Insulin injected into humans used to come from pigs. However there were some political and health issues with this. Some peoples bodies also rejected it. It is now made by genitic engineering where the human DNA for making insulin is inserted into the plasmid of a bacteria cell. This is very tricky and is done using a restricting enzyme. The bacteria are then put into a fermentor and multiply; each producing insulin. This insulin is much less likely to be rejected by the human body =)
