Drug developer Amplimmune Inc., has entered a development agreement with British drug company GlaxoSmithKline PLC that could be worth more than $500 million if certain milestones are met, according to the Associated Press. Amplimmune said the agreement focuses on experimental drugs that target molecules that mask tumors and disease pathogens from the immune system. Early studies suggest the potential treatment can induce immune responses. Amplimmune will receive a $23 million, nonrefundable payment upfront from GlaxoSmithKline and could receive up to $485 million more in regulatory, development and sales milestone payments plus royalties on global sales. The U.S. company''s responsibilities include conducting an early-stage trial in cancer patients that is expected to begin next year.