The regular ProTools build requires signed AAX plug-ins. In order to sign AAX plug-ins, you need to create an Avid developer account and follow the documentation there (some of the info is covered under an NDA and cannot be discussed outside Avid’s forums). Once you’ve created a developer account, you’ll also be able to download a developer build of ProTools that allows loading unsigned plug-ins.
There’s some more info in this thread.