Medimmune is welcoming biotech firm Amplimmune to the AstraZeneca family in a deal that could be worth up to $500m for the Johns Hopkins University spin-out.

Medimmune, the research and development unit of life sciences conglomerate AstraZeneca, acquired 100% of Amplimmune’s shares for an initial consideration of $225m. A further $275m is available based on the US-based biotech hitting certain development milestones.

Amplimmune, founded in 2007, is developing treatments which bolster the immune system and intended for patients being treated…