Long-term acceptance of major histocompatibility complex mismatched cardiac allografts induced by CTLA4Ig plus donor-specific transfusion

The use of monoclonal antibodies to restore self-tolerance in established autoimmunity

The author hopes to convince the reader that the data presented argue for a stage during the development of IDDM when beta-cell destruction can be counteracted and tolerance to beta cells restored, provided the immune aggression is arrested. This argument constitutes a solid rationale for immunointervention in established IDDM, especially by using potent agents such as CD3. The future for the application of monoclonal antibodies not only in autoimmunity but also in transplantation is exiting. With the development of humanized monoclonal antibodies, therapeutic uses for them are likely to expand. Enormous progress has been made in the last 15 years, and it is likely that before a similar time period has elapsed, monoclonal antibodies will have become standard tools that will dispense the need for long-term immunosuppression and its inherent dangers in various clinical arenas.

Mechanisms of targeting CD28 by a signaling monoclonal antibody in acute and chronic allograft rejection

There is increasing evidence that ongoing T-cell recognition of alloantigen and activation are key mediators of chronic allograft rejection. The CD28-B7 pathway is unique among costimulatory pathways in that two alternate ligands for B7 exist: CD28 and CTLA4. Recently, it has been suggested that CTLA4 negative signaling may be required for induction of acquired tolerance in vivo. A strategy by which the T cell is targeted at the CD28 receptor rather than its ligands would theoretically allow the inhibitory functions of the CTLA4-B7-1/2 axis to remain intact. Using a rat-specific monoclonal antibody, we investigated the effect of targeting CD28 in a model of chronic rejection without the confounding variable of immunosuppression. We also used an acute cardiac allograft rejection model to investigate CD28 stimulation-based strategies to induce donor-specific tolerance. We demonstrated that anti-CD28 monoclonal antibody was as effective as CTLA4 immunoglobulin in protecting against chronic allograft vasculopathy. In addition, a short course of cyclosporine therapy synergized with either anti-CD28 monoclonal antibody or CTLA4 immunoglobulin, suggesting that it may be clinically relevant to combine low-dose calcineurin inhibitors with CTLA4 immunoglobulin or anti-B7 antibodies. Finally, we report on the potential mechanisms of action of targeting CD28 in vivo.

In vivo CD86 blockade inhibits CD4+ T cell activation, whereas CD80 blockade potentiates CD8+ T cell activation and CTL effector function

To address whether a functional dichotomy exists between CD80 and CD86 in naive T cell activation in vivo, we administered anti-CD80 or CD86 blocking mAb alone or in combination to mice with parent-into-F(1) graft-vs-host disease (GVHD). In this model, the injection of naive parental T cells into unirradiated F(1) mice results in either a Th1 cytokine-driven, cell-mediated immune response (acute GVHD) or a Th2 cytokine-driven, Ab-mediated response (chronic GVHD) in the same F(1) recipient. Combined CD80/CD86 blockade beginning at the time of donor cell transfer mimicked previous results seen with CTLA4Ig and completely abrogated either acute or chronic GVHD by preventing the activation and maturation of donor CD4(+) T cells as measured by a block in acquisition of memory marker phenotype and cytokine production. Similar results were seen with selective CD86 blockade; however, the degree of CD4 inhibition was always less than that seen with combined CD80/CD86 blockade. A more striking effect was seen with selective CD80 blockade in that chronic GVHD was converted to acute GVHD. This effect was associated with the induction of Th1 cytokine production, donor CD8(+) T cell activation, and development of antihost CTL. The similarity of this effect to that reported for selective CTLA4 blockade suggests that CD80 is a critical ligand for CTLA4 in mediating the down-regulation of Th1 responses and CD8(+) T cell activation. In contrast, CD86 is critical for the activation of naive CD4(+) T cells in either a Th1 or a Th2 cytokine-mediated response.

Differential effect of CD28 versus B7 blockade on direct pathway of allorecognition and self-restricted responses

Immunosuppression with B7 antagonists might have 2 opposite effects: reducing T-cell costimulation through CD28 but also preventing CTLA-4 from transmitting its negative regulatory signal. We therefore hypothesized that a selective blockade of CD28 might be qualitatively different from blocking B7. It was previously reported that CD28 modulation prolongs allograft survival in the rat and reverses induction of experimental autoimmune encephalomyelitis in mice. However, whether CD28 or B7 blockade results in similar immunosuppression on alloimmune and self-restricted responses to soluble antigens has not yet been investigated. Here, we addressed this issue in vitro with antagonist anti-CD28 Fab fragments and in vivo using the modulating anti-rat JJ319 monoclonal antibody. As in the inhibition of B7 with CTLA4 immunoglobulin, anti-CD28 Fab fragments inhibited allogenic T-cell proliferation in mixed cultures. In vivo modulation of CD28 blocked the expansion of alloreactive T cells and promoted their apoptosis. In contrast, selective blockade of CD28 did not modify T-cell proliferative responses and antibody production to soluble antigens, whereas blocking B7 with CTLA4 immunoglobulin did. Our data show that blocking CD28, while leaving CTLA4-B7 interactions undisturbed, inhibits alloreactive CD4+ T-cell expansion but does not modify the response to nominal antigens presented in the context of a self-major histocompatibility complex. That B7 engagement is needed for self-restricted responses whereas engagement of CD28 is not essential adds to the suggestion that another unidentified ligand of B7 might deliver a costimulatory signal in the absence of CD28.

CD40/CD40L interaction is essential for the induction of EAE in the absence of CD28-mediated co-stimulation

CD28 provides a co-stimulatory signal critical for optimal T cell activation. We and others have shown that the B7/CD28 co-stimulatory pathway is a major regulatory pathway for the control of immune responses. Experimentally induced models of autoimmunity have been shown to be prevented or reduced in intensity in mice deficient for CD28. Here, we show that EAE and accompanying neuroantigen-specific immune responses are drastically reduced in the absence of CD28. However, we go on to show that EAE can be induced in CD28-deficient mice following two immunizations. After re-immunization, CD28-deficient mice develop severe EAE with myelin-specific responses equal to those of wildtype controls, and extensive demyelination in the spinal cord. Treatment of CD28-deficient mice with anti-CD40L at the time of immunization significantly reduced DTH responses and prevented the development of EAE following two immunizations, indicating a critical role for CD40/CD40L signaling in the absence of CD28. Taken together, our results indicate that CD28-mediated co-stimulation does not regulate immunological anergy. Instead, CD28 appears to adjust the threshold for activation and expansion of autoreactive cells.

