Functional comparisons of different tumour necrosis factor receptor/IgG fusion proteins

Nine different IgG fusion proteins and one non-fusion protein, all containing sequences from the extracellular domain of either of two human TNF receptors, were compared for their ability to bind and inhibit human TNF-alpha or TNF-beta. The fusion proteins differed with respect to TNF receptor type (p55 or p75 TNF receptor), receptor valency (one, two or four receptor domains per molecule), the presence or absence of a CH1 domain in the IgG constant region, and the proportion of the extracellular domain included in the construct. In vitro TNF binding assays and cytotoxicity assays indicated that, of the constructs that bound TNF, the greatest difference in affinity and neutralizing capability was between monovalent and bivalent receptor constructs. Differences were also noted between tetravalent and bivalent versions of p55 fusion proteins, as well as between a p75 fusion protein comprising the complete extracellular domain and one lacking the C-terminal 53 amino acids of the extracellular domain. p55 constructs that included only the second cysteine-rich domain (CRD) or only the second and third CRDs showed no TNF binding activity. The presence or absence of an IgG CH1 domain made no difference in the ability of fusion proteins to neutralize TNF-alpha or TNF-beta. Animal experiments comparing the tetravalent and bivalent p55 fusions and the effects of the CH1 domain did not show significant differences in their ability to protect mice from endotoxin-induced lethality, although the p55 fusion proteins appeared to be more protective than the p75 fusion proteins. Thus, this study has identified structural modifications to TNF receptor/IgG fusion proteins which have differing effects on their neutralizing ability towards TNF-alpha or TNF-beta.

Lipopolysaccharide (LPS) neutralizing peptides reveal a lipid A binding site of LPS binding protein

Endotoxic shock follows a cascade of events initiated by release of lipopolysaccharide during infection with Gram-negative organisms. Two overlapping 15-mer peptides were identified, corresponding to residues 91-108 of human lipopolysaccharide binding protein that specifically bound the lipid A moiety of lipopolysaccharide with high affinity. The peptides inhibited binding of lipopolysaccharide to lipopolysaccharide binding protein, inhibited the chromogenic Limulus amebocyte lysate reaction, and blocked release of tumor necrosis factor alpha following lipopolysaccharide challenge both in vitro and in vivo. These results suggest lipopolysaccharide binding protein residues 91-108 form at least part of the lipopolysaccharide binding site. Moreover, derivatives of lipopolysaccharide binding protein residues 91-108 might modulate lipopolysaccharide toxicity in the clinical setting.

A chimeric IgG4 monoclonal antibody directed against CD18 reduces infarct size in a primate model of myocardial ischemia and reperfusion

OBJECTIVES

This study attempted to determine whether neutrophil sequestration in reperfused myocardium can be inhibited and infarct size reduced by treatment with a chimeric, monoclonal IgG4 antibody (CLB54) directed against CD18 in a primate model of acute myocardial ischemia and reperfusion.

BACKGROUND

Reperfusion injury, in part mediated by neutrophils, may limit the potential benefit of reestablishing infarct-related artery patency in patients with acute myocardial infarction.

METHODS

Nineteen closed-chest baboons (10 control, 9 treated with CLB54) had the left anterior descending coronary artery occluded for 90 min, followed by 4 h of reflow. CLB54 (mean [+/- SD] 11 +/- 2 mg/kg body weight) or saline solution was administered intravenously 20 min before reflow. Coronary flow was determined using radiolabeled microspheres, infarct size by triphenyltetrazolium chloride staining, global and regional ventricular function by contrast ventriculography and neutrophil accumulation by a myeloperoxidase assay.

RESULTS

Risk region size was the same in both groups. CLB54 treatment reduced infarct size expressed as a percent of the risk region from 41 +/- 20% in the saline-treated group to 19 +/- 17% in the CLB54-treated group (p < 0.02). This was associated with diminished myeloperoxidase activity and greater postreperfusion coronary flow in the risk region in CLB54-treated than in control baboons. Ejection fraction declined to the same extent in both groups, whereas anterior wall regional cord shortening was better preserved in CLB54-treated baboons.

CONCLUSIONS

Inhibition of neutrophil sequestration with CLB54 administered before reperfusion reduces infarct size, preserves ischemic zone microvascular perfusion and minimizes the decline of regional wall motion.

