A total of eight amino acids containing large bulky hydrophilic side chains have been replaced with smaller polar residues within these epitopes, resulting in a new toxin endowed with much less immunogenicity than the parental one, without any loss of cytotoxic activity also when recombinantly fused to either an anti CD22 variable fragment (which was tested both in vitro and in mice model of lymphomas [173]) or used in a bispecific anti CD22 and anti CD19 IT construct carrying an ER-retrieval motif (2219KDEL7mut) [80]. Here, CD19 is linked to lymphoma.