The new immunology--the end of immunosuppressive drug therapy?

Antigen-specific blocking of CD4-specific immunological synapse formation using BPI and current therapies for autoimmune diseases

In this review, we discuss T-cell activation, etiology, and the current therapies of autoimmune diseases (i.e., MS, T1D, and RA). T-cells are activated upon interaction with antigen-presenting cells (APC) followed by a "bull's eye"-like formation of the immunological synapse (IS) at the T-cell-APC interface. Although the various disease-modifying therapies developed so far have been shown to modulate the IS and thus help in the management of these diseases, they are also known to present some undesirable side effects. In this study, we describe a novel and selective way to suppress autoimmunity by using a bifunctional peptide inhibitor (BPI). BPI uses an intercellular adhesion molecule-1 (ICAM-1)-binding peptide to target antigenic peptides (e.g., proteolipid peptide, glutamic acid decarboxylase, and type II collagen) to the APC and therefore modulate the immune response. The central hypothesis is that BPI blocks the IS formation by simultaneously binding to major histocompatibility complex-II and ICAM-1 on the APC and selectively alters the activation of T cells from T(H)1 to T(reg) and/or T(H)2 phenotypes, leading to tolerance.

Emerging opportunities for site-specific molecular and cellular interventions in autoimmune hepatitis

Current corticosteroid-based treatments of autoimmune hepatitis frequently have incomplete or unsatisfactory outcomes, side effects, and excessive immune suppression. The goal of this review is to describe the advances in developing animal models of autoimmune hepatitis and in treating diverse immune-mediated diseases that make pursuit of site-specific molecular and cellular inventions in autoimmune hepatitis feasible. Prime source and review articles in English were selected by a Medline search through October 2009. A murine model infected with an adenovirus expressing human CYP2D6 is a resource for evaluating new therapies because of its histological and serological features, persistence, and progressive hepatic fibrosis. Synthetic analog peptides that block autoantigen expression, a dimeric recombinant human fusion protein of cytotoxic T lymphocyte antigen-4, monoclonal antibodies against tumor necrosis factor-alpha, recombinant interleukin 10, tolerization techniques for disease-triggering autoantigens, T regulatory cell transfer, vaccination against antigen-specific cytotoxic CD8+ T cells, and gene silencing methods using small inhibitory RNAs are feasible interventions to explore. Treatments directed at dampening immunocyte activation with soluble cytotoxic T lymphocyte antigen-4, inhibiting immunocyte differentiation with recombinant interleukin 10, and improving immunosuppressive activity with regulatory T cell modulation have the most immediate promise. Progress in the development of an animal model of autoimmune hepatitis and experiences in other immune-mediated diseases justify the evaluation of site-specific molecular and cellular interventions in this disease.

The clinical utility of inhibiting CD28-mediated costimulation

SUMMARY

This volume covers many topics in the field of T-cell costimulation. The need for such a volume is testament to the growth of the field. From its beginning as a concept in the 1980s, we have now progressed to the point where many molecules now have functionally defined roles in T-cell costimulation. In addition, the field has progressed 'from bench to bedside'. Abatacept [cytotoxic T-lymphocyte antigen-4 (CTLA-4)-immunoglobulin (Ig) (CTLA-4-Ig)], an inhibitor of CD28-mediated T-cell costimulation, was approved for the treatment of moderate-to-severe rheumatoid arthritis in 2006 by the Food and Drug Administration and in 2007 by the European Medicines Agency. This chapter first presents a personal historical perspective on the early basic studies on the elucidation of the CD28/B7 T-cell costimulatory pathway and the discovery of CTLA-4-Ig. We next present an overview of studies of CTLA-4-Ig in preclinical animal studies. The material discussed in these first two sections is selective rather than exhaustive; their purpose is to provide context for the final section, a summary of human clinical studies performed with abatacept.

