Human anti-mouse antibody response induced by anti-CD4 monoclonal antibody therapy in patients with rheumatoid arthritis

The Epitope-Specific Anti-human CD4 Antibody MAX.16H5 and Its Role in Immune Tolerance

T cell modulation in the clinical background of autoimmune diseases or allogeneic cell and organ transplantations with concurrent preservation of their natural immunological functions (e.g., pathogen defense) is the major obstacle in immunology. An anti-human CD4 antibody (MAX.16H5) was applied intravenously in clinical trials for the treatment of autoimmune diseases (e.g., rheumatoid arthritis) and acute late-onset rejection after transplantation of a renal allograft. The response rates were remarkable and no critical allergic problems or side effects were obtained. During the treatment of autoimmune diseases with the murine MAX.16H5 IgG1 antibody its effector mechanisms with effects on lymphocytes, cytokines, laboratory and clinical parameters, adverse effects as well as pharmacodynamics and kinetics were studied in detail. However, as the possibility of developing immune reactions against the murine IgG1 Fc-part remains, the murine antibody was chimerized, inheriting CD4-directed variable domains of the MAX.16H5 IgG1 connected to a human IgG4 backbone. Both antibodies were studied in vitro and in specific humanized mouse transplantation models in vivo with a new scope. By ex vivo incubation of an allogeneic immune cell transplant with MAX.16H5 a new therapy strategy has emerged for the first time enabling both the preservation of the graft-vs.-leukemia (GVL) effect and the permanent suppression of the acute graft-vs.-host disease (aGVHD) without conventional immunosuppression. In this review, we especially focus on experimental data and clinical trials obtained from the treatment of autoimmune diseases with the murine MAX.16H5 IgG1 antibody. Insights gained from these trials have paved the way to better understand the effects with the chimerized MAX.16H5 IgG4 as novel therapeutic approach in the context of GVHD prevention.

A humanized anti-DLL4 antibody promotes dysfunctional angiogenesis and inhibits breast tumor growth

Blockage of Delta-like 4 (DLL4)-directed Notch signaling induces excessive tip cell formation and endothelial proliferation resulting in dysfunctional angiogenesis in tumors. MMGZ01, as a murine anti-human DLL4 monoclonal antibody, specifically binds to human DLL4 and blocks Notch pathway. Here, the structure of MMGZ01 variable fragment (Fv) was established and framework region (FR) residues which supported complementarily determining region (CDR) loop conformation were identified. Important residues interactions were also identified through docking MMGZ01 Fv with antigen epitope in DLL4. To humanize the murine antibody, we modified MMGZ01 Fv through CDR grafting and the reconstructed antibody (H₃L₂) maintained similar structure and binding affinity to parental MMGZ01 after back mutation of 12 canonical murine residues in the FRs. Meanwhile, H₃L₂ promoted human umbilical vein endothelial cell (HUVEC) proliferation through inhibiting DLL4-directed Notch pathway. Moreover, in MDA-MB-231-bearing nude mice, H₃L₂ induced dysfunctional angiogenesis and tumor cell apoptosis and showed superior anti-tumor activity. In conclusion, H₃L₂ is an ideal humanized antibody that inhibits tumor growth through targeting DLL4-Notch pathway and has attracting potentials for clinical applications.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

Adjuvant facilitates tolerance induction to factor VIII in hemophilic mice through a Foxp3-independent mechanism that relies on IL-10

Current treatment of hemophilia consists of the administration of recombinant clotting factors, such as factor VIII (FVIII). However, patients with severe hemophilia can mount immune responses targeting therapeutically administered FVIII through inhibitory immunoglobulins that limit treatment efficacy. Induction of immune tolerance to FVIII in hemophilia has been extensively studied but remains an unmet need. We found that nondepleting anti-CD4 monoclonal antibodies (mAbs) are effective in inducing long-term tolerance to FVIII in different strains of hemophilic mice. Tolerance induction was facilitated when anti-CD4 mAbs were administered together with FVIII adsorbed in an adjuvant (alum). The observed state of tolerance was antigen specific, with mice remaining immune competent to respond to different antigens. Importantly, we found that following immunization with FVIII, the primed cells remained susceptible to tolerance induction. Studies with Foxp3-deficient and interleukin 10 (IL-10)-deficient mice demonstrated that the underlying tolerance mechanism is Foxp3 independent but requires IL-10. Our data show that an adjuvant, when administered together with a tolerizing agent such as nondepleting anti-CD4, can facilitate the induction of long-term tolerance to recombinant proteins, possibly not only in hemophilia but also in other diseases that are treated with potentially immunogenic therapeutics.

