A red blood cell–based antigen delivery system to facilitate T cell epitope presentation to promote peripheral tolerance to ADAMTS13 in immune-mediated thrombotic thrombocytopenic purpura

Background: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare and potentially fatal autoimmune disease caused by a severe ADAMTS13 functional deficiency, mediated by autoantibodies targeting ADAMTS13. Despite high survival rates achieved with current treatments, between 20% and 50% of patients experience relapses. Ensuring longer-lasting recovery by restoring immune tolerance toward ADAMTS13 remains a significant unmet need. Objectives: T cells and induction of regulatory T cells. Methods: Specifically, we designed a fusion peptide comprising the trans-activator of transcription cell-penetrating peptide and an immunodominant ADAMTS13-derived T cell epitope (FINVAPHAR core amino acid sequence) to enable RBC surface loading. Results: We found that the fusion peptide binds to RBCs in a concentration-dependent manner. To assess whether our approach supports antigen presentation via human leukocyte antigen (HLA) class II molecules, macrophages were incubated with peptide-loaded RBCs, followed by analysis of HLA-DR-bound peptides via mass spectrometry. FINVAPHAR-containing peptides of varying lengths were mainly presented on macrophages from donors carrying the iTTP-associated HLA risk allele DRB1∗11, confirming functional antigen presentation and supporting the biological relevance of our model. Hemoglobin-derived peptides were also abundantly presented, supporting erythrophagocytosis as the entry route of our trans-activator of transcription-FINVAPHAR fusion peptide. Conclusion: Based on our results, we propose RBC-mediated delivery of ADAMTS13-derived peptides as a potential strategy for promoting tolerance in patients with iTTP.