Current and future treatments of autoimmune hepatitis

Corticosteroid therapy induces clinical, laboratory and histological improvements in 80% of patients with autoimmune hepatitis. Prednisone, alone or at a lower dose in combination with azathioprine, increases the 20-year life expectancy to 80% and prevents or reduces hepatic fibrosis in 79% of patients. The combination regimen is preferred and treatment should be considered in all patients with active disease. The duration of therapy is finite and the medication should be discontinued after resolution of all manifestations of inflammatory activity, including the histological changes. Relapse after drug withdrawal occurs in 50-79% of patients, and it should be treated with long-term azathioprine (2 mg/kg daily). Salvage therapies for individuals intolerant of or refractory to the conventional regimens include high-dose corticosteroids, with or without high-dose azathioprine, 6-mercaptopurine, mycophenolate mofetil, tacrolimus or ciclosporin. Liver transplantation should be considered in patients with hepatic failure unresponsive to corticosteroid treatment, decompensated cirrhosis with a Model for End-Stage Liver Disease score of at least 15 points, or hepatocellular carcinoma that meets transplantation criteria. Autoimmune hepatitis recurs after transplantation in at least 17% of patients, and it typically improves after adjustments in the immunosuppressive regimen. Future therapies are likely to include mesenchymal stem cell transplantation, adoptive transfer of T regulatory cells, and cytokine manipulation. The emergence of new treatments will require the development of a collaborative network of clinical and basic investigators, as the complexity and specificity of current management problems require solutions that exceed the capabilities of single institutions.

Safety issues in the management of autoimmune hepatitis

BACKGROUND

Prednisone and azathioprine are effective in the treatment of autoimmune hepatitis, but diverse side effects can diminish their net benefit.

OBJECTIVES

Describe the frequency and nature of these side effects and propose management strategies to minimize their impact.

METHODS

Pertinent articles published from 1970 to 2007 were identified by Medline search and through a personal library.

RESULTS

Medication is prematurely discontinued in 13% of patients mainly because of cosmetic changes, cytopenia, or osteopenia. Populations at high risk are the elderly, those with pre-existent co-morbidities, patients with near-zero thiopurine methyltransferase activity, individuals who are treatment-dependent, pregnant women, and asymptomatic patients who are over-treated.

CONCLUSIONS

Proper patient selection, effective pre-treatment counseling, preemptive protective measures, realistic treatment objectives, and early identification of problematic patients can reduce complications. Individualized dosing schedules and the emergence of non-steroidal medications are realistic expectations.

TIRC7 inhibits T cell proliferation by modulation of CTLA-4 expression

Ab targeting of TIRC7 has been shown previously to inhibit T cell proliferation and Th1 lymphocyte-associated cytokine production. In this study, we demonstrate that Ab targeting of TIRC7 induces early cell surface expression of CTLA-4. The majority of stimulated CD4+ and CD8+ human T cells coexpress CTLA-4 and TIRC7. Similar to CTLA-4, TIRC7 rapidly accumulates at the site of Ag adhesion upon T cell activation. TIRC7 seems to colocalize with CTLA-4 in human T cells, and both molecules are associated with clathrin-coated vesicles, indicating they share intracellular transport systems. Moreover, Ab targeting of TIRC7 results in an early activation of CTLA-4 transcription. The inhibition of cell proliferation mediated by TIRC7 is dependent on CTLA-4 expression because the TIRC7-mediated inhibitory effects on cell proliferation and cytokine expression are abolished by Ab blockade of CTLA-4. Splenocytes obtained from CTLA-4-deficient mice are not responsive to TIRC7 Ab targeting. Thus, TIRC7 acts as an upstream regulatory molecule of CTLA-4 expression.

A CD4 domain 1 CC' loop peptide analogue enhances engraftment in a murine model of bone marrow transplantation with sublethal conditioning

Host CD4(+) T cells that survive sublethal or even lethal preconditioning regimens can participate in the process of hematopoietic stem cell graft rejection, particularly when the transplantations are performed across a major histocompatibility complex (MHC) class II barrier. To enhance donor marrow engraftment, we tested the efficacy of a small synthetic cyclic heptapeptide, 802-2 (CNSNQIC), which was designed to closely mimic the CD4 domain 1 CC' surface loop, theoretically involved in CD4/MHC class II complex oligomerization and subsequent CD4(+) T-cell activation. Previously, this peptide was found to have inhibitory activity in murine models for CD4(+) T cell-dependent graft-versus-host disease and skin allograft rejection. Herein, we used the MHC class II--disparate bm12 --> B6-CD45.1 sublethal irradiation transplantation model to test the possibility that the 802-2 peptide could enhance the engraftment of donor T cell-depleted bone marrow (ATBM). Sublethally irradiated B6-CD45.1 mice that received bm12 ATBM in combination with the 802-2 peptide demonstrated increased donor marrow cell engraftment as compared with mice that received ATBM alone; this suggests that the 802-2 peptide may be useful as an immunomodulating agent to overcome MHC class II mismatch barriers in hematopoietic stem cell transplantation.