Prevention of house dust mite induced allergic airways disease in mice through immune tolerance

Allergic airways disease is a consequence of a Th2 response to an allergen leading to a series of manifestations such as production of allergen-specific IgE, inflammatory infiltrates in the airways, and airway hyper-reactivity (AHR). Several strategies have been reported for tolerance induction to allergens leading to protection from allergic airways disease. We now show that CD4 blockade at the time of house dust mite sensitization induces antigen-specific tolerance in mice. Tolerance induction is robust enough to be effective in pre-sensitized animals, even in those where AHR was pre-established. Tolerant mice are protected from airways eosinophilia, Th2 lung infiltration, and AHR. Furthermore, anti-CD4 treated mice remain immune competent to mount immune responses, including Th2, to unrelated antigens. Our findings, therefore, describe a strategy for tolerance induction potentially applicable to other immunogenic proteins besides allergens.

Developing the next generation of monoclonal antibodies for the treatment of rheumatoid arthritis

Rheumatoid arthritis is one of the commonest autoimmune diseases affecting 0.8% of the population. Over the last decade the treatment of this chronic disease has been revolutionized by the use of monoclonal antibodies and fusion proteins, targeting molecules like tumour necrosis factor alpha. Nevertheless, approximately one-third of subjects fail to respond to these therapies and therefore significant unmet medical need remains. Following a decade of use, clinical, government and regulatory agency expectations have changed for new antibodies therapies entering this highly competitive area. In this review, we discuss the current advances being made in antibody engineering and how they are being considered and used in the development of the next generation of antibodies to meet future expectations of healthcare providers, physicians and patients. Moreover, we discuss how pattern recognition receptors may provide new antibody tractable targets that may break the cycle of autoimmunity in rheumatoid arthritis.

Modulation of IL-17 and Foxp3 expression in the prevention of autoimmune arthritis in mice

BACKGROUND

Rheumatoid Arthritis (RA) is a chronic immune mediated disease associated with deregulation of many cell types. It has been reported that different T cell subsets have opposite effects in disease pathogenesis, in particular Th17 and Treg cells.

METHODOLOGY AND FINDINGS

We investigated whether non-depleting anti-CD4 monoclonal antibodies, which have been reported as pro-tolerogenic, can lead to protection from chronic autoimmune arthritis in SKG mice--a recently described animal model of RA--by influencing the Th17/Treg balance. We found that non-depleting anti-CD4 prevented the onset of chronic autoimmune arthritis in SKG mice. Moreover, treated mice were protected from the induction of arthritis up to 60 days following anti-CD4 treatment, while remaining able to mount CD4-dependent immune responses to unrelated antigens. The antibody treatment also prevented disease progression in arthritic mice, although without leading to remission. Protection from arthritis was associated with an increased ratio of Foxp3, and decreased IL-17 producing T cells in the synovia. In vitro assays under Th17-polarizing conditions showed CD4-blockade prevents Th17 polarization, while favoring Foxp3 induction.

CONCLUSIONS

Non-depleting anti-CD4 can therefore induce long-term protection from chronic autoimmune arthritis in SKG mice through reciprocal changes in the frequency of Treg and Th17 cells in peripheral tissues, thus shifting the balance towards immune tolerance.

Biologic therapies in rheumatology: lessons learned, future directions

During the past decade biologic therapies such as monoclonal antibodies and fusion proteins have revolutionized the management of rheumatic disease. By targeting key cytokines and immune cells biologics have provided more specific therapeutic interventions with less immunosuppression. Clinical use, however, has revealed that their theoretical simplicity hides a more complex reality. Efficacy, toxicity and even pharmacodynamic effects can deviate from those predicted, as poignantly illustrated by the catastrophic effects witnessed during the first-into-human administration of TGN1412. This review summarizes lessons gleaned from practical experience and discusses how these can inform future discovery and development of new biologic therapies for rheumatology.

