cardiovascular disease. Thyroid peroxidase antibodies (TPOAb) are more common in persons with SCH. The purpose of this study was to evaluate whether the presence of (TPOAb) in people with SCH is associated with markers of cardiovascular disease.

DESIGN

Cross-sectional study using multivariate regression.

PATIENTS

Adults over age 40 who, in the National Health and Nutrition Examination Survey (NHANES) III, met the criteria for SCH (n = 188).

MEASUREMENTS

Participants were stratified into TPOAb-negative (n = 82) and TPOAb-positive (n = 106) groups. Markers of cardiovascular disease risk were compared between the TPOAb-negative and TPOAb-positive groups. Multivariate regression models were performed to adjust for potential confounders.

RESULTS

In bivariate analyses, individuals with and without TPOAb had similar levels of triglycerides, high-density lipoprotein, low-density lipoprotein, total cholesterol and C-reactive protein. Homocysteine levels were higher in the patients without antibodies (P = 0.01). After adjusting for, age, gender, smoking, hypertension, diabetes and use of a lipid-lowering medication, however, no statistically significant relationships were found between the presence of TPOAb and any of the cardiovascular risk markers.

CONCLUSIONS

The presence of thyroid peroxidase antibodies does not appear to correlate with cardiovascular disease risk in patients with subclinical hypothyroidism. This study does not support the measurement of TPOAb antibodies in SCH as a strategy for guiding treatment or assessment of cardiovascular disease risk.

Effects of CD28 blockade on subsets of naive T cells in cats

OBJECTIVE

To determine whether human CTLA4-Ig ([hu]CTLA4-Ig) inhibits costimulation-dependent lymphocyte proliferation in vitro, compare the effects of (hu)CTLA4-Ig with cyclosporine and steroids on CD4+ and CD8+ T-cell lymphocyte proliferation, and determine whether memory T-cell function remains intact in the presence of (hu)CTLA4-Ig.

ANIMALS

29 cats.

PROCEDURE

Peripheral blood mononuclear cells (PBMCs) were stimulated with concanavalin A (costimulation-dependent mitogen) or phorbol 12-myristate 13-acetate and ionomycin (costimulation independent mitogens) alone or in the presence of (hu)CTLA4-Ig, cyclosporine, or dexamethasone; effects of these treatments on lymphocyte proliferation were assessed by incorporation of thymidine labeled with tritium or flow cytometry. Antigen-specific proliferation was determined by stimulating PBMCs from 2 healthy cats seropositive for Toxoplasma gondii with soluble Toxoplasma antigen alone or in the presence of (hu)CTLA4-Ig or cyclosporine.

RESULTS

(hu)CTLA4-Ig inhibited costimulation-dependent lymphocyte proliferation in vitro but had no effect on costimulation-independent lymphocyte proliferation. Compared with mitogen alone, (hu)CTLA4-Ig caused a significant decrease in responder frequency and proliferative capacity of CD4+ T cells; however, the effect on CD8+ T cells was not significant. Cyclosporine alone or with dexamethasone had a significantly greater suppressive effect on responder frequency and proliferative capacity of CD4+ and CD8+ T cells, compared with (hu)CTLA4-Ig. Compared with cyclosporine, (hu)CTLA4-Ig appeared to have a sparing effect on antigen-specific proliferation of memory CD4+ and CD8+ T cells.

CONCLUSIONS AND CLINICAL RELEVANCE

(hu)CTLA4-Ig selectively inhibited costimulation-dependent proliferation of lymphocytes in vitro and had a sparing effect on antigen-specific proliferation of memory cells. The specificity of its mechanism of action suggests that (hu)CTLA4-Ig may prevent allograft rejection but leave memory responses to previously encountered antigens intact.

Blockade of the interaction between PD-1 and PD-L1 accelerates graft arterial disease in cardiac allografts

BACKGROUND

Programmed death-1 (PD-1), a member of the CD28 family, has been identified. PD-1 is involved in the negative regulation of some immune responses. We evaluated the role of PD-ligand 1 (PD-L1) in graft arterial disease (GAD) of cardiac allografts and in smooth muscle cells (SMCs).

