Conjugating saporin to a peptide allows it to be internalized by cells that express the peptide's receptor, leading to the ablation of only those specific cells.

“So, what he figured out is he put saporin to the peptide, the peptide binds to its receptor, it gets internalized and then when it's inside the cell, saporin does the same thing that ricin does. It kills the cell, but then it can't go into the next cell. So, the only cells that get killed, or the more polite term ablated, are cells that express that receptor.”