Bath Rugby's Joe Cokanasiga, Charlie Ewels, Jonathan Joseph, Ruaridh McConnochie, Sam Underhill and Anthony Watson have been included in England's third official Rugby World Cup training camp, which takes place in Treviso.
The 12-day camp will see 38 players travel to Italy for a heat camp to help acclimatise players to conditions expected during the tournament in Japan.
Underhill and Watson will travel with the squad after spending last week doing specialised strength and conditioning work separately off site, while Joe Marchant (Harlequins) joins the group for the first time.
Jones said: “Treviso is a hard yards camp with conditions similar to Tokyo. Team training will be about being adaptable and off the field enjoying each other’s company."
On squad selection Jones added: "Selection is absolutely challenging, we have left some good players doing work at their clubs and they must be ready if called up.”
England will play Wales (11th August) and Ireland (24th August) at Twickenham Stadium and Italy (6th September) in Newcastle as part of the Quilter Internationals as well as an away fixture against Wales (17th August) in Cardiff.
England will begin their Rugby World Cup campaign in Japan against Tonga in Sapporo (22nd September, KO 11:15am UK time) before playing USA Rugby in Kobe (26th September, KO 11:45am UK time), Argentina in Tokyo (5th October, KO 09:00am UK time) and France in Yokohama (12th October, KO 09:15am UK time).
England Training Camp Squad
Dan Cole (Leicester Tigers, 85 caps)
Luke Cowan-Dickie (Exeter Chiefs, 11 caps)
Tom Curry (Sale Sharks, 10 caps)
Charlie Ewels (Bath Rugby, 10 caps)
Ellis Genge (Leicester Tigers, 9 caps)
Jamie George (Saracens, 37 caps)
Maro Itoje (Saracens, 27 caps)
George Kruis (Saracens, 32 caps)
Joe Launchbury (Wasps, 58 caps)
Courtney Lawes (Northampton Saints, 71 caps)
Lewis Ludlam (Northampton Saints, uncapped)
Joe Marler (Harlequins, 59 caps)
Brad Shields (Wasps, 8 caps)
Kyle Sinckler (Harlequins, 22 caps)
Jack Singleton (Saracens, uncapped)
Sam Underhill (Bath Rugby, 9 caps)
Billy Vunipola (Saracens, 41 caps)
Mako Vunipola (Saracens, 53 caps)
Harry Williams (Exeter Chiefs, 17 caps)
Mark Wilson (Newcastle Falcons / Sale Sharks, 13 caps)
Mike Brown (Harlequins, 72 caps)
Joe Cokanasiga (Bath Rugby, 4 caps)
Elliot Daly (Saracens, 30 caps)
Owen Farrell (Saracens, 70 caps)
George Ford (Leicester Tigers, 55 caps)
Piers Francis (Northampton Saints, 4 caps)
Willi Heinz (Gloucester Rugby, uncapped)
Jonathan Joseph (Bath Rugby, 40 caps)
Joe Marchant (Harlequins, uncapped)
Jonny May (Leicester Tigers, 45 caps)
Ruaridh McConnochie (Bath Rugby, uncapped)
Jack Nowell (Exeter Chiefs, 33 caps)
Henry Slade (Exeter Chiefs, 22 caps)
Ben Spencer (Saracens, 3 caps)
Ben Te’o (unattached, 18 caps)
Manu Tuilagi (Leicester Tigers, 32 caps)
Anthony Watson (Bath Rugby, 33 caps)
Ben Youngs (Leicester Tigers, 85 caps)