Indoleamine 2,3-dioxygenase attenuates inhibitor development in gene-therapy-treated hemophilia A mice

Abstract

A serious impediment to gene and protein replacement therapy in hemophilia A is the development of inhibitors. Mechanisms responsible for inhibitor development include T-cell-dependent adaptive immune responses and the CD28-B7 signaling pathway that eventually leads to the formation of antibodies directed against factor VIII (FVIII). Indoleamine 2,3-dioxygenase (IDO) is a potent immunosuppressive enzyme that can inhibit T-cell responses and induce T-cell apoptosis by regulation of tryptophan metabolism. Kynurenine, one of the metabolites of tryptophan, has been implicated as an immune modulator. Here we hypothesize that co-delivery of the genes for FVIII and IDO can attenuate inhibitor formation. Using transposon-based gene delivery, we observed long-term therapeutic FVIII expression and significantly reduced inhibitor titers when the genes were codelivered. Co-expression of FVIII and IDO in the liver was associated with increased plasma kynurenine levels, an inhibition of T-cell infiltration and increased apoptosis of T cells within the liver. These experiments suggest that modulation of tryptophan catabolism through IDO expression provides a novel strategy to reduce inhibitor development in hemophilia gene/protein therapy.

Gene therapy for hemophilia

“…Similarly, sustained gene transfer using the Sleeping Beauty transposon is limited by an immune response to F.VIII, unless tolerance is induced at the neonatal stage (334, 335). Interestingly, in adult mice, using SB to express both F.VIII and the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO) induced sustained F.VIII expression and reduced T cell infiltration in the liver (336). In addition to hydrodynamic injection, F.VIII-expressing plasmids have also been targeted to specific cell types using nanocapsules.…”

Transposons: Moving Forward from Preclinical Studies to Clinical Trials

“…148 To overcome this limitation, immunomodulatory agents such as gadolinium chloride, and cyclophosphamide were used. 148,156 Alternatively, the immunosuppressive enzyme indoleamine 2,3dioxygenase (IDO) 144 was employed to boost immune tolerance and prolong transgene expression in mouse models. In a recent study in MPS mice, transposition efficacy of transgene gene mediated by SB100X was 15-fold more efficient than with the SB11 system and contributed to persistent therapeutic gene expression levels for 1 year.…”

Advances in knowledge of inhibitor formation in severe haemophilia A

“…This indicates that although IDO is induced by toll‐like receptor 9 (TLR9) activation and IFN‐γ signalling (Ehlers & Ravetch, ), tryptophan catabolites have suppressive effects that can prevent hyperinflammation and autoimmunity and thus might be acting to mitigate inhibitor formation. For example, co‐delivery of the genes for FVIII and IDO resulted in increased plasma kynurenine levels, inhibition of T‐cell infiltration, increased apoptosis of T cells within the liver and significantly reduced FVIII inhibitor titres when compared to delivery of FVIII gene therapy alone in HA mice (Liu et al , ). The gut microbiota is also capable of degrading tryptophan, producing similar immunosuppressive metabolites independent of IDO (Zelante et al , ), but the role of these compounds is yet to be determined in the context of FVIII.…”