Pharmacokinetics/pharmacodynamics of nondepleting anti-CD4 monoclonal antibody (TRX1) in healthy human volunteers

PURPOSE

TRX1 is a nondepleting anti-CD4 monoclonal IgG1 antibody being developed to induce tolerance by blocking CD4-mediated functions. The purpose of this study is to describe the pharmacokinetics (PK) and pharmacodynamics (PD) of TRX1 and to develop a receptor-mediated PK/PD model that characterizes the relationships between serum TRX1 concentration and total and free CD4 expression in healthy male volunteers.

METHODS

Nine subjects from three dosing cohorts in double-blinded, placebo-controlled phase I clinical study was included in the analysis. Serum TRX1 levels were determined using enzyme-linked immunosorbent assay. Blood total and free CD4 receptor levels were determined by using flow cytometric analyses. The receptor-mediated PK/PD model was developed to describe the dynamic interaction of TRX1 binding with CD4 receptors.

RESULTS AND CONCLUSIONS

TRX1 displayed nonlinear pharmacokinetic behavior and the CD4 receptors on T cells were saturated and down-modulated following treatment with TRX1. Results from in vitro studies using purified human T cells suggested that CD4-mediated internalization may constitute one pathway by which CD4 is down-modulated and TRX1 is cleared in vivo. The developed receptor-mediated PK/PD model adequately described the data. This PK/PD model was used to simulate PK/PD time profiles after different dosing regimens to help guide the dose selection in future clinical studies.

Immunogenicity of engineered antibodies

Administration of a therapeutic antibody can lead to an anti-antibody response (AAR). Much effort has been applied to engineering antibodies with as little as possible non-human structure to minimize such responses. Here, we review reported AAR to murine, mouse-human chimeric, and humanized antibodies. Replacement of mouse immunoglobulin constant regions with human ones effects the largest immunogenicity reduction. Humanization of variable domains effects a further decrease.

Induction of immunological tolerance/hyporesponsiveness in baboons with a nondepleting CD4 antibody

Tolerance induction with anti-CD4 Abs is well established in rodent transplant and autoimmune disease models, but has yet to be demonstrated in non-human primates or in clinical studies. In retrospect, failure of anti-CD4 Abs to induce tolerance in primates may be technical, a consequence of insufficient dosing and Ab properties influencing immunogenicity and cell depletion. To circumvent these possible limitations, we constructed a novel anti-CD4 mAb, TRX1, humanized to reduce immunogenicity and Fc-modified to prevent cell depletion. Using equine immune globulin (equine Ig) as a model Ag, we examined the tolerance-inducing capacity of TRX1 in baboons. During the induction phase, TRX1 inhibited the humoral response to equine Ig in a dose-dependent manner, with complete suppression of response at the highest dose tested (40 mg/kg). Upon challenge, anti-equine Ig responses were generated in baboons treated with 1 and 10 mg/kg doses of TRX1 and in control animals. In higher dosing cohorts (20 and 40 mg/kg), however, the immune response to equine Ig was modulated in seven of nine animals, including complete unresponsiveness to Ag challenges in two animals. Five of nine were hyporesponsive to equine Ig, generating titers 50- to 250-fold lower than control groups. Repeated challenge resulted in titers falling to baseline or near baseline, with two of five hyporesponsive animals becoming unresponsive to Ag. All animals responded to neoantigen immunization, indicating that the modified response to equine Ig was Ag specific. These studies demonstrate that anti-CD4 Ab-mediated, Ag-specific tolerance can be achieved in baboons without long term immune suppression.

Characterization and humanization of a monoclonal antibody that neutralizes human leukocyte interferon: a candidate therapeutic for IDDM and SLE

We have developed a panel of murine monoclonal antibodies that recognize human interferon alpha. One of these mononclonal antibodies binds and neutralizes, with high affinity, all of seven tested recombinant human interferon alphas. This mononclonal antibody also neutralizes the interferon activity present in two independent pools of interferon alphas prepared following stimulation of human peripheral blood leukocytes. The complementary determining regions from this murine mononclonal antibody were transferred to a human IgG2 heavy chain and to a human kappa1 light chain. In addition, six (heavy chain) and two (light chain) amino acids were transferred from the framework regions. This generated a humanized mononclonal antibody that retained the specificity of the mouse parent. The humanized anti-interferon alpha antibody is a candidate therapeutic for those diseases, such as insulin-dependent diabetes, systemic lupus erythematosis, psoriasis and Crohn's disease, which are all characterized by pathological expression of interferon alpha.

