Why does Taylor hav scars on his hands in my sisters keeper?

In the movie, my sisters keeper, Kate says something about Taylors scars on his hands. How did he get the scars on his hands??Why does Taylor hav scars on his hands in my sisters keeper?
He has scars from graft versus host...an infectionWhy does Taylor hav scars on his hands in my sisters keeper?
Because The Critic was cancelled after only 2 seasons