Early Phase Clinical Immunogenicity of Valoctocogene Roxaparvovec, an AAV5-Mediated Gene Therapy for Hemophilia A

Abstract

Evaluation of immune responses to adeno-associated virus (AAV)-mediated gene therapies prior to and following dose administration plays a key role in determining therapeutic safety and efficacy. This report describes up to 3 years of immunogenicity data following administration of valoctocogene roxaparvovec (BMN 270), an AAV5-mediated gene therapy encoding human B domain-deleted FVIII (hFVIII-SQ) in a phase 1/2 clinical study of adult males with severe hemophilia A. Patients with pre-existing humoral immunity to AAV5 or with a history of FVIII inhibitors were excluded from the trial. Blood plasma and peripheral blood mononuclear cell (PBMC) samples were collected at regular intervals following dose administration for assessment of humoral and cellular immune responses to both the AAV5 vector and transgene-expressed hFVIII-SQ. The predominant immune response elicited by BMN 270 administration was largely limited to the development of antibodies against the AAV5 capsid that were cross-reactive with other common AAV serotypes. No FVIII inhibitor responses were observed within 3 years following dose administration. In a context of prophylactic or ondemand corticosteroid immunosuppression given after vector infusion, AAV5 and hFVIII-SQ peptide-specific cellular immune responses were intermittently detected by an interferon (IFN)-g and tumor necrosis factor (TNF)-a FluoroSpot assay, but they were not clearly associated with detrimental safety events or changes in efficacy measures.

Evaluation of the Humoral Response to Adeno-Associated Virus-Based Gene Therapy Modalities Using Total Antibody Assays

“…Further, it is expected that most, if not all, patients without detectable preexisting anti-AAV antibodies will seroconvert to antibody positive following systemic administration of AAV gene therapy vectors. This could present a constraint for GTx that experience a decrease in product activity over time since they may preclude re-administration of the GTx (1)(2)(3)(4). Upon GTx administration, the levels of treatment-induced antibodies in non-human primate (NHP) studies were significantly elevated as compared to the antibody levels at baseline (5).…”

Emerging Immunogenicity and Genotoxicity Considerations of Adeno-Associated Virus Vector Gene Therapy for Hemophilia

“…In clinical trials for hemophilia, T-cell responses to AAV have been associated with asymptomatic, self-limited increases in liver enzymes and loss of transgene expression. These effects have been documented across several studies, although in some cases, lack of transgene expression was not associated with detection of activated capsid-responsive T-cells in peripheral blood; similarly, detection of T-cells reactive to AAV was not associated with any clinically relevant observation [5,45].…”

“…Although several trials of gene therapy for hemophilia A are in progress (Table 1) [42], only one study has published data. In this trial, transgene expression persisted for 3 years in participants receiving an AAV vector that contained a codon-optimized, B domain-deleted factor VIII (FVIII) complementary deoxyribonucleic acid (cDNA; AAV5-hFVIII) [43][44][45]. The multiyear follow-up of AAV5-hFVIII gene therapy found that the treatment significantly reduced annualized rates of bleeding events (ABRs) and resulted in complete cessation of prophylactic FVIII use among participants who received doses of 4 × 10 13 vg/kg or 6 × 10 13 vg/kg.…”

“…In addition, while cellular immune responses (as measured by IFN-γ and TNF-α fluorospot with either AAV5 peptide stimulation or FVIII peptide stimulation) were observed intermittently, there was no apparent association between positive responses and changes in liver transaminases or FVIII activity measurements. All subjects had unmeasurable AAV5 NAb at enrollment and developed high titer AAV5 NAb after vector infusion, which persisted at high titer for years and demonstrated cross-neutralization of all other AAV serotypes tested (AAV2, AAV6, AAV8, AAVrh10) [45].…”

Novel Combinatorial MicroRNA-Binding Sites in AAV Vectors Synergistically Diminish Antigen Presentation and Transgene Immunity for Efficient and Stable Transduction

“…First isolated from adenovirus preparations in the 1960s (1,2), AAV is a non-pathogenic dependoparvovirus that is able to transduce a wide range of cell types. Recombinant AAVs (rAAVs) have been proven to confer long-lasting and safe transgene expression in a variety of human tissues (3)(4)(5)(6). rAAVs have also achieved sustained therapeutic effect for a variety of inherited diseases, including Leber's congenital amaurosis type 2 (7,8), hemophilia B (9), M-type a-1 antitrypsin deficiency (10,11), and lipoprotein lipase deficiency (12,13).…”