Analysis of Soluble and Humoral Immunological Parameters During Re-exposure with rFVIIIFc after History of Inhibitors

Little is known on the mechanisms of tolerance to factor VIII (FVIII) in haemophilia A (HA) patients. To identify immunological markers in tolerance development, samples from two patients with HA treated with rFVIIIFc after a history of inhibitors were analyzed. The patients have been followed closely during re-exposure with FVIII as part of immune tolerance induction. Plasma samples were analyzed for FVIII inhibitors and FVIII-specific antibodies. Analysis of further immunological markers was performed for patient 2 using peripheral blood mononuclear cells (PBMCs); additionally, cytokines in cell culture media were quantified. Laboratory data were compared to pharmacological parameters and clinical outcome.Both patients showed a decline in FVIII recovery (exposure day [ED] 12 for patient 1, ED 25 for patient 2). During that time patient 2 was positive for lupus anticoagulants and a low amount of FVIII-specific antibodies was detectable in ELISA. However, specificity could not be verified by competition and antibodies disappeared again after ED 25. Patient 1 developed FVIII-specific antibodies of subclass IgG4 after ED 229. Antibodies were mainly directed against the FVIII light chain. FVIII-responsive CD4⁺ T-cells were detectable in the patient's PBMCs. Additionally, PMBCs showed an elevated production of IL-23 and TNF-α when stimulated with FVIII.A prospective analysis of the described parameters might help to identify the onset of an immune response. Even though the number of analyzed patients is low, the detailed analyses may help to further understand the development of tolerance to FVIII and to define starting points for further interventions against treatment complications through inhibitor development in HA.