A humanized anti-CD3 antibody, HuM291, with low mitogenic activity, mediates complete and reversible T-cell depletion in chimpanzees

Pyoderma Gangrenosum: An Updated Literature Review on Established and Emerging Pharmacological Treatments

Pyoderma gangrenosum is a rare inflammatory skin disease classified within the group of neutrophilic dermatoses and clinically characterized by painful, rapidly evolving cutaneous ulcers with undermined, irregular, erythematous-violaceous edges. Pyoderma gangrenosum pathogenesis is complex and involves a profound dysregulation of components of both innate and adaptive immunity in genetically predisposed individuals, with the follicular unit increasingly recognized as the putative initial target. T helper 17/T helper 1-skewed inflammation and exaggerated inflammasome activation lead to a dysregulated neutrophil-dominant milieu with high levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-1α, IL-8, IL-12, IL-15, IL-17, IL-23, and IL-36. Low-evidence studies and a lack of validated diagnostic and response criteria have hindered the discovery and validation of new effective treatments for pyoderma gangrenosum. We review established and emerging treatments for pyoderma gangrenosum. A therapeutic algorithm based on available evidence is also provided. For emerging treatments, we review target molecules and their role in the pathogenesis of pyoderma gangrenosum.

Formation, Clearance, Deposition, Pathogenicity, and Identification of Biopharmaceutical-related Immune Complexes

Vascular inflammation, infusion reactions, glomerulopathies, and other potentially adverse effects may be observed in laboratory animals, including monkeys, on toxicity studies of therapeutic monoclonal antibodies and recombinant human protein drugs. Histopathologic and immunohistochemical (IHC) evaluation suggests these effects may be mediated by deposition of immune complexes (ICs) containing the drug, endogenous immunoglobulin, and/or complement components in the affected tissues. ICs may be observed in glomerulus, blood vessels, synovium, lung, liver, skin, eye, choroid plexus, or other tissues or bound to neutrophils, monocytes/macrophages, or platelets. IC deposition may activate complement, kinin, and/or coagulation/fibrinolytic pathways and result in a systemic proinflammatory response. IC clearance is biphasic in humans and monkeys (first from plasma to liver and/or spleen, second from liver or spleen). IC deposition/clearance is affected by IC composition, immunomodulation, and/or complement activation. Case studies are presented from toxicity study monkeys or rats and indicate IHC-IC deposition patterns similar to those predicted by experimental studies of IC-mediated reactions to heterologous protein administration to monkeys and other species. The IHC-staining patterns are consistent with findings associated with generalized and localized IC-associated pathology in humans. However, manifestations of immunogenicity in preclinical species are generally not considered predictive to humans.

A humanised mouse model of cytokine release: comparison of CD3-specific antibody fragments

CD3-specific antibodies have shown clinical efficacy in both transplantation and autoimmunity. However, targeting CD3 in this way can lead to T-cell activation and a serious cytokine release syndrome mediated by Fcγ receptor binding. An in vivo mouse model has been developed using severe combined immunodeficient (SCID) mice to detect human T-cell depletion and cytokine release into the circulation after administration of OKT3. This system has been used to evaluate OKT3 antibody fragments lacking the entire Fc region alongside whole antibody constructs. These data clearly show that cytokine release is detected with all OKT3 antibody constructs and fragments tested and these can be ranked from highest to lowest as follows: mIgG2a>hIgG1 (Ala-Ala)>hIgG1 diFab' maleimide (DFM)>hIgG1 F(ab')₂>mIgG2a F(ab')₂>hIgG1 Fab'. Furthermore, the monovalent hIgG1 Fab' fragment gives the least cytokine release but it does not deplete human T-cells in this assay format. This suggests that T-cell activation may be playing a role in the mechanism of action of anti-CD3 antibodies and consequently the unwanted cytokine release is potentially unavoidable for this class of molecules. This model system provides a useful tool to aid in understanding and reducing the potential risks of cytokine release following antibody therapy.

