Patricia Soldati's Answer:
Run, don't walk to your manager and have a respectful, positively-positioned heart-to-heart conversation about what you've been doing, the lack of challenge, your expectations, etc.
Offer specific examples of what you've been assigned vs. what you feel would be more challenging and worthwhile - and why you feel you are up to the challenge.
At the two year mark, this is way overdue - in fact, with such a "prestigious" program I would have thought these kinds of conversations would be built-in to the system.
Have the conversation with your manager first, and then with HR if the situation doesn't quickly change. Any manager or HR personal worth their salt will respect your desire to contribute more and take on assignments with greater impact.
Perhaps the greater lesson learned here is that one ALWAYS must forge their own way in the corporate world - look out for one's own best interests and work clearly, and always respectfully, to that end.