Signature of the Antibody Response to FVIII

The development of neutralizing antibodies to FVIII (nAbs) is still the most severe complication in modern hemophilia A treatment. In this analysis, antibody positive samples prior to any therapeutic intervention have been analyzed.

Validated FVIII-ADA assays for the detection of ADA, nAbs, and IgG subclasses (IgG1, IgG2, IgG3, and IgG4) were used in combination with assays to identify the binding domains on FVIII (human–porcine FVIII constructs, FVIII heavy and light chain and individually expressed FVIII domains). A total of 70 previously untreated patients (PUPs) with >250 samples and 96 non-PUPs with >370 samples were analyzed.

In this retrospective, in part longitudinal, analysis, samples from 70 previously untreated and from 96 previously treated patients have been analyzed. A total of 249 and 368 samples have been analyzed, respectively. Results confirm that IgG1 and IgG4 are the most prominent IgG subclasses of the specific immune response against FVIII. Furthermore, specific IgG3 has been detected in a significant number of samples. Antibodies bind to epitopes on FVIII on the heavy and light chain, whereas the light chain is predominant in the non-PUP population and the heavy chain in the PUP population. This is also reflected in binding to individual domains of FVIII.

In this analysis of a large number of inhibitor-positive samples, subclasses IgG1 and IgG4 have been confirmed and a role for specific IgG3 is being discussed. Furthermore, binding of specific antibodies to epitopes on A2 and C2 have been confirmed while also strongly supporting recent data on antibodies binding to the C1 domain.

Analysis of longitudinal immunological results challenges such data and might deliver biomarkers for inhibitor development and ITI success in the near future.

Publication History

Article published online:
13 November 2020