A Synthetic CD4-CDR3 Peptide Analog Enhances Skin Allograft Survival Across a MHC Class II Barrier

The efficacy of a synthetic peptide analogue (rD-mPGPtide), mimicking the CDR3 region in the first domain of the CD4 surface molecule, was investigated in a murine model for CD4+ T cell-mediated skin allograft rejection. A single injection of rD-mPGPtide shortly before transplantation exhibited significantly prolonged graft survival in the B6 anti-B6.C-H2bm12 MHC class II-disparate strain combination. Long-term graft survival (>100 days) was achieved when thymectomized adult recipient mice were transplanted along with rD-mPGPtide treatment. The peptide also affected secondary rechallenge responses with MHC class II allografts. In addition, the inhibitory effect of the rD-mPGPtide in this transplantation model was directed against CD4+ T cells and was exclusively specific toward donor alloantigen. In vitro analysis of CD4+ T cells isolated from the draining lymph nodes of rD-mPGPtide-treated recipients indicated a 450-fold decrease in precursor frequency in response to donor allostimulation compared with the untreated control group. There was also significant down-regulation of the frequency of IL-2-, IFN-γ-, and IL-4-producing CD4+ T cells upon in vitro allogeneic restimulation of host cells 4 days posttransplantation. However, these same CD4+ T cells maintained the capacity to produce normal cytokine levels upon third-party allostimulation. Thus, these studies demonstrate that a CD4-CDR3 peptide analogue can specifically and effectively prolong skin graft survival across MHC class II barriers.

A Synthetic CD4-CDR3 Peptide Analog Enhances Bone Marrow Engraftment Across Major Histocompatibility Barriers

The efficacy of a synthetic peptide analog mimicking the CDR3-D1 domain of the CD4 molecule was investigated in murine models of allogeneic bone marrow engraftment after transplantation across major histocompatibility complex (MHC) barriers. A single dose of a CD4-CDR3 peptide analog was administered at the time of marrow transplantation to three different allogeneic mouse strain combinations after appropriate sublethal total body irradiation: (1) B10.BR → C57BL/6J (B6), a full allogeneic MHC difference; (2) (B6xDBA/2)F1 → (B6xCBA)F1 , a haploidentical MHC combination; and (3) B6.C-H2bm12 → B6-Ly5.2, involving only a MHC class II difference. Donor-host chimerism was assessed after 1 and 2 months posttransplantation by flow cytometric analysis of spleen and/or lymph node cells. Peptide-treated animals in all three strain combinations exhibited significantly enhanced donor lymphoid engraftment, which was similarly reflected in the total lymphocyte compartment and its T-cell (CD4+, CD8+) and B-cell subsets. In addition, peptide-treated mice in the haploidentical and MHC class II-mismatched strain combinations exhibited prolonged tolerance of both donor and syngeneic host-type tail skin grafts while rejecting third-party allogeneic grafts, thus supporting the reconstitution of immunocompetence in these chimeras. Lymphocytes from the peptide-treated haploidentical chimeric mice also displayed donor-specific tolerance upon stimulation in a one-way mixed lymphocyte reaction. In a 6-day colony-forming unit–granulocyte-macrophage (CFU-GM) assay to quantitate the level of hematopoietic cell engraftment in both the haploidentical and class II-disparate strain combinations, bone marrow cells from the peptide-treated mice exhibited significant increases in CFU-GM compared with the saline-treated control groups. Finally, early multiple treatments with the peptide after transplantation significantly enhanced donor chimerism in donor-presensitized recipient mice across the MHC class II barrier and proved to be significantly more effective than anti-CD4 monoclonal antibody treatment. These results indicate that the structure-based CD4-CDR3 peptide analog may represent a valuable approach to the inhibition of graft rejection after MHC-mismatched bone marrow transplantation.

