Low-Dose Immune Tolerance Induction for Hemophilia a Children with Poor-Risk High-Titer Inhibitors

Background: Low-dose immune tolerance induction (ITI) +/- immunosuppression as a practical ITI strategy in China showed a relatively satisfactory success rate and economic advantages in pilot study. However, the outcome still needs to be verified by larger cohort. Aim: To report the efficacy of this low-dose ITI +/- immunosuppression strategy in hemophilia A children ≥ 10 BU. Methods: This was a single center, prospective study in 53 hemophilia A subjects from Sep 2016 to Apr 2019. All subjects having ≥ 10 BU receiving ~50IU/kg FVIII every other day using domestic intermediate purity pdFVIII/VWF products, either alone or in combination with rituximab and prednisone judging by inhibitors and ITI response. Results: Finally, 46 subjects received this strategy at a median of 3.2 (IQR, 2.3-6.5) years old, their pre-ITI inhibitor titer was median 30.0 (range, 10.1-416) BU. Analysis at median 15.1 (range 3.0-34.4) months follow-up, success (inhibitor <0.6BU) was achieved in 32 (69.6%) subjects, partial success (inhibitor <5BU but >0.6BU) in 11 (23.9%) subjects, and failure in 5 (10.9%) subjects. Between subjects administered ITI-alone and ITI- immunosuppression, no significant difference was observed in time to success (median 8.5; IQR 6.7-11.7 vs 10.2; IQR 5.1-25.1, P=0.164). The mean monthly bleeding rate on ITI was 0.49 which declined 59.3% compared with pre-ITI period. Subjects administered ITI-immunosuppression (0.54 ± 0.46) was higher than ITI-alone (0.42 ± 0.69) although with no significantly difference (P=0.089). Seven (21.9%) subjects experienced inhibitor recurrence, 4 subjects treated with ITI-alone, 3 with ITI-immunosuppression. Recurrence occurred at a median of 4.8 (range, 2.8-10.8) months after successful ITI with inhibitor titer transiently rising to median 0.7 (range, 0.7-1.5) BU. Conclusion: This low-dose ITI +/- immunosuppression therapy in subjects with pre-ITI inhibitor ≥ 10 BU showed a success rate similar to other high/intermediate-dose regimen for the whole inhibitor patients. The subjects treated with ITI-immunosuppression did not showed higher recurrence at present, while a longer time follow-up is still needed. Disclosures Poon: Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bioverativ/Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; World Federation of Hemophilia: Other: Not-for-profit organization affiliation: volunteer ; Novo Nordisk: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Participation in sponsored research; CSL-Behring: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Grant Funding; Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Grant Funding; Takeda/Shire: Consultancy, Membership on an entity's Board of Directors or advisory committees; Octapharma: Consultancy, Membership on an entity's Board of Directors or advisory committees.