Recombinant Factor VIII Fc Inhibits B Cell Activation via Engagement of the FcγRIIB Receptor.

The development of neutralizing antibodies (inhibitors) against factor VIII (FVIII) is a major complication of hemophilia A treatment. The sole clinical therapy to restore FVIII tolerance in patients with inhibitors remains immune tolerance induction (ITI) which is expensive, difficult to administer and not always successful. Although not fully understood, the mechanism of ITI is thought to rely on inhibition of FVIII-specific B cells (1). Its efficacy might therefore be improved through more aggressive B cell suppression. FcγRIIB is an inhibitory Fc receptor that down-regulates B cell signaling when cross-linked with the B cell receptor (BCR). We sought to investigate if recombinant FVIII Fc (rFVIIIFc), an Fc fusion molecule composed of FVIII and the Fc region of immunoglobulin G1 (IgG1) (2), is able to inhibit B cell activation more readily than FVIII. rFVIIIFc was able to bind FVIII-exposed and naïve B cells from hemophilia A mice as well as a FVIII-specific murine B cell hybridoma line (413 cells). An anti-FcγRIIB antibody and FVIII inhibited binding, suggesting that rFVIIIFc is able to interact with both FcγRIIB and the BCR. Furthermore, incubation of B cells from FVIII-exposed mice and 413 cells with rFVIIIFc resulted in increased phosphorylation of SH-2 containing inositol 5-phosphatase (SHIP) when compared to FVIII. B cells from FVIII-exposed hemophilia A mice also exhibited decreased extracellular signal-regulated kinase (ERK) phosphorylation when exposed to rFVIIIFc. These differences were absent in B cells from naïve, non-FVIII exposed hemophilic mice suggesting an antigen-dependent effect. Finally, rFVIIIFc was able to inhibit B cell calcium flux induced by anti-Ig F(ab)2. Our results therefore indicate that rFVIIIFc is able to crosslink FcγRIIB and the BCR of FVIII-specific B cells, causing inhibitory signaling in these cells.

Hemorragia intracraniana espontânea em pediatria: relato de paciente hemofílico que sobreviveu devido a cisto cerebral / Spontaneous intracranial hemorrhage in children: report of a hemophilia patient who survived due to a brain cyst

RESUMO Relatamos o caso de um uma criança de 2 anos de idade que sobreviveu após um episódio agudo de hemorragia intracraniana espontânea grave com sinais clínicos e radiológicos de hipertensão intracraniana e herniação transtentorial. O paciente foi para cirurgia de urgência para drenagem do hematoma, sendo inserido um cateter para monitorar a pressão intracraniana. Na análise da tomografia de crânio inicial, antes da drenagem do hematoma, constatou-se um cisto cerebral contralateral ao hematoma que, segundo análise do neurocirurgião e do neuroradiologista, possivelmente evitou um desfecho pior, visto que o cisto serviu de acomodação para o cérebro após a hemorragia maciça. Após investigação, constatou-se tratar de um caso de hemofilia tipo A sem diagnóstico prévio. O paciente foi tratado em terapia intensiva com controle da pressão intracraniana, reposição de fator VIII e obteve alta sem sequelas neurológicas evidentes.

ABSTRACT We report the case of a 2-year-old child who survived an acute episode of severe spontaneous intracranial hemorrhage with clinical and radiological signs of intracranial hypertension and transtentorial herniation. The patient underwent emergency surgery to drain the hematoma, and a catheter was inserted to monitor intracranial pressure. In the initial computed tomography analysis performed prior to hematoma drainage, a brain cyst was evident contralateral to the hematoma, which, based on the analysis by the care team, possibly helped to avoid a worse outcome because the cyst accommodated the brain after the massive hemorrhage. After the investigation, the patient was determined to have previously undiagnosed hemophilia A. The patient underwent treatment in intensive care, which included the control of intracranial pressure, factor VIII replacement and discharge without signs of neurological impairment.