Gentulizumab, a novel anti-CD47 antibody with potent antitumor activity and demonstrates a favorable safety profile

BACKGROUND

Targeting CD47/SIRPα axis has emerged as a promising strategy in cancer immunotherapy. Despite the encouraging clinical efficacy observed in hematologic malignancies through CD47-SIRPα blockade, there are safety concerns related to the binding of anti-CD47 antibodies to CD47 on the membrane of peripheral blood cells.

METHODS

In order to enhance the selectivity and therapeutic efficacy of the antibody, we developed a humanized anti-CD47 monoclonal antibody called Gentulizumab (GenSci059). The binding capacity of GenSci059 to CD47 was evaluated using flow cytometry and surface plasmon resonance (SPR) methods, the inhibitory effect of GenSci059 on the CD47-SIRPα interaction was evaluated through competitive ELISA assays. The anti-tumor activity of GenSci059 was assessed using in vitro macrophage models and in vivo patient-derived xenograft (PDX) models. To evaluate the safety profile of GenSci059, binding assays were conducted using blood cells. Additionally, we investigated the underlying mechanisms contributing to the weaker binding of GenSci059 to erythrocytes. Finally, toxicity studies were performed in non-human primates to assess the potential risks associated with GenSci059.

RESULTS

GenSci059 displayed strong binding to CD47 in both human and monkey, and effectively inhibited the CD47-SIRPα interaction. With doses ranging from 5 to 20 mg/kg, GenSci059 demonstrated potent inhibition of the growth of subcutaneous tumor with the inhibition rates ranged from 30.3% to complete regression. Combination of GenSci059 with 2.5 mg/kg Rituximab at a dose of 2.5 mg/kg showed enhanced tumor inhibition compared to monotherapy, exhibiting synergistic effects. GenSci059 exhibited minimal binding to hRBCs compared to Hu5F9-G4. The binding of GenSci059 to CD47 depended on the cyclization of N-terminal pyroglutamic acid and the spatial conformation of CD47, but was not affected by its glycosylation modifications. A maximum tolerated dose (MTD) of 450 mg/kg was observed for GenSci059, and no significant adverse effects were observed in repeated dosages up to 10 + 300 mg/kg, indicating a favorable safety profile.

CONCLUSION

GenSci059 selectively binds to CD47, effectively blocks the CD47/SIRPα axis signaling pathway and enhances the phagocytosis effects of macrophages toward tumor cells. This monoclonal antibody demonstrates potent antitumor activity and exhibits a favorable safety profile, positioning it as a promising and effective therapeutic option for cancer.

CD47 masks pro-phagocytic ligands in cis on tumor cells to suppress antitumor immunity

Cancer cells often overexpress CD47, which triggers the inhibitory receptor SIRPα expressed on macrophages, to elude phagocytosis and antitumor immunity. Pharmacological blockade of CD47 or SIRPα is showing promise as anticancer therapy, although CD47 blockade has been associated with hematological toxicities that may reflect its broad expression pattern on normal cells. Here we found that, in addition to triggering SIRPα, CD47 suppressed phagocytosis by a SIRPα-independent mechanism. This mechanism prevented phagocytosis initiated by the pro-phagocytic ligand, SLAMF7, on tumor cells, due to a cis interaction between CD47 and SLAMF7. The CD47-SLAMF7 interaction was disrupted by CD47 blockade and by a first-in-class agonist SLAMF7 antibody, but not by SIRPα blockade, thereby promoting antitumor immunity. Hence, CD47 suppresses phagocytosis not only by engaging SIRPα, but also by masking cell-intrinsic pro-phagocytic ligands on tumor cells and knowledge of this mechanism may influence the decision between CD47 blockade or SIRPα blockade for therapeutic purposes.

Engineered SIRPα variants as immunotherapeutic adjuvants to anticancer antibodies

CD47 is an antiphagocytic signal that cancer cells employ to inhibit macrophage-mediated destruction. Here, we modified the binding domain of human SIRPα, the receptor for CD47, for use as a CD47 antagonist. We engineered high-affinity SIRPα variants with about a 50,000-fold increased affinity for human CD47 relative to wild-type SIRPα. As high-affinity SIRPα monomers, they potently antagonized CD47 on cancer cells but did not induce macrophage phagocytosis on their own. Instead, they exhibited remarkable synergy with all tumor-specific monoclonal antibodies tested by increasing phagocytosis in vitro and enhancing antitumor responses in vivo. This "one-two punch" directs immune responses against tumor cells while lowering the threshold for macrophage activation, thereby providing a universal method for augmenting the efficacy of therapeutic anticancer antibodies.

Tremelimumab (CP-675,206), a cytotoxic T lymphocyte associated antigen 4 blocking monoclonal antibody in clinical development for patients with cancer

Tremelimumab (CP-675,206) is a fully human monoclonal antibody specific for human cytotoxic T lymphocyte-associated antigen 4 (CTLA-4, CD152) in clinical development for patients with cancer. Blocking the CTLA-4 negative costimulatory receptor with the antagonistic antibody tremelimumab results in immune activation. Administration of tremelimumab to patients with locally advanced and metastatic melanoma has resulted in a subset of patients with durable objective tumor regressions. Its IgG(2) isotype minimizes the possibility of cytotoxic effects on activated T lymphocytes and cytokine release syndrome. Preclinical testing in vitro and in large animal models predicted the target concentrations of circulating antibody in humans necessary for a pharmacodynamic effect. Phase I clinical trials provided evidence of dose- or exposure-related effects consistent with the anticipated mechanism of action. Further clinical development has led to two ongoing registration trials in patients with metastatic melanoma: a phase III randomized trial of tremelimumab versus dacarbazine or temozolomide in previously untreated patients with advanced melanoma and a phase II trial of tremelimumab in previously treated patients with advanced melanoma.

CTLA-4: From conflict to clinic

CTLA-4 was first identified in 1991 as a second receptor for the T cell costimulation ligand B7. Uncertainties about its biological function plagued the early years after its discovery until 1995, when it was confirmed to be an inhibitor of T cell responses. CTLA-4 has since scored in the clinic as a target for antitumor therapy and as a soluble inhibitor of autoimmunity.

