OC 69.3 - Mim8 interference on the measurement of FVIII Standard and Extended half-life products using selected FVIII Chromogenic Assays

Background: Mim8 is a FIXa/FX bispecific antibody (BiAb). HA patients without inhibitors treated with a BiAb may require concomitant administration of FVIII. Accurate assessment of FVIII activity in the presence of a BiAb is only possible using chromogenic assays (CSA) not containing human FIXa/FX.

Aims: In this study two CSA’s were evaluated to investigate the effect on measurement of FVIII standard (SHL) and extended half-life (EHL) products in the presence of Mim8.

Methods: Severe Hemophilia A plasma (HRF, Inc.) spiked with ADVATE®, Novoeight®, Esperoct® or ELOCTATE® to concentrations of 0.050, 0.100, 0.150, 0.200, and 1.000 IU/mL and Mim8 to 0, 3, 6 and 12 µg/mL, were used to investigate Mim8 interference. FVIII was measured by two CSA methods (COATEST®SP4 fully bovine and CRYOcheck™ mixed human/bovine), on the BCS®XP analyzer (SIEMENS Healthineers). Mim8 interference on FVIII activity was determined as the normalized % difference of each FVIII/Mim8 mixture compared to the corresponding sample without Mim8 (assigned 100% activity). An increase ≥1.2 fold was considered interference.

Results: The bovine CSA showed no notable interference at all FVIII/Mim8 concentrations for all products (Fig 1). For the bovine/human CSA (Fig 2), FVIII levels ≤0.20 IU/mL, showed a Mim8 dose dependent interference increase with the largest fold increase (2.4 to 4.5, ADVATE®) at low FVIII levels (0.05 IU/mL). More interference by Mim8 was observed in SHL products. As FVIII levels increased, interference was reduced in a Mim8 dose-dependent manner for all products. Using the bovine/human CSA the difference in Mim8 interference between the SHL and EHL products diminished as FVIII levels increased.

Conclusion(s): For all different FVIII products tested, FVIII activity could be accurately measured in the presence of Mim8 using the bovine CSA. For the bovine/human CSA, the interference observed at high Mim8 levels diminished as FVIII levels increased.