How many adjuvants in a vaccine formula are allowed? - (Apr/28/2014 )

Hi there,

I was wondering, is there any rule or regulation about the number of immunopotentiators or adjuvants that can be used in a potential vaccine formula for human use? For examples the regulations by WHO, FDA, IND, etc.? I mean, how far can we go? 1, 2, 3, more?

I thank you in advance for your inputs.

Shouldn't be the primary question rather how many are really necessary?