Prospects of immunotherapy for rheumatoid arthritis

The main challenge in the development of new modalities for the treatment of rheumatoid arthritis is to enhance the specificity while reducing the adverse side-effects of therapeutics. Biotechnology provides a variety of reagents, such as monoclonal antibodies, recombinant cytokines, cytokine antagonists, and small peptides, with the potential to interfere with selected stages of the disease process in a highly specific manner. In addition, several new therapeutic approaches have emerged as a result of extensive research with animal models of disease, including T-cell vaccination and bone marrow transplantation. This article discusses current insights into the pathogenesis of rheumatic diseases, focusing on rheumatoid arthritis. A number of new therapeutic modalities for rheumatoid arthritis, in particular those acting on the immune system, are discussed. Because it is not possible to provide a complete overview of all the developments in the field in limited space, a selection of strategies and modalities which are representative of the broad variety of immunotherapeutic approaches currently used are highlighted.

Innovative treatment approaches for rheumatoid arthritis. T-cell regulation

There is considerable evidence to implicate T cells in the pathogenesis of rheumatoid arthritis (RA). They initiate and sustain inflammation and therefore are attractive targets for immunotherapy. Several strategies targeting T cells have been tried in RA. The use of monoclonal antibodies to deplete T cells have been used extensively but with little success. Studies have shown that T cell depleting antibodies produce profound peripheral blood lymphopenia but they are less effective in depleting lymphocytes in the joint. Since clinical efficacy is likely to depend on depleting almost all synovial lymphocytes, high doses of monoclonal antibodies would have to be given. However, the invariably severe peripheral blood lymphopenia induced by such a regimen is likely to result in profound immunosuppression. Therefore, this strategy has been abandoned and recent attempts have been made to induce tolerance in RA. In animal models of RA, treatment with high dose non-depleting anti-CD4 monoclonal antibody protects them from arthritis induced by injection of streptococcal cell wall. In addition, it leads to a state of anergy which protects the animals from arthritis induction without further treatment with anti-CD4 monoclonal antibody. This is currently being used in clinical trials of RA. Other tolerance inducing treatment strategies include T cell or T cell receptor vaccination and oral tolerance. The former is particularly difficult since the rheumatoid arthritogenic antigen and the pathogenic T cell remain unknown. The latter has shown promise in placebo controlled trials although the ideal dosage remains unknown. The mechanism of action of oral tolerance involves either immunosuppressive T cell cytokines, T cell anergy or depletion.

New agents for scintigraphy in rheumatoid arthritis

Radiopharmaceuticals have been used as investigative tools for the detection and treatment of arthritis activity in rheumatoid arthritis (RA) since the 1950s. Against the background of the pathophysiology of RA, the current status of joint scintigraphy and possible future developments are reviewed. Both non-specific (radiolabelled leucocytes and technetium-99m labelled human immunoglobulin) and specific targeting radiopharmaceuticals (including radiolabelled antibodies) are considered. The use of radiopharmaceuticals in the detection of arthritis activity has the advantages of allowing direct imaging of joints by means of whole-body scintigraphy and of joints that are difficult to assess clinically or radiographically. Promising results have been obtained with radiolabelled anti-CD4 and anti-E-selectin antibodies and with somatostatin receptor imaging, but more data are available regarding 99mTc-IgG scintigraphy, which differentiates between the various degrees of arthritis activity and thus facilitates the choice of antirheumatic drug. Newer promising approaches to the imaging of RA include the use of radiolabelled J001 and cytokines, though studies on these are limited at present.

Double-blind, placebo-controlled multicenter trial using chimeric monoclonal anti-CD4 antibody, cM-T412, in rheumatoid arthritis patients receiving concomitant methotrexate

OBJECTIVE

To evaluate the clinical response to and safety of single and repeat doses of a chimeric anti-CD4 monoclonal antibody, cM-T412, in patients with rheumatoid arthritis (RA) concomitantly treated with a stable regimen of low-dose methotrexate.

METHODS

Sixty-four patients with refractory RA, who were already receiving stable doses of methotrexate, were randomized into a multicenter, double-blind, placebo-controlled trial to receive 3 monthly treatments with either a placebo, or 5, 10, or 50 mg cM-T412, given intravenously.

