Polarized secretion of transgene products from salivary glands in vivo

Previously (Kagami et al, Hum. Gene Ther, 1996;7:2177-2184) we have shown t hat salivary glands are able to secrete a transgene-encoded protein into se rum as well as saliva. This result and other published data suggest that sa livary glands may be a useful target site for vectors encoding therapeutic proteins for systemic delivery. The aim of the present study was to assess in vivo if transgene-encoded secretory proteins follow distinct, polarized sorting pathways as has been shown to occur "classically" in cell biologica l studies in vitro. Four first-generation, E1(-), type 5 recombinant adenov iruses were used to deliver different transgenes to a rat submandibular cel l line in vitro or to rat submandibular glands in vivo. Subsequently, the s ecretary distribution of the encoded proteins was determined. Luciferase, w hich has no signal peptide, served as a cell-associated, negative control a nd was used to correct for any nonspecific secretory protein release from c ells. The three remaining transgene products tested, human tissue kallikrei n (hK1), human growth hormone (hGH), and human alpha(1)-antitrypsin (h alph a 1AT), were predominantly secreted (>96%) in vitro, Most importantly, in v ivo, after a parasympathomimetic secretory stimulus, both hK1 and hGH mere secreted primarily in an exocrine manner into saliva, Conversely, h alpha 1 AT was predominantly secreted into the bloodstream, i.e., in an endocrine m anner. The aggregate results are consistent with the recognition of signals encoded within the transgenes that result in specific patterns of polarize d protein secretion from rat submandibular gland cells in vivo.