Primate erythrocyte (E) complement receptor (CR1) as an anchor site for bispecific-based therapies to clear pathogens or autoantibodies safely from the circulation

We have prepared cross-linked, bispecific complexes [heteropolymers (HP) and antigen-based heteropolymers (AHP)] that facilitate complement-independent binding of target model pathogens or autoantibodies to primate erythrocytes (E) via complement receptors (CR1). The method is based on using monoclonal antibodies (mAb) specific for CR1 that either are cross-linked to an mAb specific for a prototype pathogen (e.g., IgE) or are cross-linked to an autoantigen (e.g., dsDNA) that is recognized by circulating pathogenic autoantibodies in the autoimmune disease systemic lupus erythematosus (SLE). The underlying assumption in this research is that complexed ligands containing IgG bound to primate E CR1 should be recognized and processed via the same mechanism by which complement-opsonized immune complexes bound to E CR1 are cleared from the circulation and phagocytosed in the liver and spleen. Our work in experimental monkey models has demonstrated that binding of substrates to primate E via this method does indeed lead to the safe and rapid clearance of the target pathogens or autoantibodies from the circulation, without any lysis or loss of the E. Although a number of questions must still be resolved, it may be possible to generalize these findings and use this CR1-based approach to develop a simple noninvasive bispecific therapy that can be used to clear pathogens or autoantibodies from the circulation.

Antigen-based heteropolymers facilitate, via primate erythrocyte complement receptor type 1, rapid erythrocyte binding of an autoantibody and its clearance from the circulation in rhesus monkeys

We investigated the feasibility of using the primate E complement receptor (CR1), in concert with Ag-based heteropolymers (AHP), as a potential therapy to remove autoantibodies from the circulation. AHP are prepared by cross-linking an anti-CR1 mAb with the acetylcholine receptor (AChR), the principal target Ag in myasthenia gravis. In vitro studies demonstrate that this methodology facilitates specific, rapid, and quantitative binding of an anti-AChR mAb to primate Es. In vivo experiments in rhesus monkeys indicate that AHP-mediated binding of an anti-AChR mAb to Es leads to the clearance of the mAb from the circulation. Once bound to the E via the AHP, the autoantibody is transported to the liver and spleen, where it is degraded without destruction of the E. It is therefore likely that the complexes of AHP and target mAb, when bound to Es, are recognized in vivo and processed by a mechanism quite similar to that which occurs when complement-opsonized immune complexes, bound to primate Es, are cleared from the circulation. It may be possible to extend and generalize this work to allow for the development of a simple, noninvasive therapy that can be made specific for the treatment of several different autoimmune diseases.

Antigen-based heteropolymers facilitate, via primate erythrocyte complement receptor type 1, rapid erythrocyte binding of an autoantibody and its clearance from the circulation in rhesus monkeys

We investigated the feasibility of using the primate E complement receptor (CR1), in concert with Ag-based heteropolymers (AHP), as a potential therapy to remove autoantibodies from the circulation. AHP are prepared by cross-linking an anti-CR1 mAb with the acetylcholine receptor (AChR), the principal target Ag in myasthenia gravis. In vitro studies demonstrate that this methodology facilitates specific, rapid, and quantitative binding of an anti-AChR mAb to primate Es. In vivo experiments in rhesus monkeys indicate that AHP-mediated binding of an anti-AChR mAb to Es leads to the clearance of the mAb from the circulation. Once bound to the E via the AHP, the autoantibody is transported to the liver and spleen, where it is degraded without destruction of the E. It is therefore likely that the complexes of AHP and target mAb, when bound to Es, are recognized in vivo and processed by a mechanism quite similar to that which occurs when complement-opsonized immune complexes, bound to primate Es, are cleared from the circulation. It may be possible to extend and generalize this work to allow for the development of a simple, noninvasive therapy that can be made specific for the treatment of several different autoimmune diseases.

