THE IN-VIVO ANTITUMOR-ACTIVITY OF IMMUNOTOXINS CONTAINING 2 VERSUS ONE DEGLYCOSYLATED RICIN-A CHAINS

We have compared the in vitro and in vivo activities of three deglycos ylated ricin A chain (dgA)-containing immunotoxins (ITs) with one vers us two molecules of dgA per molecule of IgG, Two of the ITs (anti-CD19 -dgA(2) and anti-CD25-dgA(2)) had 3-0-fold improvements over their dgA (1) counterparts in vitro. However, the in vivo anti-tumor activity of both constructs of each IT was the same. In contrast, anti-CD22-dgA(2 ) was 7-fold more potent in vitro and significantly more potent in viv o than its dgA(1) counterpart. These studies suggest that monoclonal a ntibodies must be individually tested to determine whether the additio n of two versus one dgA will improve cytotoxic activity in vivo.