Prevention of acute lung allograft rejection in rat by CTLA4Ig

CTLA4 immunoglobulin (CTLA4Ig), which binds with a high affinity to B7-1 and B7-2, interrupts T-cell activation by inhibiting costimulatory signal. CTLA4Ig has been used in hopes of achieving antigen-specific tolerance induction in several solid organ transplants. In lung allograft rejection, however, its use has been controversial in terms of its effect on prevention of rejection. In the present study, the effect of murine CTLA4Ig on rat-lung allograft rejection was investigated. Rat left-lung transplantation was performed in an RT1 incompatible donor (Brown Norway; BN)-recipient (F344) combination. All allografts (n = 12) without any treatment were rejected within 7 days after transplantation. A single injection of murine form CTLA41g at a dose of 100 microg intraperitoneally (ip) or intravenously (iv) on day 1 post-transplantation achieved long-term graft survival (>90days) in 2/5 (40%) and 3/8 (38%), respectively. Moreover, 6/7 (86%) allografts in rats that received iv injection of 500 microg CTLA4Ig survived more than 90days. Allograft survival in the CTLA4Ig 500 microg iv recipient group was significantly longer than that in the no-treatment control or control immunoglobulin group (p <0.01). Four out of seven recipients bearing functional allografts for more than 90 days with the CTLA4Ig treatment accepted donor-specific skin grafts, whereas all third-party skin grafts (n=3) were rejected. Prevention of rat-lung allograft rejection could be achieved by intravenous administration of CTLA4Ig, resulting in long-term allograft survival with acceptance of donor-specific skin grafts.

Blockade of CD28/B7-2 costimulation inhibits experimental obliterative bronchiolitis in rat tracheal allografts: suppression of helper T cell type1-dominated immune response

T cell activation is a proximal event in the initiation of chronic rejection that may ultimately lead to obliterative bronchiolitis (OB) after lung transplantation. In addition to primary signals generated by the T cell receptor, T cell activation relies on costimulatory signals, of which the most important are mediated via interaction between CD28 and its ligands B7-1 and B7-2. In nontreated rat tracheal allografts, B7-2, but not B7-1, expression peaked 10 d after transplantation, unlike in syngeneic grafts, where no B7-2 upregulation was observed. Selective blockade of the CD28/B7-1 T cell costimulatory pathway by a mutant form of CTLA4Ig (cytotoxic T lymphocyte antigen 4 immunoglobulin), CTLA4IgY100F, did not affect epithelial injury or degree of luminal occlusion in rat tracheal allografts. Treatment with CTLA4Ig fusion protein, which blocks both CD28/B7-1 and CD28/B7-2 interaction, significantly delayed the development of epithelial injury and airway occlusion. Immunohistochemical analyses of allografts showed that selective inhibition of the CD28/B7-1 pathway did not affect cytokine expression. In contrast, treatment with CTLA4Ig was associated with a significant decrease in the intragraft production of tumor necrosis factor alpha, interleukin 2, and interferon gamma, as well as slightly increased intragraft expression of interleukin 10. In conclusion, CTLA4Ig-mediated costimulatory blockade delays epithelial injury and attenuates obliterative changes and is associated with marked suppression of helper T cell type 1 (Th1)-dominated cytokine response. These observations emphasize the role of the CD28/B7-2 costimulatory pathway in regulating proinflammatory and Th1 cytokine responses and thereby in the development of epithelial and graft injury gradually leading to obliteration of the airway lumen.

Blockade of B7/CD28 in mixed lymphocyte reaction cultures results in the generation of alternatively activated macrophages, which suppress T-cell responses

Blockade of B7/CD28 costimulation allows human haploidentical bone marrow transplantation without graft-versus-host disease. This study shows that blockade of B7/CD28 in anergizing mixed lymphocyte reaction (MLR) cultures of peripheral blood mononuclear cells results in the generation of alternatively activated macrophages (AAMphi). In contrast, priming MLR cultures result in generation of classically activated macrophages (CAMphi). AAMphi had enhanced expression of CD14, major histocompatibility complex class II, and CD23; produced alternative macrophage activation-associated CC-chemokine 1 (AMAC-1) chemokine; and displayed increased phagocytotic activity but decreased ability for antigen presentation. Suppression subtractive hybridization revealed that although AAMphi had undergone terminal maturation and differentiation, they entered a distinct gene expression program as compared with CAMphi and selectively expressed beta2-microglobulin, lysozyme, ferritin heavy and light chain, and the scavenger receptors macrophage mannose receptor and sortilin. Anergic T cells isolated from cultures that led to the development of AAMphi produced low amounts of interleukin-2 (IL-2), IL-4, and interferon-gamma, but high amounts of IL-10. Addition of anti-IL-10 neutralizing monoclonal antibody in anergizing cultures reversed the functional characteristics of AAMphi, indicating that at least one mechanism involved in the generation of AAMphi was mediated by IL-10. Importantly, when added in MLR cultures, AAMphi suppressed T-cell responses. Therefore, besides direct inhibition of T-cell costimulation, blockade of B7/CD28 may facilitate induction of T-cell unresponsiveness by generating AAMphi. Because in healthy individuals, AAMphi are found in the placenta and lung, where they protect from unwanted immune reactivity, the results suggest that AAMphi may play a critical role in the induction of transplantation tolerance.

Feasibility of immunosuppression in composite tissue allografts by systemic administration of CTLA4Ig

BACKGROUND

Although recent experimental studies have demonstrated CTLA4Ig to be a potent immunosuppressant in vascularized solid organ allografts, little attention has been given to the effect of this soluble recombinant fusion protein on immunosuppression in composite tissue allografts (CTAs). Using a rat hind limb allograft model, we examined the efficacy of CTLA4Ig against the allograft rejection of composite tissue.

METHODS

The hind limbs of ACI rats (RT1a) were heterotopically transplanted to Lewis rats (RT11). Controls received no immunotherapy. Experimental recipients were treated with a single i.p. injection of either human immunoglobulin (Ig)G (0.5 mg/body) or CTLA4Ig (0.5 mg/body) according to different time schedules. Graft survival time and histopathological changes for each experimental group were evaluated and statistically compared.

RESULTS

Graft survival times were prolonged significantly in rats treated with CTLA4Ig on day 1 and day 2 after transplantation, compared with survival times of controls. In particular, the most significant prolongation was found in rats treated on day 2. At 7 days after transplantation, moderate-to-severe histological rejection occurred in all tissues in control rats. On the other hand, in rats treated with CTLA4Ig, all tissues showed significantly better preservation. Among these treated rats, the rats treated on day 2 showed excellent histopathological conditions in each tissue.

CONCLUSIONS

This study supports the feasibility of using CTLA4Ig for preventing acute rejection in CTA. On the basis of the current results, the administration of CTLA4Ig for CTA is more effective at 24-48 hr after transplantation, after the initial immune response has been allowed to begin.

Calcineurin inhibitor-free CD28 blockade-based protocol protects allogeneic islets in nonhuman primates

Recent success using a steroid-free immunosuppressive regimen has renewed enthusiasm for the use of islet transplantation to treat diabetes. Toxicities associated with the continued use of a calcineurin inhibitor may limit the wide-spread application of this therapy. Biological agents that block key T-cell costimulatory signals, in particular the CD28 pathway, have demonstrated extraordinary promise in animal models. LEA29Y (BMS-224818), a mutant CTLA4-Ig molecule with increased binding activity, was evaluated for its potential to replace tacrolimus and protect allogeneic islets in a preclinical primate model. Animals received either the base immunosuppression regimen (rapamycin and anti-IL-2R monoclonal antibody [mAb]) or the base immunosuppression and LEA29Y. Animals receiving the LEA29Y/rapamycin/anti-IL-2R regimen (n = 5) had significantly prolonged islet allograft survival (204, 190, 216, 56, and >220 days). In contrast, those animals receiving the base regimen alone (n = 2) quickly rejected the transplanted islets at 1 week (both at 7 days). The LEA29Y-based regimen prevented the priming of anti-donor T- and B-cell responses, as detected by interferon-gamma enzyme-linked immunospot and allo-antibody production, respectively. The results of this study suggest that LEA29Y is a potent immunosuppressant that can effectively prevent rejection in a steroid-free immunosuppressive protocol and produce marked prolongation of islet allograft survival in a preclinical model.

