This study consists of two trials. The goal of Trial A, a dose-escalation trial, is to determine the maximum tolerated dose (MTD) of PDGF-B/Ad5, an adenovirus vector designed to overexpress PDGF-B, with respect to local and systemic toxicity and biologic feasibility. The primary objective is to evaluate the acute safety, both local and systemic, of an intra-ulcer injection of PDGF-B/Ad5, thereby determining the recommended dose. Upon evaluating patients, they will be treated with a single intra-ulcer injection of PDGF-B/Ad5 in the wound. Patients will receive only one dose, which will be administered during a 72-hour inpatient stay in a research unit at the Hospital of the University of Pennsylvania.