Exploring Red Blood Cells As an Antigen Delivery System to Modulate the Immune Response Towards FVIII in Hemophilia a

The main complication in hemophilia A treatment is the development of inhibitory antibodies against factor VIII (FVIII). Immune tolerance induction, the gold standard for eradicating anti-FVIII antibodies, is efficient in only 60-80% of cases. This underscores the need for more efficient induction of tolerance in hemophilia A patients with FVIII inhibitors. In this study we explored whether red blood cells (RBCs) can be utilized as antigen delivery system to modulate the immune response against FVIII. Two promiscuously HLA-DR presented peptides derived from the A2 and C1 domains of FVIII were fused to the TAT-cell penetrating peptide and incubated with RBCs. Biotinylated TAT-A2 and TAT-C1 peptides were found to interact with RBCs as shown by flow cytometry and imaging flow cytometry. Moreover, macrophages efficiently phagocyted TAT-FVIII peptide-treated RBCs. Using mass spectrometry based immunopeptidomics we established that TAT-FVIII peptides were presented on MHC class II of macrophages that phagocyted TAT-peptide pulsed RBCs. Specifically, the TAT-A2 peptide exhibited efficient processing and presentation on HLA-DR molecules. Importantly, incubation of TAT-C1 peptide treated RBCs loaded macrophages with a FVIII-specific T cell hybridoma led to a significant increase in IL-2 production, suggesting functional presentation of TAT-C1 derived peptides by macrophages. Our findings indicate that RBCs can serve as effective vehicle for the delivery of FVIII derived peptides to antigen presenting cells. The successful display of T cell epitopes on APC using ex vivo loaded RBC may be potentially utilized to modulate pathogenic immune responses such as observed in a subset of patients with hemophilia A.

Fijnvandraat:SOBI: Consultancy, Research Funding; Sanofi: Consultancy; NovoNordisk: Consultancy, Research Funding; Roche: Consultancy; CSL Behring: Research Funding; ISTH SSC: Membership on an entity's Board of Directors or advisory committees. Voorberg:Sanquin: Patents & Royalties.