Specific removal of anti-A and anti-B antibodies by using modified dialysis filters

Selective capture of anti-A antibodies from human blood using a novel integrated bead and hollow fiber module

Anti-A/B antibody removal from blood in the peritransplantation period facilitates ABO-incompatible transplantation and significantly increases the donor pool. We have been developing an anti-A/B immunoadsorption device (BSAF), compatible with whole blood perfusion. The BSAF is based on integrated microfiltration hollow fibers with antibody capturing beads uniformly distributed within the fiber interstitial space. In this study we fabricated BSAF prototypes, appropriately scaled down from a conceptual clinical scale device. We then, for the first time, measured the time course of anti-A capture from blood samples recirculating through the scaled down BSAF devices. We observed a significant reduction in IgM (96% ± 5%, n = 5, p < 0.001), and IgG (81% ± 18%, n = 5, p < 0.05) anti-A antibody titers within 2 h. We did not observe a significant change between the initial and final values of hematocrit, total plasma protein concentration, plasma free hemoglobin concentration, and anti-B antibody titer over five experiments. In conclusion we showed that the BSAF modules selectively removed anti-A antibodies from blood in a simple one step process, without requiring a separate plasmapheresis unit.

Specific antibody filter (SAF) binding capacity enhancement to remove anti-A antibodies

Removal of Anti-A/B antibodies prior to ABO-incompatible transplantation can prevent hyperacute organ rejection. We are developing a specific antibody filter (SAF) device to selectively remove ABO blood group antibodies from the whole blood by utilizing immunoaffinity adsorption. The device consists of ultrafiltration hollow fiber membranes with synthetic antigens specific to bind blood group antibodies immobilized on the inner lumenal walls of the fibers. The aim of this study was to evaluate the effect of antigen molecular weight and surface activation process to increase the antibody binding capacity of the fiber membrane surface. A new higher molecular weight antigen Atri-pNSA-1000 compared with Atri-pNPA-30 (A-trisaccharide (Atri) conjugated to activated polymers of Mol. wt. 1000 kDa and 30 kDa, respectively) was employed to improve accessibility of the antigen to bind antibodies. Also, a cyanogen bromide (CNBr) based surface activation method mediated by TEA in neutral pH medium was used to enhance the number of active sites for antigen binding compared to a strong basic medium of NaOH. Using a CNBr/TEA activation method and by immobilizing Atri-pNSA-1000 antigen, an antibody binding capacity (∼0.01 monoclonal anti-A IgM nmol/cm(2)) was achieved on the fiber surface. This binding capacity was sufficient to reduce monoclonal antibody titer from 1:128 to final titer below 1:4 with a surface area to volume ratio that is similar to commercial dialysis device (∼1.1 m(2) surface area for an average body blood volume of 5 L).

High molecular weight blood group A trisaccharide-polyacrylamide glycoconjugates as synthetic blood group A antigens for anti-A antibody removal devices

Specific immunoadsorption of blood group antibodies by synthetic antigens immobilized on support matrices in the peri-transplantation period provides a promising solution to hyperacute rejection risk following ABO-incompatible transplantation. In this study, we investigated binding interactions between anti-A antibodies and synthetic blood group A trisaccharide conjugated with polyacrylamide of different molecular weights (30 and 1000 kDa). The glycopolymers were equipped with biotin tags and deposited on streptavidin-coated sensor chips. The affinity and kinetics of anti-A antibodies binding to glycoconjugates were studied using surface plasmon resonance (SPR). The high molecular weight conjugate (Atri-PAA(1000)-biotin) enhanced antibody binding capacity by two to three fold compared with the low molecular weight conjugate (Atri-PAA(30)-biotin), whereas varying the carbohydrate content in Atri-PAA(1000)-biotin (20 mol % or 50 mol %) did not affect antibody binding capacity of the glycoconjugate. The obtained results suggest that immunoadsorption devices, especially hollow fiber-based antibody filters which are limited in available surface area for antigen immobilization, may greatly benefit from the new synthetic high molecular weight polyacrylamide glycoconjugates.

