GPA33 and colorectal cancer: In this sense, we have previously produced and characterized two immunoconjugates, IMTXA33αS and scFvA33T1, based in the ribotoxin α-sarcin or the nontoxic RNase T1, respectively, fused to the variable domains (scFv) of the monoclonal antibody A33, which recognize and bind specifically the tumor-associated antigen GPA33, overexpressed in most of colorectal cancers [30,36,48,49].