RESULTS

Using > or = 50% improvement in swollen joint counts as a criterion for clinical response, 13%, 13%, 18%, and 13% of patients receiving 50, 10, or 5 mg cM-T412, or the placebo, respectively, exhibited a clinical response at 3 months of therapy. Using > or = 50% improvement in tender joint counts as a measure of clinical efficacy at 3 months, 19%, 13%, 12%, and 6% of patients receiving 50, 10, or 5 mg cM-T412, or the placebo, respectively, exhibited a clinical response. "Flu-like" symptoms (fever, chills, rigor) within 24 hours of the infusion occurred more frequently in the groups receiving 50-mg (29%) and 10-mg (31%) doses of cM-T412 than those receiving 5 mg cM-T412 (12%) or the placebo (13%). Significant CD4+ T cell depletion occurred in the 50-mg group (mean of 353 CD4+ T cells/mm3 at 6 months versus 856 CD4+ T cells/mm3 at baseline). All patients were followed up for 12 months after the final treatment; no opportunistic infectious complications occurred.

CONCLUSION

Treatment with cM-T412 in this cohort of RA patients who were also taking methotrexate was not associated with clinical efficacy or enhanced toxicity from infectious complications, despite significant peripheral CD4+ T cell depletion.

Treatment of refractory juvenile chronic arthritis by monoclonal CD4 antibodies: a pilot study in two children

OBJECTIVE--To study the effect of anti-CD4 treatment in patients suffering from refractory systemic onset juvenile chronic arthritis (JCA). METHODS--Two children were treated with the mouse CD4 antibody MAX.16H5. The effects on numbers of circulating CD4 T cells, clinical symptoms and C reactive protein (CRP) level were studied and the appearance of human antimouse immunoglobulin antibodies investigated. RESULTS--In patient one, disappearance of fever and malaise and a reduction of arthritic activity were observed together with a reduction in CRP. When disease activity returned eight weeks later, a second successful course of treatment was administered. It was possible to reduce the corticosteroid dosage permanently. In the other child, a first treatment cycle did not alter disease activity. A marked reduction in clinical and laboratory disease activity markers was observed after the second course. Only transient and mild side effects were observed. One patient exhibited a short lasting febrile reaction with chills, the other an urticarial rash. In both patients, human antibodies to mouse immunoglobulin became detectable. The decrease in the number of CD4 T cells in the peripheral blood was only short lasting and numbers returned to normal values within one to eight weeks, even after the second course of antibody treatment and under concomitant immunosuppressive treatment. No sustained clinical remissions could be achieved. CONCLUSIONS--These preliminary observations support the evidence of positive effects of CD4 antibody treatment in refractory systemic onset JCA. Long term efficacy, however, remains to be established.

Will immunogenicity limit the use, efficacy, and future development of therapeutic monoclonal antibodies?

While monoclonal antibodies show promise for use in the treatment of a variety of disease states, including cancer, autoimmune disease, and allograft rejection, generation of anti-antibody responses still remains a problem. For example, 50% of the patients who receive OKT3 produce blocking antibodies that interfere with its binding to T cells, thus decreasing the therapeutic effect (51). HAMA responses have also interfered with tumor imaging (39,40) and radioimmunotherapy (56). The generation of an anti-antibody response is dependent on many factors. These include the dose of antibody, the number of injections of antibody, the immunogenicity of the antibody, the form of the antibody, and the immunocompetence of the recipient. Predictably, both the number of injections of antibody and the dosage are influential in the generation of an anti-antibody response. It is apparent that human antibodies, chimeric antibodies, and mouse Fab fragments are much less likely to induce anti-antibody responses than intact mouse monoclonal antibodies or mouse F(ab')2 fragments when one injection is administered. Injections of human or chimeric antibodies appears to reduce immunogenicity, but the probability that anti-antibody responses can still be induced on multiple injections must be considered and appropriately evaluated. Several areas demand extensive investigation to enhance the clinical utility of monoclonal antibodies. First, results of thorough clinical trials with human or chimeric antibodies need to be evaluated for the induction of anti-antibodies after multiple injections of antibodies. Second, less immunogenic forms of antibodies (Fab, Fv) need to be studied for their clinical efficacies and for their abilities to induce anti-antibody responses.

