Modulation of factor VIII‐specific memory B cells

Abstract

Summary. The development of inhibitory antibodies against factor VIII (FVIII) is the major complication in patients with haemophilia A who are treated with FVIII products. Memory B cells play an essential role in maintaining established antibody responses. Upon re-exposure to the same antigen, they are rapidly re-stimulated to proliferate and differentiate into antibody-secreting plasma cells (ASC) that secrete high-affinity antibodies. It is, therefore, reasonable to believe that memory B cells have to be eradicated or inactivated for immune tolerance induction therapy to be successful in patients with haemophilia A and FVIII inhibitors. The aim of our studies was the development of strategies to prevent FVIII-specific memory B cells from becoming re-stimulated. We established a 6-day in vitro culture system that enabled us to study the regulation of FVIII-specific murine memory-B-cell re-stimulation. We tested the impact of the blockade of co-stimulatory interactions, of different concentrations of FVIII and of ligands for toll-like receptors (TLR). The blockade of B7-CD28 and CD40-CD40 ligand interactions prevented FVIII-specific murine memory B cells from becoming re-stimulated by FVIII in vitro and in vivo. Furthermore, high concentrations of FVIII blocked re-stimulation of FVIII-specific murine memory B cells. Triggering of TLR7 amplified re-stimulation by low concentrations of FVIII and prevented blockade by high concentrations of FVIII. We conclude that we defined modulators that either amplify or inhibit the re-stimulation of FVIII-specific murine memory B cells. Currently, we are investigating whether the same modulators operate in patients with haemophilia A and FVIII inhibitors.

Gene therapy for hemophilia

“…This mechanism depends on induction of Tregs, and the continued presence of these cells is required to maintain tolerance. The high expression of F.IX in mice following hepatic gene transfer (~20-40% of normal) may also be responsible for this rapid clearance of F.IX-specific antibodies due to suppression of memory B cells (4, 51). Though this phenomenon is understandably difficult to verify in human studies, it is encouraging that, to date, none of the patients treated with a liver-directed AAV vector have formed a F.IX-specific immune response (52, 53).…”

Galectin-9 Is a Suppressor of T and B Cells and Predicts the Immune Modulatory Potential of Mesenchymal Stromal Cell Preparations

“…To further validate Gal-9 as a new MSC-driven immune regulator, we extended our investigation and analyzed MSCs and Gal-9 in vivo in a disease model of allo immunization. Immunization against FVIII is the most frequent complication in hemophilia A treatment and FVIII triggers a profound IgG response in mice [54]. Because Rafei et al [55] demonstrated that MSC application support the clearance of anti-FVIII titers in mice, we wanted to know whether activated MSCs were capable of suppressing FVIII immune response simultaneously.…”

Strategies to target long-lived plasma cells for treating hemophilia A inhibitors

“…Therefore, it is paramount to treat patients with high-titer inhibitory antibodies with effective strategies to reduce and best eliminate pre-existing inhibitory antibodies before attempting tolerance induction. Blockade of co-stimulatory pathway has been shown to prevent FVIII-specific murine memory B cells from becoming re-stimulated by FVIII in vitro and in vivo[37]. In our previous experiments, we have demonstrated that the combination treatment of IL-2/IL-2mAb complexes + rapamycin + anti-CD20 + FVIII reduced FVIII-specific memory B cells and ASCs from the spleen, leading to transient decreases of pre-existing neutralizing antibody titers [17].…”