CD22 and hairy cell leukemia: Instead of using small-molecule payload, moxetumomab pasudotox consists of moxetumomab targeting CD22 conjugated to a 38kD fragment of Pseudomonas exotoxin A (PE38).171 CD22 is expressed on mature B cells and much more intensively on 100 % of hairy cells, which provides an ideal therapeutic target for the treatment of HCL.172,173 Upon binding to CD22, moxetumomab pasudotox is internalized, cleaved and released catalytic domain of the exotoxin inside cancer cells, which inhibits the translation of proteins leading to apoptosis.