Monoclonal anti-A antibody removal by synthetic A antigen immobilized on specific antibody filters

Removal of blood group anti-A and anti-B antibodies can prevent hyperacute organ rejection in ABO-incompatible transplantation. We are developing an extracorporeal-specific antibody filter (SAF) as an immunoadsorption device for direct removal of ABO blood group antibodies from whole blood, without the need for plasma separation and plasma exchange. A hollow fiber-based small scale SAF (mini-SAF) device was fabricated and synthetic A antigen, Atrisaccharide (Atri) conjugated to activated polyacrylic acid, was immobilized on the fiber lumen surface. Monoclonal antibody anti-A IgM were specifically removed up to 70% of initial antibodies using mini-SAF device. The monoclonal anti-A capture experiments on mini-SAF indicated that antibody removal relative to the initial concentration is independent of inlet concentration in the beginning; however, as the surface starts saturating with bound antibodies, removal becomes dependent on inlet concentration. No significant effect of flow rate on removal rate was observed. The radial diffusion and axial convection-based mathematical model developed for unsteady state antibody removal was in good agreement with the experimental data and showed that the antibody removal rate can be maximized by increasing the antibody-binding capacity of the SAF.

The persistent elimination of B cells responding to blood group A carbohydrates by synthetic group A carbohydrates and B-1 cell differentiation blockade: novel concept in preventing antibody-mediated rejection in ABO-incompatible transplantation

We demonstrated a novel strategy for specific and persistent inhibition of antibody (Ab) production against blood group A or B carbohydrate determinants necessary for successful ABO-incompatible transplantation. Similar to human blood group O or B individuals, mice have naturally occurring Abs against human blood group A carbohydrates in their sera. B cells with receptors for A carbohydrates in mice belonging to the CD5+CD11b+B-1a subset have phenotypic properties similar to those of human B cells. These cells could be temporarily eliminated by injecting synthetic A carbohydrates (GalNAcα1–3, Fucα1–2Gal) conjugated to bovine serum albumin (A-BSA) and anti-BSA Abs. In mice that received the injection of A-BSA/anti-BSA Abs, the serum levels of anti-A IgM were reduced, but immunization with human A erythrocytes resulted in increased serum levels of anti-A Abs. When combined with cyclosporin A (CsA) treatment, which blocks B-1a cell differentiation, and treatment with A-BSA/anti-BSA Abs, the serum levels of anti-A Abs were persistently undetectable in the mice even after the immunization. B cells with receptors for A carbohydrates were markedly reduced in these mice. These results are consistent with the hypotheses that treatment with A-BSA/anti-BSA Abs temporarily depletes B cells responding to A determinants, and CsA treatment prevents the replenishment of these cells.

Synthetic blood group antigens for anti-A removal device and their interaction with monoclonal anti-A IgM

Removal of blood group antibodies against the donor organ prior to ABO-incompatible transplantation can prevent episodes of hyperacute rejection. We are developing a specific antibody filter (SAF) device consisting of immobilized synthetic Atrisaccharide antigens conjugated to polyacrylamide (Atri-PAA) to selectively remove anti-A antibodies directly from whole blood. In this study, we evaluated eight anti-A IgM monoclonal antibodies (mAbs) using Enzyme-Linked Immunosorbent Assay (ELISA) to determine their specificity for binding to Atri-PAA. Five of the eight mAbs met our criteria for specificity by binding to Atri-PAA with at least five times greater affinity compared to the negative controls. These selected mAbs will be studied for their binding characteristics to Atri-PAA which will aid in the development of the SAF. The study of kinetics of antibody removal and quantification of antibody removal will be used in our mathematical model to maximize the antibody removal rate and binding capacity of the SAF.