Development of a human whole blood assay for prediction of cytokine release similar to anti-CD28 superagonists using multiplex cytokine and hierarchical cluster analysis

Anti-CD28 superagonist (SA) mediated cytokine release syndrome (CRS), an adverse event resulting in systemic release of cytokines, is an emergent issue in drug development. CRS is of potential concern for all monoclonal antibodies (mAbs) particularly those directed against cell surface targets on lymphocytes. Concern regarding patient safety requires development of novel methods to predict these adverse reactions. Due to the inability of animal studies to predict CRS, we have developed a whole blood in vitro screen to support First in Human studies and assess the potential for mAbs to cause anti-CD28 SA-like CRS. For this purpose we have immobilized marketed mAbs, whose potential for causing CRS and milder infusion reactions is known, on Protein A beads and used these beads to stimulate cytokine release. After culture, supernatants are harvested and frozen for later multiplex analysis of cytokines using Searchlight™ technology. We have employed hierarchicalluster analysis (HCA) to allow comparison of 12 different cytokine levels across numerous donors, treatments, and experiments. Results conclusively distinguish test mAb responses from an anti-CD28 superagonist mAb response. As part of a global analysis of preclinical data, the results of this assay can facilitate entry into First in Human clinical trials, help with selection of starting doses and may allow more rapid dose escalation using smaller cohorts.

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

Safety and immunotoxicity assessment of immunomodulatory monoclonal antibodies

Most therapeutic monoclonal antibodies (mAbs) licensed for human use or in clinical development are indicated for treatment of patients with cancer and inflammatory/autoimmune disease and as such, are designed to directly interact with the immune system. A major hurdle for the development and early clinical investigation of many of these immunomodulatory mAbs is their inherent risk for adverse immune-mediated drug reactions in humans such as infusion reactions, cytokine storms, immunosuppression and autoimmunity. A thorough understanding of the immunopharmacology of a mAb in humans and animals is required to both anticipate the clinical risk of adverse immunotoxicological events and to select a safe starting dose for first-in-human (FIH) clinical studies. This review summarizes the most common adverse immunotoxicological events occurring in humans with immunomodulatory mAbs and outlines non-clinical strategies to define their immunopharmacology and assess their immunotoxic potential, as well as reduce the risk of immunotoxicity through rational mAb design. Tests to assess the relative risk of mAb candidates for cytokine release syndrome, innate immune system (dendritic cell) activation and immunogenicity in humans are also described. The importance of selecting a relevant and sensitive toxicity species for human safety assessment in which the immunopharmacology of the mAb is similar to that expected in humans is highlighted, as is the importance of understanding the limitations of the species selected for human safety assessment and supplementation of in vivo safety assessment with appropriate in vitro human assays. A tiered approach to assess effects on immune status, immune function and risk of infection and cancer, governed by the mechanism of action and structural features of the mAb, is described. Finally, the use of immunopharmacology and immunotoxicity data in determining a minimum anticipated biologic effect Level (MABEL) and in the selection of safe human starting dose is discussed.

Prospective randomized open-label multicenter phase I/II dose escalation trial of visilizumab (HuM291) in severe steroid-refractory ulcerative colitis

BACKGROUND

Visilizumab is a humanized IgG(2) monoclonal anti-CD3 antibody. We evaluated its safety and dose response in severe intravenous steroid-refractory ulcerative colitis (UC).

METHODS

In all, 104 patients were treated. In Stage I, 73 patients were randomly assigned to receive intravenous visilizumab 5, 7.5, 10, or 12.5 microg/kg/day for 2 consecutive days. In Stage II, 33 patients received visilizumab at the optimal clinical dose (OCD) of 5 microg/kg/day for 2 days. Symptomatic response and remission were defined by the modified Truelove-Witts severity index. Clinical response and remission were defined by the Mayo score.

