Artikel
Efficient killing of CD22+ tumor cells by a humanized diabody-RNase fusion protein
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Veröffentlicht: | 20. März 2006 |
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Gliederung
Text
CD22-specific immunotoxins are highly potent drugs for the treatment of patients with refractory B-cell non-Hodgkin’s lymphoma. However, systemic toxicity and immunogenicity hamper the wide clinical application of these powerful reagents in cancer patients. To overcome these limitations we have developed a dimeric CD22-specific immunoenzyme capable of simultaneously delivering two RNase effector domains on one molecule to CD22+ tumor cells. As targeting moiety we first generated a highly stable humanized scFv by grafting the specificity of the clinically established anti-CD22 mAb RFB4 into robust, pre-selected frameworks from a human antibody phage display library. A derived diabody with further engineered interface (VL36Leu->Tyr) retained the same high affinity as the murine anti-CD22 mAb RFB4 (KD = 0.2 nM) as well as full antigen binding after 8 days of incubation in human serum at 37°C. A dimeric immunoenzyme comprising this diabody and Rana pipiens liver ribonuclease I (rapLRI) was generated, expressed as soluble protein in bacteria, and purified to homogeneity. The dimeric fusion protein killed several CD22+ tumor cell lines with high efficacy (IC50 = 3-20 nM) and exhibited 9-48-fold stronger cytotoxicity than a monovalent rapLRI-scFv counterpart. Our results suggest dimeric antibody-ribonuclease fusion proteins as potent immunotherapeutic reagents with presumably large therapeutic index.
Figure 1 [Fig. 1]