Update on anti-CTLA-4 antibodies in clinical trials

Breaking immune tolerance against tumor self-antigens is presently an area of intense research in the design of cancer therapies. One possible method to enhance immune system activation against tumor antigens is by blocking the inhibitory co-stimulatory signals mediated by cytotoxic T lymphocyte antigen 4, (CTLA-4) expressed on activated T cells. The fully human monoclonal antibodies that are directed against human CTLA-4, ipilimumab (Medarex/Bristol-Myers Squibb) and CP-675,206 (Pfizer/Abgenix, now Amgen), have demonstrated activity against metastatic melanoma, hormone refractory prostate cancer and other malignancies. They have also uncovered unusual immune-related adverse events manifesting as self-limiting inflammatory reactions of the bowel, skin and pituitary. This article reviews preclinical development and data generated from Phase I, II and III studies with regard to the end points reported and immune-related adverse events.

Soluble PD-1 Facilitates 4-1BBL–Triggered Antitumor Immunity against Murine H22 Hepatocarcinoma In vivo

PURPOSE

The use of costimulatory molecules targeting distinct T-cell signaling pathways has provided a means for triggering and enhancing antitumor immunity; however, it is still not fully understood what types of costimulatory molecules are suitable for the combination in tumor therapy. Our purpose in this study is to establish an effective antitumor immune approach by using costimulatory molecule 4-1BBL in combination with soluble PD-1.

EXPERIMENTAL DESIGN

The murine H22 hepatocarcinoma served as an ectopic tumor model. Local gene transfer was done by injection with naked plasmid p4-1BBL and/or psPD-1. The synergistic mechanism of dual-gene therapy was elucidated by detecting the change of gene expression of immunoregulatory factors in tumor microenvironment. The effects of immunotherapy were evaluated by testing the function of tumor-specific T cells, measuring tumor weight or volume, survival of mice, and H&E staining of tissues.

RESULTS

4-1BBL expressed by normal nonimmune cells effectively enhanced antitumor immune response but up-regulated PD-L1 and did not reduce IL-10 and transforming growth factor-beta (TGF-beta). sPD-1 synergized with 4-1BBL to establish efficient antitumor immune environment, including down-regulation of IL-10 and TGF-beta, further up-regulation of interleukin (IL)-2 and IFN-gamma, and higher CD8(+) T-cell infiltration. The combined treatment by 4-1BBL/sPD-1 eradicated tumors from mice with small amounts of preexistent tumor cells or tumors from approximately 60% of individuals with larger amounts of preexistent tumor cells.

CONCLUSIONS

Our findings in this report imply a great potential of 4-1BBL in combination with sPD-1 in tumor therapeutics with the in vivo existent tumor cells as antigens.

Tumor progression despite massive influx of activated CD8(+) T cells in a patient with malignant melanoma ascites

Although melanoma tumors usually express antigens that can be recognized by T cells, immune-mediated tumor rejection is rare. In many cases this is despite the presence of high frequencies of circulating tumor antigen-specific T cells, suggesting that tumor resistance downstream from T cell priming represents a critical barrier. Analyzing T cells directly from the melanoma tumor microenvironment, as well as the nature of the microenvironment itself, is central for understanding the key downstream mechanisms of tumor escape. In the current report we have studied tumor-associated lymphocytes from a patient with metastatic melanoma and large volume malignant ascites. The ascites fluid showed abundant tumor cells that expressed common melanoma antigens and retained expression of class I MHC and antigen processing machinery. The ascites fluid contained the chemokines CCL10, CCL15, and CCL18 which was associated with a large influx of activated T cells, including CD8(+) T cells recognizing HLA-A2 tetramer complexes with peptides from Melan-A and NA17-A. However, several functional defects of these tumor antigen-specific T cells were seen, including poor production of IFN-gamma in response to peptide-pulsed APC or autologous tumor cells, and lack of expression of perforin. Although these defects were T cell intrinsic, we also observed abundant CD4(+)CD25(+)FoxP3(+) T cells, as well as transcripts for FoxP3, IL-10, PD-L1/B7-H1, and indoleamine-2,3-dioxygenase (IDO). Our observations suggest that, despite recruitment of large numbers of activated CD8(+) T cells into the tumor microenvironment, T cell hyporesponsiveness and additional negative regulatory mechanisms can limit the effector phase of the anti-tumor immune response.

CTLA-4 gene polymorphisms and natural soluble CTLA-4 protein in psoriasis vulgaris

CTLA-4 molecule is an important inhibitor of T-lymphocyte activation. Several single nucleotide polymorphisms (SNPs) in the CTLA-4 gene were found, and their associations with many human diseases were described. So far, however, such studies have not been performed in psoriasis vulgaris in Caucasoids. Therefore, we examined the distribution of three CTLA-4 SNPs: -1147C/T, -318C/T and +49 A/G in 116 patients with psoriasis vulgaris and 123 healthy blood donors using the polymerase chain reaction-restriction fragment length polymorphism method. For all three SNPs, the frequencies of alleles, genotypes and three-point haplotypes were very similar in patients and controls, suggesting no contribution of these genetic variants to psoriasis.

CTLA4 blockade and GM-CSF combination immunotherapy alters the intratumor balance of effector and regulatory T cells

CTL-associated antigen 4 (CTLA4) blockade releases inhibitory controls on T cell activation and proliferation, inducing antitumor immunity in both preclinical and early clinical trials. We examined the mechanisms of action of anti-CTLA4 and a GM-CSF-transduced tumor cell vaccine (Gvax) and their impact on the balance of effector T cells (Teffs) and Tregs in an in vivo model of B16/BL6 melanoma. Tumor challenge increased the frequency of Tregs in lymph nodes, and untreated tumors became infiltrated by CD4+Foxp3- and CD4+Foxp3+ T cells but few CD8+ T cells. Anti-CTLA4 did not deplete Tregs or permanently impair their function but acted in a cell-intrinsic manner on both Tregs and Teffs, allowing them to expand, most likely in response to self antigen. While Gvax primed the tumor-reactive Teff compartment, inducing activation, tumor infiltration, and a delay in tumor growth, the combination with CTLA4 blockade induced greater infiltration and a striking change in the intratumor balance of Tregs and Teffs that directly correlated with tumor rejection. The data suggest that Tregs control both CD4+ and CD8+ T cell activity within the tumor, highlight the importance of the intratumor ratio of effectors to regulators, and demonstrate inversion of the ratio and correlation with tumor rejection during Gvax/anti-CTLA4 immunotherapy.

