Therapeutic hFIX Activity Achieved after Single AAV5-hFIX Treatment in Hemophilia B Patients and NHPs with Pre-existing Anti-AAV5 NABs

Abstract

Currently, individuals with pre-existing neutralizing antibodies (NABs) against adeno-associated virus (AAV) above titer of 5 are excluded from systemic AAV-based clinical trials. In this study we explored the impact of pre-existing anti-AAV5 NABs on the efficacy of AAV5-based gene therapy. AMT-060 (AAV5-human FIX) was evaluated in 10 adults with hemophilia B who tested negative for pre-existing anti-AAV5 NABs using a GFP-based assay. In this study, using a more sensitive luciferase-based assay, we show that 3 of those 10 patients tested positive for anti-AAV5 NABs. However, no relationship was observed between the presence of pre-treatment anti-AAV5 NABs and the therapeutic efficacy of AMT-060. Further studies in non-human primates (NHPs) showed that AAV5 transduction efficacy was similar following AMT-060 treatment, irrespective of the pre-existing anti-AAV5 NABs titers. We show that therapeutic efficacy of AAV5-mediated gene therapy was achieved in humans with pre-existing anti-AAV5 NABs titers up to 340. Whereas in NHPs circulating human factor IX (hFIX) protein was achieved, at a level therapeutic in humans, with pre-existing anti-AAV5 NABs up to 1030. Based on those results, no patients were excluded from the AMT-061 (AAV5-hFIX-Padua) phase IIb clinical trial (n = 3). All three subjects presented pre-existing anti-AAV5 NABs, yet had therapeutic hFIX activity after AMT-061 administration.

Keywords: AAV; FIX; NABs; anti-AAV NABs; gene therapy; hFIX; hemophilia.

Figure 1

GFP-Based Anti-AAV5 NABs Assay Was Performed on 50 Healthy Donors’ Serum Samples Inhibition of transduction of HEK293 cells with AAV5-GFP after pre-incubation with 50 healthy donor serum samples is plotted, and only one donor that is represented as an empty circle was considered to be positive for anti-AAV5 NABs (A). No unequivocal correlation was observed between the anti-AAV5 NABs as measured with GFP-based assay and anti-AAV5 IgG results as measured by ELISA (B). The same 50 healthy donor sera samples were screened for anti-AAV5 NABs with the use of luciferase-based assay (C). A strong correlation was observed between the anti-AAV5 NABs as measured with luciferase-based assay and anti-AAV5 IgG results as measured by ELISA (r = 0.85; p < 0.0001) (D). Limits of quantitation of both methods: for the anti-AAV5 NABs assay, this corresponds to the starting titer of 2; for the ELISA, this corresponds to 0.230 OD. AAV, adeno-associated virus; IgG, immunoglobulin G; NABs, neutralizing antibodies; OD, optical density.

Figure 2

Pre-existing Anti-AAV5 NABs Titers in Serum Samples from Patients Participating in the CT-AMT-060-01 Study versus Mean hFIX Activity after Systemic Administration of Low-Dose AMT-060 (AAV5-hFIX) Anti-AAV5 NABs were measured using the luciferase-based assay. AAV, adeno-associated virus; hFIX, human factor IX; NABs, neutralizing antibodies.

Figure 3

Anti-AAV5 NABs Titers in Serum Samples from Study CT-AMT-060-01 Patients 3, 4, and 5, before and after IgG Depletion Anti-AAV5 NABs were measured using the luciferase-based assay. AAV, adeno-associated virus; Ig, immunoglobulin; NABs, neutralizing antibodies.

Figure 4

Changes in Anti-AAV5 IgG and IgM Antibody Titers over Time in CT-AMT-060-01 Study Participants Patients received a single systemic administration of AMT-060 (AAV5-hFIX) on day 0. IgG and IgM levels were determined using ELISAs. The lower limit of detection for IgG/IgM was 50. Dotted lines represent the upper limit of detection for the anti-AAV5 IgG ELISA (109350). AAV, adeno-associated virus; hFIX, human factor IX; Ig, immunoglobulin.

Figure 5

Lack of Correlation between Pre-Existing Anti-AAV5 NABs Titers in Serum Samples from NHPs and Efficacy of AMT-060 (AAV5-hFIX) Treatment Pre-existing anti-AAV5 NABs titers in serum samples from NHPs versus (A) levels of hFIX DNA in the liver 6 months after a single intravenous administration of AMT-060 (AAV5-hFIX) and (B) percentage of hFIX protein in plasma 1 week after a single intravenous administration of AMT-060 (AAV5-hFIX). Anti-AAV5 NABs titers were measured using the luciferase-based assay, hFIX DNA was measured using qPCR, and percentage of hFIX protein was measured in an ELISA-based assay. AAV, adeno-associated virus; hFIX, human factor IX; NABs, neutralizing antibodies; NHPs, non-human primates.

Figure 6

Changes in Percentage of hFIX in NHPs Plasma over Time, after a Single Intravenous Administration of AAV5-hFIX Different colors represent different doses of AAV5-hFIX. Percentage of hFIX protein was measured using ELISA-based assay. AAV, adeno-associated virus; hFIX, human factor IX; NHPs, non-human primates.

Figure 7

An Additional 100 Healthy Male Donor Serum Samples Were Screened for Presence of Pre-existing Anti-AAV5 NABs Forty-seven donors who tested above the lower limit of detection (above anti-AAV5 NABs titer of 2) are plotted and median with 95% CI (A). Dotted lines represent current highest pre-existing anti-AAV5 NABs titers that were found not to interfere with the efficacy of AMT-060 (AAV5-hFIX) treatment in humans (titer of 340) or in NHPs (1030). (B) Anti-AAV5 NABs titers versus anti-AAV5 IgG ELISA results are plotted for those 47 donors (each black dot symbol represents paired anti-AAV5 NABs titer and anti-AAV5 IgG ELISA titer). Anti-AAV5 NABs titers and anti-AAV5 IgG ELISA results of hemophilia B clinical trial of patients who tested positive in those assays are shown superimposed (red diamond symbols, patients 3, 4, and 5 as specified). AAV, adeno-associated virus; IgG, immunoglobulin G; NABs, neutralizing antibodies; NHPs, non-human primates.