The insect cell as host for protein production is relative new. Therefore few data are available. This creates a vicious circle because it makes the choice of insect cells as basis for a pharmaceutical process less attractive. There are three main issues when comparing insect-cells to "traditional" systems as mammalian and bacterial cells. First, since the expression vector is not incorporated in the cells, a virus stock similar to the cell bank system has to be laid down and tested. This will cost time and money. Secondly the vector is subject to mutation and therefore the decrease in infectivity has to be characterized and validated. Third, the post-translational modification of the protein may differ. None of the mentioned issues, however, forms an obstacle that can not be overcome.