Revisiting liver transplant immunology: from the concept of immune engagement to the dualistic pathway paradigm

Ever since the demonstration that allografts are rejected through immune reactions of the host, clinical therapies for organ allografts have relied on immune suppression to prevent these destructive events. A growing body of clinical and experimental data suggests that allografts elicit multiple, interactive immune responses. The result is not inevitably graft rejection, and "spontaneous" acceptance of fully allogeneic liver grafts occurs in rodents without immunosuppression. A spectrum of results range from spontaneous acceptance without immunosuppression to rejection with immunosuppression. The "dualistic pathway paradigm" aims to reconcile apparently conflicting observations in liver transplantation and proposes that: (1) immune engagement between the host and the allograft is instrumental in both rejection and acceptance; (2) there exist in all mammalian species congruent interactive pathways of immune activation whereby the fate of the allograft is determined by the quantitative results of these interactions; (3) the dualistic effect of immunosuppressive drugs on pathways of immune activation, conferring the capacity for favorable or unfavorable graft outcome should be investigated in experimental models in which organ allografts are spontaneously accepted. In conclusion the design of clinical strategies based on this research may contribute to protocols resulting in allograft acceptance without chronic immunosuppression.

Selective blockade of CD28 and not CTLA-4 with a single-chain Fv-alpha1-antitrypsin fusion antibody

B7-1 and B7-2 are costimulatory molecules expressed on antigen-presenting cells. The CD28/B7 costimulation pathway is critical for T-cell activation, proliferation, and Th polarization. Blocking both cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and CD28 interactions with a CTLA-4/Ig fusion protein inhibits various immune-mediated processes in vivo, such as allograft rejection and autoimmunity. However, selective blockade of CD28 may represent a better strategy for immunosuppression than B7 blockade, because CTLA-4/B7 interactions have been shown to participate in the extinction of the T-cell receptor-mediated activation signal and to be required for the induction of immunologic tolerance. In addition, selective CD28 inhibition specifically decreases the activation of alloreactive and autoreactive T cells, but not the activation of T cells stimulated by exogenous antigens presented in the context of self major histocompatibility complex (MHC) molecules. CD28 blockade cannot be obtained with anti-CD28 dimeric antibodies, which cluster their target and promote T-cell costimulation, whereas monovalent Fab fragments can block CD28 and reduce alloreactivity. In this study, we report the construction of a monovalent single-chain Fv antibody fragment from a high-affinity antihuman CD28 antibody (CD28.3) that blocked adhesion of T cells to cells expressing the CD28 receptor CD80. Genetic fusion with the long-lived serum protein alpha1-antitrypsin led to an extended half-life without altering its binding characteristics. The anti-CD28 fusion molecule showed biologic activity as an immuno-suppressant by inhibiting T-cell activation and proliferation in a mixed lymphocyte reaction.

Successful major surgical recovery of a patient following haploidentical stem cell transplantation for chronic myeloid leukemia in blast crisis and aspergillosis

A 44-year-old woman who underwent haploidentical stem cell transplantation (haplo SCT) for chronic myeloid leukemia in blast crisis and aspergillosis was admitted to the emergency room 7 months later because of severe right upper quadrant abdominal pain, fever, leukocytosis and peritoneal signs. Computer tomography disclosed cholecystitis and gallbladder perforation. Within hours, she underwent urgent open laparatomy and cholecystectomy. The postoperative period was uneventful and she was discharged 10 days later without any complications. Currently, she is 2(1/2) years posttransplantation in full hematological, cytogenetic and molecular remission with 100% Karnofsky performance status. Most notably, normal and fast recovery was observed following major surgery 7 months post-haplo SCT which is usually considered to result in long-lasting immunosuppression and malfunction of the immune system.