METHODS AND RESULTS

C57BL/6 murine hearts were transplanted into B6.C-H2KhEg mice for examination of GAD. PD-L1 was expressed in SMCs of the thickened intima in the graft coronary arteries, and administration of anti-PD-L1 monoclonal antibody (mAb) enhanced the progression of GAD (luminal occlusion: 55+/-5.0% versus 9.8+/-4.3%, P<0.05). The expressions of interferon gamma (IFN-gamma) and tumor necrosis factor alpha of cardiac allografts were upregulated in response to anti-PD-L1 mAb treatment. In vitro, PD-L1 expression was induced in SMCs in response to IFN-gamma stimulation. Sensitized splenocytes increased SMC proliferation, and anti-PD-L1 mAb in combination with IFN-gamma stimulation increased this proliferation.

CONCLUSIONS

The PD-L1 pathway regulates both the proliferation of SMCs and GAD. Thus, control of this interaction is a promising strategy for suppression of GAD.

ACE inhibition limits chronic injury of kidney transplant even with treatment started when lesions are established

BACKGROUND

Inhibition of the renin-angiotensin system (RAS) prevents development of chronic allograft dysfunction in experimental animals. Whether this therapeutic approach is effective even if started when signs of allograft nephropathy are already manifested has not been investigated.

METHODS

To address this issue, we studied the effect of a late treatment with the angiotensin-convertine enzyme (ACE) inhibitor trandolapril in the Fisher 344 to Lewis rat kidney transplant model. Seven months after transplant a renal biopsy was done for graft histology examination. Thereafter rats received either no treatment (allograft-none) or trandolapril until sacrifice at month 13.

RESULTS

All animals were alive at the end of the study with the exception of a rat in the untreated group that died of renal insufficiency at day 292. Despite the fact that the grafts had already signs of structural injury and function impairment at the time treatment was stated, trandolapril completely restored renal function to baseline pretransplant values. Trandolapril also halted the progression of glomerular damage and suppressed intragraft T-lymphocyte infiltration and reduced the expression of the chemokine monocyte chemoattractant protein-1 (MCP-1). However, trandolapril had no direct effect on T cell function, since in vivo treatment did not modify recipient T-cell alloreactivity against donor antigens.

CONCLUSION

These findings provide the basis for a novel treatment intervention with RAS blockade that, together with pharmacologic inhibition of the immune response, could interrupt progression of chronic allograft dysfunction and injury.

T-cell costimulatory pathways in allograft rejection and tolerance

The destiny of activated T cells is critical to the ultimate fate of immune response. After encountering antigen, naïve T cells receive signal 1 through the T-cell receptor (TCR)-major histocompatibility complex (MHC) plus antigenic peptide complex and signal 2 through "positive" costimulatory molecules leading to full activation. "Negative" T-cell costimulatory pathways, on the other hand, function to downregulate immune responses. The purpose of this article is to review the current state of knowledge and recent advances in our understanding of the functions of the positive and negative T-cell costimulatory pathways in alloimmune responses. Specifically, we discuss the functions of the CD28:B7 and the tumor necrosis factor receptor (TNFR):tumor necrosis factor (TNF) family of molecules in allograft rejection and tolerance. We address the following important questions: are T-cell costimulatory pathways merely redundant or do they provide distinct and unique functions? What are the important and unique interactions between the various pathways? And, what are the effects and mechanisms of targeting of these pathways in different types and patterns of allograft rejection and tolerance models?

Attenuation of graft arterial disease by manipulation of the LIGHT pathway

OBJECTIVE

The tumor necrosis factor (TNF) superfamily member LIGHT, which binds herpes virus entry mediator (HVEM) and lymphotoxin beta receptor (LTbetaR), plays important roles in regulating the immune response. To clarify the mechanism underlying graft arterial disease (GAD), we investigated the role of the LIGHT pathway in the progression of GAD.

