Haemophilia gene therapy: From trailblazer to gamechanger

Abstract

Haemophilia is an attractive disease target for gene therapy that fostered the development of the field at large. The delivery of the clotting factor genes into the patients' cells could be accomplished using different types of gene delivery vehicles or vectors. Adeno-associated viral vectors (AAV) and lentiviral vectors represent some of the most promising gene delivery technologies that allow for a relatively efficient delivery of the therapeutic FVIII and FIX transgenes into the relevant target cells. To reduce the risks associated with insertional mutagenesis due to random vector integration, gene-editing approaches have also been considered based primarily on zinc finger nuclease (ZFN) and CRISPR/Cas. However, comprehensive analysis of off-target effects is still required. It is particularly encouraging that relatively stable therapeutic FVIII or FIX expression levels were reached in severe haemophilia patients in recent clinical trials after liver-directed AAV gene therapy. This success could be ascribed in part to improvements in vector design. In particular, clotting factor levels could be increased by codon optimization of coagulation factor transgenes. Alternatively, incorporation of a hyperactive gain-of-function R338L mutation (FIX Padua) in the FIX gene improved the overall efficacy. However, some patients still show transient liver toxicity, especially at high vector doses, possibly due to inflammatory immune responses, requiring the need for transient immunosuppression. The exact immune mechanisms are not fully understood, but may at least in some patients involve an AAV-capsid specific T cell response. Moreover, there is a need to identify the key factors that contribute to the interpatient variability in therapeutic efficacy and safety after gene therapy.

Broad gene expression throughout the mouse and marmoset brain after intravenous delivery of engineered AAV capsids

“…Adeno-associated viruses (AAVs) are increasingly utilized as delivery vehicles due to their strong clinical safety record, low pathogenicity, and stable, non-integrating expression in vivo 1 . AAVs were first approved for gene therapy in humans in 2012 to treat lipoprotein lipase deficiency 2 , and have more recently been approved to treat spinal muscular atrophy 3 , retinal dystrophy and hemophilia 4,5 . Many more advanced-stage clinical trials using AAVs are underway [6][7][8][9][10][11] .…”

Patient Perspectives on Novel Treatments in Haemophilia: A Qualitative Study

“…Some of these products may be administered subcutaneously and no longer require intravenous injections. However, new treatments may have drawbacks of their own, including known and unknown risks, as summarised in Table 1 [10][11][12][13][14].…”

“…Overview of haemophilia A and B treatment products currently under development or marketed recently, with their benefits, potential disadvantages and mechanisms of action[10][11][12][13][14] …”

Multiyear Follow-up of AAV5-hFVIII-SQ Gene Therapy for Hemophilia A

“…1 Here, we describe 2-year and 3-year safety and efficacy data after the administration of AAV5-hFVIII-SQ (valoctocogene roxaparvovec) in men with severe hemophilia A. In addition to providing clinical safety and efficacy data, this research contributes to a mechanistic understanding of the variability observed in gene therapy studies, [2][3][4][5][6] thus providing insights into mechanisms of DNA persistence and durable expression.…”