Development of allogeneic hematopoietic stem cell transplantation (HSCT)

The field of BMT has entered a new phase based on insights into basic molecular and cellular biology. The mechanism of cure mediated by allogeneic HSCT is now believed to be at least partially mediated by cellular attack against tumor-associated antigens. Better understanding of these cellular targets and the means of targeting them specifically will allow a more precise application of cellular therapy than is currently possible. This in turn may make it possible to design therapies that are increasingly selective without the collateral toxicities of GVHD, infection, and direct organ damage that currently are the limiting features of allogeneic HSCT as practiced until recently. However, it remains a challenge to demonstrate that disease-control using reduced intensity preparative regimens is at least comparable to that achieved by traditional myeloablative HSCT. This will require carefully controlled studies in each the major diseases that have shown sensitivity to the immune-mediated effects of HSCT. The chapters below will highlight progress towards the goals of elucidating the role of NST.

Successful prospective prediction of type 1 diabetes in schoolchildren through multiple defined autoantibodies: an 8-year follow-up of the Washington State Diabetes Prediction Study

OBJECTIVE

Almost 90% of type 1 diabetes appears in individuals without a close family history. We sought to evaluate the best current predictive strategy, multiple defined autoantibodies, in a long-term prospective study in the general population.

RESEARCH DESIGN AND METHODS

Autoantibodies to pancreatic islets (islet cell antibodies [ICAs]) and defined autoantibodies (d-aab) to human GAD, IA2/ICA512, and insulin were tested in 4,505 Washington schoolchildren. Eight years later, 3,000 (67%) subjects were recontacted, including 97% of subjects with any test >99th percentile.

RESULTS

Six subjects developed diabetes (median interval 2.8 years), all from among the 12 individuals with multiple d-aab, representing 50% positive predictive value (95% CI 25-75%) and 100% sensitivity (58-100%). Among the others, diabetes occurred in 0 of 6 with one d-aab plus ICA, 0 of 26 with ICA only, 0 of 7 with one d-aab equaling the 99th percentile and another d-aab equaling the 97.5th percentile, 0 of 86 with one d-aab, and 0 of 2,863 with no d-aab or ICA. Adjusted for verification bias, multiple d-aab were 99.9% specific (99.86-99.93%). At this age, new d-aab seldom appeared. Once present, d-aab usually persisted regardless of disease progression, although less so for insulin autoantibodies. Insulin secretion by sequential glucose tolerance testing remained normal in four multiple d-aab subjects not developing diabetes. Of children developing diabetes, five of six (83%) would be included if HLA-DQ genotyping preceded antibody testing, but HLA-DQ did not explain outcomes among high-risk subjects, even when considered along with other genetic markers.

CONCLUSIONS

Multiple d-aab were established by age 14 years and prospectively identified all schoolchildren who developed type 1 diabetes within 8 years.

Current concepts in the diagnosis, pathogenesis, and treatment of autoimmune hepatitis

Autoimmune hepatitis has a global distribution and affects all ages. Genetic factors strongly influence susceptibility, clinical expression, and treatment response. The diagnosis of autoimmune hepatitis has been codified by an international panel. An acute or fulminant presentation is recognized but not a cholestatic form. Subclassifications by predominant autoantibody profile have been proposed, but they lack etiologic and prognostic differences. Autoantibodies continue to be characterized to improve diagnostic specificity, predict outcome, and identify pertinent antigenic targets. Cytosolic enzymes are prime candidates as autoantigens. DRB1*0301 and DRB1*0401 are the susceptibility alleles in Caucasoid Northern Europeans and North Americans, and they also affect clinical expression and treatment outcome. Other autoimmune promoters affecting cytokine production and immunocyte activation may act in synergy with the susceptibility alleles to affect disease behavior. Cell-mediated and antibody-dependent forms of cytotoxicity are probably interactive pathogenic mechanisms, and novel site-specific therapies are feasible because these mechanisms are defined. Potent new immunosuppressive agents are emerging from the transplantation arena, but prednisone alone or in combination with azathioprine remains the mainstay of treatment. Corticosteroid therapy is effective but not ideal.

