Aim of the research proposal: To engineer a bispecific sdAb complex to restore the binding of endogenous FVIII to VWF and thereby increase FVIII half-life as prophylactic treatment for type 2N VWD.

Hypothesis: Previous examples of targeted treatment have proven to be effective in the treatment of bleeding or thrombotic disorders (PMID: 34752601, 39196196). We propose to target endogenous FVIII to VWF with a bispecific sdAb to increase the half-life of FVIII in type 2N VWD patients and protect FVIII from proteolysis by activated protein C. The resulting increase of FVIII levels will resolve the bleeding phenotype in this patient group.
FVIII binding to VWF is mediated through the D’D3 domain on VWF. Therefore, our bispecific sdAb would preferentially target this domain on VWF. However, as this is the affected domain of VWF in type 2N VWD, sdAbs against the wild-type D’D3 domain would potentially not recognize the D’D3 in VWF-2N. An alternative strategy encompasses targeting of VWF to an unaffected VWF domain, which is remote from regions with effector functions, such as the CK domain located at the C-terminal end of
VWF. We already have a suitable anti-CK sdAb candidate (clone sVWF; PMID: 34752601, 37061132).
The responsible domain on FVIII for association with VWF is the A3 domain. Our bispecific sdAb would preferentially target the N-terminal part of the A3 domain, as this part is specifically responsible for FVIII binding and does not interfere with FVIII dissociation from VWF or thrombin mediated activation of FVIII.