RESULTS

The rates of symptomatic response at day 15 in the 5, 7.5, 10, or 12.5 microg/kg dose groups were 71%, 70%, 50%, and 61%, respectively, in Stage I and in 54% in Stage II. The symptomatic remission rates were 35%, 5%, 22%, and 11% in Stage I and 18% in Stage II. The rates of clinical response at day 30 in the 5, 7.5, 10, or 12.5 microg/kg dose groups were 71%, 65%, 50%, and 67%, respectively, in Stage I and 55% in Stage II. The clinical remission rates were 6%, 5%, 0%, and 11% in Stage I and 6% in Stage II. All patients experienced adverse events. Serious adverse events included abdominal abscess, cytomegalovirus infection, atrial fibrillation, herpes zoster, and esophageal candidiasis.

CONCLUSIONS

Treatment with visilizumab induced symptomatic response and clinical response. Results with 5 microg/kg/day were similar to those observed with higher doses.

T cell targeted immunotherapy for autoimmune disease

Much emphasis has been placed on the so-called "biologics" in the treatment of immune disorders within the last few years. Here we discuss the expanding horizon of potential strategies for immunotherapies targeting T lymphocytes as key effectors and regulators of autoimmunity. We review emerging reagents in a variety of animal models and human disorders that may offer new therapeutic options in current or modified iterations.

Transient cytokine-induced liver injury following administration of the humanized anti-CD3 antibody visilizumab (HuM291) in Crohn's disease

OBJECTIVES

Monoclonal antibodies to CD3 and CD4 T-cell receptors are evolving for Crohn's disease (CD) and ulcerative colitis. Their administration is often associated with a cytokine release syndrome (CRS).

METHODS

We evaluated data from two prospective clinical trials (NCT00267709 and NCT00267722) of visilizumab (HuM291), a novel humanized anti-CD3 antibody, in 34 patients with CD who received 10 microg/kg intravenously on 2 consecutive days. Serum hepatic tests including bilirubin, alkaline phosphatase (AP), gamma-glutamyltransferase (GGT), alanine aminotransferase (ALT) and aspartate aminotransferase (AST), visilizumab concentrations, and a panel of 16 cytokines were measured pre- and postadministration of visilizumab.

RESULTS

Patients experienced CRS symptoms at a median of 45 min postinfusion. The cytokine profile was characterized by interferon-inducible protein-10 (IP-10), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma, monocyte chemotactic protein 1 (MCP-1), interleukin-8 (IL-8), interleukin-6 (IL-6), interleukin-2 (IL-2), and interleukin 1 receptor antagonist (IL-1Ra), which were elevated between 6 (IL-1Ra) and 870 (IP-10) times their baseline concentrations. TNF-alpha and IL-2 peaked at the first day 1 h post infusion, whereas all others peaked at 6 h post infusion. Eighty-six percent of patients experienced an elevation above the upper limit of normal in hepatic enzymes (GGT 73%, AST 73%, ALT 64%, and AP 42% of patients), but not bilirubin, within 6 h postinfusion.

CONCLUSIONS

Transient elevation of hepatic enzymes occurred frequently in patients with CD treated with visilizumab and was associated with CRS. CD patients could be predisposed due to an aberrant expression of adhesion molecules in the liver that promotes CRS upon engagement of the T-cell receptor and may relate to extraintestinal disease manifestations such as primary sclerosing cholangitis.

Functional characterization of N297A, a murine surrogate for low-Fc binding anti-human CD3 antibodies

Several low- or non-FcR binding anti-human CD3 monoclonal antibodies have been under investigation for the treatment of autoimmune diseases. To model the mechanism of action of these anti-human CD3 mAbs in the murine system, an Fc-modified anti-mouse CD3 antibody (N297A) was generated. N297A exhibited similar biological effects as Fc-modified anti-human CD3 antibodies including rapid, reversible reduction in peripheral leukocyte numbers, differential modulation of activated versus resting T cells, and reduced levels of induced cytokine release compared to the non-Fc-modified parent antibody. In an in vivo model of colitis induced by adoptive transfer of IL–10-deficient cells, administration of N297A significantly reduced body weight loss. As N297A shared many functional characteristics of non-FcR binding anti-human CD3 mAbs both in vitro and in vivo, it provides a means to model the mechanisms of action of Fc-modified anti-human CD3 antibodies in mouse.