New developments in the prophylaxis and treatment of graft versus host disease

Graft versus host disease (GVHD) remains the major obstacle to successful allogeneic bone marrow transplantation. Cyclosporin with methotrexate is the most common prophylactic regimen. Tacrolimus is associated with less GVHD and is gaining ground especially in unrelated donor transplants where current regimens are unsatisfactory. Mycophenolate mofetil (MMF) and rapamycin have not yet shown benefit in acute GVHD prophylaxis. In vivo T-cell depletion with Campath 1H or thymoglobulin used during transplant conditioning are increasingly used in place of ex vivo T-cell depletion, where results remain disappointing. Steroids remain first choice for therapy of GVHD but anti-CD25 antibodies, daclizumab or basiliximab are gaining popularity as second-line therapy ahead of ATG. Chronic GVHD is increasing with greater use of peripheral blood stem cell grafts and older patients. The combination of tacrolimus and MMF is promising for patients with extensive disease. Tolerance induction using CTLA-4-Ig, anti-CD40L, tresperimus and/or rapamycin may revolutionise GVHD therapy. However, due to the desirability of tumour intolerance, tolerance is likely to be developed in organ transplantation before bone marrow transplantation for traditional indications. Bone marrow transplants performed to induce organ tolerance may see increasing use of these agents. TNF blockade using infliximab or etanercept (Enbrel) is promising but the role of these agents is not yet defined.

Blockade of T lymphocyte costimulation with cytotoxic T lymphocyte-associated antigen 4-immunoglobulin (CTLA4Ig) reverses the cellular pathology of psoriatic plaques, including the activation of keratinocytes, dendritic cells, and endothelial cells

Efficient T cell activation is dependent on the intimate contact between antigen-presenting cells (APCs) and T cells. The engagement of the B7 family of molecules on APCs with CD28 and CD152 (cytotoxic T lymphocyte-associated antigen 4 [CTLA-4]) receptors on T cells delivers costimulatory signal(s) important in T cell activation. We investigated the dependence of pathologic cellular activation in psoriatic plaques on B7-mediated T cell costimulation. Patients with psoriasis vulgaris received four intravenous infusions of the soluble chimeric protein CTLA4Ig (BMS-188667) in a 26-wk, phase I, open label dose escalation study. Clinical improvement was associated with reduced cellular activation of lesional T cells, keratinocytes, dendritic cells (DCs), and vascular endothelium. Expression of CD40, CD54, and major histocompatibility complex (MHC) class II HLA-DR antigens by lesional keratinocytes was markedly reduced in serial biopsy specimens. Concurrent reductions in B7-1 (CD80), B7-2 (CD86), CD40, MHC class II, CD83, DC-lysosomal-associated membrane glycoprotein (DC-LAMP), and CD11c expression were detected on lesional DCs, which also decreased in number within lesional biopsies. Skin explant experiments suggested that these alterations in activated or mature DCs were not the result of direct toxicity of CTLA4Ig for DCs. Decreased lesional vascular ectasia and tortuosity were also observed and were accompanied by reduced presence of E-selectin, P-selectin, and CD54 on vascular endothelium. This study highlights the critical and proximal role of T cell activation through the B7-CD28/CD152 costimulatory pathway in maintaining the pathology of psoriasis, including the newly recognized accumulation of mature DCs in the epidermis.

