A material transfer agreement is essentially an agreement that is put in place to help articulate the exchange of a material between two institutions. They are concerned primarily with protecting intellectual property rights, though they can also include additional clauses regarding things such as the rights to redistribute or transfer viruses or the handling of these viruses.
In the context of risk group 4 pathogens, it's important to know that most of the non-IP provisions are actually covered by other parts of the legislative requirements, and as a result, MTA's, in this case, are focused exclusively on IP rights as they pertain to the risk group 4 pathogens.