Co-stimulatory blockade and tolerance induction in transplantation

Recipients of organ and tissue transplants require lifelong immunosuppression to prevent rejection. Better understanding of the processes culminating in allograft rejection has led to novel approaches to modulating the immune response. Co-stimulatory signals between antigen-presenting and -responding cells are essential for a normal alloimmune response, and blockade of these pathways during initial graft-host interaction may be used to ameliorate or prevent a destructive response from proceeding. A large number of experimental studies now support this concept, and early clinical trials have been initiated. Despite some early difficulties and many unanswered questions, co-stimulatory blockade has major potential as a future immune-modulating mechanism for use in clinical transplantation.

Pattern of alloimmune response in second same donor allografts after induction of tolerance using CTLA4Ig

BACKGROUND

The pattern of allograft acceptance in the presence of costimulatory blockade is manifested by the sequential appearance of Th1 cells, followed by Th2 cells. The aim of this study was to examine whether this phenomenon repeats itself after second same donor allotransplantation, hoping to determine whether acceptance in this setting provokes a predominance of the Th2 response.

METHODS

Tolerance was achieved by transplantation of CTLA4Ig-transduced ACI liver allografts in Lewis recipients. Recipient long-term survivors received a second transplant, consisting of a cervical heterotopic heart from the same ACI donor strain. Animals were sacrificed at predetermined intervals following the second transplant and the heart and liver were processed for histology and cytokine mRNA expression.

RESULTS

Recipients of CTLA4Ig-transduced livers survived indefinitely. Rechallenge with same donor strain second allograft was manifested by an anergic immune response in the second cardiac allograft, and a very mild transient infiltrate within the first accepted liver graft. Cardiac function was maintained with resolution of all infiltrates. The cytokine cascade was activated within the allografts; however, the pattern of acceptance was not associated with predominance of a specific Th subtype.

CONCLUSIONS

The pattern of acceptance of an allograft following CTLA4Ig-mediated costimulatory blockade is not related to long-term predominance of Th2 cells, a phenomenon that may be unique to the setting of a tolerant liver. It may be likely that the infiltrating lymphocytes that are dominant in the second graft are suppressed by other memory mechanisms.

Role of CD28 for the generation and expansion of antigen-specific CD8(+) T lymphocytes during infection with Listeria monocytogenes

Infection of mice with the intracellular bacterium Listeria monocytogenes results in a strong CD8(+) T cell response that is critical for efficient control of infection. We used CD28-deficient mice to characterize the function of CD28 during Listeria infection, with a main emphasis on Listeria-specific CD8(+) T cells. Frequencies and effector functions of these T cells were determined using MHC class I tetramers, single cell IFN-gamma production and Listeria-specific cytotoxicity. During primary Listeria infection of CD28(-/-) mice we observed significantly reduced numbers of Listeria-specific CD8(+) T cells and only marginal levels of specific IFN-gamma production and cytotoxicity. Although frequencies were also reduced in CD28(-/-) mice during secondary response, we detected a considerable population of Listeria-specific CD8(+) T cells in these mice. In parallel, IFN-gamma production and cytotoxicity were observed, revealing that Listeria-specific CD8(+) T cells in CD28(-/-) mice expressed normal effector functions. Consistent with their impaired CD8(+) T cell activation, CD28(-/-) mice suffered from exacerbated listeriosis both after primary and secondary infection. These results demonstrate participation of CD28 signaling in the generation and expansion of Ag-specific CD8(+) T cells in listeriosis. However, Ag-specific CD8(+) T cells generated in the absence of CD28 differentiated into normal effector and memory T cells.

Costimulation blockade promotes the apoptotic death of graft-infiltrating T cells and prolongs survival of hepatic allografts from FLT3L-treated donors

BACKGROUND

Mouse liver grafts are accepted across major histocompatibility complex (MHC) barriers and induce donor-specific tolerance without immunosuppressive therapy. By contrast, hepatic allografts from donors treated with the hematopoietic growth factor fms-like tyrosine kinase 3 ligand (FL), which dramatically increases hepatic interstitial dendritic cells (DC), are rejected acutely (median survival time 5 days). This switch from tolerance to rejection is associated with a marked reduction in apoptotic activity of graft-infiltrating T cells. We hypothesized that T-cell costimulation, provided by markedly enhanced numbers of donor antigen presenting cells (APCs), might inhibit apoptosis, promote expansion of T helper 1 cells and play a key role in acute liver rejection.

METHODS

C3H (H2k) recipients of orthotopic liver grafts from FL-treated B10 (H2b) donors were given cytotoxic T-lymphocyte antigen 4: immunoglobulin (CTLA4Ig), a chimeric fusion protein that blocks the B7-CD28 costimulatory pathway, or control human immunoglobulin (200 microg) on the day of transplantation (day 0). Livers and spleens were removed on day 4. Cryostat sections were stained for interleukin (IL)-12 or by terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL). Expression of mRNA encoding interferon (IFN)-gamma and IL-10 was determined by RNase protection assay. Suspensions of graft-infiltrating cells (GICs) and spleen cells were analyzed for apoptotic (TUNEL+) T-cell subsets by flow cytometry. CTL activity of GICs and circulating alloantibody levels were determined by cytotoxicity assays.

RESULTS

Survival of liver grafts from FL donors was markedly prolonged by CTLA4Ig administration. This effect was associated with reductions in IFN-gamma and IL-10 gene transcripts within the GIC population, and with decreases in donor-specific CTL and NK cell activities and circulating anti-donor alloantibody levels. At the same time, there were marked increases in TUNEL+ CD4+ and especially CD8+ cells, both within the grafts and in the spleens of CTLA4Ig-treated mice.

CONCLUSIONS

Signaling via the B7-CD28 pathway appears to play a key role in the switch from tolerance to rejection that is precipitated by markedly enhanced numbers of donor DCs. Inhibition of acute liver allograft rejection by CTLA4Ig, linked to restoration of apoptotic activity of graft-infiltrating T cells, further suggests that deletion of these cells may be critical for promotion of long-term allograft survival.

Alloantigen-induced specific immunological unresponsiveness

When the immune system encounters alloantigen it can respond in any one of a number of different ways. The choice that is made will take into account factors such as where, when and how the contact with the alloantigen takes place, as well as the environmental conditions that prevail at the time the alloantigen is encountered. Alloantigen administration before transplantation either alone or in combination with therapeutic agents that modulate the functional activity of the responding leucocytes can be a powerful way of inducing specific unresponsiveness to alloantigens in vivo. The molecular mechanisms that influence the way the outcome of the immune response to alloantigen develops, either activation or unresponsiveness to the triggering antigen, hold the key to our ability to manipulate the immune system effectively by exposing it to donor antigen for therapeutic purposes. This review will focus on alloantigen-induced immunological unresponsiveness and how insights into the mechanisms of unresponsiveness have driven the development of novel tolerance-induction strategies that show promise for translation into the clinic in the future.