Complement-independent binding of microorganisms to primate erythrocytes in vitro by cross-linked monoclonal antibodies via complement receptor 1

Under certain circumstances, soluble antigens, particulate antigens, and/or microorganisms have been shown to bind to primate erythrocytes via complement receptor 1 (CR1) in the presence of specific antibodies and complement. This immune adherence reaction, specific for CR1, can lead to neutralization of antigens in the circulation and their subsequent clearance from the blood. The present experiments utilized cross-linked monoclonal antibody complexes (heteropolymers) with specificity for both CR1 and either 35S-labeled herpes simplex virus capsid or Haemophilus influenzae as prototype viral and bacterial particulate antigens, respectively. In each case, the respective specific heteropolymers facilitated binding of the target antigens (> or = 70 to 90%) in vitro to erythrocytes in the absence of complement. Several experimental protocols were employed to demonstrate that heteropolymers mediate specific, rapid (> or = 30 s), and quantitative binding of prototypical particulate pathogens to human and monkey erythrocytes but not to sheep erythrocytes, which lack CR1. These results extend the potential use of the erythrocyte-heteropolymer system to the neutralization and clearance of particulate viral and bacterial pathogens from the blood.

Antigen-based heteropolymers. A potential therapy for binding and clearing autoantibodies via erythrocyte CR1

OBJECTIVE

To determine if complexes containing monoclonal antibodies to CR1 cross-linked with antigen (antigen-based heteropolymers [AHP]) can bind the corresponding autoantibody to primate erythrocyte CR1 and promote autoantibody clearance from the circulation.

METHODS

AHP were constructed by cross-linking double-stranded DNA (dsDNA) to monoclonal antibodies to CR1. The ability of AHP to facilitate binding of human anti-dsDNA antibodies to primate erythrocytes was studied in vitro using a variety of radioimmunoassays (including Farr assays), enzyme immunoassays, and fluorescence-activated cell sorting. In addition, we used a monkey model to study in vivo the AHP-mediated clearance of passively infused human anti-dsDNA antibodies.

RESULTS

Large amounts of lupus IgG anti-dsDNA antibodies can be specifically bound to human erythrocytes via the complexes, and studies in 2 rhesus monkeys indicate that the erythrocyte-bound antibodies are rapidly cleared from the circulation.

CONCLUSION

This methodology may allow for development of a new therapy to facilitate autoantibody clearance in autoimmune disease.

Attachment of biotinylated antibody to red blood cells: antigen-binding capacity of immunoerythrocytes and their susceptibility to lysis by complement

A biotinylated monoclonal antibody (mAb) to human IgM (b-anti-IgM) has been attached to human red blood cells (RBC) by two different approaches. The first method is performed with biotinylated RBC (b-RBC) and involves stepwise binding of streptavidin (SA) to b-RBC followed by addition and binding of specific b-anti-IgM or b-IgG. b-RBC were prepared with differing input levels of biotin N-hydroxysuccinimide ester (BNHS). At moderate BNHS levels (100 microM) the resulting b-RBC (designated b4-RBC) bound 50,000 molecules of b-IgG after treatment with SA. However, at high BNHS levels (> 1000 microM) the resulting b-RBC bound b-IgG poorly, presumably due to multivalent binding of each SA to several biotins in close proximity on the RBC. b-RBC prepared at high BNHS inputs (but not b4-RBC) were lysed by serum plus SA. Stepwise attachment of b-anti-IgM to SA-coated b4-RBC allows binding of up to 6 x 10(4) molecules of b-anti-IgM/RBC. The second method is based on attachment of b-anti-IgM to RBC via CR1, the primate RBC complement receptor. The SA-biotin system is used to prepare bi-specific mAb complexes (heteropolymers) in which a biotinylated mAb to CR1 is cross-linked with b-anti-IgM via SA. Binding of these heteropolymers to RBC via CR1 is specific and saturable and can facilitate binding of up to 2500 molecules of b-anti-IgM/RBC.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-linked bispecific monoclonal antibody heteropolymers facilitate the clearance of human IgM from the circulation of squirrel monkeys