Novel antibody approaches for T-cell lymphomas

T-cell lymphomas are biologically more aggressive--and less responsive than their B-cell counterparts--to conventional chemotherapy. The understanding of the normal physiology of T-cell signaling as well as the pathophysiology of T-cell neoplasia has advanced dramatically in the past decade. Thus, a number of novel cell surface therapeutic targets specific for T-cells have been identified and evaluated as potential monoclonal antibody (MoAb)-based therapeutic targets. Herein, we review a number of these cell surface targets and discuss the development and the clinical evaluation of MoAb therapies directed against these antigens.

Visilizumab induces apoptosis of mucosal T lymphocytes in ulcerative colitis through activation of caspase 3 and 8 dependent pathways

Visilizumab, a humanized low-Fc receptor binding anti-CD3 antibody, induces rapid clinical response in patients with steroid-refractory ulcerative colitis (UC). Several effective treatments in IBD have been linked to the induction of mucosal T cell apoptosis. The aim of the present study was to evaluate the effect of visilizumab on the apoptosis of lamina propria (LP) and peripheral blood (PB) lymphocytes isolated from patients with UC. Visilizumab induced dose- and time-dependent apoptosis of LP T cells isolated from non-IBD individuals, UC or CD patients. Maximal effect was seen at a concentration of 100 ng/ml and it was 33% for normal, 34% for UC and 23% for CD LP T cells following 24 h stimulation. Visilizumab induced apoptosis predominantly of CD4(+) LP T cells, whereas CD8(+) LP T cells were relatively resistant to apoptosis. Visilizumab did not induce apoptosis of PB T cells from UC patients. Visilizumab-induced apoptosis of LP T cells was dependent on caspase 3 and 8, but not caspase 9 activation and did not involve the Fas/FasL pathway. Low-Fc receptor binding Abs such as visilizumab may be highly effective for the treatment of UC through induction of apoptosis of LP T cells and rapid elimination of lesional pathogenic T cells in the gut mucosa.

Antibodies for HIV treatment and prevention: window of opportunity?

Monoclonal antibodies are routinely used as therapeutics in a number of disease settings and have thus also been explored as potential treatment for human immunodeficiency virus (HIV)-1 infection. Antibodies targeting viral antigens, and those directed to the cellular receptors, have been considered for use in prevention and therapy. For virus-targeted antibodies, attention has focused primarily on their neutralizing activity, but such antibodies also have the potential to exert antiviral effects via effector functions, such as antibody-dependent cellular cytotoxicity (ADCC), opsonization, or complement activation. Anti-cell antibodies act through occlusion or down-modulation of the viral receptors with notable impact in vivo, as recent trials have shown. This review summarizes the diverse specificities and modes of action of therapeutic antibodies against HIV-1 infection. Successes, challenges, and future opportunities of harnessing antibodies for therapy of HIV-1 infection are discussed.

Pharmacologic approaches to composite tissue allograft

This article discusses the pharmacologic approaches and the most promising new compounds for composite tissue allograft tolerance. Although some approaches rely on a combination of immunosuppressive agents that act synergistically against rejection, other strategies use immunologic manipulation, including major histocompatibility complex matching, induction of chimerism, and use of monoclonal antibodies to abrogate the immune response. There is still a need, however, to reproduce these findings in species phylogenetically closer to humans. This may be the target of future research efforts, which may overcome the challenge of limb and face transplant rejection.

