Blockade of Complement Cell Lysis and C3d Fixation by Patient <scp>HLA</scp> ‐ <scp>A1</scp> Antibodies: Towards a New Therapy for Prevention of Antibody‐Mediated Rejection

Donor-specific HLA antibodies (DSA) occurring prior to or appearing de novo after transplantation play a major role in kidney graft loss, mainly caused by complement activation by DSA. As potential therapeutics, immunologically inert human monoclonal antibodies (mAbs) preventing binding of DSA to HLA-A1 molecules would limit their detrimental effects. In this study, the complement-activating potential of anti-HLA-A1 mAbs (WIM8E5), modified by single amino-acid changes inhibiting C1q binding, Fc-Fc interactions, or FcγR binding, was assessed in the classical crossmatch and by detection of C3d fixation in single antigen Luminex beads. Subsequently, the efficacy of these modified human mAbs was assessed in combination with patient sera to determine whether they could prevent complement-mediated cell lysis and HLA antibodies-induced C3d fixation. Point mutations in anti-HLA-A1-WIM8E5 mAb preventing C1q binding resulted in reduced to absent complement-mediated cell lysis and C3d fixation. Patient sera containing anti-HLA-A1 antibodies are able to activate complement, and WIM8E5-K322A-P329R-S440K (preventing C1q, Fc:Fc interaction and FcyR binding) mAb could prevent cell lysis induced by patient antibodies and inhibit C3d binding to HLA-A1 coated beads. Furthermore, the 109F epitope recognized by the mAb differed from those recognized by patient antibodies, indicating that a single modified mAb can block multiple HLA-A1 recognition sites. In conclusion, single amino-acid mutations in anti-HLA-A1-WIM8E5 directed to inhibit C1q binding, Fc:Fc interactions, or FcγR binding could be used to prevent complement-mediated cell lysis and C3d formation in kidney transplant recipients. Further research is needed to investigate the applicability of modified mAb as potential therapeutics in the clinic.