METHODS AND RESULTS

Hearts from Bm12 mice were transplanted into C57BL/6 (B/6) mice (class II mismatch). Recipients were injected intraperitoneally with HVEMIg (100 microg per treatment) every 7 days for 8 weeks. Treatment with HVEMIg significantly attenuated GAD (luminal occlusion=16.5+/-7.7% versus control allograft=62.6+/-12.1%, P<0.05), and significantly decreased intragraft IL-4, IL-6, and interferon-gamma (IFN-gamma) mRNA expression compared with controls. LTbetaR was expressed in smooth muscle cells (SMCs) with or without cytokine stimulation, whereas HVEM was detected in SMCs stimulated by IFN-gamma. Coculture of SMCs with T cells after transplantation induced SMC proliferation, and addition of HVEMIg resulted in inhibition of SMC proliferation.

CONCLUSIONS

These results indicate that the LIGHT pathway plays important roles in the regulation not only of T-cell activation but also of SMC proliferation. Blockade of the LIGHT pathway is a promising avenue for the prevention of GAD.

Immunosuppression and transplant vascular disease: benefits and adverse effects

Cardiac allograft vasculopathy (CAV) occurs within 5 years of transplantation surgery and represents the main cause of death in long-term heart transplant survivors. The detailed pathogenesis of CAV is unknown, but there are strong indications that immunologic mechanisms, which are regulated by nonimmunologic factors, are the major cause of this phenomenon. Cyclosporine A (CsA) is a frequently used immunosuppressive agent in transplant medicine to prevent rejection. The mechanism of action of CsA involves initial binding to cyclophilin to form a complex that then inhibits calcineurin (CN), leading to reduced interleukin (IL)-2 production as part of the signal transduction pathway for the activation of B-lymphocytes and T-lymphocytes. Based on this proposed mechanism, it was expected that CsA should be an effective strategy in attenuating the host immune response against transplanted allograft tissue; however, CsA has not changed the outcome of CAV. Several mechanisms have been suggested for the ineffectiveness of CsA in long-term prevention of CAV. For example, routine therapeutic doses of CsA may block CN incompletely (50%), whereas complete blockade requires doses that are not clinically tolerable. Another explanation is the possible activation of T-cell receptors directly (CN independent) by the immune response, which induces protein kinase C theta (PKCtheta) and leads to IL-2 production and immune rejection. Moreover, there may be a role for nonimmunologic mechanisms, such as complement, which cannot be controlled by CsA, or CsA may cause hypercholesterolemia or induce overexpression of transforming growth factor-beta (TGF-beta). This review also compares the effect of CsA with other immunosuppressants in allograft artery preservation and their clinical efficacy.

Coronary artery vasculopathy in pediatric cardiac transplant patients: the therapeutic potential of immunomodulators

The single largest cause of late graft loss in pediatric cardiac transplantation is transplant coronary artery vasculopathy (CAV). The mechanism of CAV remains unknown; it appears to have both immune and non-immune causes. The final common pathway of these mechanisms is endothelial activation, a prothrombotic environment, and endothelial damage with subsequent diffuse intimal proliferation. The disease process has largely been thought to be progressive and unresponsive to treatment. Re-transplantation has been advocated as the only definitive treatment. The appropriate management is largely unknown; intervention or surgical management has had limited utility, while medical management appears to have the most promise. Improvement in outcome can be achieved by optimizing non-immune factors and aggressive management of the immune mechanisms. Long-term survival of transplant patients after diagnosis with CAV is now being reported.

Balanced expression of mitochondrial apoptosis regulatory proteins correlates with long-term survival of cardiac allografts

