ADCC lysis of human erythrocytes sensitized with rhesus alloantibodies. IV. Characterization of anti-D sera which are inactive in ADCC

Functional assessment of therapeutic anti-D immunoglobulin using Fc-mediated assays

Therapeutic anti-D immunoglobulin preparations issued by the Scottish National Blood Transfusion Service, between 1980 and 1986, were evaluated using in-vitro Fc-mediated functional tests that reflect potential in-vivo mechanisms of specific red cell destruction and clearance. All batches tested were found to: (a) contain anti-D of mainly IgG1 subclass and lesser amounts of IgG3; (b) mediate lymphocyte and monocyte rosetting; and (c) produce lytic activity in both K cell and monocyte ADCC. The functional activity of the therapeutic immunoglobulin preparations over this period of production had not altered despite increased plasma contributions latterly to the pool from deliberately immunized male donors. This is the first in-vitro study of the Fc-mediated function of therapeutic polyclonal anti-D preparations. As these preparations were clinically effective in the prophylactic anti-D programme, such bioassays of FcRI/II and FcRIII activity are justified for the future evaluation of immune plasma before blending for fractionation and production of therapeutic anti-D immunoglobulin.

Production and use of human monoclonal anti-D antibodies

Rhesus haemolytic disease of the newborn is a condition which can result in intrauterine or perinatal death. Although the passive administration of therapeutic anti-D post-partum is a most effective method for the prevention of this condition, there is currently a shortage of immune plasma for the preparation of the therapeutic anti-D immunoglobulin product. In addition the availability of anti-D for use in blood grouping has also been reduced. The advances made in recent years in the techniques for the production of human monoclonal antibodies raise the possibility that human monoclonal anti-D-based products may provide solutions to both of these problems. There are now a number of reports of the production of stable cell lines secreting high titre human anti-D. In this review we consider the various strategies used in the production of human monoclonal anti-D-secreting cell lines, the basic properties of these reagents and their potential usefulness in blood grouping, in therapy and as research tools.

Immunogenic and antigenic epitopes of immunoglobulins binding of human monoclonal anti-D antibodies to FcRI on the monocyte-like U937 cell line

Seventeen human monoclonal IgG1- or IgG3 anti-D-secreting clones have been examined for their ability to sensitise O+ red cells for Fc-receptor-mediated rosette formation with U937 cells. IgG3 but not IgG1 anti-D antibodies were able to mediate stable rosette formation with unstimulated U937 cells via interaction with the FcRI receptor. Decreasing FcRI density by incubating U937 cells with di-butyryl cAMP almost completely abolished rosette formation, whilst increasing FcRI density by incubating U937 cells with interferon-gamma increased the percentage of cells forming rosettes with IgG3- and IgG1-sensitised red cells. These data suggest that rosette formation between IgG anti-D-sensitised red cells and FcRI-expressing cells is dependent upon the density of IgG3 on the red cell surface, the density of FcRI on the effector cell, multiple FcRI/IgG interactions are required for stable rosette formation and that more FcRI/IgG1 than FcRI/IgG3 interactions are required.

Heterogeneity of IgG1 monoclonal anti-Rh(D): an investigation using ADCC and macrophage binding assays

Three monoclonal IgG1 anti-Rh(D), UCH D4, ARC 7D5 and UKTS FC3, produced by Epstein-Barr virus transformed cells from Rh(D)-sensitized individuals, were compared with polyclonal single donor anti-D sera and therapeutic immunoglobulin preparations in antibody dependent cellular cytotoxicity (ADCC) and macrophage binding tests. When assayed at equal anti-D concentrations monoclonal antibodies varied considerably in their ADCC and macrophage binding activities: only UKTS FC3 showed significant activity in both assays, but these were substantially lower than those of the polyclonal anti-D sera and immunoglobulins. When examined in different combinations the monoclonal antibodies showed little synergism in mediating red cell destruction by the effector cells. Factors which might contribute to the diverse ADCC and macrophage binding activities of the monoclonal anti-Ds of the same IgG subclass are discussed.