Complexities of CD28/B7: CTLA-4 costimulatory pathways in autoimmunity and transplantation

Recent advances in the understanding of T cell activation have led to new therapeutic approaches in the treatment of immunological disorders. One attractive target of intervention has been the blockade of T cell costimulatory pathways, which result in more selective effects on only those T cells that have encountered specific antigen. In fact, in some instances, costimulatory pathway antagonists can induce antigen-specific tolerance that prevents the progression of autoimmune diseases and organ graft rejection. In this review, we summarize the current understanding of these complex costimulatory pathways including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2 (CD86) molecules. We present evidence that suggests that multiple mechanisms contribute to CD28/B7-mediated T cell costimulation in disease settings that include expansion of activated pathogenic T cells, differentiation of Th1/Th2 cells, and the migration of T cells into target tissues. Additionally, the negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection supports a dynamic but complex process of immune regulation that is prominent in the control of self-reactivity. This is most apparent in regulation of the CD4(+)CD25(+)CTLA-4(+) immunoregulatory T cells that control multiple autoimmune diseases. The implications of these complexities and the potential for use of these therapies in clinical immune intervention are discussed.

Immunotherapy with nondepleting anti-CD4 monoclonal antibodies but not CD28 antagonists protects islet graft in spontaneously diabetic nod mice from autoimmune destruction and allogeneic and xenogeneic graft rejection

BACKGROUND

T-cell activation and the subsequent induction of effector functions require not only the recognition of antigen peptides bound to MHC molecules by T-cell receptor (TCR) for antigen but also a costimulatory signal provided by antigen presenting cells. CD4 T-cell activation and function require the CD4 molecule as a coreceptor of TCR. The CD28/B7 pathway is a major costimulatory signal for T-cell activation and differentiation.

METHODS

The effect of targeting CD4 by nondepleting anti-CD4 monoclonal antibodies (mAbs) versus blocking CD28/B7 by CTLA4Ig, anti-CD80 mAbs, and anti-CD86 mAbs on the prevention of recurrence of autoimmune diabetes after MHC-matched nonobese diabetes-resistant (NOR) islet transplantation in nonobese diabetic (NOD) mice were compared. Whether nondepleting anti-CD4 mAbs prolong allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice were studied. Furthermore, the effect of nondepleting anti-CD4 mAbs combined with CTLA4Ig on allogeneic islet graft survival in NOD mice was investigated.

RESULTS

Recurrence of autoimmune diabetes can be prevented by nondepleting anti-CD4 mAbs. Blocking the CD28/B7 costimulatory pathway by CTLA4Ig or by anti-CD80 mAbs and anti-CD86 mAbs cannot prevent recurrence of autoimmune diabetes after islet transplantation. Short-term treatment with nondepleting anti-CD4 mAbs significantly prolongs allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice. But nondepleting anti-CD4 mAbs combined with CTLA4Ig decreased allogeneic islet graft survival.

CONCLUSIONS

Nondepleting anti-CD4 mAbs but not CD28 antagonists protect islet grafts in diabetic NOD mice from autoimmune destruction and allogeneic and xenogeneic graft rejection. The efficacy of nondepleting anti-CD4 mAbs is compromised when it combines with CTLA4Ig.

Successful gene therapy via intraarticular injection of adenovirus vector containing CTLA4IgG in a murine model of type II collagen-induced arthritis

We previously constructed an adenovirus vector carrying a gene encoding a soluble form of fusion protein, consisting of the extracellular portion of cytotoxic lymphocyte antigen 4 (CTLA4) and the Fc portion of human immunoglobulin G1 (Adex1CACTLA4IgG). Murine type II collagen-induced arthritis (CIA) was treated with Adex1CACTLA4IgG. A single intraarticular injection of 1 x 10(5) PFU was able to support serum CTLA4IgG at more than 10 microg/ml for at least 12 weeks and was able to inhibit the CIA clinically and histologically. In contrast, intravenous, intramuscular, or subcutaneous injection of 1 x 10(5) PFU was unable to support a significant level of serum CTLA4IgG and thus was unable to inhibit the development of arthritis. Thus, we demonstrated that (1) a low-dose intraarticular injection of Adex1CACTLA4IgG was effective in delaying the onset of CIA and reducing the severity of arthritis; (2) an intraarticular (knee joint) injection of Adex1CACTLA4IgG effectively blocked the development of arthritis in distal paws; (3) the inhibitory effect of Adex1CACTLA4IgG lasted at least up to 20 weeks; (4) although serum CTLA4IgG at more than 10 microg/ml persisted for at least 12 weeks, mice treated by intraarticular injection of Adex1CACTLA4IgG were not anergic to adenovirus and were able to mount antibody responses against various antigens.

Human alloantigen-specific anergic cells induced by a combination of CTLA4-Ig and CsA maintain anti-leukemia and anti-viral cytotoxic responses

The success of allogeneic hematopoietic stem cell transplantation from HLA-disparate donors depends on the development of new strategies for graft-versus-host disease prevention able to target specifically donor antihost alloreactivity, while preserving GVL and antiviral immune surveillance. Recent experimental and clinical work has shown the feasibility of an approach based on induction of anergy to host alloantigens through blockade of B7/CD28 costimulatory signal in donor T cells, but data on the impact of this strategy on the recovery of the immune system are still lacking. We devised an ex vivo method for induction of host alloantigen-specific unresponsiveness based on treatment with the B7/CD28 blocking agent CTLA4-Ig associated with CsA. We then proceeded to assess the maintenance of an effective immune response towards viral pathogens and tumor cells after CTLA4-Ig/CsA treatment, by measuring the frequency of CTL precursors directed against CMV- and EBV-infected targets, and against autologous leukemic blasts. We demonstrated that (1) CTLA4-Ig and CsA can act synergistically in inducing a state of unresponsiveness to alloantigens; (2) the number of leukemia-reactive, EBV-specific and CMV-specific CTLp is not impaired by CTLA4-Ig/CsA treatment. Our data provide the first direct in vitro evidence that it is possible to preserve antiviral and antileukemia effector cells after blockade of CD28/B7 interaction during MLR.

Transcriptional regulation of CD28 expression by CD28GR, a novel promoter element located in exon 1 of the CD28 gene

CD28 provides an essential costimulatory signal required for Ag-mediated T cell activation via the TCR. Although accumulating evidence exists for the signaling properties of CD28, less is known regarding the regulation of CD28 expression. In this study, we have identified a novel promoter element of CD28, CD28GR (GGGGAGGAGGGG), which is located between +181 and +192 in exon 1 of the CD28 gene. Mutations within the 12-bp CD28GR sequence abolished its transcriptional activity. CD28GR contains a Sp1/EGR-1 binding site, which was found to act as the predominant functional element for regulating CD28 gene expression in Jurkat cells. Exon 1/CD28GR-driven transcription in Jurkat cells was augmented by cotransfection with Sp1 or EGR-1 expression plasmid. Similar augmentation was also shown with pharmacologic activation. This study is the first to identify a regulatory element that is critical for conferring constitutive and activation-induced transcriptional activation of the CD28 gene. Furthermore, our results proposed potential involvement of Sp1 in regulating CD28 expression. The linkage between Sp1 and the expression of CD28 has important implications in how viral infections, such as HIV, can induce immunosuppression.