Imaging of Pneumocystis carinii pneumonia with 111In-labelled non-specific polyclonal IgG: an experimental study in rats

The relative sensitivity of imaging with 67Ga-citrate (67Ga) and non-specific human polyclonal IgG radiolabelled with 111In (111In-IgG) for the detection of Pneumocystis carinii pneumonia (PCP) was determined in rats. Pneumocystis carinii pneumonia was induced by low protein diet and dexamethasone. The course of the disease was monitored by serial imaging with 111In-IgG and 67Ga. Diffuse accumulation of both radiopharmaceuticals was observed in the lungs of infected animals (infection was verified by histological examination of the lungs), however, accumulation of 111In-IgG was consistently higher. In rats with early PCP, 111In-IgG imaging revealed pulmonary accumulation in animals with normal chest radiographs and 67Ga scans. In animals successfully treated for PCP, decreased pulmonary accumulation of 111In-IgG coincided with histological improvements. Several animals developed superinfection with bacteria or fungi. These animals had striking focal accumulation of 111In-IgG, in addition to the pattern of generalized uptake. Gallium concentration in these animals did not show this focal accumulation. These observations suggest that 111In-IgG may be useful for detecting PCP and pulmonary abscesses in the immunocompromised host.

Localization of Fc and Fab fragments of nonspecific polyclonal IgG at focal sites of inflammation

Intact IgG, Fc, Fab, and 1/2Fc (reduced and alkylated Fc) were coupled to DTPA, labeled with indium-111 and administered to rats to compare the ability of fragments of IgG to localize at focal sites of inflammation. Two sets of experiments were performed: First, 1, 6, 24, and 48 hr after injection, biodistribution was determined in healthy animals; second, localization at sites of inflammation was determined by scintillation camera imaging of animals with deep-thigh infection due to Escherichia coli. The biodistribution studies demonstrated differences in kidney and liver localization: IgG less than Fc less than Fab less than 1/2Fc (kidney), Fc less than 1/2Fc less than IgG less than Fab (liver). The imaging studies revealed that target-to-background ratio (T/B) and percent residual activity (%RA) for IgG was significantly greater (p less than 0.01) than 1/2 Fc or Fab, and T/B for IgG was greater (p less than 0.01) than Fc. These studies suggest that the Fc portion of IgG is the fragment with the best imaging properties.

Detection of acute inflammation with 111In-labeled nonspecific polyclonal IgG

The detection of focal sites of inflammation is an integral part of the clinical evaluation of the febrile patient. When anatomically distinct abscesses are present, lesion detection can be accomplished by standard radiographic techniques, particularly in patients with normal anatomy. At the phlegmon stage, however, and in patients who have undergone surgery, these techniques are considerably less effective. While radionuclide methods, such as Gallium-67 (67Ga)-citrate and Indium-111 (111In)-labeled WBCs have been relatively successful for the detection of early inflammation, neither approach is ideal. In the course of studies addressing the use of specific organism-directed antibodies for imaging experimental infections in animals, we observed that nonspecific polyclonal immunoglobulin G (IgG) localized as well as specific antibodies. Preliminary experiments suggested that the Fc portion of IgG is necessary for effective inflammation localization. Since polyclonal IgG in gram quantities has been safely used for therapy in patients with immune deficiency states, we decided to test whether milligram quantities of radiolabeled IgG could image focal sites of inflammation in humans. Thus far, we have studied a series of 84 patients with suspected lesions in the abdomen, pelvis, vascular grafts, lungs, or bones/joints. In 48 of 52 patients with focal lesions detected by surgery, computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound (US), the IgG scan correctly localized the site, while 31 patients without focal inflammation had no abnormal focal localization of the radiopharmaceutical. Four patients had false negative scans and one patient had a false positive scan. For this small series, the overall sensitivity and specificity were 92% and 95%, respectively. In this report, we review our experience with this exciting new agent.

Specific and nonspecific imaging of localized Fisher immunotype 1 Pseudomonas aeruginosa infection with radiolabeled monoclonal antibody

To determine if radiolabeled specific antibodies directed against bacterial antigens could be used to detect sites of infection, gamma camera imaging studies were performed in animals infected with Pseudomonas aeruginosa. Murine monoclonal antibodies (Mabs) directed against Fisher Immunotype 1 Pseudomonas aeruginosa and a nonmicrobial, nonmammalian haptene, p-arsanilic acid, were labeled with 125I by the lodogen-Bead method. Unilateral, deep thigh infections were created by innoculation with 2 X 10(8) Fisher Immunotype 1 P. aeruginosa. Twenty-four hours later, one of the radiolabeled antibodies was injected intravenously at a dose of 0.25 mg/kg (100-150 microCi). Serial gamma imaging was then carried out beginning at 4 hr and at approximately 24-hr intervals thereafter. Beginning as early as 4 hr postinjection, the area of inflammation could be visualized with either the specific or nonspecific Mab, with the images continuing to intensify until 24-48 hr postinjection. At 48 hr, the contrast between lesion and background with the nonspecific Mab began to fade, while the contrast in the specific Mab-generated images continued to intensify until approximately 192 hr postinjection. Clear-cut differentiation between specific and nonspecific Mab-generated images was possible by 72 hr postinjection. We conclude that specific immune imaging of localized infection with Mab's directed against specific microbial antigens is possible and should be clinically useful. In addition, images created by the localization of immunoglobulin non-specifically at the site of inflammation in the first 24-48 hr postinjection may also provide useful information as to the anatomic location of hidden abscesses.