Background: Low-dose immune tolerance induction (ITI) using plasma-derived factor VIII/von Willebrand factor (pdFVIII/VWF) +/- immunosuppression showed satisfactory success rate and economically practical in China in our pilot study.

Aims: To confirm the efficacy of this strategy in hemophilia A inhibitor children with poor-ITI risk.

Methods: This was a single center, prospective study in 53 hemophilia A inhibitor children from September 2016 to October, 2018. All had pre-ITI inhibitors ≥10 BU +/- other poor-ITI risk and received ITI at ~50 FVIII IU/kg (domestic pdFVIII/VWF) every-other-day alone, or combined with immunosuppression (rituximab and prednisone).

Results: Forty-six subjects [median age 3.5 (IQR, 2.5-6.4) years] with pre-ITI inhibitor titer 29.5 (IQR, 15.0- 64.8) BU were included in final analysis with a total response rate 82.6% (38/46) [success (negative inhibitor) 71.7% (33/46) in median 8.6 (IQR, 4.4-10.4) months, partial success 10.9% (5/46)]. In subjects only used ITI alone, success was achieved in 94.1% (16/17), and 58.6% (17/29) in subjects added immunosuppression. The mean monthly bleeding rate during ITI was 0.49, a 59.3% declination from 1.18 in the pre-ITI period. Younger age (< 4.5 years) was predictor for ITI success. Relapse occurred in 8 of 33 successes but 7 of these returned to negative. No severe adverse reaction was reported.

Conclusions: In poor ITI-risk subjects, this low-dose ITI (pdFVIII/VWF) +/- immunosuppression strategy showed a success rate of ~70% which is similar to that in other high/intermediate-dose regimens. Younger age was related to better response. We are performing longer follow-up to further confirm the results.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/successful-inhibitor-eradication-for-hemophilia-a-children-with-poor-risk-high-titer-inhibitor-using-low-dose-immune-tolerance-induction-strategy/