CTLA-4-Fas ligand functions as a trans signal converter protein in bridging antigen-presenting cells and T cells

Co-stimulator blockade and trans inhibitory signaling, using agents such as CTLA-4-Ig and Fas ligand (FasL) respectively have been invoked as alternative strategies for suppressing pathogenic T cells. This study describes a novel hetero-bifunctional fusion protein, CTLA-4-FasL, designed to combine within a single protein both co-stimulator blocking and trans inhibitory signaling potentials. A chimeric expression cassette, in which the ectodomain coding sequences for CTLA-4 and FasL were linked in-frame, was used to produce a CTLA-4-FasL fusion protein. CTLA-4-FasL binding to both B7-1/B7-2-expressing Daudi B cells and Fas-expressing Jurkat T cells was documented by immunofluorescence and flow cytometry. The capacity of CTLA-4-FasL to induce apoptosis in Jurkat targets was markedly enhanced by the addition of Daudi and other B7-1/B7-2(+) B cell lines, which provided a membrane platform for the otherwise soluble CTLA-4-fusion protein. Moreover, in dual-chamber experiments, Daudi cells pre-coated with CTLA-4-FasL demonstrated Jurkat inhibitory activity that was cell-contact dependent. Significantly, when used to inhibit in vitro cellular proliferation of peripheral blood mononuclear cells, CTLA-4-FasL was approximately 1000-fold more potent than the extensively characterized CTLA-4-Ig fusion protein. Furthermore, the degree of inhibition induced by CTLA-4-FasL substantially surpassed that observed for CTLA-4-Ig and a soluble FasL when used in combination. CTLA-4-FasL represents the first of a novel class of fusion proteins, designated here as 'trans signal converter proteins', that combine trans signal masking and direct trans signaling functions.

Tolerance induction post in utero stem cell transplantation

The potential advantage of in utero HSC transplantation over a postnatal BMT is that early curative therapy could be given to an affected fetus, thus eliminating standard intensive immunosuppressive, marrow-ablative conditioning. It is apparent from studies in animals and humans that MHC-mismatched donor HSC of either fetal or adult origin can engraft in fetal recipients if the transplants are done sufficiently early in gestation. However, except for SCID, the percentage of donor pluripotent HSC that engraft is unacceptably low. We had hoped that for diseases such as thalassemia there would be a selective survival advantage for committed donor progenitor cells resulting in a high percentage of donor cell engraftment. At least based upon the experience in human fetuses with alpha- or beta-thalassemia, this has not been the case. Furthermore, for the majority of potential recipients of in utero HSC transplants, the marrow is non-defective, and the small percentage of pluripotent donor HSC that engraft would not be expected to selectively expand post-transplant. Our own results suggest that the non-defective fetal mouse and rhesus monkey are excellent models in which to study both stem cell engraftment, rejection, and tolerance induction. In our studies in non-defective mice with normal hematopoiesis, while the percentage of donor cells that are present is quite low, in only a small number of these animals were we able to induce permanent skin graft tolerance. Thus, while we found microchimerism in approximately 75% of recipients, less than 10% became tolerant. Even when we co-injected a large number of DC precursors, similar to what has been shown to induce tolerance to allogeneic liver, most of the animals failed to become tolerant to donor skin grafts. Interestingly, donor c-kit+ cells can be recruited with cytokines into the peripheral blood in engrafted mice, although these cells do not seem to be sufficient to induce tolerance to donor skin grafts, suggesting that the type (and location) of the engrafted donor cell plays a key role in tolerance induction. Our results in the fetal monkey model parallel those in the mouse, i.e., only a small number of donor cells engraft with limited tolerance induction. Interestingly, we found in our study of DC that GVHD was induced in those murine recipients of both allogeneic marrow and DC. It is likely that there were a sufficient number of mature DC in the preparation to facilitate a donor cytotoxic response towards the host. As a consequence there was also a significant increase in the percentage of donor cells that engrafted in the survivors. Future studies will focus on ways of blocking the graft vs host reaction while still maintaining the graft-promoting role of the donor T cell.

Development and applications of surface-linked single chain antibodies against T-cell antigens

In this report the use of surface-linkage to expand the potential experimental and therapeutic applications of single chain antibody (scFv) constructs is reviewed. A strategy for the generation and functional characterization of surface-linked scFvs that bind selectively to the T-cell proteins CD3epsilon, CD28, and CD152 (CTLA-4) is described in detail. Experimental examples are provided of the use of these constructs to study the positive and negative regulation of T-cell activation and to manipulate the in vivo immunogenicity of tumor cells. In addition, a novel system for Simultaneous T-cell Activation and Retroviral Transduction (START) is described in which retroviral packaging cells are rendered mitogenic for T lymphocytes by combined expression of surface-linked scFvs. Finally, the use of random mutagenesis and yeast surface display to increase the affinity and functional efficacy of scFv constructs is demonstrated.

CTLA4Ig-induced linked regulation of allogeneic T cell responses

The mechanisms by which CTLA4Ig exerts its powerful immunomodulatory effects are not clear. We show here that CTLA4Ig can induce linked regulation of allogeneic porcine T cell responses in vitro. Naive miniature swine SLA(dd) T cells were rendered hyporesponsive to specific allogeneic Ag after coculturing with MHC-mismatched SLA(cc) stimulators in the presence of CTLA4Ig. These Ag-specific hyporesponsive T cells were subsequently able to actively inhibit the allogeneic responses of naive syngeneic T cells in an MHC-linked fashion, as the responses of naive SLA(dd) responders against specific SLA(cc) and (SLA(ac))F(1) stimulators were inhibited, but allogeneic responses against a 1:1 mixture of SLA(aa) (I(a), II(a)) and SLA(cc) (I(c), II(c)) were maintained. This inhibition could be generated against either class I or class II Ags, was radiosensitive, and required cell-cell contact. Furthermore, the mechanism of inhibition was not dependent upon a deletional, apoptotic pathway, but it was reversed by anti-IL-10 mAb. These data suggest that CTLA4Ig-induced inhibition of naive allogeneic T cell responses can be mediated through the generation of regulatory T cells via an IL-10-dependent mechanism.

Allogeneic chimerism with low-dose irradiation, antigen presensitization, and costimulator blockade in H-2 mismatched mice

We have previously shown that the keys to high-level nontoxic chimerism in syngeneic models are stem cell toxic, nonmyelotoxic host treatment as provided by 100-cGy whole-body irradiation and relatively high levels of marrow stem cells. This approach was unsuccessful in H-2 mismatched B6.SJL to BALB/c marrow transplants, but with tolerization, stable multilineage chimerism was obtained. Ten million B6.SJL spleen cells were infused intravenously into BALB/c hosts on day -10 and (MR-1) anti-CD40 ligand monoclonal antibody (mAb) injected intraperitoneally at varying levels on days -10, -7, -3, 0, and +3 and the BALB/c mice irradiated (100 cGy) and infused with 40 million B6.SJL/H-2 mismatched marrow cells on day 0. Stable multilineage chimerism at levels between 30% to 40% was achieved in the great majority of mice at 1.6 mg anti-CD40 ligand mAb per injection out to 64 weeks after transplantation, without graft-versus-host disease. The transplanted mice were also tolerant of donor B6.SJL, but not third-party CBA/J skin grafts at 8 to 9 and 39 to 43 weeks after marrow transplantation. These data provide a unique model for obtaining stable partial chimerism in H-2 mismatched mice, which can be applied to various clinical diseases of man such as sickle cell anemia, thalassemia, and autoimmune disorders.