Unraveling the complex relationship between cancer immunity and autoimmunity: lessons from melanoma and vitiligo

A relationship between melanoma and vitiligo, a skin disorder characterized by the loss of melanocytes, has been postulated for many decades. In some cases, vitiligo is almost certainly a manifestation of autoimmune-mediated destruction of melanocytes. Melanocytes and melanoma cells share melanocyte differentiation antigens. Based on a number of observations, de novo vitiligo developing in patients with melanoma has been regarded as a sign of good prognosis. The immune system tolerates or ignores differentiation antigens because these antigens are self-derived. Therefore, immune tolerance or ignorance must be overcome to prime naive T and B cells to induce cancer immunity and autoimmunity against melanocyte differentiation antigens. Mouse models of concurrent melanoma and autoimmune vitiligo have revealed strategies to overcome immune ignorance or tolerance to melanocyte differentiation antigens: immunization with self-antigens as altered self (e.g., orthologues or mutated versions), expression in viral vectors, passive immunization with antibodies or T cells, incorporating potent adjuvants into active immunization, and blockade or removal of a downregulatory mechanism. Extensive investigations into the mechanisms that lead to tumor immunity and autoimmunity elicited by certain differentiation antigens have further revealed a variety of distinct cellular and molecular requirements, which are redundant and alternative.

Tumor regression and autoimmunity in patients treated with cytotoxic T lymphocyte-associated antigen 4 blockade and interleukin 2: a phase I/II study

BACKGROUND

Cytotoxic T lymphocyte-associated antigen (CTLA)-4 can inhibit T-cell responses and is involved in tolerance against self antigens. We previously reported autoimmune manifestations and objective cancer regressions in patients with metastatic melanoma treated with CTLA-4 blockade. The possibility of activating tumor-reactive T cells while removing inhibitory activity with CTLA-4 blockade has stimulated interest in using anti-CTLA-4 antibodies in combination with other cancer immunotherapies to improve clinical outcomes. In this study, we assessed the antitumor activity and autoimmune toxicity of CTLA-4 blockade in combination with an immune-activating stimulus, interleukin (IL)-2, in patients with metastatic melanoma.

METHODS

Thirty-six patients received anti-CTLA-4 antibody every 3 weeks. Three patients per cohort received doses of .1, .3, 1.0, and 2.0 mg/kg. Twenty-four patients received 3.0 mg/kg. All patients received IL-2 therapy (720,000 IU/kg every 8 hours to a maximum of 15 doses).

RESULTS

Eight patients (22%) experienced objective tumor responses (three complete and five partial), including metastases in the lungs, lymph nodes, mediastinum, and subcutaneous tissues. Six of the eight patients have ongoing objective responses at 11 to 19 months. Five patients (14%) developed grade III/IV autoimmune toxicities secondary to anti-CTLA-4 administration, including four patients with enterocolitis and one with arthritis and uveitis.

CONCLUSIONS

There is not evidence to support a synergistic effect of CTLA-4 blockade plus IL-2 administration, because the 22% objective response rate is that expected from the sum of these two agents administered alone. Durable cancer regressions were seen in patients treated with this combination.

New immunosuppressive therapies in renal transplantation: monoclonal antibodies

Remarkable advances in understanding the mechanisms of immune recognition and allograft rejection have been made in the past few years, leading to the development of innovative immunosuppressive strategies in the field of renal transplantation. Monoclonal antibodies (mAbs) have emerged as a new class of immunosuppressive agents, which appear to be effective (in both the treatment and the prevention of acute rejection) and well-tolerated in renal transplant recipients. The highly specific effects of these drugs make them less toxic than the oral long-term maintenance agents such as corticosteroids and the calcineurin inhibitors. Some of these mAbs have already confirmed their efficacy in preventing acute rejection in clinical phase III studies, and are now part of the well-established immunosuppressive regimens; these are the anti-CD25 mAbs (basiliximab and daclizumab). Other recently developed mAbs, like anti-CD52 (Campath-1H), anti-CD20 (rituximab), anti-LFA-1, anti-ICAM-1 and anti-tumour necrosis factor (TNF)-alpha (infliximab), are currently being tested, and show encouraging immunosuppressive potential. Blocking either the binding of cell-surface molecules or intracellular signal transduction, these mAbs could become an effective method to promote the holy grail of solid-organ transplantation, antigen-specific tolerance.

Costimulation blockade with belatacept in renal transplantation

BACKGROUND

Renal transplantation is the standard of care for patients with end-stage renal disease. Although maintenance immunosuppression with calcineurin inhibitors yields excellent one-year survival, it is associated over the long term with high rates of death and graft loss, owing in part to the adverse renal, cardiovascular, and metabolic effects of these agents. The use of potentially less toxic agents, such as belatacept, a selective blocker of T-cell activation, may improve outcomes.

METHODS

We randomly assigned renal-transplant recipients to receive an intensive or a less-intensive regimen of belatacept or cyclosporine. All patients received induction therapy with basiliximab, mycophenolate mofetil, and corticosteroids. The primary objective was to demonstrate the noninferiority of belatacept over cyclosporine in the incidence of acute rejection at six months (with an upper bound of the 95 percent confidence interval around the treatment difference of less than 20 percent).