Engineering of therapeutic antibodies to minimize immunogenicity and optimize function

One of the first difficulties in developing monoclonal antibody therapeutics was the recognition that human anti-mouse antibody (HAMA) response limited the administration of murine antibodies. Creative science has lead to a number of ways to counter the immunogenicity of non-human antibodies, primarily through chimeric, humanized, de-immunized, and most recently, human-sequence therapeutic antibodies. Once therapeutic antibodies of low or no immunogenicity were available, the creativity then turned to engineering both the antigen-binding domains (e.g., affinity maturation, stability) and altering the effector functions (e.g. antibody-dependent cellular cytotoxicity, complement-dependent cellular cytotoxicity, and clearance rate).

Limited role of charge matching in the interaction of human immunoglobulin A with the immunoglobulin A Fc receptor (Fc alpha RI) CD89

Human immunoglobulin A (IgA) mediates protective effector mechanisms through interaction with specific cellular Fc receptors (Fc alpha RI). Two IgA Fc interdomain loops (Leu257-Leu258 in the CH2 domain and Pro440-Phe443 in the CH3 domain) have previously been identified as critical for binding to Fc alpha RI. On the receptor, the interaction site for IgA has been localized to the EC1 domain. The essential Fc alpha RI residues involved are Tyr35, Tyr81 and Arg82, with contributions also from Arg52 and to a lesser extent from His85 and Tyr86. The basic nature of the side chains of some of the receptor residues implicated in ligand binding suggested that charge matching might play some role in the interaction. To address this possibility, we have generated five IgA1 mutants with point substitutions in acidic residues lying close to the putative interaction site and assessed their abilities to bind Fc alpha RI on human neutrophils. Mutants E254A, E254L and E437A displayed affinities for Fc alpha RI comparable to that of wild-type IgA1, while mutants D255A and D255V had only slightly reduced affinities for the receptor. Therefore, electrostatic interactions appear unlikely to play a significant role in the IgA-Fc alpha RI interaction. Moreover, the lack of effect of mutations in residues adjacent to those previously implicated in binding, reaffirms the importance of the interdomain loops in Fc alpha RI binding.

In vivo pharmacodynamic effects of Hu1D10 (remitogen), a humanized antibody reactive against a polymorphic determinant of HLA-DR expressed on B cells

The humanized monoclonal antibody Hu1D10 (Remitogen, Protein Design Labs, Fremont, CA) recognizes a polymorphic determinant of human leukocyte antigen-DR expressed on the majority of B-cell lymphomas and on normal B cells of most individuals. Hu1D10 mediates complement-mediated cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and apoptosis of 1D10 antigen (Ag)-positive B cells in vitro. The 1D10 Ag is expressed on a variety of tissues but is restricted primarily to lymphocytes, macrophages, and mesenchymal dendritic cells. The safety and pharmacology of Hu1D10 were investigated in rhesus macaques. Animals were prescreened for 1D10 Ag expression on circulating B cells. Sixteen animals received either placebo (4 Ag+ animals), 1 mg/kg Hu1D10 (4 Ag+ animals), or 10 mg/kg Hu1D10 (4 Ag+ animals and 4 Ag- animals) daily via intravenous (i.v.) bolus-injection for 5 consecutive days, and 4 Ag+ animals received 10 mg/kg Hu1D10 via 90 min i.v. infusion x 5 days. Bolus-injection of Hu1D10 resulted in type 1 hypersensitivity reactions in the majority of Ag+ animals and one death due to anaphylaxis. Slow infusion of Hu1D10 was associated with only mild hypersensitivity reactions after the first dose but not subsequent doses. In animals treated with 10 mg/kg Hu1D10 via bolus-injection, the median terminal elimination half-life of Hu1D10 was 2.6 and 8.4 days in Ag+ and Ag- animals, respectively. Administration of Hu1D10 to Ag+ animals resulted in rapid and profound depletion of circulating B cells for 7-10 days following the last dose. No B-cell depletion was observed in Ag- animals, despite slower elimination of Hu1D10. These studies demonstrate that Hu1D10 reacts with antigen-presenting cells in rhesus macaques. It can be safely administered as a slow i.v. infusion but causes severe toxicity when given as a bolus. This study provides the foundation for testing Hu1D10 for the treatment of B-cell malignancies in humans.

