Pseudoallergy Induced by Factor VIII Injection in Three Subjects with Hemophilia A

Hypersensitivity reactions to factor VIII (FVIII) concentrates are rare but well known complications of hemophilia treatment with FVIII concentrates. Occasional reports have suggested IgE mediation. Many cases have presented circumstantial evidence for the implication of FVIII but have failed to clearly identify FVIII-targeting antibodies (Abs). The absence of evidence for IgE contribution to those reactions, but the presence of FVIII specific IgM and/or IgG1 and/or IgG3, could support the hypothesis of complement mediation. These reactions have been called “complement activation-related pseudoallergy” (CARPA). As we did not study complement we call these reactions CARPA-like. We report 3 cases of CARPA-like reactions to FVIII which we believe could contribute to alert clinicians to this potential serious side effect of FVIII replacement therapy and could shed some light on its pathophysiology.

Subject A, 5 y. old Caucasian previously untreated patient (PUP) with mild hemophilia A (FVIII 0.12 IU/mL, 6955C>T exon 26 P2300S, H1 haplotype, no inhibitor with Nijmegen < 0.4 unit), developed a CARPA-like reaction with his sixth injection of a von Willebrand factor-containing FVIII concentrate (Wilate^®, Octapharma) for traumatic knee hemarthrosis. He never needed further FVIII replacement. Subject B, 5 y. old African PUP with severe hemophilia A (FVIII < 0.01 IU/mL, intron 22 inversion, H1 haplotype, no inhibitor with Nijmegen < 0.4 unit) developed a CARPA-like reaction with his sixth injection of Wilate^®. He was switched to a B-domain deleted recombinant FVIII concentrate (Xyntha™, Pfizer) and has yet to relapse with CARPA-like reaction after more than 100 exposure days. Subject C, 15 y. old Caucasian PUP with severe hemophilia A (FVIII < 0.01 IU/mL, intron 22 inversion, H1 haplotype, inhibitor with Nijmegen 10 units) developed a CARPA-like reaction with his second dose of a full length recombinant FVIII concentrate (Kogenate^®,Bayer) while on ITI induction program. Blood samples were obtained from each patient shortly before and after their CARPA-like reaction.

ELISA assays (AM. Vincent, Haemophila 2009) were used to test the presence of IgG, IgM, IgE Abs reacting with different types of FVIII (Baxter’s Advate, Wilate^®, Kogenate^®, Xyntha™) in patients’ plasma. The x-MAP technology was used to confirm the presence of IgG and IgM Abs, and to better define their isotypic profile. For that purpose, Abs specific for the heavy chain (HC; MAb 8860) or light chain (LC; MAb ESH8) of the FVIII were first immobilized on magnetic fluorescent beads, and then incubated with EDTA-dissociated FVIII. After incubation with patients’ plasma samples, binding of IgG subclasses (IgG₁ to IgG₄) and IgM were revealed by specific anti-human phycoerythrin-labeled Abs.

For patients A and B (with negative Bethesda titre), we identified an immune response characterized by the presence of IgM, as well as IgG (patient A IgG₁; patient B IgG₁, IgG₃), simultaneously directed against the HC and the LC. ELISA assays on these 2 patients showed the presence of IgM and IgG, as well as the absence of IgE compatible with a CARPA-like reaction. Similar results with the 4 different FVIII concentrates are in favour of an immune response specific to FVIII rather than an immune response to anything else than FVIII. To further support this contention, ELISA assays were all negative for patient A’s mother and for his PUP hemophilic brother, as well as for subject B’s mother and for six normal control plasma tested on the same ELISA plate. Patient C (with positive Bethesda titre) presented anti-FVIII IgG (IgG₁ to IgG₄) and IgM Abs also targeting the HC and the LC simultaneously. These 3 patients developed a CARPA-like reaction associated with injection of FVIII concentrates. Subjects A and C were not rechallenged with FVIII after their reaction and progressively lost their anti-FVIII Abs. Subject B was rechallanged over 100 times with the B-domain deleted Xyntha™ without reaction and with progressive lost of his anti-FVIII Abs, suggesting that his reaction might have been mediated by Abs reacting to the B-domain of FVIII.

CARPA-like reactions to FVIII concentrates can be associated with anti-FVIII Abs. ELISA and x-MAP are useful technologies to investigate this complication of hemophilia treatment and could help select an optimal choice of FVIII concentrate for further replacement therapy.

No relevant conflicts of interest to declare.