HAT and HAT RI: Novel Factor VIII Molecules Addressing Patients' Needs

On Sunday, Peter Herbener of Biotest AG in Dreieich, Germany, presented results from research that looked into the development of novel recombinant factor VIII (FVIII) molecules, addressing all major limitations of current FVIII substitution therapy. Current FVIII replacement therapies still have several limitations, such as a short plasma half-life, the lack of subcutaneous bioavailability, and a high immunogenic potential, resulting in the development of inhibitory antibodies or precluding the subcutaneous administration route; this was the reason behind this particular research.

Herbener commented that Biotest's Hemophilia A Therapeutic (HAT) molecule was generated by introducing four albumin-binding domains into a single-chain FVIII sequence. In parallel, 19 deimmunizing mutations were incorporated into the FVIII sequence of HAT, resulting in HAT RI (reduced immunogenicity). Both molecules were produced in a human cell line, purified, and extensively tested in vitro. Subcutaneous administration was tested in hemophilia A mice and Göttingen minipigs. A tail transection assay in hemophilia A mice was used to determine in vivo functionality. As FVIII-bound albumin may shield HAT and HAT RI from present FVIII inhibitors, the bypassing activity of both molecules was assessed by a modified Bethesda assay.

The results showed that both FVIII molecules HAT and HAT RI showed full in vitro and in vivo functionality while providing up to a 4-fold longer half-life, compared with Moroctocog alfa in the albumin-deficient mouse model. Subcutaneous administration resulted in up to 50% bioavailability in the minipig model. Bypassing activity in the presence of inhibitors was observed in combination with reduced major histocompatibility complex class II (MHC II) presentation, showing improved immunological compatibility. Herbener concluded that the work addressed the major challenges of FVIII substitution therapy, as both molecules have a superior half-life, showed high subcutaneous bioavailability in mice and pig models, and reduced FVIII immunogenicity according to utilized in vitro models.

Read the full abstract here.