RESULTS

At six months, the incidence of acute rejection was similar among the groups: 7 percent for intensive belatacept, 6 percent for less-intensive belatacept, and 8 percent for cyclosporine. At 12 months, the glomerular filtration rate was significantly higher with both intensive and less-intensive belatacept than it was with cyclosporine (66.3, 62.1, and 53.5 ml per minute per 1.73 m2, respectively), and chronic allograft nephropathy was less common with both regimens of belatacept than with cyclosporine (29 percent, 20 percent, and 44 percent, respectively). Lipid levels and blood-pressure values were similar or slightly lower in the belatacept groups, despite the greater use of lipid-lowering and antihypertensive medications in the cyclosporine group.

CONCLUSIONS

Belatacept, an investigational selective costimulation blocker, did not appear to be inferior to cyclosporine as a means of preventing acute rejection after renal transplantation. Belatacept may preserve the glomerular filtration rate and reduce the rate of chronic allograft nephropathy.

Technology evaluation: Belatacept, Bristol-Myers Squibb

Bristol-Myers Squibb is developing belatacept, a soluble fusion protein of the B7-binding domain of CTLA4 with amino acid changes A29Y and L104E and an Ig tail, which inhibits lymphocyte co-stimulation through CD28, for the potential treatment of solid organ transplant rejection. Belatacept is currently undergoing phase III clinical trials.

Immune-mediated inhibition of metastases after treatment with local radiation and CTLA-4 blockade in a mouse model of breast cancer

PURPOSE

Ionizing radiation therapy (RT) is an important component in the management of breast cancer. Although the primary tumor can be successfully treated by surgery and RT, metastatic breast cancer remains a therapeutic challenge. Here we tested the hypothesis that the combination of RT to the primary tumor with CTLA-4 blockade can elicit antitumor immunity inhibiting the metastases.

EXPERIMENTAL DESIGN

The poorly immunogenic metastatic mouse mammary carcinoma 4T1 was used as a model. Mice were injected s.c. with 4T1 cells, and treatment was started 13 days later when the primary tumors measured 5 mm in average diameter. Mice were randomly assigned to four treatment groups receiving: (1) control IgG (IgG), (2) RT + IgG, (3) 9H10 monoclonal antibody against CTLA-4, (4) RT + 9H10. RT was delivered to the primary tumor by one or two fractions of 12 Gy. 9H10 and IgG were given i.p. thrice after RT.

RESULTS

Consistent with the fact that 4T1 is poorly immunogenic, 9H10 alone did not have any effect on primary tumor growth or survival. RT was able to delay the growth of the primary irradiated tumor, but in the absence of 9H10 survival was similar to that of control mice. In contrast, mice treated with RT + 9H10 had a statistically significant survival advantage. The increased survival correlated with inhibition of lung metastases formation and required CD8+ but not CD4+ T cells.

CONCLUSIONS

The combination of local RT with CTLA-4 blockade is a promising new immunotherapeutic strategy against poorly immunogenic metastatic cancers.

Development of a Chimeric Anti-CD40 Monoclonal Antibody That Synergizes with LEA29Y to Prolong Islet Allograft Survival

In recent years, reagents have been developed that specifically target signals critical for effective T cell activation and function. Manipulation of the CD28/CD80/86 and CD40/CD154 pathways has exhibited extraordinary efficacy, particularly when the pathways are blocked simultaneously. Despite the reported efficacy of anti-CD154 in rodents and higher models, its future clinical use is uncertain due to reported thromboembolic events in clinical trials. To circumvent this potential complication, we developed and evaluated a chimeric Ab targeting CD40 (Chi220, BMS-224819) as an alternative to CD154. Although Chi220 blocks CD154 binding, it also possesses partial agonist properties and weak stimulatory potential. The anti-CD40 was tested alone and in combination with a rationally designed, high affinity variant of CTLA4-Ig, LEA29Y (belatacept), in a nonhuman primate model of islet transplantation. Although either agent alone only modestly prolonged islet survival (Chi220 alone: 14, 16, and 84 days; LEA29Y alone: 58 and 60 days), their combination (LEA29Y and Chi220) dramatically facilitated long term survival (237, 237, 220, >185, and 172 days). We found that the effects of Chi220 treatment were not mediated solely through deletion of CD20-bearing cells and that the combined therapy did not significantly impair established antiviral immunity.

[New biological therapeutic options for the treatment of RE: inhibition of costimulatory molecules and blockade of Interleukin-6-interaction]

After approval of TNF and interleukin-1 inhibiting agents for treatment of refractory rheumathoid arthritis, new agents inhibiting interleukin-6 and costimulatory pathways are entering clinical phase I and II trials. Blockade of costimulation by using a CTLA4 immunoglobulin fusion protein (CTLA4Ig), which inhibits the interaction between CD 28 and CD80/86, has been studied in humans and was demonstrated to be well tolerated and efficacious. A monoclonal antibody to the IL-6 receptor (MRA) blocks bioactivity of IL-6 and also showed favorable effects in first clinical trials. Drug safety data on both substances revealed no severe toxicity or increased incidence of severe infections. For the first time combinations of biological substances like CTLA4Ig and etanercept were demonstrated to be effective and showed no evidence for an increased rate of severe infectious complications. Encouraged by data on these two agents there is substancial hope for a broadened therapeutic armentarium of biological agents in refractory rheumatoid arthritis.

New paradigms in immunosuppression

With the decrease in donor quality and the increase in recipient co-morbidities, transplantation immunosuppression is changing. New paradigms in transplantation include co-stimulation, lymphocyte retrafficking, and inhibiting antibody production. With these new paradigms come new immunosuppressive agents. While these new agents show great promise, their use in day-to-day clinical transplantation remains to be seen.

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.

Overexpressed differentiation antigens as targets of graft-versus-leukemia reactions

The graft-versus-leukemia (GVL) effect associated with allogeneic blood and marrow transplantation has largely been a clinically described phenomenon until recently. We are beginning to understand the cellular and molecular nature of GVL, and in this review the authors highlight the potential for self-antigen-specific T lymphocytes to contribute to GVL. The authors focus on myeloid tissue-restricted proteins as GVL target antigens in CML and AML, and in particular on proteinase 3 and other azurophil granule proteins as targets for both autologous and allogeneic T-cell responses. Finally, the authors discuss myeloid self-antigen-directed alloreactivity in the context of our evolving understanding of the critical molecular determinants of allogeneic T-cell recognition. By altering T-cell receptor affinity, peptide specificity can be maintained and the potency of immunity can be enhanced in the MHC-mismatched setting.

