This, because you already made commitments to school A's interview date, and as mentioned above, it would be rude to expect them to change it for you.
It seems like some people have received interviews for U Chicago Biochemistry and Molecular Biophysics already. However, I wouldn't fret because a large bulk of admissions always come out in January. Columbia Systems Biology appears to have not sent out anything yet (don't quote me on this)
Feel free to refer to this page for the latest admissions updates:
http://www.thegradcafe.com/survey/