We have previously demonstrated that cross-linked bispecific monoclonal antibodies (mAb) heteropolymers (HP), specific for primate erythrocyte (E) complement receptor type 1 (CR1) and target antigen (Ag), facilitate the binding of these target Ag to human and non-human primate E. Once bound in vitro to rhesus monkey E, upon re-infusion these HP/Ag complexes are recognized in vivo by cells of the reticuloendothelial system (RES) and removed from the circulation without loss of the E. We now show, in squirrel monkeys, that an HP specific for E CR1 and human IgM (anti-CR1 x anti-IgM) can be used to facilitate in vivo E binding and clearance from the circulation of a previously injected and circulating model protein pathogen, human IgM. Approximately 70-80% of 125I-labeled human IgM is cleared from the circulation of each of five squirrel monkeys via the HP system. We observe, in experiments analogous to previous studies on immune complex (IC) clearance, that subsequent to HP/Ag clearance there is a decrease in the number of CR1 epitopes per E which is manifested when we use both monoclonal and polyclonal anti-CR1 probes. Our results indicate that the primary organs responsible for uptake of the complexes are the liver and spleen. This work strongly suggests that the HP/Ag complexes, bound to E, function as IC prototypes and are recognized and processed as such in vivo. Thus, the HP-E system may eventually serve as a viable immunotherapy for the clearance of blood-borne pathogens from the circulation.

Extracorporeal life support for severe pediatric respiratory failure: an updated experience 1991-1993

OBJECTIVE

The purpose of this study was to examine our recent experience with children who had acute respiratory failure managed with extracorporeal life support (ECLS) from 1991 to 1993, to determine whether a change in survival rate had occurred in comparison with our previous experience.

DESIGN

Historic and prospective cohort study.

SETTING

A tertiary pediatric referral center.

PATIENTS

All non-neonatal pediatric patients treated with ECLS for severe, life-threatening respiratory failure were examined. Overall, 25 patients have been managed with this life-support technique in the past 28 months. Eighty-four percent (21/25) were transferred to our medical center because of failure of conventional mechanical ventilation therapy. Descriptive data of the recent cohort were as follows (mean +/- SD): age 60 +/- 75 months, weight 23.6 +/- 24.8 kg, and male gender 44%. Duration of intubation before ECLS was 5.8 +/- 2.7 days. Arterial blood gas values and ventilator settings immediately before ECLS were as follows: fraction of inspired oxygen, 0.98 +/- 0.08; mean airway pressure, 21.6 +/- 6.2 cm H2O; peak inspiratory pressure, 45.5 +/- 9.6 cm H2O; positive end-expiratory pressure, 11.0 +/- 4.3 cm H2O; partial pressure of oxygen (arterial), 56 +/- 20 mm Hg (7.4 +/- 2.7 kilopascals); partial pressure of carbon dioxide (arterial), 46 +/- 17 mm Hg (6.1 +/- 2.3 kPa); and estimated alveolar-arterial oxygen tension difference, 572 +/- 81 mm Hg (76.3 +/- 10.8 kPa). Mean duration of ECLS was 373 +/- 259 hours. Of 25 recently treated patients, 22 (88%) survived their life-threatening respiratory illness to be discharged home; this represented a statistically improved survival rate in comparison with the 58% survival rate previously reported by us for similar patients (p < 0.05). Comparisons of arterial blood gas and mechanical ventilation-related variables measured 24 hours before and again immediately before bypass were similar in the two cohorts with the exception of higher mean partial pressure of carbon dioxide (arterial) 24 hours before bypass in the recent treatment group. For our entire experience, younger age groups had greater survival rates; 100% of infants less than 1 year of age survived.

