
Basically this is what I could gathered. Cheese is made by heating milk and adding a coagulating agent referred to as rennet or enzymes, producing the cheese product. The majority of cheese manufacturers now are using vegetable rennet and synthetic rennet manufactured in laboratories from various fungi microbial rennet.
From an Islamic perspective, animal rennet can be divided into three categories:
1) The rennet derived from animals that have been slaughtered in accordance with the Sharīaah. There is no difference of opinion that such rennet is completely pure.

2) The rennet derived from permissible animals (e.g., cows, sheep and goats) that have not been slaughtered according to the Sharīaah. There is a difference of opinion amongst the four madhabs. The position in the Shafī’ī and Mālikī schools, is that such rennet is impure, and the cheese derived from it also impure
In the some Hanafi Schools, rennet obtained from an animal slaughtered by a non-Muslim or Muslim in accordance with Islamic law or contrary to it, in all cases is permissible, as long as the animal in question is not a pig.
3) There is no significant difference of opinion on the rennet derived from impermissible animals, such as pigs, as the source of it is impure. The enzyme derived from pigs is commonly referred to as pepsin. Just like the meat, milk and bones of such animals are impure; similarly the rennet derived from their stomachs is also impure.
However, it is better to avoid whenever reasonably possible when its source is unknown. Allah alone knows all. For us we prefer to buy halal cheese from Islamic shops here.