Drug therapy for acute graft-versus-host disease prophylaxis

The mechanisms of many immunosuppressive drugs have been defined, allowing for a rational approach to the use of these agents in GVHD prophylaxis. In addition to standard drugs such as methotrexate, cyclosporine, tacrolimus, and glucocorticoids, new agents-mycophenolate mofetil, tresperimus, rapamycin, basiliximab, and daclizumab-are now part of the immunosuppressive armamentarium. Improved understanding of tolerance has resulted in new approaches to prevention of GVHD. Anti-CD40L, CTLA-4-Ig, tresperimus, and rapamycin are agents that are being explored in this area and have shown impressive results in animal models. Currently, the standard therapy for acute GVHD prophylaxis in matched sibling transplants remains cyclosporine and methotrexate. Lower dose methotrexate, particularly in combination with tacrolimus, has shown good results in single arm studies with low toxicity, but this has not been tested in a randomized study. For unrelated donor transplants there is less GVHD when tacrolimus, rather than cyclosporine, is combined with methotrexate; there seems little reason to use cyclosporine in this setting. GVHD is still the major barrier to more widespread use of unrelated donor transplants and improved regimens are needed. In vivo T-cell depletion using Campath-1 or ATG is being used in high-risk patients. Data on its efficacy are so far anecdotal. Due to the variation in grading of GVHD between centers, randomized studies are needed to quantify the relative merits of different regimens, and participation in such studies is encouraged.

Effects of humanized monoclonal antibody to rhesus CD11a in rhesus monkey cardiac allograft recipients

INTRODUCTION

Leukocyte function-associated antigen-1 (LFA-1, CD11a) monoclonal antibody (mAb) affects many leukocyte functions without cell depletion. We hypothesized that the use of a humanized, anti-rhesus modified LFA-1 mAb (H2C12) in rhesus monkeys would cause: (1) prolonged heart allograft survival, (2) inhibition of primary but not secondary antibody responses, and (3) minimal drug toxicity.

METHODS AND RESULTS

Control (n=5) and H2C12-treated (n=7) (8-20 mg/kg i.v. on day -1 followed by 10 mg/kg/day) adult male rhesus recipients were inoculated with GP120 protein antigen on day -28 and -1 and grafted with heterotopic abdominal hearts (day 0). Donor-recipient pairs were equally MLR mismatched (4329.8+/-1124.1 CPM controls vs. 7289.0+/-1926.5 treated, P=NS). Mean heart allograft survival as evaluated by daily abdominal palpation was significantly prolonged in high dose recipients (23.0+/-2.6, n=4) vesus controls (8.2+/-1.3, n=5, P<0.02, Mann-Whitney U test). H2C12 treatment did not produce signs of cytokine release or toxicity, was nondepleting, but down-modulated PBL CD11a expression to 43.4+/-3.6% (n=4) of control levels (n=5) at day 7 as demonstrated by flow cytometry. It had no effect on postoperative Con A or MLR and did not prevent mAb clearance due to the rhesus-antihuman antibody response. The addition of mycophenolate mofitil prevented rhesus-antihuman antibody response with therapeutic H2C12 levels seen for >35 days.

CONCLUSIONS

The use of this mAb to block CD11a had the benefit of being a well tolerated, highly targeted therapy. These are the first results showing that monotherapy with anti-leukocyte function-associated antigen-1 mAb prolonged survival of MLR mismatched allogenic cardiac grafts in primates.

Tolerance and hematopoietic stem cell transplantation 50 years after Burnet's theory

OBJECTIVE

In 1949, the original formulation of Burnet's theory on the mechanisms responsible for the capacity of the immune system to discriminate between foreign antigens (i.e., the "non-self") and the cells of its own body (i.e., the "self") was published. Since then, further refinements and reconsiderations of the basic concepts underlying the achievement of a state of tolerance toward a certain antigen have been reported. Here, we attempt to analyze critically new clinical and experimental strategies aimed at inducing alloantigen-specific unresponsiveness.

DATA SOURCES

The data discussed in this review are drawn from articles and abstracts published in journals covered by the Science Citation Index and Medline.

STATE OF THE ART

Induction of tolerance toward alloantigens still remains one of the most elusive goals of clinical immunology. Until now, nonspecific immunosuppressive drugs have been used to successfully perform both solid organ and hematopoietic stem cell transplantation. However, using this approach, patients given an allograft are exposed to the threat of infections, tumors, and other side effects. Moreover, in solid organ transplant recipients, permanent tolerance toward the graft's alloantigens is never achieved. Recently, considerable progress has been made in expanding our knowledge of transplant tolerance. The traditional model of central tolerance, derived from Burnet's concept, has been complemented by knowledge of mechanisms of peripheral tolerance.

