Another way is to use Reaper on an instrument track in Pro Tools and use Rewire.
This will explain how that works. I use both Blue Cat patchwork and Reaper. The advantage of Reaper is that it will host 32bit and make a bridge for the 64bit set up whereas Bluecat Patchwork will only host 64bit VSTs.
The advantage of Patchwork is that you can host more than just VI's and use them directly on PT tracks. While you can host any VST in Reaper, there's no way to use Rewire to use an effect on an PT track. So, while you can route the audio output of ANY Reaper track to a PT AUX track for further processing in PT, if all you want is to use a VST effect of some kind..a certain Reverb say...then you have to export the audio from PT into Reaper, add the effect there, and route the audio back to PT via Rewire. A bit cumbersome.
But, for straightout hosting VST VI's for creating tracks, Reaper is also a great way to host and use them in PT via Rewire.