Leslie and Hyndman, who pulled out of the Gloucester match last week at the last minute with flu, will replace Bruce Reihana at outside centre and Mark Tucker at inside centre respectively.
New Zealander Reihana moves back to the left-wing, while Tucker drops out of the squad because of a broken jaw.
In the final change, former Wallaby fly-half Shane Drahm drops down to the bench because of a bruised thigh.
Drahm has been cited for his inolvement in the mass-brawl that erupted during the Gloucester match, along with team-mate Mark Robinson, who starts against Quins at halfback, and Gloucester's Duncan McRae (fly-half) and Andy Hazell (flanker).
Northampton Saints: 15 Nick Beal, 14 Jon Sleightholme, 13 Chris Hyndman, 12 John Leslie (captain), 11 Bruce Reihana, 10 James Brooks, 9 Mark Robinson, 8 Andrew Blowers (captain), 7 Darren Fox, 6 Mark Connors, 5 Rob Hunter, 4 Matt Lord, 3 Chris Budgen, 2 Dan Richmond, 1 Brett Sturgess.Replacements – from: Matt Miles, Robbie Morris, Jon Golding, Jon Phillips, Grant Seely, Oriol Ripol, Mark Soden, Johnny Howard, John Clarke, Shane Drahm.