Anti-CD40 therapy extends renal allograft survival in rhesus macaques

BACKGROUND

Organ transplant recipients currently require lifetime immunosuppressive therapy, with its accompanying side effects. Biological agents that block T-cell costimulatory pathways are important components of strategies being developed to induce transplantation tolerance. The aim of this study was to test the effect of a novel chimeric anti-human CD40 monoclonal antibody (Chi 220), either alone or in combination with CTLA4-Ig, on the survival of renal allografts in a nonhuman primate model.

METHODS

Captive-bred adolescent male rhesus monkeys (Macaca mulatta) (4-10 kg) were used as recipients and donors. Four treatment protocols were tested: Chi220 monotherapy, CTLA4-Ig monotherapy, Chi220 combined with CTLA4-Ig, and H106 (anti-CD40L) combined with CTLA4-Ig. Control animals received human albumin. Recipients were followed for survival, renal allograft function as determined by measurement of serum blood urea nitrogen (BUN) and creatinine, chemistries (sodium, potassium, chloride, and bicarbonate), complete blood cell count (CBC) with differential, and the development of donor-specific alloantibody.

RESULTS

Treatment with Chi220 for 14 days prolonged renal allograft survival (MST 38.5 vs. 7 days in untreated controls). Notably, simultaneous blockade of the CD28/B7 pathway did not further augment graft survival but did suppress the development of donor-specific antibodies, an effect not achieved with Chi220 alone, despite peripheral B cell depletion. Finally, treatment with Chi220 suppressed the primary immune response to cytomegalovirus, resulting in severe systemic manifestations.

CONCLUSIONS

Blockade of the CD40 pathway with anti-CD40 mAb is immunosuppressive in a large animal, preclinical renal transplant model. The potential effect of this therapy on viral immune responses will be important to consider for the design of safe clinical trials.

Immunotherapy as a means to induce transplantation tolerance

There have been several recent advances in the use of immunotherapy to induce transplantation tolerance. These include newer and safer protocols to create hematopoietic chimerism, the development of more-powerful T cell depleting antibodies, the identification of additional costimlulatory pathways as molecular targets and the identification of a role for suppressor cells in transplant tolerance.

Mechanisms of transplant tolerance induction using costimulatory blockade

The potential use of costimulation-blocking reagents to induce transplantation tolerance has recently created considerable excitement. Recent evidence has begun to delineate the mechanisms by which these powerful effects occur. It has become increasingly clear, firstly, that T cell costimulation is mediated by a delicate network of signaling pathways and, secondly, that interference with these systems can lead to numerous different tolerance mechanisms, including immune regulation, anergy and deletion.

CTLA-4: new insights into its biological function and use in tumor immunotherapy

The discovery of multiple costimulatory cell surface molecules that influence the course of T cell activation has increased our appreciation of the complexity of the T cell response. It remains clear, however, that CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) are the critical costimulatory receptors that determine the early outcome of stimulation through the T cell antigen receptor (TCR). Details of how the T cell integrates TCR stimulation with the costimulatory signals of CD28 and the inhibitory signals of CTLA-4 remain to be established, but unique features of the cell biology of CTLA-4 provide important insights into its function. We summarize here recent findings that suggest a previously unrecognized role for CTLA-4 in the regulation of T cell responses. We also describe preclinical and clinical results that indicate manipulation of CTLA-4 has considerable promise as a strategy for the immunotherapy of cancer.

Effects of CTLA4-Fc on glomerular injury in humorally-mediated glomerulonephritis in BALB/c mice

The effect of cytotoxic T-lymphocyte-associated molecule 4-immunoglobulin fusion protein (CTLA4-Fc) on humorally-mediated glomerulonephritis was studied in accelerated anti-glomerular basement membrane (anti-GBM) glomerulonephritis induced in BALB/c mice. This strain of mice develops antibody and complement dependent glomerulonephritis under this protocol. Sensitized BALB/c mice developed high levels of circulating autologous antibody titres, intense glomerular deposition of mouse immunoglobulin and complement, significant proteinuria, renal impairment, significant glomerular necrosis and a minor component of crescent formation 10 days after challenge with a nephritogenic antigen (sheep anti-GBM globulin). Early treatment during the primary immune response, or continuous treatment throughout the disease with CTLA4-Fc, significantly suppressed mouse anti-sheep globulin antibody titres in serum, and immunoglobulin and complement deposition in glomeruli. The degree of glomerular necrosis was improved and proteinuria was reduced, particularly in the earlier stages of disease. Late treatment by CTLA4-Fc starting one day after challenge with sheep anti-mouse GBM did not affect antibody production and did not attenuate glomerulonephritis. The low level of crescent formation found in BALB/c mice developing glomerulonephritis was not prevented by the administration of CTLA4-Fc. These results demonstrate that CTLA4-Fc is of benefit in this model of glomerulonephritis by its capacity to attenuate antibody production, without affecting the minor degree of cell-mediated glomerular injury.

Combination treatment with FTY720 and CTLA4IgG preserves the respiratory epithelium and prevents obliterative disease in a murine airway model

BACKGROUND

Mouse heterotopic tracheal transplantation offers a reproducible model of obliterative bronchiolitis after lung transplantation. CTLA4IgG inhibits signaling of the CD28/B7 pathway and induces antigen-specific T-cell unresponsiveness. FTY720 induces T-cell apoptosis and sequestration of circulating mature lymphocytes. We previously found that CTLA4IgG could prevent the development of obliterative airway disease but could not preserve the respiratory epithelium of grafted tracheae. We evaluated whether treatment with either FTY720 or CTLA4IgG, or with combination FTY720 and CTLA4IgG could preserve the respiratory epithelium and inhibit the development of obliterative airway disease.

