PB0211 - A translational analysis of immune components in peripheral blood from severe hemophilia A patients treated with TAK-754, an AAV8 vector with a codon-optimized B-domain–deleted factor VIII transgene

Background: Immune responses to gene therapies have been associated with infusion reactions, transaminase elevation, and loss of transgene expression. Here, we describe an immunogenicity analysis in peripheral blood from three hemophilia A (HA) patients following infusion of TAK-754, an AAV8-based FVIII gene therapy (NCT 03370172).

Aims: (1) To report clinical biomarkers of immunogenicity from patients treated with TAK-754.
(2) To present an immunogenicity transcriptomics analysis from peripheral blood.

Methods: HA patients received TAK-754 in two cohorts: 2×10^12 and 6×10^12 capsid particles (cp)/kg. Serum cytokines, complete blood counts (CBC), anti-capsid immunoglobulin assays, and enzyme linked immunospot (ELISpot) assays were collected. Bulk mRNA sequencing was performed on whole blood compared to healthy volunteers. This study was approved by local ethics committees, and patients provided informed consent.

Results: No changes in cytokines were observed within 24 hours of infusion. Transaminase elevation and decline of FVIII expression occurred 4-9 weeks post-infusion despite use of glucocorticoids. No significant changes in complete blood count populations were observed. ELISpot assays did not correspond with loss of FVIII transgene expression or transaminase elevation. Bulk mRNA transcriptomic analysis did not demonstrate significant changes in NK cell, dendritic cell, NF-kB, IL-6, TLRs 1-8, or T cell pathway signals. A small transient increase in TLR9, TNF-a, CCL5, and IRF7 signals occurred 8 hours after infusion without activating a Type 1 IFN response.

Conclusion(s): TAK-754 evoked a limited immune response as measured in blood with highly sensitive methodology, demonstrating that such methods have limited value for clinical decision-making or post hoc analysis. Efforts to optimize AAV gene therapy should focus on target tissue-specific analysis and improving preclinical immunogenicity models.