Gene therapy with adeno-associated virus vector 5-human factor IX in adults with hemophilia B

Abstract

Gene therapy for hemophilia B aims to ameliorate bleeding risk and provide endogenous factor IX (FIX) activity/synthesis through a single treatment, eliminating the requirement for FIX concentrate. AMT-060 combines an adeno-associated virus-5 (AAV5) vector with a liver-specific promoter driving expression of a codon-optimized wild-type human FIX gene. This multinational, open-label study included 10 adults with hemophilia B (FIX ≤2% of normal) and severe-bleeding phenotype. No participants tested positive for AAV5-neutralizing antibodies using a green-fluorescent protein-based assay, and all 10 were enrolled. A single dose of 5 × 10¹² or 2 × 10¹³ genome copies of AMT-060/kilogram was administered to 5 participants each. In the low-dose cohort, mean endogenous FIX activity increased to 4.4 IU/dL. Annualized FIX use was reduced by 81%, and mean annualized spontaneous bleeding rate (ASBR) decreased from 9.8% to 4.6% (53%). In the higher-dose cohort, mean FIX activity increased to 6.9 IU/dL. Annualized FIX use decreased by 73%, and mean ASBR declined from 3.0 to 0.9 (70%). There was no reduction in traumatic bleeds. FIX activity was stable in both cohorts, and 8 of 9 participants receiving FIX at study entry stopped prophylaxis. Limited, asymptomatic, and transient alanine aminotransferase elevations in the low-dose (n = 1) and higher-dose (n = 2) cohorts were treated with prednisolone. No decrease in FIX activity or capsid-specific T-cell responses were detected during transaminase elevations. A single infusion of AMT-060 had a positive safety profile and resulted in stable and clinically important increases in FIX activity, a marked reduction in spontaneous bleeds and FIX concentrate use, without detectable cellular immune responses against capsids. This trial was registered at www.clinicaltrials.gov as #NCT02396342; EudraCT #2013-005579-42.

Figure 1.

Study design. ^aAfter the administration of AMT-060 to each of the first 2 participants in each cohort, the Data Monitoring Committee evaluated available safety data during 24 hours before dosing of the next participant could be initiated. ^bProphylactic FIX replacement therapy was generally tapered between weeks 6 and 12 if FIX activity was ≥2.0 IU/dL in at least 2 consecutive visits. Investigators could taper prophylaxis later than 12 weeks at their discretion. The decision to continue tapering/withholding of prophylactic FIX replacement therapy was based on the individual assessment by the investigator but included the requirement to document that the participant could maintain a FIX activity level ≥2.0 IU/dL. ^cCohort 2 dosing was initiated after the completion of cohort 1 dosing and review of initial safety data by the Data Monitoring Committee.

Figure 2.

FIX activity across time. (A) Cohort 1; (B) cohort 2. Only values at least 10 days after the preceding FIX concentrate administration, so that they are uncontaminated by exogenous FIX, are included. Participant 3 continued with prophylaxis after AMT-060 treatment so that only limited samples uncontaminated by exogenous FIX were available. The dotted line at FIX activity of 2 IU/dL indicates the threshold required for ceasing prophylaxis per protocol. FIX prophylaxis was continued after AMT-060 and tapered between week 6 and week 12. *Participant 4 had a moderate hemophilia B phenotype at baseline (FIX activity 1.5 IU/dL).

Figure 3.

Annualized FIX usage and bleeds. (A) Annualized FIX usage; (B) annualized bleeds. Cumulative annualized FIX activity excludes use of factors related to surgery. The total use of FIX was collected retrospectively from patient diaries and hospital record data at the year before screening and prospectively after AMT-060 (excluding the tapering/prophylaxis period) as part of the statistical analysis. Follow-up after discontinuation of prophylaxis ranged from 39 to 65 weeks for the participants in cohort 1 and from 11 to 34 weeks for the participants in cohort 2. One participant in cohort 1 continued FIX prophylaxis after AMT-060 infusion. One participant in cohort 2 used on-demand FIX therapy before study entry. One participant in cohort 2 was missing historical bleed data.