Human monoclonal antibodies to glycolipid A that exhibit complement species-specific effector functions

Minireview: Therapeutic intervention in sepsis with antibody to endotoxin: is there a future?

Within the last 24 months a number of studies that tested the efficacy of immunologic reagents in the treatment of sepsis were concluded. Among these reports were 4 studies1-4completed on 2 anti-endotoxin monoclonal antibodies (MAb, HA-1A and E-5). These clinical trials did not generate data sufficient to support product licensure. Given the attention and expectations surrounding the anti-endotoxin MAbs, the disappointing results raised the question whether the use of anti-endotoxin antibodies in the treatment of sepsis was still a viable concept.5The question was rendered even more relevant given the decade-old controversy surrounding the efficacy of polyclonal antibodies to endotoxin, particularly antibody to the J5 (Rc chemotype) mutant of Escherichia coli 0111:B4, a conceptual progenitor of the HA-1A and E-5 MAbs.6In this review we shall examine whether anti-endotoxin antibodies may yet offer any therapeutic potential in the treatment of sepsis. It will be our contention that antibodies to core glycolipid will be useful adjuncts to therapy, particularly if used as part of combination immunotherapy.

Review: Bacterial endotoxin and the human monoclonal antibody HA-IA: specificity, potential mechanisms of action, and limits to its effectiveness

Bacterial endotoxins are lipopolysaccharides present in the outer membrane of all Gram-negative bacteria (GNB). Endotoxins consist of a lipid moiety, lipid A, that is covalently linked to highly variable, serotype O-specific polysaccharide lateral chains. In contrast, the endotoxin core, which includes lipid A, is better conserved and can be recognized by antibodies showing cross-reactivity among various GNB. Such polyclonal and monoclonal antibodies have been developed in an attempt to neutralize the biological and dele. terious effects of endotoxin, thus preventing lipid A from binding to macrophages. In fact, almost all the biological activities of endotoxin are elicited by lipid A, and there is substantial evidence to the effect that the monocyte-macrophage is the principal mediator of endotoxicity. Antiserum against LPS isolated from rough mutants of GNB (expressing virtually only the central core-lipid A), has been shown to counteract the lethal effects of endotoxin in animals and humans. However, such serum or plasma contains antibodies of different specificities and isotypes which represent different effector functions, insofar as LPS is a very complex and highly heterogenous macromolecule. Because of the difficulties encountered in investigating the nature and specificity of the protection afforded by these antisera, and their limited capacity of production for therapeutic use, specific anti-lipid A monoclonal antibodies have been produced in their stead. A variety of mouse and human monoclonal antibodies against LPS have been generated and selected for their ability to cross-react with many GNB species. The most recent clinical trials involving the treatment of septic patients with human HA-IA (Centoxin) or with murine (E5) anti-lipid A monoclonal antibody showed no difference in survival rates, as compared to treatment with a placebo. However, statistical significance was demonstrated in subsets of patients suffering from documented Gram-negative septicemia or Gram-negative sepsis without refractory shock. The usefulness of anti-lipid A antibodies will undoubtedly remain controversial, since they appear to benefit only a minority of all patients treated, and also because no consensus exists regarding their specificity and modes of action. The aim of this review is to describe results which demonstrate the requirements for, difficulties in and limits to, elucidating the ability of certain antibodies to recognize structural elements present in the lipid A domain of LPS. A clear demonstration of antibody cross-reactivity was obtained only when rough LPS bacteria were used, and was markedly enhanced when smooth bacteria had been pretreated with cell wall active antibiotics. Further, new data have recently demonstrated the specific involvement of HA-IA in the immunocytoadherence assay in the presence of human complement and human red blood cells. Such phenomena may form part of the potential role for natural or monoclonal human IgM anti-lipid A antibodies, which will be to remove IgM-lipid A immune complexes through transhepatic clearance via C3b binding to the CR1 present on circulating human erythrocytes. Insofar as immunocytoadherence is a multiparameter phenomenon, various limiting factors probably interfere with its mechanism of clearance. These factors may be absent in various subsets of septic patients under treatment, thus explaining therapeutic failures with HA-IA in humans or preclinical animal studies. Several clinical settings involving defects to CR1 expression, C3b production, LPS recognition and hepatic clearance dysfunction are described. Long term, however, it will impossible to specify the patient subsets suitable for monoclonal therapy without first defining their characteristics. HA-IA may be able to inhibit one of the earliest stages in activation of the cytokine cascade by sequestrating and eliminating biologically active lipid A. The major problem today in terms of using anti-lipid A antibodies is an efficiently early detection of specific pathway defects which detract from or nullify the HA-IA therapeutic effect.

