Also called up are Paul Hodgson (London Irish), Matt Hopper (Harlequins), lock Ed Slater (Leicester Tigers) and flanker Kearnan Myall (Sale Sharks).
Hodgson and Harden are temporary injury replacements for Karl Dickson (Harlequins) and Henry Thomas (Sale Sharks).
Hopper, Slater and Myall step up in place of Henry Trinder (Gloucester Rugby), Geoff Parling (Leicester Tigers) and Dave Attwood (Bath Rugby), who have joined the senior squad training in Leeds this week.
Slater and Harden make their first appearances at this level, Myall returns after first featuring for the Saxons in the 2010 Churchill Cup and experienced scrum half Hodgson, who won the last of his nine England caps two years ago, "will bring his energy and experience to the group".
Saxons coaches Callard and Simon Hardy have an experienced contingent of backs, including British & Irish Lion Ugo Monye and World Cup squad members Matt Banahan, Delon Armitage as well as the likes of in-form Gloucester duo Freddie Burns and Jonny May.
Up front Harden, 25, Myall, 25, and Slater, 23, join a group of forwards with an average age of 24 years nine months.
"This squad has got a great deal of longevity," said Callard. "They've all got something to offer to the national team, whether they're coming down from the senior squad, or they've been injured, or if they're young players going up. Everyone's got a contribution to make and it's all about the future."
The Saxons assemble at Woodbury Park in Devon today and the side to face the Wolfhounds is due to be named on Thursday, January 26.
England Saxons squad
Nick Abendanon (Bath Rugby)
Delon Armitage (London Irish)
Matt Banahan (Bath Rugby)
Freddie Burns (Gloucester Rugby)
Matt Hopper (Harlequins)
Paul Hodgson (London Irish)
Ryan Lamb (Northampton Saints)
Jonny May (Gloucester Rugby)
Ugo Monye (Harlequins)
Billy Twelvetrees (Leicester Tigers)
Micky Young (Leicester Tigers)
Chris Brooker (Harlequins)
Paul Doran-Jones (Northampton Saints)
Matt Garvey (London Irish)
James Gaskell (Sale Sharks)
Joe Gray (Harlequins)
Rupert Harden (Gloucester Rugby)
Tom Johnson (Exeter Chiefs)
Matt Mullan (Worcester Warriors)
Kearnan Myall (Sale Sharks)
George Robson (Harlequins)
Andy Saull (Saracens)
Ed Slater (Leicester Tigers)
Thomas Waldrom (Leicester Tigers)
Nick Wood (Gloucester Rugby)