Prompt Immune Tolerance Induction at Inhibitor Diagnosis Regardless of Titer May Increase Overall Success in Hemophilia A With Inhibitors: Experience of Two US Centers

Immune tolerance induction (ITI) for patients (pts) with hemophilia A with inhibitors is the only modality known to effectively eradicate inhibitors with an overall reported success of ∼60-80%. One debate concerns the optimal time to start ITI; recent guidelines recommend delaying ITI until inhibitor titer is <10 Bethesda units (BU).

We report results of an analytic project to determine the success of ITI relative to time from inhibitor detection to ITI initiation.

Data was collected retrospectively at 2 US hemophilia centers on pts with severe/moderate (≤5%) factor VIII (FVIII) deficiency undergoing ITI including time interval from inhibitor detection to ITI start, inhibitor titer and outcome. High-dose ITI was practiced by both centers (i.e. ≥100 IU/kg/day). Success, partial success and failure were defined practically with success as a negative inhibitor titer and ability to use FVIII concentrate routinely for treatment and prevention of bleeding; partial success was an inhibitor titer <5 BU with ability to use FVIII concentrate to treat bleeding episodes; failure as ongoing ITI >3 years without achieving success/partial success or discontinuation of ITI. IRB approvals were obtained at both centers for this data analysis.

Pts were first divided into low responding inhibitor (LRI) and high responding inhibitor (HRI) based on peak inhibitor titer; the HRI subgroup was further subdivided based on time to start ITI, including within 1 month, 1-6 months and greater than 6 months. The HRI subgroup starting ITI within 1 month was analyzed based on pre-ITI inhibitor titer.

Fifty eight male pts with adequate ITI history documentation were included; 55 (95%) were severe (<1%), 3 moderately deficient (1-3%). Forty-seven pts (48%) were Caucasian, 6 Hispanic, 2 African American, 2 Asian and 1 Native American. Outcome is summarized in Table 1. Overall, 49 of 58 pts (84%) underwent successful ITI.

Low responding Inhibitors: Among 19 (33%) pts with LRI, ITI success was 100%. Most pts with LRI 15/19 (79%) started ITI within 1 month from inhibitor detection.

High responding inhibitors: Among 39 (67%) pts with HRI, 30/39 (77%) achieved tolerance, 1 achieved partial success and continued ITI, 1 was ongoing, 7 pts failed. The 39 pts with HRI were further subdivided based on time to ITI start.

ITI start within 1 month of detection: Twenty three pts started ITI within 1 month from detection; 21 achieved success (91%), 1 partially succeeded and 1 failed. Eight of 10 pts (80%) with a pre-ITI titer <10 BU achieved success, 1 partially succeeded and 1 failed. All 13 pts (100%) starting ITI with pre-ITI inhibitor titer ≥ 10 BU achieved success.

ITI start > 6 months: Eleven pts had an interval > 6 months until ITI start; 7 (64%) achieved success and 4 (36%) failed.

These results suggest that the time interval from inhibitor detection to start of ITI may play a critical role in outcome. A titer ≥10 BU did not influence outcome in pts where ITI was utilized within 1 month, supporting this approach in contrast to the commonly accepted practice of delaying ITI start until a titer <10 BU is achieved. Pts may benefit from prompt ITI regardless of current inhibitor titer and are not subjected to wait periods where bleeding is more likely to occur. Prompt ITI should be considered a viable therapeutic option in newly identified inhibitor pts regardless of current inhibitor titer.

Manco-Johnson:Bayer HealthCare: Membership on an entity’s Board of Directors or advisory committees, Research Funding; CSL Behring: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Baxter BioScience: Membership on an entity’s Board of Directors or advisory committees; Biogen Idec: Membership on an entity’s Board of Directors or advisory committees; Novo Nordisk: Membership on an entity’s Board of Directors or advisory committees; Eisai: Research Funding. Maahs:Baxter BioScience: Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Biogen Idec: Membership on an entity’s Board of Directors or advisory committees; Novo Nordisk: Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau. Shapiro:Baxter BioScience: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novo Nordisck: Consultancy, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Bayer Healthcare: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Biogen Idec: Consultancy, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Chugai Pharma: Consultancy; Kedrion Biopharma: Consultancy, Research Funding; Cangene Pharmaceuticals: Research Funding; CSL Behring: Research Funding; Octopharma: Research Funding; PTC Therapeutics: Research Funding; Eli Lilly: Research Funding.