Head coach Alan Dickens has named scrum-half van Poortvliet as captain, with hooker Vanes among the replacements.
There is one change to the starting line-up after the 45-3 win against Wales last Wednesday with Tommy Mathews given a first start of the tournament at fly-half.
Dickens said: “I think the players have really grown together as a group throughout the competition. Each week we have asked them to go out and improve on the previous performance and each time they’ve done that.
“They’ve worked really hard and really driven each other to get better every training session and I’ve been pleased to see such great character from the squad.
“We know the Italians are a tough outfit and I think they have been excellent so far in this competition. I’m sure they’ll be looking to take their first-half performance from their game against Ireland and build on that.
“This will be the last time this group of players takes to the pitch together and I want them to put in a good performance, enjoy the moment and take away some special memories from our time here in Cardiff.”
15 Orlando Bailey (Bath Rugby)
14 Tom Roebuck (Sale Sharks)
13 Jack Bates (Bristol Bears)
12 Dan Lancaster (Leeds Tykes)
11 Arthur Relton (Exeter Chiefs)
10 Tommy Mathews (Hartpury University RFC)
9 Jack van Poortvliet (Leicester Tigers) (c)
1 Fin Baxter (Harlequins)
2 Sam Riley (Harlequins)
3 Harvey Kindell-Beaton (Saracens)
4 Arthur Clark (Gloucester Rugby)
5 Alex Groves (Bristol Bears)
6 Ewan Richards (Bath Rugby)
7 Jack Clement (Gloucester Rugby)
8 Nahum Merigan (Bath Rugby)
16 Archie Vanes (Leicester Tigers)
17 Tarek Haffar (London Irish)
18 Luke Green (London Irish)
19 Freddie Thomas (Gloucester Rugby)
20 Josh Gray (Gloucester Rugby)
21 Ollie Stonham (Saracens)
22 Tom Carr-Smith (Bath Rugby)
23 Fin Smith (Worcester Warriors)
24 Phil Cokanasiga (London Irish)
25 Deago Bailey (Bristol Bears)
26 Charlie Atkinson (Wasps)