Targeting signal 1 through CD45RB synergizes with CD40 ligand blockade and promotes long term engraftment and tolerance in stringent transplant models

The induction and maintenance of allograft tolerance is a daunting challenge. Although combined blockade of CD28 and CD40 ligand (CD40L)-costimulatory pathways prevents allograft rejection in some murine models, this strategy is unable to sustain engraftment in the most immunogenic allograft and strain combinations. By targeting T cell activation signals 1 and 2 with the novel combination of anti-CD45RB and anti-CD40L, we now demonstrate potent enhancement of engraftment in C57BL/6 recipients that are relatively resistant to costimulatory blockade. This combination significantly augments the induction of tolerance to islet allografts and dramatically prolongs primary skin allograft survival. Compared with either agent alone, anti-CD45RB plus anti-CD40L inhibits periislet infiltration by CD8 cells, B cells, and monocytes; inhibits Th1 cytokines; and increases Th2 cytokine expression within the graft. These data indicate that interference with activation signals one and two may provide synergy essential for prolonged engraftment in situations where costimulatory blockade is only partially effective.

Inhibition of the allograft response by donor specific blood transfusion: association with reduced local TH1 cytokines and nitric oxide but enhanced prostaglandin E2 production

BACKGROUND

Donor-specific blood transfusion (DST) may improve allograft survival in human and animal models, but the mechanisms for this graft protective effect are incompletely understood. The sponge matrix allograft model was used to determine if DST induces regulatory factors within the allograft.

METHODS

C57BL/6 (H-2b) recipients received donor-specific (DBA/2J, H-2d) or syngeneic (C57BL/6) blood 7 days before sponge matrix allograft (DBA/2J) implantation. Fourteen days postgrafting, the sponge infiltrating cells (SIC) were examined for cytotoxic T cell (CTL) and natural killer (NK) activity, and sponge exudate fluid (SEF) was assessed for nitric oxide (.N=O) and prostaglandin E2 (PGE2) content. Interleukin- (IL) 2, IL-4, IL-10, and interferon-gamma (IFN-gamma) production by SIC was also determined. Recipient splenocytes were simultaneously assessed for anti-donor cytotoxic and proliferative responses and .N=O production.

RESULTS

SIC from mice receiving syngeneic transfusions (ST) acquired both CTL and NK activity postgrafting, with maximal activity by day 14. DST suppressed both CTL and NK activity throughout the postgrafting period. Limiting dilution analysis (LDA) of SIC to determine precursor and native CTL frequency showed significantly lower responder cell frequency after DST compared with ST. SEF .N=O levels and SIC production of IL-2 and IFN-gamma in grafted DST mice were significantly lower than in grafted mice receiving ST. No significant amounts of IL-4 and very low levels of IL-10 were produced by SIC from grafted mice after either ST or DST. Conversely, PGE2 content of sponge fluid and serum from DST mice was higher than in mice receiving ST. Antigen stimulated splenocyte proliferation and CTL development assessed by LDA were also inhibited by DST.

CONCLUSIONS

Reduction in local TH1 cytokines, absence of detectable TH2 cytokines, with enhanced PGE2 and depressed .N=O were observed in the local graft environment after DST. These data support the hypothesis that DST induces donor-specific intragraft suppressor factors, accompanied by reduced local and systemic immune activation.

Rejection responses to allogeneic hepatocytes by reconstituted SCID mice, CD4, KO, and CD8 KO mice

INTRODUCTION

The purpose of the current study was to investigate the capacity of CD4+, CD8+, or non-T cells to independently initiate acute rejection of allogeneic hepatocytes using reconstituted SCID, CD4 or CD8 knockout (KO) recipient mice.

METHODS

Allogeneic hepatocytes (FVB/N, H-2q) were transplanted into C57BL/6.SCID (H-2b), CD4 KO (H-2b), CD8 KO (H-2b), or beige/beige (H-2b) mice. SCID mice with functioning hepatocellular allografts subsequently received purified non-T cells (NTC), CD4+, or CD8+ splenocytes. Some mice were treated with anti-CD4, anti-CD8, and/or anti-nkl.1 mAb. Recipient mice were also assessed for donor-reactive delayed-type hypersensitivity (DTH) responses and donor-reactive alloantibody production.

RESULTS

Median hepatocellular allograft survival time (MST) was 28 days in CD4+ reconstituted SCID mice and 14 days in CD8+ reconstituted SCID mice. SCID hosts reconstituted with NTC demonstrated indefinite hepatocellular allograft survival (>120 days). MST was 10 days in untreated beige/beige (NK cell deficient) mice. MST was 14 days in untreated, 35 days in anti-CD4 mAb treated, and 10 days in anti-nkl.1 mAb treated CD8 KO mice. MST was 10 days in untreated, 35 days in anti-CD8 mAb treated, and 7 days in anti-nk1.1 mAb treated CD4 KO mice. Donor-reactive DTH responses were not detected in reconstituted SCID mice, were minimal in CD4 KO mice, and were prominent in CD8 KO mice after rejection of allogeneic hepatocytes. Similarly, donor-reactive alloantibody, was not detected in CD4 KO hosts, but was readily detected in CD8 KO hosts.

CONCLUSIONS

These studies show that both CD4+ and CD8+ T cells (but not host NTC) can independently initiate the rejection of allogeneic hepatocytes. While hepatocyte rejection by isolated CD4+ T cells is not surprising, rejection by CD8+ T cells (in the absence of CD4+ T cells) was unusual, and may explain the failure of "standard" immunosuppressive regimens to suppress acute rejection of allogeneic hepatocytes, as noted in prior studies. Furthermore, NK cells do not appear to be required for either CD4+ T cell or CD8+ T cell initiated hepatocyte rejection.

Enhanced antitumor immunity by fusion of CTLA-4 to a self tumor antigen

The idiotypic determinant (Id) of the immunoglobulin expressed by a B-cell malignancy can serve as an effective tumor-specific antigen but is only weakly immunogenic. This study demonstrates that the immunogenicity of the tumor Id protein can be dramatically increased by directing it to antigen-presenting cells (APCs). Cytotoxic T-lymphocyte antigen 4 (CTLA-4) present on activated T cells has a strong binding affinity to both B7-1 and B7-2 molecules, which are primarily expressed on APCs. After construction of a fusion protein consisting of Id and CTLA-4 (Id-CTLA4), mice immunized with the fusion protein induced high titers of Id-specific antibody and T-cell proliferative responses without adjuvants and were protected from lethal tumor challenge. The Id-CTLA4 fusion protein was so potent that even low doses (down to 0.1 μg) of the immunogen were able to elicit strong antibody responses. By using an Id-CTLA4 mutant protein, the ability to bind B7 molecules on APCs was shown to be required for the enhanced immunogenicity of Id-CTLA4. These findings demonstrate that fusing CTLA-4 to a potential tumor antigen represents an effective approach to prime antitumor immunities in vivo and may be applicable to the design of vaccines for a variety of other diseases.