METHODS

Tracheae with main bronchi from C3H/He mice were transplanted heterotopically into BALB/C mice and harvested on Day 35. Recipient mice received either no treatment or treatment with intraperitoneal FTY720, CTLA4IgG, or the combination of the 2.

RESULTS

Either FTY720 or CTLA4IgG alone significantly inhibited the development of obliterative airway disease. However, normal ciliated columnar respiratory epithelial cells were lost in the allografts. In contrast, combination therapy preserved the respiratory epithelium of the allografted tracheae. FTY720 concentration in the tissue was very high; treatment with FTY720 inhibited mixed lymphocyte reactions and augmented T-cell apoptosis.

CONCLUSION

Combination treatment with FTY720 and CTLA4IgG may prevent obliterative airway disease.

Inhibition of pro-inflammatory cytokine generation by CTLA4-Ig in the skin and colon of mice adoptively transplanted with CD45RBhi CD4+ T cells correlates with suppression of psoriasis and colitis

Transfer of CD45RBhi CD4 + naïve T cells into severe combined immunodeficient (SCID) mice induces colitis and skin lesions. Recipients treated with cyclosporin A (CsA), CTLA4-Ig, or vehicle were evaluated for weight loss, skin lesions, and cutaneous blood flow. Necropsy, histological, hematological and cytokine analyses were performed at the conclusion of the experiment to confirm the clinical findings. Vehicle-treated mice lost weight and had 100% incidence of skin lesions by 46-days. CsA-treated mice also lost weight, but only 3/8 mice developed mild, clinically evident skin lesions. In contrast, all CTLA4-Ig-treated mice gained weight and did not develop skin lesions. Increase in cutaneous blood flow correlated with the development of skin lesions. Granulocyte numbers, which were high or moderately high in the vehicle- or CsA-treated mice, respectively, remained as low in the CTLA4-Ig-treated group as in untreated mice. IFN-gamma, IL-1beta, and TNF-alpha levels in the gut and skin correlated with the extent of inflammation in both organs. Histology revealed that CTLA4-Ig but not CsA effectively prevented both autoimmune disorders. The ability of CTLA4-Ig to prevent both colitis and skin lesions suggests that CD28-dependent co-stimulation of T cells is critical for generation of pro-inflammatory cytokines and induction of clinical disease in such autoimmune disorders.

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.

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.

[Treatment of organ transplant rejection with low doses of CsA and CTLA4-Ig]

OBJECTIVE

To study on treating organ transplant rejection with low doses of CsA and CTLA4-Ig.

METHODS

We set up a rat's cardiac transplant rejection model by Ono's way. The experimental rats were divided into four groups: group A: without any treatment; group B: intraperitoneal injection of CsA at 10 mg / (-1) / (-1) 1 - 7 days; after operation group C: intraperitoneal injection of 100 microgram CTLA4-Ig after 2nd operative day; group D: intraperitoneal injection of CsA 2 mg / (-1) / (-1) 1- 7 days after operation. 50 microgram CTLA4-Ig was given intraperitoneally on the 2nd day postoperation. The survival days of allograft, serum concentration of IL-2, and histological changes were tested.

RESULTS

The allograft survival time of the four groups was 7.2 +/- 0.7 (group A), 19.4 +/- 2.07 (group B), 31.6 +/- 1.8 (group C) and 24.6 +/- 2.07 (group D) respectively. There were significantly differences among the groups (P < 0.05). The survival time in group D was more prolonged than that in group B (P < 0.05). The concentration of IL-2 was significantly decreased after operation. Significant difference was observed between the control group and each treated group (P < 0.01). In group A, B, C and D allograft rejection was graded IV, II, I and I respectively.

CONCLUSION

CTLA4-Ig had a stronger immunosuppression than did CsA. The low doses of CsA and CTLA4-Ig had show a synergistic immunosuppression in allograft transplantation.

CD40-ligand in primate cardiac allograft and viral immunity

Our laboratory has studied the role of CD40 ligand (CD40L, CD154) in the primate immune response to allogenic and infectious challenges. We find that intensive early blockade of CD40L reliably attenuates acute rejection of primate cardiac allografts. Monotherapy fails to prevent late graft loss, which often occurs in association with rising antidonor antibody titers and allograft vasculopathy, despite continuing anti-CD40L therapy. In contrast, the primary humoral response to T helper dependent influenza viral antigen is inhibited during anti-CD40L therapy, and responses to subsequent immunization are blunted after discontinuation of therapy. These results are encouraging with regard to the tolerogenic potential of costimulatory blockade for specific T helper dependent antigens. However, these findings also indicate that pathogenic allograft responses in primates are probably not entirely CD40L-dependent. As such, additional immunomodulatory strategies are needed to facilitate tolerance to a transplanted organ.

CTLA-41g in combination with anti-CD40L prolongs xenograft survival and inhibits anti-gal ab production in GT-Ko mice

The generation of GT-Ko mice has provided unique opportunities to study allograft and xenograft rejection in the context of anti-alpha1,3-Gal antibody (anti-Gal Ab) responses. In this study we used the allotransplantation model of C3H hearts into galactosyltransferase-deficient (GT-Ko) mice and the xenotransplantation model of baby Lewis rat hearts into GT-Ko mice to investigate the ability of CTLA-41g in combination with anti-CD40L mAb to control graft rejection and anti-Gal Ab production. Murine CTLA-41g or anti-CD40L monotherapy prolonged allograft survival, and the combination of these reagents was most immunosuppressive. However short-term treatment with murine cytotoxic T lymphocyte associated antigen-4 (muCTLA-41g) and/or CD40 ligand (CD154) monoclonal antibodies (anti-CD40L mAbs) was unable to induce indefinite allograft survival. CTLA-4-immunoglobulin fusion protein (CTLA-41g) or anti-CD40L monotherapy only marginally prolonged xenograft survival; the combination of human CTLA-41g and anti-CD40L significantly prolonged xenograft survival (74days), while the combination of murine CTLA-41g and anti-CD40L resulted in graft survival of >120days. CTLA-41g or anti-CD40L monotherapy or the combination of these agents inhibited the production of alloAbs, including anti-Gal Abs. CTLA-41g or anti-CD40L monotherapy partially controlled xenoAb and anti-Gal Ab production, while the combination was more effective. These observations corroborate our previous observations that humoral, including anti-Gal Ab, responses and rejection following allograft or concordant xenograft transplantation in GT-Ko mice are T-cell dependent and can be controlled by costimulation blockade.