Potential approaches to prevent uncommon hemolytic side effects of AB0 antibodies in plasma derivatives

Since hemolytic reactions in patients after administration of plasma derivatives like immunoglobulins or coagulation factor preparations have been described, titers of anti-A and anti-B-antibodies have to be below defined levels for batch release of these plasma-derived therapeutic products according to the European Pharmacopoeia. We have summarized clinical relevance of AB0 antibodies in plasma derivatives and related legal issues in the European Union, United States of America, and Japan. We have also discussed potential approaches for the prevention of hemolytic side effects with feasible steps in preparation of plasma derivatives, viz., (1) selection of donors, (2) exclusion of "dangerous donors", (3) optimizing ratio of the types of plasma, (4) removal of antibodies, (5) production of blood-group-specific plasma derivatives, (6) rejection of batches of plasma derivatives with high titers of antibodies, and (7) crossmatching before administration. For harmonization of standards for anti-A and anti-B in plasma-derived therapeutics the regulators and manufacturers will have to realistically deal with complex clinical, practical, and economic issues.

NOD/SCID mice engrafted with human peripheral blood lymphocytes can be a model for investigating B cells responding to blood group A carbohydrate determinant

Human antibodies (Abs) against blood group A or B carbohydrate determinant are a major barrier to ABO-incompatible organ transplantation; however, the phenotype and other properties of B cell types responding to A or B carbohydrate epitopes have not been defined. Studies here, which use fluorescein-labeled synthetic A determinant (GalNAcalpha1-3Fucalpha1-2Gal), demonstrate that B cells bearing surface IgM (sIgM) receptors recognizing blood group A carbohydrate determinant are found exclusively in a small B cell subpopulation, i.e. sIgM+ CD11b+ CD5+ B1 cells, in blood group O human peripheral blood mononuclear cells (PBMC). In order to test anti-A Abs producing capacity of the human PBMC, nonobese diabetic (NOD)/severe combined immune-deficient (SCID) mice that have been treated with rabbit anti-asialo GM1 serum to deplete natural killer cells and with 3 Gy of whole body irradiation were engrafted with blood group O or A human PBMC, followed by sensitization of human blood group A red blood cells. Anti-A-specific human Abs were detected in the sera of the mice that received blood group O human PBMC, whereas they were not detected in the sera of the mice that received blood group A human PBMC, indicating profound tolerance of auto-reactive B cells. The human PBMC-NOD/SCID chimera developed by injection of blood group O human PBMC might be a useful in vivo model to test effects of immunosuppressants or other approaches on human B cells that respond to blood group A antigens.

Immunoaffinity removal of xenoreactive antibodies using modified dialysis or microfiltration membranes

Hyperacute rejection following xenogeneic transplantation in primates is mediated by naturally occurring IgM antibodies, which are specifically directed to alpha-Galactosyl residues on many nonprimate mammalian cells. Current approaches to remove these anti-alphaGal IgM include plasmapheresis followed by immunoaffinity adsorption on bead columns using synthetic Gal epitopes, which requires two pieces of complex equipment. In this study, we explored the use of immunoaffinity adsorption with hollow fiber microporous or dialysis membranes to which a synthetic alphaGal trisaccharide ligand is bound. Covalent attachment of ligand directly to the surface produced negligible binding, but use of long-chain polyamines as reactive spacers yielded binding densities for anti-alphaGal IgM as high as 89 mg/mL membrane volume in breakthrough curve experiments with microporous nylon membranes having an internal surface area of 4.2 m(2)/mL membrane volume. A crossflow microfilter fabricated from the membranes described in this study and having about 0.4 m(2) luminal surface area would be able to carry out plasma separation and immunoadsorption in a single device with a large excess of binding capacity to ensure that all plasma that filters across the device and is returned to a human patient is essentially free of anti-alphaGal IgM. We conclude that immunoaffinity removal of xenoreactive antibodies using microfiltration hollow fiber membranes is feasible and has potential advantages of efficiency and simplicity for clinical application.