Evidence for the Systemic Delivery of a Transgene Product from Salivary Glands

Abstract

The aim of this study was to assess the feasibility of using gene transfer to salivary glands to direct the systemic delivery of therapeutic protiens in vivo. We used a replication-deficient recombinant adenovirus vector (Adα1AT) that encodes human α1-antitrypsin (hα1-AT), which we used as a marker protein. Adα1AT (5 × 10⁹ pfu) was administered by retrograde ductal instillation to the submandibular glands of male rats. The amount of hα1-AT found in the salivary glands, saliva, serum, and other tissues was analyzed by a sensitive enzyme-linked immunosorbent assay (ELISA). Maximal levels of the marker protein were detected at 24–48 hr post-virus administration for glands (274 ng/mg protein), saliva (∼313 ng/ml), and serum (∼5 ng/ml) Serum levels remained elevated for 96 hr, whereas the measured half-life for the marker protein was ∼2 hr Generally little to no hα1-AT was detectable in most other organs. However, we were able to measure low levels of marker protein in tissues immediately surrounding infected glands. In all animals studied, levels of hα1-AT were higher in the glandular venous effluent than in arterial blood. Similar results were found with parotid glands. The aggregate data demonstrate that salivary glands may be a target for the nonsurgical, systemic delivery of transgene-encoded therapeutic proteins for diseases that require relatively low circulating protein levels.

Overview summary

Adenovirus-mediated gene transfer has been proposed as a tool to direct the systemic delivery of therapeutic proteins. The purpose of this study was to determine if adenovirus-mediated gene transfer to the salivary glands is suitable to elevate serum levels of a virus-encoded protein. The results demonstrate low serum levels of a marker protein (human α1-antitrypsin), which are stable for 4–5 days, after gene transfer to the parotid and submandibular glands. Furthermore, transgene expression was largely limited to the glands themselves. Recent developments of adenovirus-based gene transfer could improve the efficacy of this approach.