CTLA4-IgG reverses asthma manifestations in a mild but not in a more "severe" ongoing murine model

We investigated whether CTLA4-Ig can reverse established asthma manifestations in a novel murine model of ongoing disease. In BALB/c mice, sensitized to ovalbumin (OVA) without adjuvant, airway inflammation was induced by a first series of OVA aerosol challenges. Murine CTLA4-IgG was then administered, followed by a second series of OVA inhalations. In control-treated mice, two series of OVA challenges induced upregulation of OVA-specific IgE in serum, eosinophils in the bronchoalveolar lavage fluid (BALF), and IL-5 production by lung lymphocytes upon OVA restimulation in vitro, compared with saline-challenged mice. CTLA4-IgG significantly inhibited all of these parameters in OVA-challenged mice. Importantly, mCTLA4-IgG performed better than the gold-standard dexamethasone because this corticosteroid did not inhibit the upregulation of OVA-specific IgE in serum. In a more "severe" ongoing model, induced by sensitization to OVA emulsified in aluminum hydroxide, resulting in airway hyperresponsiveness to methacholine and stronger inflammatory responses, mCTLA4-IgG was less effective in that only the number of eosinophils in the BALF was reduced (P = 0.053), whereas dexamethasone inhibited both BALF eosinophilia and cytokine production by lung lymphocytes. Thus, CTLA4-Ig might be an effective alternative therapy in established allergic asthma, especially in situations of mild disease.

The role of CD28-B7 costimulation in allergen-induced cytokine release by bronchial mucosa from patients with moderately severe asthma

BACKGROUND

T cells play an important role in airway inflammation in asthma through the release of T(H)2 cytokines. Optimal T-cell activation by antigen-presenting cells requires co-stimulatory signaling, such as the interaction of CD80, CD86, or both with CD28. In patients with mild allergic asthma, the fusion protein cytotoxic T-lymphocyte antigen 4Ig (CTLA-4Ig), which inhibits CD28-mediated signaling, blocks the release of IL-5 and IL-13 from bronchial explant cultures exposed to the allergen Dermatophagoides pteronyssinus.

OBJECTIVES

To assess costimulation in more severe forms of atopic asthma, we have compared the ability of CTLA-4Ig to block allergen-induced cytokine responses of bronchial explants and PBMCs from patients with moderately severe asthma.

METHODS

Bronchial explants and PBMCs were cultured in vitro, and cytokine expression was measured by means of quantitative RT-PCR and ELISA.

RESULTS

Constitutive mRNA transcripts for IL-5, IL-13, and GM-CSF were detected in the tissue explants, but only IL-5 mRNA increased significantly with allergen stimulation. Consistent with increased transcription, allergen-stimulated IL-5 protein release into explant supernatants, but this was not blocked by CTLA-4Ig. Allergen did not induce GM-CSF release, and IL-13 protein could not be detected in the explant supernatants under any condition. In contrast, allergen enhanced production of IL-5 and IL-13 by PBMC cultures from the same subjects, and this was inhibited effectively by CTLA-4Ig.

CONCLUSIONS

These data suggest that IL-5 production in the airways of subjects with moderately severe asthma is largely independent of CD28-mediated costimulation. The different requirements for CD28-mediated costimulation in PBMC cultures and bronchial tissue cultures emphasizes the importance of the tissue microenvironment in pulmonary inflammatory responses in severe asthma.

Role of galectin-3 in adenocarcinoma liver metastasis

Galectin-3 is a lactosamine-specific lectin that binds to laminin sugar-sites, and up-regulated expression of galectin-3 in primary colorectal cancer is involved in cancer progression and metastasis. Inhibitory effects of cell adhesion and liver metastasis of adenocarcinoma via portal vein by lectin-binding sugar and anti-galectin-3 antibody was examined to determine the role of galectin-laminin binding in cancer liver metastasis. Highly metastatic adenocarcinoma cell lines XK4-A3 and RPMI4788 were used in in vitro cell attachment and nude mice liver metastatic experiments, and inhibitory effects of anti-galectin-3 antibody or lectin-binding sugars were examined. The in vitro adhesion assay demonstrated that the anti-galectin-3 antibody and alpha-lactose inhibited XK4-A3 and RPMI4788 cell adhesion to laminin in a dose-dependent manner. The liver metastasis of XK4-A3 and RPMI4788 was reduced 50 and 60%, respectively (P<0.001) by alpha-lactose treatment. Anti-galectin-3 antibody also inhibited liver metastasis in a dose-dependent manner, and maximum inhibition rate was 66% for XK4-A3 and 90% for RPMI4788. Galectin-3 plays an important role in liver metastasis of adenocarcinoma by the mechanisms of galectin-3 binding to laminin. Inhibition of galectin-3 on cancer cell surface induces reduced cell attachment to laminin and liver metastasis.