Enhanced antitumor immunity by fusion of CTLA-4 to a self tumor antigen

The idiotypic determinant (Id) of the immunoglobulin expressed by a B-cell malignancy can serve as an effective tumor-specific antigen but is only weakly immunogenic. This study demonstrates that the immunogenicity of the tumor Id protein can be dramatically increased by directing it to antigen-presenting cells (APCs). Cytotoxic T-lymphocyte antigen 4 (CTLA-4) present on activated T cells has a strong binding affinity to both B7-1 and B7-2 molecules, which are primarily expressed on APCs. After construction of a fusion protein consisting of Id and CTLA-4 (Id-CTLA4), mice immunized with the fusion protein induced high titers of Id-specific antibody and T-cell proliferative responses without adjuvants and were protected from lethal tumor challenge. The Id-CTLA4 fusion protein was so potent that even low doses (down to 0.1 μg) of the immunogen were able to elicit strong antibody responses. By using an Id-CTLA4 mutant protein, the ability to bind B7 molecules on APCs was shown to be required for the enhanced immunogenicity of Id-CTLA4. These findings demonstrate that fusing CTLA-4 to a potential tumor antigen represents an effective approach to prime antitumor immunities in vivo and may be applicable to the design of vaccines for a variety of other diseases.

Costimulation of T cells

Costimulation is critical to T cell activation. On the antigen-presenting cell the key players are found in the extended family of B7 genes comprising cd80, cd86, B7h/B7RP-1 and B7-H1. cd80 and cd86 encode proteins that bind to CD28 and CTLA4 on T cells. Blocking this pathway with the potent CTLA4-Ig fusion protein shows encouraging potential as a therapeutic agent. While cd80 and cd86 pathways act mainly on naive T cells, B7h/B7RP-1 and B7-H1 seem to exert their effects on antigen-experienced lymphocytes.

Porcine CTLA4-Ig lacks a MYPPPY motif, binds inefficiently to human B7 and specifically suppresses human CD4+ T cell responses costimulated by pig but not human B7

The CTLA4 receptor (CD152) on activated T lymphocytes binds B7 molecules (CD80 and CD86) on APC and delivers a signal that inhibits T cell proliferation. Several regions involved in binding to B7 are known, but the relative importance of these is not clear. We have cloned porcine CTLA4 (pCTLA4). Although highly homologous to human CTLA4 (hCTLA4), the predicted protein sequence contains a leucine for methionine substitution at position 97 in the MYPPPY sequence. A fusion protein constructed from the extracellular regions of pCTLA4 and the constant regions of human IgG1 (pCTLA4-Ig) bound porcine CD86 with equivalent affinity to that of hCTLA4-Ig. However, pCTLA4-Ig bound poorly to human CD80 and CD86 expressed on transfectants and EBV-transformed human B cells. In functional assays with MHC class II-expressing porcine endothelial cells and human B cells, pCTLA4-Ig blocked human CD4+ T cell responses to pig but not human cells, whereas control hCTLA4-Ig inhibited responses to both. Comparison between mouse, human, and porcine CTLA4-Ig suggests that the selective binding of pCTLA4-Ig to porcine CD86 molecules is due to the L for M substitution at position 97. Our results indicate that pCTLA4-Ig may be a useful reagent to define the precise nature of the interaction between B7 and CTLA4. By failing to inhibit the delivery of costimulatory signals provided by human B7, it may also prove to be a relatively specific inhibitor of the direct human T cell response to immunogenic pig tissue.

A critical role for interleukin 4 in activating alloreactive CD4 T cells

To generate antigen-specific responses, T cells and antigen presenting cells (APCs) must physically associate with each other and elaborate soluble factors that drive the full differentiation of each cell type. Immediately after T cell activation, CD4 T cells can produce both interferon gamma (IFN-gamma) and interleukin 4 (IL-4) before polarization into distinct T helper subsets. Inhibition of IL-4 during mixed allogeneic lymphocyte culture resulted in a defect in the ability of APCs to generate sufficient costimulatory signals for activation of alloreactive T cells. In vivo, a deficiency in IL-4 production inhibited the activation of alloreactive IL-2-, IL-4- and IFN-gamma-producing CD4 T cells in mice challenged with allogeneic skin grafts, resulting in prolonged skin graft survival. Thus, production of IL-4 by CD4T cells helps activate alloreactive T cells by affecting APC function.

Intragraft expression of transforming growth factor-beta 1 by a novel quantitative reverse transcription polymerase chain reaction ELISA in long lasting kidney recipients

BACKGROUND

Chronic allograft nephropathy (CAN) remains a major problem in clinical transplantation. It has been associated with increased transforming growth factor (TGF-beta1). Our goal was to correlate CAN and levels of TGF-beta1 by using a novel competitive quantitative for reverse transcription-polymerase chain reaction-ELISA (RT-PCR-ELISA) assay.

METHODS

We studied 12 transplantation patients (posttransplant time: 36.5+/-11.2 months, range (r): 13-52) with stable creatinine and blood pressure and varied proteinuria. A Kidney biopsy was performed in all patients. Six patients with acute tubular necrosis (ATN) immediately after transplantation were used as controls. Histopathological evaluation was based on Banff working classification criteria. We designed an heterologous RNA competitor (IC) for RT-PCR-ELISA, which co-amplified with the same primer as TGF-beta1. Products were viewed on 96-well plates labeled with probes for IC at the desired sequence.

RESULTS

Results were expressed as the number of TGF-beta1 copies/microg of total RNA. Six patients showed more than 1000 mg/24 hr proteinuria (2446+/-1421 mg/24 hr, r: 1200-5000) higher CAN Banff scores, and the other six presented <1,000 mg/24 hr (348+/-267 mg/24 hr, r: 114-800). This difference was significant (P=0.01). There were not significant differences in posttransplant time, creatinine, or blood pressure between groups. TGF-beta1 levels by RT-PCR-ELISA were statistically significant (6038+/-5317, r: 1239-12100 versus 177+/-119.7, r: 51-400, P=0.04). The control group showed levels of 228+/-111, r. 140-444, P=0.04) with significant difference only for the higher proteinuria group (P=0.03).

CONCLUSIONS

This study showed that those patients with elevated CAN scores and higher proteinuria levels had higher TGF-beta1 intragraft expression.

Adenovirus-mediated gene transfer of CTLA-4Ig fusion protein in the suppression of experimental autoimmune arthritis

OBJECTIVE

Blockade of CD28-B7 interactions with soluble CTLA-4Ig fusion protein (which binds and blocks both B7-1 and B7-2 costimulatory molecules on antigen-presenting cells) has been shown to ameliorate experimental autoimmune diseases such as lupus, experimental autoimmune encephalomyelitis, diabetes, and, in our laboratory, collagen-induced arthritis (CIA). Because prolonged inhibition of this costimulatory pathway may be required, and the adenovirus-mediated gene-transfer technology is very efficient in achieving sustained expression of proteins in vivo, we examined the effects of adenovirally delivered CTLA-4Ig in established murine CIA.

