We have successfully harnessed a two‐step strategy with inteins to fuse SUMOylated Bystin to a truncated recombinant form of P. aeruginosa exotoxin A. However, the application of these identified BCR reactivities to target subgroups of relapsed/refractory lymphoma seems unrealistic at t present because of the rarity of the disease. Here, BYSL is linked to lymphoma.