In vivo assays demonstrated that the anti-Id Abs pool not only neutralized polyclonal IgG purified from haemophilia A patient plasma but also protected the function of FVIII when injected

together with FVIII in a mouse ABT-263 solubility dmso previously reconstituted with anti-FVIII antibodies. Such results have been confirmed by evaluating the anti-FVIII Abs neutralization in the plasma of haemophilia patients [5 with auto-antibodies, 9 with allo-antibodies and 4 allo-antibodies previously but unsuccessfully treated by immune tolerance induction (ITI)] by the combination of the five anti-Ids (anti-anti-A2, -C1 and -C2). In 16 of 18 cases, the inhibiting FVIII activity from the plasma was neutralized up to 100% by the anti-Id Abs mixture and full FVIII activity was restored. Neutralization of circulating inhibitors is only one aspect of the therapeutic potential of anti-idiotypic Abs, of interest in emergency situations such as prior to surgery or to increase FVIII half-life upon infusion in haemophilia patients with

inhibitor. A second aspect is to evaluate whether anti-Id Abs carry the potential to modulate signaling of memory B cells bearing the corresponding antigen specific receptor (BCR for B-cell receptor). This modulation could lead to a significant alteration in the function of the memory B-cell pool, and thereby provide to induce long-term antigen-specific tolerance. High concentrations of FVIII can induce immune tolerance by interacting at Talazoparib price the BCR level [13]. Whether this could also be achieved by providing an anti-Id Ab as an alternative ligand remains to be seen to induce inactivation of FVIII-specific B cells. That memory B-cell compartment can be efficiently altered following the binding of anti-idiotypic Abs to the B-cell receptor (BCR) is strongly supported by our current knowledge of BCR-dependent B-cell activation and by experimental data. However, in contrast to the neutralization of circulating Abs, which has been amply demonstrated

in human diseases (e.g. the neutralization many of IgE Abs by administration of anti-IgE Abs in allergy), no direct evidence of memory B-cell specific modulation has been shown in man. It is worth noting that high doses of FVIII inhibit the restimulation of FVIII-specific memory B cells and their differentiation into Ab-secreting plasma cells, in vitro and in vivo, in a murine model of haemophilia A [13]. This indicates that anti-idiotypic Abs could potentially also modulate memory B-cell function. We have now demonstrated that anti-idiotypic Ab bind to anti-FVIII human B-cell line producing the corresponding anti-FVIII Ab. Preliminary studies on immortalized B cells demonstrated that anti-Ids Abs specifically bound to B cells producing the corresponding anti-FVIII Ab. This specific binding is followed by capping of the complexes.