text: Upon identifying the target subunit and its encoding gene, the gene will be isolated and transferred to a second, non-pathogenic organism, and cultured for mass production. The process is also known as heterologous expression.
  A suitable expression system is selected based on the requirement of post-translational modifications, costs, ease of product extraction and production efficiency. Commonly used systems for both licensed and developing recombinant subunit vaccines include bacteria, yeast, mammalian cells, insect cells.