Coversin and eculizumab both prevent the splitting of complement C5 into its active components, but they each accomplish this effect by binding to specific and different sites on the molecule. It has recently been discovered that a small but identifiable subgroup of eculizumab-treated patients have a C5 polymorphism affecting the eculizumab binding site which prevents high affinity binding and makes these patients resistant to treatment — but does not appear to affect binding by Coversin in those patients tested to date. While this polymorphism has been identified in 3.5% of the Japanese population, the prevalence of this and other potential mutations that may interfere with eculizumab binding activity in non-Japanese patients remains unknown.
A currently available blood test enables some of these eculizumab-resistant patients to be identified. We have identified several non-Japanese patients to date and have demonstrated that Coversin fully inhibits complement activity in the blood of these patients by blocking C5. As noted above, we have also been treating a patient with PNH and eculizumab resistance due to a C5 polymorphism for over 28 months and recently initiated treatment of a second eculizumab resistant patient.