Abnormal regulation of apoptosis is observed in ischemic injury and may contribute to the pathogenesis of atherosclerosis. However, its role in cardiac allograft vasculopathy (CAV), the fundamental lesion of chronic rejection (CR) in heart transplantation, remains uncertain. To clarify this issue, apoptosis was quantitated in myocardium and coronary arteries from 5 cardiac allograft donors (NL) and explanted hearts of 24 patients with ischemic cardiomyopathy (IsCM) and 15 patients with CR. Tissue samples were analyzed via end-labeling fragmented DNA [via deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)] and immunoblotting for activated caspase-3 and -9. Myocyte apoptosis assessed by TUNEL was similarly increased over NL (0.21%) in both the CR (0.88%; P < 0.01) and IsCM (0.88%; P < 0.01) groups. Activated caspase-9 levels were significantly higher in CR (14.7%) compared with IsCM (6.9%; P < 0.01) and NL (0%) groups, whereas activated caspase-3 levels were similarly elevated in both CR and IsCM (7.8 and 6.5% vs. 0% in NL; P < 0.01 and P < 0.05) groups. Expression of myocardial Bcl-2 and Bax was increased in CR compared with both NL (Bax, 4.3-fold; P < 0.01; Bcl-2, 5.9-fold; P < 0.01) and IsCM (IsCM: Bax, 2.2-fold; P < 0.05; Bcl-2, 3.2-fold; P < 0.01) groups. The rate of apoptosis and the Bcl-2/Bax ratio independently correlated to graft survival in CR (activation of caspase-9: r = 0.87; P < 0.01; Bcl-2/Bax: r = 0.57; P = 0.05). Compared with native atherosclerosis, coronary arteries with CAV showed more medial apoptosis (7.8-fold; P < 0.01) and higher Bcl-2 levels (5.1-fold; P < 0.01) with lower Bax levels (threefold; P < 0.05) in the intima. These results indicate that abnormal Bcl-2 and Bax expression in myocardium and coronary arteries of cardiac allografts with CR is distinct from that in IsCM and suggest that balancing Bcl-2 to Bax in transplanted hearts promotes long-term graft survival.

CD45RB-targeting strategies for promoting long-term allograft survival and preventingchronic allograft vasculopathy

BACKGROUND

CD45RB is a potent immunomodulatory target to achieve long-term allograft survival. We evaluated the in vivo effect of anti-CD45RB monoclonal antibody (mAb) treatment in combination with conventional immunosuppression or costimulatory blockade strategies as a therapeutic modality for future clinical application.

METHODS

A fully MHC-mismatched vascularized mouse cardiac allograft model was used to test the interactions between anti-CD45RB mAb and conventional immunosuppressive drugs or costimulatory blockade of the CD40/CD154 or B7/CD28 pathway. Chronic rejection was examined histologically for development of chronic allograft vasculopathy.

RESULTS

Cyclosporine significantly abrogated the effect of anti-CD45RB therapy. In contrast, rapamycin acted synergistically with anti-CD45RB mAb in promoting long-term allograft survival. CD154 blockade further enhanced the tolerogenic efficacy of anti-CD45RB mAb. These synergistic effects of combination treatments also prevented the development of chronic allograft vasculopathy.

CONCLUSION

CD45RB-targeting strategy in combination with the use of rapamycin or costimulatory blockade promotes allograft tolerance and prevents chronic rejection.

FTY720, an immunosuppressant that alters lymphocyte trafficking, abrogates chronic rejection in combination with cyclosporine A

BACKGROUND

Chronic rejection remains the leading cause of failure after transplantation (Tx). FTY720, a new immunosuppressant altering lymphocyte trafficking, is effective against acute rejection, but its activity against chronic rejection is not known.

METHODS

A valid model of chronic rejection was produced. Heart transplantation (HTx) was performed using fully mismatched RA (RT1p) and PVG (RT1c) rats. Administration of donor-specific blood transfusion 12 days before HTx prolongs graft survival, but features of chronic rejection including intimal hyperplasia and vascular obliteration (VO) develop with time only in allogeneic Tx. This is therefore a valid model of chronic rejection. VO was assessed on post-Tx day 90 in six groups differing according to the maintenance immunosuppressive regimen administered. group 1, donor-specific blood transfusion only and no other treatment; group 2, FTY720 (0.3 mg/kg/day orally) for 90 days; group 3, cyclosporine A (CsA) (1 mg/kg/day orally) for 90 days; group 4, combined administration of FTY720 and CsA for 90 days; group 5, transient administration of combined FTY720 and CsA for 7 days; and group 6, syngeneic HTx (RA to RA). Graft infiltrate, endothelial immunoglobulin (Ig) G deposition, and complement binding were also examined on post-Tx day 90.