A humanized non-FcR-binding anti-CD3 antibody, visilizumab, for treatment of steroid-refractory acute graft-versus-host disease

Visilizumab is a humanized anti-CD3 monoclonal antibody characterized by a mutated IgG2 isotype, lack of binding to Fcgamma-receptors, and ability to induce apoptosis selectively in activated T cells. To test pharmacokinetics, safety, and immunosuppressive activity of visilizumab, 17 patients with glucocorticoid-refractory acute graft-versus-host disease (GVHD) were enrolled in a phase 1 study. Six patients were given 7 doses of visilizumab (0.25 or 1.0 mg/m(2)) on days 1, 3, 5, 7, 9, 11, and 13. Because multiple doses of 1 mg/m(2) caused delayed visilizumab accumulation and prolonged lymphopenia, the next 11 patients received a single dose of 3.0 mg/m(2) on day 1. GVHD improved in all patients; 15 were evaluable through day 42. Multiple dosing resulted in 1 of 6 complete responses (CRs) and 5 partial responses (PRs), but all 6 patients died at a median of 87 days after starting visilizumab therapy. Single dosing resulted in 6 of 9 CRs, 3 PRs, and 7 of 11 patients surviving after 260 to 490 days (median, 359 days; P =.03). There were no allergic reactions and 3 grade 1 acute infusional toxicities. Plasma Epstein-Barr virus (EBV) DNA titers more than 1000 copies/mL and posttransplant lymphoproliferative disease (PTLD) developed in 2 of the first 7 patients. Based on rising EBV DNA titers, 5 of the next 10 patients were given the B cell-specific monoclonal antibody, rituximab. EBV DNA became undetectable and no overt PTLD developed. Visilizumab is well tolerated and has activity in advanced GVHD. A phase 2 study incorporating preemptive therapy for PTLD is warranted to determine the efficacy of visilizumab in GVHD.

Down regulation of B cells by immunization with a fusion protein of a self CD20 peptide and a foreign IgG.Fc fragment

In vivo studies of mice were performed to investigate whether auto-reactive antibodies specific for self CD20 antigen on B cells could be induced by immunizing with a CD20 peptide linked to a foreign, human IgG.Fc fragment through a T cell immunologically inert linker peptide and how such an auto-reactivity, if generated, would affect the levels of B cells. The dimeric Fc fusion protein containing the extracellular 44-amino acid portion of CD20, and the CH2-CH3 domains of human gamma 1 immunoglobulin were prepared. After several subcutaneous immunizations with this CD20-Fc protein, mice produced anti-CD20 antibodies that can bind to native CD20 on normal B cells and B-lymphoma cells. In mice immunized with the CD20-Fc protein, the fraction of B cells in total peripheral blood lymphocytes decreased to about 40%, significantly lower than that of mice immunized with human IgG. In addition, antibody response towards an irrelevant bystander antigen, chicken ovalbumin, was weakened compared with that of mice immunized with human IgG. These results show that auto-reactive antibodies specific for CD20 can be induced by immunizing with an autologous CD20 peptide fused with a foreign IgG.Fc and that the auto-antibodies can partially reduce the levels of B cells and their response to other antigens.

The immunologic basis for the treatment of psoriasis with new biologic agents

Psoriasis vulgaris is the most prevalent T-cell-mediated inflammatory disease in humans. The pathogenesis of psoriasis is linked to activation of several types of leukocytes that control cellular immunity and to a T-cell-dependent inflammatory process in skin that accelerates the growth of epidermal and vascular cells in psoriasis lesions. Critical steps in immunologic activation include Langerhans cell maturation (activation), T-cell activation, differentiation and expansion of type 1 T cells, selective trafficking of activated T cells to skin, and induction of an inflammatory cytokine and chemokine cascade in skin lesions. In turn, each of these steps offers an opportunity for intervention with engineered biologic therapeutics.

