Phase 2 clinical trial of a recombinant adeno-associated viral vector expressing α1-antitrypsin: interim results

Abstract

Recombinant adeno-associated virus (rAAV) vectors offer promise for the gene therapy of α(1)-antitrypsin (AAT) deficiency. In our prior trial, an rAAV vector expressing human AAT (rAAV1-CB-hAAT) provided sustained, vector-derived AAT expression for >1 year. In the current phase 2 clinical trial, this same vector, produced by a herpes simplex virus complementation method, was administered to nine AAT-deficient individuals by intramuscular injection at doses of 6.0×10(11), 1.9×10(12), and 6.0×10(12) vector genomes/kg (n=3 subjects/dose). Vector-derived expression of normal (M-type) AAT in serum was dose dependent, peaked on day 30, and persisted for at least 90 days. Vector administration was well tolerated, with only mild injection site reactions and no serious adverse events. Serum creatine kinase was transiently elevated on day 30 in five of six subjects in the two higher dose groups and normalized by day 45. As expected, all subjects developed anti-AAV antibodies and interferon-γ enzyme-linked immunospot responses to AAV peptides, and no subjects developed antibodies to AAT. One subject in the mid-dose group developed T cell responses to a single AAT peptide unassociated with any clinical effects. Muscle biopsies obtained on day 90 showed strong immunostaining for AAT and moderate to marked inflammatory cell infiltrates composed primarily of CD3-reactive T lymphocytes that were primarily of the CD8(+) subtype. These results support the feasibility and safety of AAV gene therapy for AAT deficiency, and indicate that serum levels of vector-derived normal human AAT >20 μg/ml can be achieved. However, further improvements in the design or delivery of rAAV-AAT vectors will be required to achieve therapeutic target serum AAT concentrations.

Trial registration: ClinicalTrials.gov NCT01054339.

FIG. 1.

Serum M-specific α₁-antitrypsin (AAT) concentration after injection of rAAV1-CB-hAAT produced by plasmid transfection (TFX) or the herpes simplex virus (HSV) method. Values shown represent means±SD. The dose of vector administered to subjects is indicated in the figure legend. Values for the TFX group are from a previous study (Brantly et al., 2009). Values for the 6×10¹¹ VG/kg HSV group do not include results for subject 303, who had an AAT phenotype of SZ; the monoclonal antibody used to determine serum M-specific AAT concentrations has little cross-reactivity with Z-type AAT but cross-reacts strongly with S-type AAT, causing results for this assay in this subject to be spuriously high. Color images available online at www.liebertonline.com/hum

FIG. 2.

Serum M-specific α₁-antitrypsin (AAT) concentration (solid symbols) and serum creatine kinase (CK) levels (open symbols) after injection of rAAV1-CB-hAAT in individual subjects. Subject 303 had an AAT phenotype of SZ, and results for the M-specific AAT ELISA in this subject are spuriously high. Subjects 305 and 307 were the two male subjects.

FIG. 3.

Time course of IFN-γ ELISPOT responses to pools of AAV1 capsid peptides or controls. PBMCs were obtained at screening, baseline, and 1, 2, and 3 months after vector administration and were stimulated with each of three pools (A, B, and C) of AAV1 capsid peptides (15-mers overlapping by 10 amino acids) or with a positive control peptide pool (CEF). SFC, spot-forming cells.

FIG. 4.

Histology and immunohistochemical study of skeletal muscle. (A) H&E-stained section showing a moderate endomysial inflammatory reaction composed primarily of mononuclear cells. (B) H&E-stained section showing a marked endomysial inflammatory reaction. (C) Immunohistochemistry for AAT, showing individual weak to moderate granular reactivity in individual myofibers on cross-section. (D) Immunohistochemistry for AAT, showing individual weak to moderate granular reactivity in individual myofibers cut longitudinally. (E) Immunohistochemistry for CD3, showing a high proportion of T lymphocytes comprising the inflammatory infiltrate. (F) CD8-immunoreactive T cells comprise a significant subset of the total lymphocytic infiltrate.