Safety and Bioactivity of rAAV2-hAAT in alpha-1 Antitrypsin-Deficient Patients in a Phase I Clinical Trial

INTRODUCTION: Recombinant adeno-associated virus (rAAV) vectors are capable of sustained expression of therapeutic proteins when administered to skeletal muscle. A single injection of a rAAV2 vector in mice resulted in sustained secretion of human alpha-1 antitrypsin (hAAT) at levels that would be therapeutic for prevention of lung disease in humans (11,000 nM). There is currently no definitive therapy for these patients, since protein replacement products are in short supply and require weekly intravenous infusions. Recently, we completed the ongoing preclinical testing (mouse, rabbit, and primate) of the rAAV2-hAAT vector in muscle, completed clinical grade production of rAAV2-hAAT, and initiated a phase I trial of rAAV-hAAT gene therapy in patients with AAT deficiency. MEHODS: The trial is an open-labeled, single administration study being performed in a total of 15 adult AAT- deficient patients. Five cohorts of three subjects each are being used with a dose escalation between cohorts. The dosages for the four cohorts range from 2 × 1012 vector genomes (vg) per patient to 2 × 1014 vg/patient. Subjects are screened and allowed a 28-day period for washout of protein replacement. An ultrasound-guided injection technique is used to avoid intravascular injection. The study endpoints address safety with examinations of the injection site, hematology, chemistry, coagulation studies, and pulmonary function tests. Biological activity of the vector is assessed by detection of normal M-variant hAAT protein by ELISA. Serum is also assayed for antibodies and lymphocyte proliferation responses to rAAV2 capsid and to AAT. Blood and semen DNA are also being assayed for vector DNA sequences. RESULTS: At the time of submission of this abstract, twelve subjects have been treated, and there have been no vector-related adverse events to date. All patients have demonstrated increases in anti-AAV2 capsid protein titers by ELISA, but none have shown increases in anti-hAAT antibody titers or in lymphocyte proliferation responses. Patients in the cohorts 2–4 show PCR evidence of vector DNA in the blood within the first 14 days, but without obvious ill effects. At least one subject in cohorts 3 shows evidence of M-AAT expression in the range of 50–100 nm. CONCLUSIONS: Preliminary evidence of the safety and bioactivity of rAAV2-hAAT are being generated. These support the feasibility of future clinical studies, including one recently begun with rAAV1, a serotype that shows a 500–1000-fold greater bioactivity than the current rAAV2 vector in mice.