The Privileges and Immunities Clause, Section 2 of Article IV of the United States Constitution, also referred to as "PIC4," prevents states from discriminating against the fundamental rights of out-of-state citizens. Basically, it means that the citizens of one state are on an equal footing when they travel to another state. Out-of-state citizens are entitled to the same rights as other citizens in the state in which they happen to be in.
The Privileges and Immunities Clause does not, however, extend to all commercial activity. It only covers fundamental individual rights and does not include businesses and corporations. A corporation is not considered to be a citizen under PIC4. The "special" privileges granted to a corporation by its home state do not accompany that corporate entity when its activities cross state lines.