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. 2025 Jul;31(4):625-633.
doi: 10.1111/hae.70056. Epub 2025 May 5.

Profiling of Anti-FVIII Antibodies in Acquired Haemophilia A: 'Insights into Domain Specificity, Isotype Variability, and Clinical Correlations'

Ann-Cristin Berkemeier  1 , Isabell Matuschek  1 , Katrin Hartlieb  1 , Thilo Albert  1 , Natascha Marquardt  1   2 , Johannes Oldenburg  1   2 , Behnaz Pezeshkpoor  1
Affiliations

Profiling of Anti-FVIII Antibodies in Acquired Haemophilia A: 'Insights into Domain Specificity, Isotype Variability, and Clinical Correlations'

Ann-Cristin Berkemeier et al. Haemophilia. 2025 Jul.

Abstract

Introduction: Acquired haemophilia A (AHA) is a rare autoimmune disorder caused by autoantibodies against coagulation factor VIII (FVIII), resulting in significant bleeding risks.

Aim: To characterize the anti-FVIII antibody profile in AHA patients by assessing isotypes, subclasses, and correlations with key clinical parameters.

Methods: Eighty AHA patients were retrospectively analysed by assessing FVIII inhibitor levels, antibody isotypes (IgG, IgA, IgM), IgG subclasses, and domain specificity using a bead-based assay. Clinical data were correlated with antibody profiles. IgG domain profiles were compared with a congenital haemophilia A (CHA) cohort.

Results: The cohort had a median age of 74 years, with 60% males. Idiopathic cases accounted for 67%, and 17% had bleeding linked to medical interventions. Major bleeding sites were musculoskeletal/retroperitoneal (45%) and skin (36%). Within six months, 18% of patients died, mostly from sepsis. Anti-FVIII IgG antibodies were present in all patients, with IgG4 (96%) and IgG3 (60%) being the most common subclasses. IgM and IgA anti-FVIII antibodies were detected in 17.5% and 18.8% of patients, respectively, with IgM positivity associated with higher mortality (33%). IgG4 subclass correlated significantly with inhibitor titres (rs = 0.54; p < 0.001). Compared to CHA, AHA showed a higher prevalence of C1C2 domain-targeting antibodies (49% vs. 77%), associated with NBA levels (rs = 0.51; p < 0.001).

Conclusion: Anti-FVIII antibody profiling reveals distinct patterns in AHA, with IgG4 linked to higher inhibitor levels. The C1C2 domain specificity of the anti-FVIII antibodies suggests a potential role of this FVIII domain in the immunopathology of AHA patients, warranting further investigation to improve prognostic tools.

Keywords: FVIII inhibitors; acquired haemophilia A; anti‐FVIII antibodies; bleeding; immunoglobulin isotypes; mortality.

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Conflict of interest statement

A.C.B. reports no conflicts of interest. I.M. and K.H. report no conflicts of interest. N.M. received grants/research supports/honoraria/consultation fees from: Bayer, Chugai, CSL Behring, LFB, NovoNordisk, Octapharma, Pfizer, Roche, Takeda and Sobi. T.A. reports having received grants for a patient support association from Bayer, Biotest, Chugai, CSL‐Behring, Grifols, Novo Nordisk, Octapharma, Roche, Swedish Orphan Biovitrum and Takeda, as well as personal fees for advisory board meetings, consulting and/or travel support from Bayer, Biomarin, Biotest, CSL‐Behring, Grifols, Novo Nordisk, Octapharma, Pfizer, Swedish Orphan Biovitrum and Takeda. J.O. reports having received grants for studies and research from Bayer, Biotest, CSL‐Behring, Octapharma, Pfizer, SOBI and Takeda, and travel support as well as personal fees for lectures and advisory board meetings from Bayer, Biogen Idec, Biomarin, Biotest, CSL‐Behring, Chugai, Freeline, Grifols, Novo Nordisk, Octapharma, Pfizer, Roche, Sanofi, Sparks, Swedish Orphan Biovitrum and Takeda. B.P. reports having received grants for research from Biotest and Octapharma as well as personal fees for lectures and advisory board meetings from NovoNordisk and Octapharma.

Figures

FIGURE 1
FIGURE 1
Venn diagram showing patients positive for any combination of immunoglobulin isotype and subclass of anti‐FVIII antibodies. (A) Number of positive patients in the corresponding Ig classes [n], % positive (out of 80 patients). The overlaps of the circles correspond to patients with more than one isotype. (B) Number of positive patients in the corresponding IgG subclass [n], % positive (out of 80 patients). The overlaps of the circles correspond to patients with more than one subclass. IgG, IgG1, IgG2, IgG3, IgG4, IgM, IgA = Immunoglobulin G, ‐G1, ‐G2, ‐G3, ‐G4, M and A.
FIGURE 2
FIGURE 2
Isotype and Domain pattern of AHA patients. (A) Frequency of anti‐FVIII‐ and anti‐FVIII‐domain specific antibodies in acquired hemophilia A patients. Isotype specific domain profiling was done for 80 patients. The absolute number of patients with antibodies against the corresponding domain is shown. (B) Positive patients with their Ig specific domain pattern and signal intensity [IgG 80 patients, IgA 15 patients, IgM 14 patients]. MFI value of each bead was subtracted by the cut off, negative values were set as zero. Red Line = Median of MFI signal of positive Ig patients; No: number, pos = positive, spec.: specific, LC: Lightchain, IgG, IgM, IgA: Immunoglobulin G, M and A, FLFVIII: Full‐length FVIII, BDDFVIII: B‐domain‐deleted FVIII, MFI: Mean fluorescence Intensity, anti‐hu: anti‐human, rFVIII: recombinant FVIII products.
FIGURE 3
FIGURE 3
Heat‐Map of patients with multiple positive anti‐FVIII Isotypes (IgG, IgM, IgA). Patients’ MFI values were subtracted from the cut‐off, plotted and colored according to their intensities. The patient identities were anonymized using patient numbers written on the left axis. (A) IgM and IgG positive patients with no IgA anti‐FVIII antibodies. (B) IgA and IgG positive patients with no IgM anti‐FVIII antibodies. (C) IgG, IgM and IgA anti‐FVIII positive patients.
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