EXHIBIT 7.3 AGREEMENT REGARDING STOCK TRANSFER RESTRICTIONS THIS AGREEMENT REGARDING STOCK TRANSFER RESTRICTIONS is entered into as of August 6, 1997 by and between Progenitor, Inc., a Delaware corporation ("Progenitor") and Amgen Inc., a Delaware...Agreement Regarding • August 22nd, 1997 • Amgen Inc • Biological products, (no disgnostic substances) • Delaware
