Uncapped Twelvetrees is in line to make his international debut. With Manu Tuilagi out injured, the 24-year-old has been preferred to London Irish outside centre Jonathan Joseph.
Saracens wing David Strettle has also been included, which means no place in the squad for Northampton full-back Ben Foden.
England head coach Stuart Lancaster will confirm his starting XV on Thursday.
In that scenario, Twelvetrees would come in at inside centre with Brad Barritt in the number 13 jersey, which he wore for his first two Test appearances in last year's Six Nations.
Another option is that either Owen Farrell or Toby Flood are pressed into action at inside centre, but Farrell is the incumbent fly-half from England's record 38-21 triumph over New Zealand on December 1 and the experiment of using Flood as an emergency inside centre failed in the World Cup quarter-final defeat to France.
Lancaster's other selection posers are at scrum-half, where Danny Care and Ben Youngs are battling for the nine jersey, and at hooker between Tom Youngs and Dylan Hartley.
Alex Goode made his comeback from a shoulder injury for Saracens last Sunday but it remains to be seen whether he has done enough after five weeks out to retain the full-back jersey.
If so, then Lancaster must choose between Mike Brown and Strettle on the left wing. If not, then both would start with Brown switching to his natural position at full-back.
Mouritz Botha, who has revealed he is heading to New York "for the rest of the week", Thomas Waldrom, Lee Dickson, Billy Vunipola, Ugo Monye, Henry Thomas and Matt Kvesic were the other players released by England on Tuesday night.
Lancaster said: "We've had to make some tough calls with a lot of competition for places.
"The players' attitude and application in training has been first rate and we know those going back to their clubs and playing in the LV= Cup will be pushing hard for contention for the Ireland match."
Forwards: Cole, Hartley, Haskell, Launchbury, Lawes, Marler, Morgan, Parling, Robshaw, M Vunipola, Wilson, Wood, T Youngs.
Backs: Ashton, Barritt, Brown, Care, Farrell, Flood, Goode, Strettle, Twelvetrees, B Youngs.
Kick-off at Twickenham on Saturday is at 4pm.
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