Chimaeric anti-CD4 monoclonal antibody cross-linked by monocyte Fc gamma receptor mediates apoptosis of human CD4 lymphocytes

Previous studies have shown that murine anti-CD4 monoclonal antibody, cross-linked by rabbit anti-mouse immunoglobulin, could mediate apoptosis of murine CD4+ lymphocytes when they were stimulated by T cell receptor antibody. In this study, we have shown that the murine anti-CD4 monoclonal antibody, OKT4, can induce apoptosis in human CD4+ T cells stimulated by the recall antigen tuberculin purified protein derivative (PPD) only when cross-linked by rabbit anti-mouse immunoglobulin. The chimeric anti-CD4 monoclonal antibody, cM-T412 whose Fc fragment is human, was able to cause apoptosis without cross-linking by a second antibody. Similarly, abolition of PPD-induced proliferation of peripheral blood mononuclear cells by cM-T412 did not require cross-linking with rabbit anti-human immunoglobulin. Inhibition of proliferation by cM-T412 could be reduced by pre-treating monocytes with heat-aggregated human IgG. This suggested that monocyte Fc gamma receptors might be cross-linking the human Fc of cM-T412. Propidium iodide staining together with immunofluorescence showed that the apoptotic cells were indeed CD4+ lymphocytes. It is proposed that during treatment with cM-T412 in autoimmune disease such as rheumatoid arthritis, cM-T412-coated CD4 T cells, when they are subsequently stimulated by the unknown arthritogenic antigen, may undergo apoptotic cell death through cross-linking of cM-T412 on Fc gamma receptor-positive cells within the joint.

Effects of administration of an anti-CD5 plus immunoconjugate in rheumatoid arthritis. Results of two phase II studies. The CD5 Plus Rheumatoid Arthritis Investigators Group

OBJECTIVE

To evaluate the safety and activity of an immunoconjugate of ricin A chain and anti-CD5 monoclonal antibody (anti-CD5 IC), with and without concomitant methotrexate and/or azathioprine, in the treatment of rheumatoid arthritis (RA).

METHODS

Seventy-nine patients with active RA were enrolled in 2 prospective open-label protocols.

RESULTS

Using composite criteria, response rates were 50-68% at 1 month and 22-25% at 6 months. Transient depletion of CD3/CD5 T cells was observed on days 2 and 5 of treatment, with reconstitution on day 15 or day 29. Treatment-associated adverse effects were common but resolved rapidly without sequelae.

CONCLUSION

These findings suggest activity of anti-CD5 IC in active RA and warrant confirmation in a multicenter randomized study (currently underway).

Use of a chimeric monoclonal anti-CD4 antibody in patients with refractory rheumatoid arthritis

OBJECTIVES

To evaluate the safety, immunogenicity, and biologic effects of chimeric monoclonal anti-CD4 (cM-T412) in patients with refractory rheumatoid arthritis (RA), and to obtain preliminary data on the clinical response to this treatment.

METHODS

Twenty-five patients with active refractory RA were treated with incremental doses (10 to 700 mg) of cM-T412 in an open-label, escalating-dose phase I trial.

RESULTS

Infusion with cM-T412 was followed by an immediate, rapid decline in CD4+ T cells. The level of circulating CD4+ T cells remained depressed in most patients even at 6 months posttreatment. Following antibody infusion, proliferative responses of peripheral blood lymphocytes to mitogens and antigens were determined; mitogen and antigen responses were decreased compared with pretreatment responses. Mitogen responses tended to return to baseline values more rapidly than did responses to antigen. Adverse events included fever (19 patients), which was associated with myalgias, malaise, and asymptomatic hypotension; these symptoms were self-limited and appeared to correlate with transient elevations in interleukin-6. No significant human antibody response to the cM-T412 variable region was detected; only 2 patients developed transiently low levels of antibodies reactive with cM-T412. Significant clinical improvement, defined as > or = 50% decrease in tender joint counts compared with baseline, was noted in 43% of patients at 5 weeks and 33% at 6 months following cM-T412 infusion.

CONCLUSIONS

Treatment of refractory RA with cM-T412 appears to be safe and is associated with sustained decreases in circulating CD4+ T cell counts and depressed in vitro T cell responses. No significant human antichimeric antibody response was detected. Nonblinded assessment of clinical end points suggests that treatment with cM-T412 may have beneficial effects in these patients with refractory RA. A double-blind clinical trial is warranted to determine its clinical efficacy in treating RA.