Aggressive skin allograft rejection in CD28-/- mice independent of the CD40/CD40L costimulatory pathway

CD28-/- mice have been utilized to study the role of B7/CD28 and B7-CTLA4 interactions. There is evidence that CTLA4 ligation may be critical for tolerance induction. The aim of the current study is to further investigate rejection responses of CD28-/- mice and to define the role of B7-CTLA4 interactions in the absence of the CD40 and CD28 pathways. Balb/c skin allografts were transplanted onto C57BL/6 (B6) wild type or CD28-/- mice treated with anti-CD40L, CTLA4-Ig, or combination blockade. To investigate the cellular mechanism of rejection in CD28-/- recipients, mice were treated with anti-CD4 or anti-CD8 antibodies prior to treatment with costimulation blockade. The fluoroscein dye CFSE was utilized to study T cell expansion in vivo. Surprisingly, treatment of B6 CD28-/- mice with CTLA4-Ig alone (MST 12d), anti-CD40L alone (MST 13d), or combined blockade (MST 13d) had no effect on allograft survival compared to untreated B6 CD28 mice (MST 11d). CD28-/- recipients depleted of CD4+ cells and treated with CTLA4-Ig, anti-CD40L, or combination blockade also did not have prolonged survival compared with untreated mice (MST 10d). In contrast, CD28-/- recipients depleted of CD8+ cells had markedly prolonged allograft survival when treated with either anti-CD40L alone (MST 49d) or with combination blockade (MST 57d). Studies utilizing CFSE demonstrated that CD28-/- CD8+ T cells are not defective in in vivo proliferation responses compared with wild type CD8 cells. Thus, CD28-/- CD8+ T cells are responsible for aggressive rejection responses of CD28-/- mice independent of the CD40 pathway. In addition, CD40L blockade does not result in CD4+ T cell tolerance in CD28 recipients, despite an intact B7-CTLA4 pathway.

Blockade of the CD28 and CD40 pathways result in the acceptance of pig and rat islet xenografts but not rat cardiac grafts in mice

Previously, we demonstrated that combination CTLA4-Fc and anti-CD40L mAb treatment results in tolerance to concordant, cellular islet xenografts. The aim of this study was to determine its effectiveness in a model of fetal pig pancreas (FPP) xenotransplantation. Survival of FPP fragment grafts were compared to the survival of rat islet or cardiac xenografts following short term CTLA4-Fc and anti-CD40L mAb treatment. Rat islet and FPP fragment grafts survived long-term. However, rat cardiac grafts were rejected by 52-91 days. Both rat islet and FPP grafts showed similar histology with intact islet structures and adjacent 'nests' of lymphocytes. Concordant vascularised rat hearts showed extensive polymorphonuclear infiltrate, concentric vasculitis and a perivascular infiltrate predominantly of CD8+ T cells. This suggests that this therapy is effective for prolonging islet xenografts and demonstrates that the cellular mechanism of rejection for vascularised and non-vascularised xenografts are different.

An antagonist IL-15/Fc protein prevents costimulation blockade-resistant rejection

IL-15 is a powerful T cell growth factor (TCGF) with particular importance for the maintenance of CD8(+) T cells. Because costimulation blockade does not result in universal tolerance, we hypothesized that "escape" from costimulation blockade might represent a CD8(+) and IL-15/IL-15R(+)-dependent process. For this analysis, we have used an IL-15 mutant/Fcgamma2a protein, a potentially cytolytic protein that is also a high-affinity receptor site specific antagonist for the IL-15Ralpha receptor protein, as a therapeutic agent. The IL-15-related fusion protein was used as monotherapy or in combination with CTLA4/Fc in murine islet allograft models. As monotherapies, CTLA4/Fc and an IL-15 mutant/Fcgamma2a were comparably effective in a semiallogeneic model system, and combined treatment with IL-15 mutant/Fcgamma2a plus CTLA4/Fc produced universal permanent engraftment. In a fully MHC-mismatched strain combination known to be refractory to costimulation blockade treatment, combined treatment with both fusion proteins proved to be highly effective; >70% of recipients were tolerized. The analysis revealed that the IL-15 mutant/Fc treatment confers partial protection from both CD4(+) and CD8(+) T cell graft infiltration. In rejections occurring despite CTLA4/Fc treatment, concomitant treatment with the IL-15 mutant/Fcgamma2a protein blocked a CD8(+) T cell-dominated rejection processes. This protection was linked to a blunted proliferative response of alloreactive T cells as well silencing of CTL-related gene expression events. Hence, we have demonstrated that targeting the IL-15/IL-15R pathway represents a new and potent strategy to prevent costimulation blockade-resistant CD8(+) T cell-driven rejection.

Interferon-gamma is not involved in the intestinal manifestations of the acute murine semiallogenic graft-versus-host disease

BACKGROUND

The acute murine semiallogenic graft-versus-host disease (GvHD) is known to be associated with Th1 cytokines secreting lymphocytes in the spleen and lymph nodes. However, whether this cytokine secretion pattern is also involved in the intestinal manifestations of acute GvHD (crypt hyperplasia and villous atrophy) is not known, so far.

METHODS

We first investigated the secretion of interleukin (IL) 4 (indicative of Th2-type differentiation) and interferon (IFN) 7 (Th1-type differentiation) by splenic and by small bowel lamina propria lymphocytes. In addition, animals were treated with neutralizing antibodies to IL-4 or IL-12. The effect of this treatment on the intestinal morphology was examined. Second, we also investigated the effect of donor-derived IFN-gamma by using donor lymphocytes from IFN-gamma knock-out animals. Third, animals were treated with the fusion protein OX40-Ig which interferes with the OX40-OX40L interaction and thereby inhibits the intestinal manifestations of acute GvHD.

RESULTS

We found that, whereas splenic lymphocytes secrete an excess of IFN-gamma, lymphocytes of the intestinal lamina propria secrete less IFN-gamma and IL-4 than control animals. When OX40-Ig is administered to animals with acute GvHD, the intestinal histology normalizes as well as the secretion of IFN-y and IL-4, indicating that the intestinal morphology is not affected by the secretion of IFN-gamma by lamina propria lymphocytes. The treatment of animals suffering from acute GvHD with anti-IL-4 and anti-IL-12, which blocks the differentiation of IFN-gamma secreting T-lymphocytes, did not significantly affect the development of crypt hyperplasia or villous atrophy. Furthermore, donor lymphocytes of IFN-gamma knock-out animals also induced the intestinal manifestations of acute GvHD.

CONCLUSIONS

These findings indicate that IFN-gamma is not crucial for the development of crypt hyperplasia and villous atrophy in the murine semiallogenic GvHD.

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.