Multicenter evaluation of a human monoclonal antibody to Enterobacteriaceae common antigen in patients with Gram-negative sepsis

OBJECTIVE

To evaluate in Gram-negative sepsis patients the human monoclonal immunoglobulin M antibody (MAB-T88) directed at the enterobacterial common antigen which is a specific surface antigen closely linked to lipopolysaccharide and shared by all members of the Enterobacteriaceae family of Gram-negative bacteria.

DESIGN

Prospective, randomized, double-blinded, placebo-controlled, multicenter trial.

SETTING

Thirty-three academic medical centers in the United States.

PATIENTS

Patients were entered with a clinical diagnosis of sepsis, the presence of either shock or multiple organ dysfunction, and presumptive evidence for Gram-negative infection.

INTERVENTIONS

Patients received a single intravenous infusion, over 30 mins, of either 300 mg of MAB-T88 formulated in albumin, or placebo (albumin).

MEASUREMENTS AND MAIN RESULTS

The primary analysis group was prospectively identified as those patients with documented evidence of an infection with bacteria of the family Enterobacteriaceae at any site. The primary end point was survival within the first 28 days. A total of 826 patients were enrolled with 55% (n = 455) in the primary analysis group. There were no significant differences between the intervention and control primary analysis group study groups for sites of infection, severity of illness, underlying medical conditions, adequacy of antibiotic or surgical treatment, or other baseline variables except for a higher frequency of chronic renal failure in the MAB-T88 group (4.4% vs. 1.3%, p=.051). The average Acute Physiology and Chronic Health Evaluation II scores were 26.8 +/- 8.6 (mean +/- sd) in the MAB-T88-treated group and 26.5 +/- 8.3 in the placebo-treated group (p =.72). There was no significant difference between MAB-T88- and placebo-treated groups during the first 28-day all-cause mortality in the primary analysis group (34.2% vs. 30.8%, p=.44) or in all 826 patients enrolled (37.0% vs. 34.0%, p=.36). On subset analysis, the use of MAB-T88 was not associated with significant mortality trends. More adverse events were seen with the use of MAB-T88 in the bacteremic enterobacterial common antigen group (p <.05).

CONCLUSIONS

Use of the human monoclonal antibody, MAB-T88, did not improve the mortality in patients with presumed Gram-negative sepsis or in those patients with proven enterobacterial common antigen infections. No subset trends were identified that would support further investigation of this agent in sepsis.

Human IgG anti-DNA antibodies deposit in kidneys and induce proteinuria in SCID mice

We investigated the capacity of five human monoclonal IgG anti-DNA antibodies derived from lupus patients to produce glomerular immune deposits. The hybridomas secreting these antibodies were administered intraperitoneally to severe combined immunodeficiency (SCID) mice. Three of the five antibodies (B3, 35.21, 33.C9) were detected in the kidneys, but only one (33.C9) deposited exclusively in the glomeruli in the mesangium and capillary wall, whereas the other two antibodies bound to nuclei both in the kidney and in other organs. The antibodies were tested against a variety of autoantigens by ELISA, the only unique feature of 33.C9 was that it also bound strongly to histones. There were no particular amino acid motif that was related to immunoglobulin deposition in the kidney. All the mice that had immunoglobulin deposited in the kidney, either extracellularly or intranuclearly developed 2 to 3+ proteinuria, whereas the other mice had only trace amounts of proteinuria. This study demonstrates that some human monoclonal IgG anti-dsDNA antibodies are capable of binding to the glomerulus while others can penetrate cells and bind to nuclei in vivo. Although no abnormal pathology was observed, proteinuria was detected, perhaps representing an early phase of disease. These results indicate that the affinity for dsDNA is not the sole determining factor governing the biological properties of human anti-DNA antibodies in vivo.

Phase I study of antilipopolysaccharide human monoclonal antibody MAB-T88

Monoclonal antibody MAB-T88 is a human monoclonal immunoglobulin M antibody directed at the lipopolysaccharide of gram-negative bacteria. In this study, nine patients who were expected to become neutropenic from antineoplastic chemotherapy received an infusion of MAB-T88, three patients at each of three doses: 1, 4, and 8 mg/kg of body weight. MAB-T88 was shown to be safe, with an effective half-life in plasma of 25.4 h, and no patient developed immunoglobulin G antibody to MAB-T88.