CONCLUSIONS

New experimental and therapeutic trials based on the blockade of costimulatory molecules, as well as on generation and infusion of either regulatory or nonimmunogenic cells, have been recently proposed for inducing alloantigen-specific tolerance.The achievements obtained in understanding the mechanisms of unresponsiveness toward non-self antigens are fundamental prerequisites for successful allogeneic transplants, and they could open a new exciting era of specific, immunosuppressive therapies.

Allogeneic hematopoietic chimerism in mice treated with sublethal myeloablation and anti-CD154 antibody: absence of graft-versus-host disease, induction of skin allograft tolerance, and prevention of recurrent autoimmunity in islet-allografted NOD/Lt mice

We describe a tolerance-based stem cell transplantation protocol that combines sublethal radiation with transient blockade of the CD40-CD154 costimulatory pathway using an anti-CD154 antibody. With this protocol, we established hematopoietic chimerism in BALB/c mice transplanted with fully allogeneic C57BL/6 bone marrow. The percentage of donor-origin mononuclear cells in recipients was more than 99%. In addition, all chimeric mice treated with anti-CD154 antibody remained free of graft-versus-host disease (GVHD) and accepted donor-origin but not third-party skin allografts. It was similarly possible to create allogeneic hematopoietic chimerism in NOD/Lt mice with spontaneous autoimmune diabetes. Pancreatic islet allografts transplanted into chimeric NOD/Lt mice were resistant not only to allorejection but also to recurrence of autoimmunity. We conclude that it is possible to establish robust allogeneic hematopoietic chimerism in sublethally irradiated mice without subsequent GVHD by blocking the CD40-CD154 costimulatory pathway using as few as 2 injections of anti-CD154 antibody. We also conclude that chimerism created in this way generates donor-specific allograft tolerance and reverses the predisposition to recurrent autoimmune diabetes in NOD/Lt mice, enabling them to accept curative islet allografts.

Progress in the treatment of proliferative lupus nephritis

Lupus nephritis is often well developed at the time of diagnosis. High-dose corticosteroids are universally accepted as the initial approach to the control of severe inflammation in the kidney. Long-term disease control and the minimization of iatrogenic risk usually require adjunctive therapies that target the more fundamental immunoregulatory disturbances of lymphoid cells. Of the available cytotoxic drugs, cyclophosphamide is currently among the most effective, although it cannot be considered ideal in terms of efficacy or toxicity. New prospects for the treatment of proliferative lupus nephritis include novel immunosuppressive agents (e.g. mycophenolate, cyclosporine, fludarabine), combination chemotherapy (e.g. cyclophosphamide plus fludarabine), and sequential chemotherapy (e.g. cyclophosphamide-azathioprine), immunological reconstitution using intensive cytoreductive chemotherapy (with or without stem cell rescue), co-stimulatory molecule inhibition (e.g. humanized anti-CD154 monoclonal antibody, CTLA4-Ig). Gene therapy remains an attractive prospect, but its feasibility clearly depends on the further definition of lupus-promoting genes and the availability of methods to establish stable expression of disease-corrective genes in the appropriate lymphoid cells.

Prevention and treatment of factor VIII inhibitors in murine hemophilia A

Inhibitory antibody formation is a major complication of factor VIII replacement therapy in patients with hemophilia A. To better understand the pathogenesis of this immunologic reaction, we evaluated the role of T-cell costimulatory signals for antifactor VIII antibody formation in a murine model of hemophilia A. Repeated intravenous injections of factor VIII in these factor VIII–deficient mice induced an antifactor VIII inhibitor antibody response. This response was shown to be T-cell dependent by its absence in hemophilic mice also deficient for the T-cell costimulatory ligand B7-2. In separate experiments, injection of murine CTLA4-Ig completely blocked the primary response to factor VIII in hemophilic mice with intact B7 function. This reagent also prevented or diminished further increases in antifactor VIII when given to hemophilic mice with low antifactor VIII antibody titers. These studies suggest that strategies targeting the B7-CD28 pathway are potential therapies to prevent and treat inhibitory antifactor VIII antibodies. Moreover, because the development of antibodies to replaced proteins may limit the success of many human gene therapy approaches, our results may be broadly applicable.