Management of early inflammatory arthritis. Intervention with immunomodulatory agents: monoclonal antibody therapy

Over the last three years there has been a dramatic rise in the number of trials using monoclonal antibodies in the treatment of rheumatoid arthritis. So far, the numbers of patients treated in the individual studies have been small, and the study designs not comparable. All these trials have been conducted in a non-blinded, uncontrolled fashion. The patient populations tended to represent the severe end of the disease spectrum, being usually individuals for whom all other conventional and sometimes even unconventional experimental therapeutic approaches have failed. Clearly, therefore, larger controlled double blind studies in patients with less advanced stages of rheumatoid arthritis are needed. In the trials thus far, long-standing diseases afflicting the joints, usually with severe destruction, have frequently made clinical evaluation very difficult. Moreover, apparently with the exception of one or two reagents (16H5 and possibly B-F5) routine laboratory parameters which are helpful in determining disease activity such as CRP or the rheumatoid factor usually remain unaltered with anti-T cell therapy. In addition, in some individuals there was no clinical improvement despite sometimes severe CD4 cell depletion. The notion that the mere depletion of CD4+ cells is not sufficient to permanently suppress disease activity in autoimmune disease is further supported by studies carried out by Conolly and Wofsy in 1990. In a mouse lupus model, these investigators demonstrated that a small subpopulation of CD4+ T cells may be refractory to depletion by anti-CD4 and may be able to promote the full expression of the disease. Similar mechanisms could apply to certain individuals with human autoimmune disorders. Many additional questions remain open. The most important of these is which markers identify clinical responders to therapy. Attempts to correlate clinical response to the level of T cell depletion, modulation of the target antigens or in vitro functional assays so far have not yielded significant results. Other questions relate to the frequency of antibody administration and the amounts needed to permanently suppress disease activity. The initial hope based on animal experiments of inducing a permanent tolerance to certain antigens by anti-CD4 treatment has been clearly shown not to apply to rheumatoid arthritis. Even though there are individual variations, the efficacy of anti-T cell treatment tends to wear off after 3 or even 1 month, necessitating retreatment. Protocols will have to be designed for either longer treatment periods, repeated courses or more frequent single administrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of antibody responses in rats to murine anti-CD4 monoclonal antibodies by conjugates with monomethoxypolyethylene glycol

The effectiveness of therapeutically relevant xenogeneic monoclonal antibodies (MoAb) may be counteracted by their inherent immunogenicity. Since conjugates of diverse proteins with mono-methoxypolyethylene glycol (mPEG) were shown to induce Ag-specific tolerance in mice and rats, we used outbred rats in this study as an experimental model for establishing the tolerogenicity of mPEG conjugates of murine MoAb. The results demonstrate that: (i) murine anti-rat CD4 MoAb (W3/25) were more immunogenic than murine anti-human CD4 MoAb (MAX.16H5) in rats; (ii) W3/25 preferentially induced an anti-idiotypic (anti-id) antibody response; and (iii) antibodies to both common and idiotypic determinants could be suppressed in rats by treatment with W3/25(mPEG)28.

[Human anti-murine immunoglobulin antibodies as disturbing factors in TSH determination]

Monoclonal murine antibodies are increasingly used for immunotherapy and in vivo diagnostic procedures such as immunoscintigraphy. The therapeutic or diagnostic reagent however, is a foreign antigen, which may induce host reactivity. This may interfere with the therapeutic or diagnostic reagent in vivo, resulting in a loss of efficacy or the necessity to increase dosages. In addition, there is an important interference to in vitro immunoassays detecting specific antigens utilizing murine monoclonal antibodies. In the present study, sera of patients who had undergone a therapeutic trial using 140 mg of an anti-CD4 antibody, were investigated. Human anti-murine-immunoglobulin-antibodies (HAMA) were detected 2-3 weeks after treatment was started and reached maximal amounts of 0.8 micrograms/ml after a single and 2 micrograms/ml after a repeated treatment course. Parallely raised values of TSH were found in sera containing HAMAs of more than 0.3 micrograms/ml. Elevations of TSH levels up to 13 microU/ml were most pronounced after a repeated trial of the murine antibody and were detectable up to 20 weeks.