RESULTS

In control group 1, severe VO was observed, compared with syngeneic HTx (group 6). Monotherapy with FTY720 (group 2) or with CsA (group 3) significantly but partially reduced VO. On the contrary, combined administration of FTY720 and CsA (group 4) abrogated VO. A 1-week treatment with combined FTY720 and CsA (group 5) reduced VO but only partially. In group 1, arteriosclerosis was accompanied by graft infiltrate, endothelial IgG deposition, and complement binding. In groups 2, 3, and 5, graft infiltrating scores were partially decreased compared with group 1 but remained higher than in syngeneic controls; endothelial IgG deposition and complement binding were still present. In group 4, continuous administration of combined FTY720 and CsA reduced graft infiltrate to the level of syngeneic control and abrogated both endothelial IgG deposition and complement binding.

CONCLUSIONS

Maintenance treatment with either FTY720 or CsA monotherapy partially prevents chronic rejection; short-term treatment with combined FTY720 and CsA reduces chronic rejection only partially; and continuous treatment with combined FTY720 and CsA abrogates chronic rejection, and this is accompanied by dramatic reduction of graft infiltrating cells, endothelial IgG deposition, and complement binding. Prevention of chronic rejection by maintenance treatment with FTY720 and CsA represents indirect evidence that normal lymphocyte trafficking and function are mandatory for development of chronic rejection.

Inhibition of prolyl-4-hydroxylase ameliorates chronic rejection of mouse kidney allografts

Interstitial fibrosis, glomerulosclerosis and arteriosclerosis are the major components of chronic allograft nephropathy (CAN), the leading cause of late graft failure after transplantation. To investigate the mechanism of collagen deposition in CAN, we studied the effects of prolyl-hydroxylase inhibitor (PHI), an enzyme essential for collagen formation, using a mouse model of kidney transplantation. Kidneys from H-2b mice were transplanted into MHC-incompatible H-2d recipients (allografts) and at 3 weeks post-transplant, received either PHI or vehicle treatment daily for 3 weeks. At 6 weeks post-transplant, GFR was significantly improved in the allografts receiving PHI (3.3 +/- 0.5 mL/min/kg) compared with those receiving vehicle (1.8 +/- 0.5 mL/min/kg, p < 0.05), while renal function was relatively unimpaired in the nonrejecting isografts (6.45 +/- 0.53 mL/min/kg). Allografts had histologic changes of CAN but the severity was significantly reduced with PHI treatment compared with vehicle, with reductions in interstitial inflammation and fibrosis. Furthermore, TGFâ and connective tissue growth factor mRNA expression was enhanced in both allograft groups compared with the isografts. In conclusion, PHI-treated allografts had improved renal function and reduced the severity of renal injury as a result of CAN. Inhibition of matrix synthesis may be a useful adjunct in ameliorating the development of CAN in humans.

The role of the CD134-CD134 ligand costimulatory pathway in alloimmune responses in vivo

The CD134-CD134 ligand (CD134L) costimulatory pathway has been shown to be critical for both T and B cell activation; however, its role in regulating the alloimmune response remains unexplored. Furthermore, its interactions with other costimulatory pathways and immunosuppressive agents are unclear. We investigated the effect of CD134-CD134L pathway blockade on allograft rejection in fully MHC-mismatched rat cardiac and skin transplantation models. CD134L blockade alone did not prolong graft survival compared with that of untreated recipients, and in combination with donor-specific transfusion, cyclosporine, or rapamycin, was less effective than B7 blockade in prolonging allograft survival. However, in combination with B7 blockade, long-term allograft survival was achieved in all recipients (>200 days). Moreover, this was synergistic in reducing the frequency of IFN-gamma-producing alloreactive lymphocytes and inhibiting the generation of activated/effector lymphocytes. Most impressively, this combination prevented rejection in a presensitized model using adoptive transfer of primed lymphocytes into athymic heart transplant recipients. In comparison to untreated recipients (mean survival time (MST): 5.3 +/- 0.5 days), anti-CD134L mAb alone modestly prolonged allograft survival (MST: 14 +/- 2.8 days) as did CTLA4Ig (MST: 21.5 +/- 1.7 days), but all grafts were rejected within 24 days. Importantly, combined blockade further and significantly prolonged allograft survival (MST: 75.3 +/- 12.7 days) and prevented the expansion and/or persistence of primed/effector alloreactive T cells. Our data suggest that CD134-CD134L is a critical pathway in alloimmune responses, especially recall/primed responses, and is synergistic with CD28-B7 in mediating T cell effector responses during allograft rejection. Understanding the mechanisms of collaboration between these different pathways is important for the development of novel strategies to promote long-term allograft survival.