HuM291(NUVION), A HUMANIZED Fc RECEPTOR-NONBINDING ANTIBODY AGAINST CD3, ANERGIZES PERIPHERAL BLOOD T CELLS AS PARTIAL AGONIST OF THE T CELL RECEPTOR1

BACKGROUND

Humanized Fc receptor (FcR)-nonbinding antibodies against CD3 are promising immunosuppressive agents that may overcome both the neutralizing response to and the cytokine release syndrome seen with conventional monoclonal antibodies against CD3. In addition, evidence from several murine models suggests that these recombinant antibodies may actively induce T cell unresponsiveness by a mechanism other than modulation of the T cell receptor (TCR) or T cell depletion. We hypothesized that FcR-nonbinding antibodies against CD3 could induce T cell unresponsiveness by acting as partial agonist ligands of the TCR and thus, inducing T cell anergy.

METHODS

To test this hypothesis, we examined the signaling and functional effects of HuM291 (Nuvion), a FcR-nonbinding humanized antibody against CD3, on primary human T cells.

RESULTS

Short exposure of human peripheral blood T lymphocytes to HuM291 caused a partial agonist type of signaling through the TCR characterized by incomplete phosphorylation of TCR zeta, failure to activate ZAP-70 and to phosphorylate LAT but activation of ERK-1/-2 and subsequent up-regulation of CD69 expression. These changes correlated with a dose-dependent induction of anergy in human, primary resting T cells, which was reversed by exogenous interleukin-2.

CONCLUSIONS

The tolerogenic properties of FcR-nonbinding monoclonal antibodies against CD3 correlate with its ability to reproduce the biochemical and functional effects of TCR partial agonist ligands. Thus, generation of engineered antibodies against CD3 with low TCR oligomerization potential may provide a clinically applicable partial agonist-based strategy for the prevention of polyclonal T cell responses.

Phase I trial of HuM291, a humanized anti-CD3 antibody, in patients receiving renal allografts from living donors

BACKGROUND

HuM291 is a humanized anti-CD3 monoclonal antibody engineered to reduce binding to Fcgamma receptors and complement fixation. HuM291 has a long serum half-life and mediated profound depletion of circulating T cells in chimpanzees; HuM291 also has significantly less mitogenic and cytokine-releasing activity than OKT3 in vitro.

METHODS

A phase I dose-escalation study was conducted in 15 end-stage renal disease patients scheduled for renal allografts from living donors. Patients received one i.v. HuM291 injection before transplantation. Five doses were tested: 0.015 microg/kg, 0.15 microg/kg, 0.0015 mg/kg, 0.0045 mg/kg, and 0.015 mg/kg. Patients were followed for adverse events, laboratory abnormalities, serum cytokine levels, pharmacokinetics, and CD2+, CD3+, CD4+, and CD8+ T cell counts.

RESULTS

HuM291 was well tolerated; most adverse events were mild to moderate in severity and included headache, nausea, chills, and fever. These occurred within the first few hours after HuM291 administration, resolved within 24 to 48 hr, and were likely related to cytokine release. In general, peak tumor necrosis factor-alpha, interferon-gamma, and interleukin-6 levels were detected 1 to 6 hr postdosing only at the three highest doses and were generally undetectable by 24-hr postdosing. Serious adverse events possibly related to HuM291 included clotting of a fistula (two patients), chemical cellulitis (one patient), and increased serum creatinine/decreased hematocrit (one patient). At doses > or = 0.0015 mg/kg (0.1 mg/70 kg), HuM291 induced rapid, marked depletion of peripheral T cells within 2 hr; duration of T cell depletion was dose dependent. At the two highest dose levels, T cells remained depleted for approximately 1 week.

CONCLUSIONS

A single HuM291 dose rapidly depleted circulating T cells in a dose-dependent manner and was associated with only mild to moderate symptoms of cytokine release.

