von Willebrand factor alloantibodies in type 3 von Willebrand disease

Emicizumab in Type 3 von Willebrand Disease: Report of a Case with an Alloantibody and Literature Review

Type 3 von Willebrand disease (VWD), the most severe form of VWD, is an inherited recessive bleeding disorder caused by the complete deficiency of von Willebrand factor (VWF). The reported prevalence is 1 per million but varies worldwide according to the frequency of consanguineous marriages. The clinical phenotype is characterized not only by mucocutaneous bleedings, but also by hemarthroses and muscle hematoma, as in patients with moderate hemophilia. Long-term prophylaxis with factor (F)VIII/VWF concentrates is recommended in patients with a history of severe and frequent bleeds. A rare complication of replacement therapy is the development of alloantibodies against VWF, with the consequences of an ineffective therapy and risk of anaphylactic reactions upon treatment. Emicizumab is the first bispecific monoclonal antibody that mimics FVIII coagulant activity and is approved for prophylaxis of bleeding in patients with inherited hemophilia A with or without inhibitors and recently also for acquired hemophilia. In this manuscript we report and discuss available data in the literature on the use of emicizumab in type 3 VWD and describe the case of a female patient with type 3 VWD with a history of alloantibodies against VWF and posttransfusion anaphylaxis, recently and successfully put on off-label prophylaxis with emicizumab.

Phage display broadly identifies inhibitor-reactive regions in von Willebrand factor

BACKGROUND

Correction of von Willebrand factor (VWF) deficiency with replacement products containing VWF can lead to the development of anti-VWF alloantibodies (i.e., VWF inhibitors) in patients with severe von Willebrand disease (VWD).

OBJECTIVE

Locate inhibitor-reactive regions within VWF using phage display.

METHODS

We screened a phage library displaying random, overlapping fragments covering the full-length VWF protein sequence for binding to a commercial anti-VWF antibody or to immunoglobulins from three type 3 VWD patients who developed VWF inhibitors in response to treatment with plasma-derived VWF. Immunoreactive phage clones were identified and quantified by next-generation DNA sequencing (NGS).

RESULTS

Next-generation DNA sequencing markedly increased the number of phages analyzed for locating immunoreactive regions within VWF following a single round of selection and identified regions not recognized in previous reports using standard phage display methods. Extending this approach to characterize VWF inhibitors from three type 3 VWD patients (including two siblings homozygous for the same VWF gene deletion) revealed patterns of immunoreactivity distinct from the commercial antibody and between unrelated patients, though with notable areas of overlap. Alloantibody reactivity against the VWF propeptide is consistent with incomplete removal of the propeptide from plasma-derived VWF replacement products.

CONCLUSION

These results demonstrate the utility of phage display and NGS to characterize diverse anti-VWF antibody reactivities.