How to grant access to a user to all content created by certain users? I've been looking all the options commented on Controlling Acces to Content Overview but I don't see any that allow one particular user to access all content created by other particular users. 

Something like: User A have permissions to see all nodes created by users B, C and D.
(No need to include a reference or a taxonomy term to each node).

Any insights?

Thank you so much!
Sorry telling you that as far as I know there is nothing like this out of box.
Maybe if you mention the requirement we will be able to help you.
For now don't think about users and think about roles. if you want to make it more flexible I suggest using workbench access so the created content will have a section (Taxonomy term) and the section will be accesed by user A and B only.
Hope that help