CD4+ T-cell epitope determination using unexposed human donor peripheral blood mononuclear cells

The engineering of protein therapeutics to improve their stability, their efficacy, or to create "humanized" versions introduces changes to the amino acid sequence that are potential T-cell epitopes. Until now, there has been no available assay to detect primary T-cell responses to novel epitopes in humans. Currently available in vitro protocols for epitope determination rely on peripheral blood lymphocytes from environmentally exposed or disease-bearing donors. This severely limits the opportunity to confirm T-cell epitopes in novel proteins, because exposed donors are not available to novel or engineered proteins. Other methods for determining T-cell epitopes are either computer-modeled predictions based on potential binding to HLA molecules or the identification of peptides presented by HLA molecules removed from the surface of tumor cells or protein-pulsed antigen-presenting cells. Because HLA binding is necessary, but not sufficient, for T-cell responses, these methods must be validated by in vitro presentation assays. The authors describe a dendritic cell-based assay that identifies CD4+ T-cell epitopes in novel proteins using unexposed donors. Predicted T-cell epitopes in the protein of interest were confirmed using cells from two verified exposed donors. The major CD4+ T-cell epitope of the novel protein examined in this study associated with the expression of HLA DRb1*15. This assay reflects de novo priming in vitro, and it accurately identifies primary T-cell epitopes. This assay is a powerful tool for determining relevant immunostimulatory T-cell epitopes for all types of immunoregulatory applications.

Monoclonal antibody-based therapy of lymphoid neoplasms: what's on the horizon?

Although exciting advances in monoclonal antibody therapy have already occurred, a review of agents in earlier stages of development reveals that many new agents may be approaching the clinic in the years to come. A look at the horizon of monoclonal antibody therapy reveals the following: novel strategies for augmenting the efficacy of monoclonal antibodies with which many clinicians are already familiar; novel antibodies with activity against lymphoma cells; novel technologies for generating and humanizing monoclonal antibodies; novel types of antibody-based therapeutics; and novel uses for these agents as modulators of the host immune system or other aspects of host-tumor interaction. Research in each of these areas will be reviewed.

HuM291, a humanized anti-CD3 antibody, is immunosuppressive to T cells while exhibiting reduced mitogenicity in vitro

BACKGROUND

OKT3, a mouse monoclonal antibody (Ab) specific for the human CD3 complex on T cells, is a potent immunosuppressive agent used for the treatment of acute allograft rejection. The utility of the drug has been limited by a neutralizing anti-mouse Ab response and adverse side effects resulting from T cell activation and systemic cytokine release. T cell activation is caused by OKT3-mediated cross-linking of T cells and Fc receptor-bearing cells. Studies in the mouse model have shown that global T cell activation is not necessary for immunosuppression, as Fc receptor-nonbinding anti-CD3 Abs can suppress graft rejection in the absence of the activation effects seen with Fc receptor-binding Abs. Thus, a humanized anti-CD3 antibody with a low affinity for Fc receptors might improve immunosuppressive therapy by reducing the side effects associated with OKT3.

METHODS

We developed a mouse monoclonal Ab, M291, which competes with OKT3 for binding to T cells. Humanized, complementary-determining region-grafted versions of M291 featuring various Fc were engineered, including a previously described IgG2 mutant deficient in Fc receptor binding (HuM291).

RESULTS

Compared with OKT3 and HuM291-IgG1, HuM291 was significantly less mitogenic to T cells in vitro and induced the release of much lower levels of the cytokines tumor necrosis factor-alpha, interferon-gamma, and interleukin-10. Despite this reduction in T cell activation, HuM291 retained the ability to modulate the CD3 complex and inhibit the mixed lymphocyte reaction.

CONCLUSIONS

When evaluated in vivo, HuM291 may be an immunosuppressive agent associated with less of the acute toxicity and immunogenicity seen with OKT3 therapy.