New insights into the interactions between T-cell costimulatory blockade and conventional immunosuppressive drugs

OBJECTIVE

To determine the precise in vivo interaction between T-cell costimulatory blockade and conventional immunosuppression in transplantation.

SUMMARY BACKGROUND DATA

Blocking B7 or CD154 T-cell costimulatory activation pathways prevents allograft rejection in small and large animal transplant models and is considered a promising strategy for clinical organ transplantation.

METHODS

A fully MHC-mismatched vascularized mouse cardiac allograft model was used to test the interactions between anti-CD154 or CTLA4Ig monotherapy and conventional immunosuppressive drugs in promoting long-term graft acceptance. The frequency of alloreactive T cell was measured by ELISPOT. Chronic rejection was examined by histology.

RESULTS

Cyclosporine, tacrolimus, and anti-IL-2R monoclonal antibody therapy abrogated the effect of a single-dose protocol of anti-CD154 therapy. In contrast, rapamycin acted synergistically with anti-CD154 therapy in promoting long-term allograft survival. The addition of calcineurin inhibitors did not abolish this synergistic effect. Intense CD154-CD40 blockade by a multiple-dose schedule of anti-CD154 resulted in long-term graft survival and profound alloreactive T-cell unresponsiveness and overcame the opposite effects of calcineurin inhibitors. CTLA4Ig induced long-term graft survival, and the effect was not affected by the concomitant use of any immunosuppressive drugs.

CONCLUSIONS

The widespread view that calcineurin inhibitors abrogate the effects of T-cell costimulatory blockade should be revisited. Sufficient costimulatory blockade and synergy induced by CD154 blockade and rapamycin promote allograft tolerance and prevent chronic rejection.

T-cell response to cardiac myosin persists in the absence of an alloimmune response in recipients with chronic cardiac allograft rejection

BACKGROUND

Immune-mediated injury to the graft has been implicated in the pathogenesis of chronic rejection. However, little is known regarding the nature of the antigen(s) involved in this immune process. We demonstrated that cardiac transplantation in mice induces an autoimmune T-cell response to a heart tissue-specific protein, cardiac myosin (CM). This response contributes to transplant rejection in that its modulation affects cardiac graft survival. This study investigates whether anti-CM T cells undergo activation and expansion in mice with chronic cardiac allograft rejection.

METHODS

The frequency of CM- and donor major histocompatibility complex (MHC)-specific interferon (IFN)-gamma-producing T cells were assessed by ELISPOT in BALB/c mice, which were injected with anti-CD40L (MR1) mAb (chronic rejection group) or CTLA4Ig fusion protein (tolerant group) and transplanted with C57BL/6 cardiac allografts.

RESULTS AND CONCLUSIONS

MR1-treated BALB/c recipients of C57BL/6 hearts with chronic rejection displayed a high frequency of activated CM-specific T cells, whereas the frequency of activated alloreactive T cells were similar to naïve, nontransplanted mice. In contrast, no activation of CM-reactive T cells was detected in tolerant recipients after CTLA4Ig treatment. Therefore, in the absence of alloimmunity, chronic rejection is associated with persistence of a T-cell response against CM. Our data indicate that anti-CM autoimmunity may be involved in the immune mechanisms of chronic rejection and suggest that tolerance strategies should target both allo- and autoimmune responses to prevent this process.