CONCLUSIONS

Treatment with ECLS is an evolving pulmonary rescue therapy with an 88% survival rate in our recent experience. The survival rate has improved to levels that may not greatly improve in the near future, especially for patients less than 1 year of age. Better patient selection or improved management strategies or both may be responsible for the improved patient outcome.

The analysis of metabolites in human sweat: analytical methods and potential application to investigation of pressure ischaemia of soft tissues

A straightforward technique was developed for sweat collection applicable to tissues subjected to external load without introducing distortion of underlying tissues, and for analysis of six metabolites in the collected sweat. Chloride was measured colorimetrically and lactate, urea and urate by enzymatic methods on a centrifugal analyser. Sodium and potassium were measured by flame photometry. The methods showed good precision, recovery and linearity. To assess the technique sweat was collected: (i) from the sacrum, ischium, forearm and calf in healthy individuals at 32 degrees C for 1 h; (ii) from the sacrum of healthy subjects at ambient temperature for 9 h; (iii) at ambient temperature from the sacrum of a patient with a history of pressure sores. Sweat rates were greater at the sacrum and ischium than the calf or forearm. There were differences in the concentrations of lactate and urea between sites but these were smaller when expressed as amount secreted. Sweat rates were significantly lower in groups (ii) and (iii), but sweat could be collected reliably. This technique has potential clinical application to the investigation of susceptibility to pressure sores.

Antigens pre-bound to the primate erythrocyte complement receptor via cross-linked bispecific monoclonal antibody heteropolymers are rapidly cleared from the circulation

We have used cross-linked, bispecific monoclonal antibody heteropolymers, specific for primate erythrocyte (E) complement receptor (CR1) and target antigen (Ag), to attach 125I-labeled Ag to 51Cr-labeled monkey erythrocytes (E) in vitro. Injection of these sensitized E into monkeys leads to rapid clearance from the circulation of several different 125I-labeled Ag with little, if any sequestration, lysis, or clearance of the E. It should now be possible, in principle, to use the heteropolymer-E system to facilitate the clearance of blood-borne pathogens from the circulation.

Human IgG in immune complexes bound to human erythrocyte CR1 is recognized differently than human IgG bound to an erythrocyte surface antigen

We have developed several methods, including a new use of magnetic cell separation techniques, to examine how human IgG bound to human erythrocytes can be recognized. We find that human IgG in complement-opsonized immune complexes bound to erythrocyte CR1 is less accessible to several probes than human IgG bound to the rhesus antigen on erythrocytes. These findings suggest that the mechanism by which immune complexes are removed and cleared from erythrocyte CR1 in the circulation is different from the mechanisms which lead to splenic clearance of IgG sensitized erythrocytes.

Human anti-endotoxin antibody HA-1A mediates complement-dependent binding of Escherichia coli J5 lipopolysaccharide to complement receptor type 1 of human erythrocytes and neutrophils

HA-1A has been shown clinically to decrease mortality in septic patients with gram-negative bacteremia. In this study, the ability of HA-1A to augment the serum complement-dependent immune adherence of 125I-labeled Escherichia coli J5 lipopolysaccharide (LPS) to human erythrocytes (RBC) and polymorphonuclear leukocytes (PMNL) was evaluated. In vitro studies indicated three things: HA-1A mediates immune adherence of 125I-J5 LPS to human RBC and PMNL in a dose-dependent manner; under these conditions, high concentrations of LPS (400 ng/mL) could be specifically bound. Immune adherence occurs via the classical complement pathway as demonstrated by its calcium dependence; HA-1A-J5 LPS-C' immune complexes bound to CR1 on human RBC and PMNL. PMNL binding and internalization of immune complexes was demonstrated by trypsin stripping of externally bound immune complexes. These studies support the proposal that HA-1A can lower the bioavailability of endotoxin by mediating binding and potential clearance of LPS via human RBC through the reticuloendothelial system or via direct internalization by peripheral blood PMNL.