hEPO expression is viral vector dose-dependent. Three groups of BALB/c mice received 108, 109, or 5 × 109 particles per animal of the AAVhEPO vector via retrograde ductal cannulation of the submandibular SGs, as described in Fig. 2. Bars represent mean (+SE) serum hEPO levels 12 weeks after vector administration for each dosage group (n = 3, 5, and 4 animals per group, respectively).