The recombinant DNA technological processes have made immense impact in the area of healthcare. The recombinant therapeutics do not induce unwanted immunological responses as is common in case of similar products isolated from non-human sources.
In mammals, including humans, insulin is synthesised as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide. Therefore insulin from animals may cause reactions.