Maternal microchimerism accelerates immune tolerance induction to factor VIII in children with hemophilia A and FVIII inhibitors.

BACKGROUND: Predictors for the successful eradication of neutralizing anti-FVIII alloantibodies (inhibitors) in hemophilia A patients receiving immune tolerance induction (ITI) therapy remain limited. Maternal microchimerism (MMc) showed potential to protect hemophilia A patients from inhibitor development. OBJECTIVES: To investigated the role of MMc in ITI therapy. PATIENTS/METHODS: This observational study enrolled 121 pediatric with hemophilia A and inhibitors. MMc was determined using droplet digital PCR. Low-dose ITI (FVIII ~50IU/kg every other day) was administered, with adjunctive rituximab given to patients with higher risk clinical features. RESULTS: Of the 101 patients evaluable for MMc, 88 completed ITI, 18 were MMc positive (MMc+) and 70 were MMc negative (MMc-). Success was achieved in 75 (85.2%) patients, including 16 of 18 MMc+ patients (88.9%) and 59 of 70 MMc- patients (84.3%). Compared with MMc- patients, MMc+ patients had a lower peak inhibitor during ITI (median, 5.3 vs. 37.8 BU/ml, p = 0.029), less frequent rituximab use (27.8% vs. 61.4%; p = 0.011), and a shorter time to ITI success (median, 3.0 vs 9.9 months; p = 0.009). Multivariate Cox regression identified MMc+ (HR = 2.770), pre-ITI inhibitor <10BU/ml (HR = 2.663), peak inhibitor during ITI<200BU/ml (HR = 4.954) and non-large deletion/duplication F8 mutations (HR = 2.344) as independent predictors of shorter time to ITI success. CONCLUSION: MMc was associated with more rapid ITI success in children with hemophilia A and inhibitors receiving low-dose ITI regimen, suggesting the potential role of MMc in facilitating the eradication of FVIII inhibitors.