Wellens was set to start the race in Napoli this Saturday, but the Belgian second-year pro, who has knee problems, failed to prove his fitness and will miss out on making his debut in a Grand Tour.
Kaisen, who made a splash during last year's race with his attacking riding, suffered a crash on the fourth stage of the Tour of Turkey and will also not be fit to race for three weeks in Italy.
In their place Vicente Reynes and Brian Bulgaç have been called up.
Spaniard Reynes, who has ridden three previous editions of the Giro, will be expected to support Kenny Dehaes in the sprints.
Dutchman Bulgaç, 25, will race his second Giro.
The first of the year's Grand Tours begins on Saturday and ends three weeks later in Brescia.
Revised Lotto Belisol line-up for the Giro d’Italia: Lars Bak, Dirk Bellemakers, Francis De Greef, Kenny Dehaes, Gert Dockx, Adam Hansen, Frederik Willems, Vicente Reynes and Brian Bulgaç.
- Sports & Recreation
- Kenny Dehaes
- Brian Bulgaç