METHOD

Replication-deficient recombinant adenoviruses encoding a chimeric CTLA-4Ig fusion protein, or beta-galactosidase as control, were injected intravenously into male DBA/1 mice once at arthritis onset. Disease activity was monitored by the assessment of clinical score, paw thickness, and type II collagen (CII)-specific cellular and humoral responses for 3 weeks. Groups of mice were also serially injected with a CTLA-4Ig fusion protein and an anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) monoclonal antibody (mAb), and disease activity was compared with that in the adenovirally transfused groups.

RESULTS

Both the adenovirally delivered and the recombinant CTLA-4Ig fusion protein suppressed established CIA, whereas anti-CTLA-4 mAb and the control beta-galactosidase adenovirus did not significantly affect the disease course. CII-specific lymphocyte proliferation, interferon-gamma production, and anti-CII antibody levels, both IgG1 and IgG2a, were significantly reduced by CTLA-4Ig treatment.

CONCLUSION

Blockade of the B7-CD28 costimulatory pathway by adenovirus-mediated CTLA-4Ig gene transfer is as effective as the recombinant fusion protein in treating established CIA, without the need for repeated administrations. Significant reduction in pathogenic cellular and humoral responses is achieved even after the onset of arthritis, thus suggesting the valuable therapeutic potential of this gene-transfer method in human rheumatoid arthritis.

Costimulatory blockade by the induction of an endogenous xenospecific antibody response

Xenogeneic tissues induce vigorous T cell immunity, reflecting the ability of costimulatory molecules to function across species barriers. We describe a strategy to inhibit costimulation that exploits species differences using the model of porcine pancreatic islet transplantation into mice. Mice were immunized with chimeric peptides that contained a known T cell epitope and selected sequences of the porcine costimulatory molecule CD86. This resulted in anti-peptide antibody responses that recognized intact porcine CD86, blocked costimulation by porcine CD86 but not murine CD86 in vitro, and prolonged the survival of porcine islet grafts in vivo. This strategy of inducing endogenous donor-specific costimulatory blockade has potential clinical applicability.

Feasibility of CTLA4Ig gene delivery and expression in vivo using retrovirally transduced myeloid dendritic cells that induce alloantigen-specific T cell anergy in vitro

Dendritic cells (DC) are highly specialised, bone marrow (BM)-derived antigen-presenting cells (APC) that initiate and regulate immune responses. They provide costimulatory signals (in particular, CD40 and the CD28 ligands CD80 and CD86) necessary for naive T cell activation. Functional expression of CD80 and CD86 is blocked by the fusion protein cytotoxic T lymphocyte antigen 4-immunoglobulin (CTLA4Ig), that promotes tolerance induction in animals. Here, replicating mouse (B10; H2b) myeloid DC progenitors, were retrovirally transduced to express CTLA4Ig using the centrifugal enhancement method. Gene product was detected by immunocyto- or histochemistry. Maximal DC transduction efficiency was 62%. Compared with control, zeomycin-resistance gene (Zeo)-transduced DC, CTLA4Ig-expressing cells showed markedly impaired capacity to stimulate naive allogeneic (C3H; H2k) T cell proliferation and cytotoxic T lymphocyte (CTL) generation. Their ability to induce alloantigen-specific T cell hyporesponsiveness was reversed by exogenous IL-2 in secondary mixed leukocyte reactions (MLR). Following local (s.c.) transfer to allogeneic recipients, the genetically modified DC trafficked to T cell areas of draining lymphoid tissue, where transgene expression was detected. Ex vivo analysis of proliferative and CTL responses revealed donor-specific inhibition of alloimmune reactivity by the CTLA4Ig-transduced DC. This effect was associated with marked inhibition of interferon (IFN)-gamma production, but significant augmentation of IL-4 and IL-10 secretion. Thus, retroviral transduction of DC permits in vivo delivery of CTLA4Ig to the precise microenvironment where antigen (Ag) presentation occurs. Comparatively nonimmunogenic retroviral vectors, that allow permanent transgene expression in DC, and promote localized delivery of the immunosuppressive transgene product, promote immune deviation and Ag-specific T cell hyporesponsiveness.

The role of costimulation in autoimmune demyelination

Experimental allergic encephalomyelitis (EAE) is a T cell-mediated, autoimmune disorder characterized by central nervous system (CNS) inflammation and demyelination, features reminiscent of the human disease, multiple sclerosis (MS). In addition to the signal the encephalitogenic T cell receives through the T cell receptor (TCR), a second signal, termed costimulation, is required for complete T cell activation. The B7 family of cell surface molecules expressed on antigen presenting cells (APC) is capable of providing this second signal to T cells via two receptors, CD28 and CTLA-4. Our studies have shown that costimulation provided by B7 molecules to its ligand CD28 is important in the initiation of the autoimmune response in EAE. Further, it appears the costimulation provided by B7-1 is important in disease development, while B7-2 may play an important regulatory role. We and others later showed that B7/CTLA-4 interaction plays a critical role in down-regulating the immune response. Previous work has shown that activated T cells and T cells of a memory phenotype are less dependent on costimulation than naive T cells. T cells reactive with myelin components that are involved in the pathogenesis of EAE and possibly MS would be expected to have been activated as part of the disease process. Building upon our prior work in the EAE model, we have tested the hypothesis that myelin-reactive T cells, which are relevant to the pathogenesis of CNS inflammatory demyelination, can be distinguished from naive myelin-reactive T cells by a lack of dependence upon costimulation for activation and that the costimulatory requirements of these myelin-reactive T cells change during the course of disease. Our studies in the EAE model have also addressed the mechanisms of extrathymic (peripheral) T cell tolerance following intravenous (i.v. ) administration of high dose antigen. It is believed that TCR signaling in the absence of costimulation is a vital component of peripheral tolerance mechanisms. However, recent evidence suggests that peripheral tolerance of antigen-specific T cells induced in vivo may require CTLA-4 engagement of the tolerized T cells. We have begun to examine the molecular mechanisms of tolerance induction following intravenous and intraperitoneal administration of myelin antigens in the EAE model and test the hypothesis that tolerance induction is dependent on the B7:CD28/CTLA-4 pathway. The results from our studies will enhance our understanding of the role that myelin-reactive T cells may play in the pathogenesis of MS. We have determined that MBP-reactive T cells in MS patients are less dependent upon CD28 costimulation than in normal controls, suggesting that these T cells were previously primed in vivo. Characterization of these CD28-independent myelin-specific T cells will have broad implications for a variety of immunologically based therapies in diseases such as MS.

Therapeutic activity of agonistic monoclonal antibodies against CD40 in a chronic autoimmune inflammatory process

The use of agonistic monoclonal antibody against CD40 has emerged as one the most effective ways to boost immune responses against infectious agents or to fight cancer. Here, we report that the same monoclonal antibodies against CD40 (FGK45 and 3/23) previously used to elicit protective immune responses treated the autoimmune inflammatory process of chronic collagen-induced arthritis in DBA/1-TCR-beta transgenic mice, as well as collagen-induced arthritis in DBA/1 mice, both animal models of rheumatoid arthritis. This study indicates that agonistic monoclonal antibody against CD40 can potentially be used to treat chronic autoimmune inflammatory processes.