An improved recombinant Fab-immunotoxin targeting CD22 expressing malignancies

Moxetumomab pasudotox (HA22) is a recombinant immunotoxin, now in clinical trials, that combines an anti-CD22-Fv with a 38-kDa fragment of Pseudomonas exotoxin A. To produce a less immunogenic molecule without reducing the half-life in circulation, we constructed LMB11 combining an anti-CD22 Fab with a less immunogenic version of PE38. We found that LMB11 retains full activity toward CD22-expressing cells. In mice, the half-life of LMB11 is 29 min and the antitumor activity of LMB11 is better than that of HA22. Because it can be safely given at much higher doses, LMB11 produced complete tumor remissions in 7/7 mice.