Use of Factor VIII/Von Willebrand Factor Complex for Inducing Immune Tolerance in Hemophilia a Patients Who Have Failed with Recombinant Fviii: Recent Canadian Experience

Immune tolerance induction (ITI) is effective in approximately 63–83% of hemophilia patients with inhibitors. Poor prognostic factors are age > 18 years, ITI started > 4 years after inhibitor development, inhibitor peaks > 200 BU, inhibitor titre > 10 BU at ITI initiation, and previously failed ITI. It has been reported that patients who have failed ITI with a recombinant FVIII concentrate achieved and maintained immune tolerance when VWF/FVIII complex concentrates were used. We present our Canadian experience with a factor VIII/von Willebrand factor concentrate (Humate-P) for inducing immune tolerance in patients who have previously failed ITI. A questionnaire was sent to all Hemophilia Treatment Centers of Canada. Data collected included baseline FVIII level, mutation, date at initial diagnosis of inhibitor, peak titer, concentrate associated with development of inhibitor, inhibitor titer at initiation of first ITI, concentrate and regimen used, and concentrate, dosing and outcome of secondary ITI with Humate-P. All Hemophilia Centers agreed to participate. 5 Centers submitted data about 8 patients. One patient resistant to initial ITI with Kogenate FS achieved good partial response with Humate-P, with titers going down from 40 to values between 0,6 and 4 BU. One patient who responded to initial ITI with Kogenate FS with peaking of inhibitor to 380 BU was remaining above 100 BU and lowered to 28 BU on Humate-P. In three patients, Humate-P induced an anamnestic response. Two of those patients had a concomitant line infection at time of switching to Humate-P. The third of those three patients had a transient anamnestic response after introduction of Humate-P. One patient had successfull induction of immune tolerance using multiple therapies (cyclophosphamide, Immunate, IVIG, Rituximab) and maintained remission under Humate-P. One patient was on ITI for 27 months using Recombinate and switched to Humate-P when Recombinate was withdrawn from the market. After 12 months, the inhibitor had gone from 12 to 7.3 BU. One patient attained complete remission during primary ITI using recombinant FVIII concentrate (Advate) and maintained remission when switched to Humate-P. In subjects failing ITI with recombinant factor VIII concentrates, Humate-P may be considered as a second line for inducing immune tolerance.