The problem is that the CC121 needs some special unlocking code to work properly and currently only Cubase, Wavelab, Nuendo and REAPER support this. Aside from this it’s a very simple MIDI controller that should work with every DAW out there.
So someone has to adapt Protools to support the CC121. This must be done by Avid or some 3rd party developer (I don’t know if 3rd party developers are even allowed to do such things).