Shen G L, Li J L, Ghetie M A, Ghetie V, May R D, Till M, Brown A N, Relf M, Knowles P, Uhr J W
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235.
Int J Cancer. 1988 Nov 15;42(5):792-7. doi: 10.1002/ijc.2910420527.
Ricin A chain-containing immunotoxins (IT-As) specific for the human B-cell antigen, CD22, were prepared from 4 monoclonal antibodies (MAbs) or their Fab' fragments: RFB4, HD6, UV22-I and UV22-2. The ITs were tested for their ability to kill cells from the Burkitt lymphoma line, Daudi, the pre-B-cell leukemia line, NALM-6, and the myeloma cell line, ARH-77. Daudi expresses high levels of CD22, whereas NALM-6 and ARH-77 express low levels of CD22. The IgG-RFB4-A was highly toxic to all 3 cell lines; it killed 50% of the Daudi cells at a concentration of 1.2 x 10(-12) M and 50% of NALM-6 and ARH-77 cells at concentrations of 1.5 to 2.1 x 10(-11) M. IgG-RFB4-A was 10-30 times more toxic to Daudi cells than were the IgG-As constructed from the other 3 CD22 MAbs and 10 times more toxic than ricin itself. IT-As constructed from the Fab' fragments of the 4 CD22 antibodies were 2 to 5 times less toxic to Daudi cells than their IgG-A counterparts. Fab'-RFB4-A was twice as toxic to Daudi cells as ricin, whereas the other Fab'-As were about 7 times less toxic than ricin. Scatchard analyses of the binding of the radio-iodinated antibodies to Daudi cells showed that the intact RFB4 antibody bound 3-10 times more strongly than the other antibodies, whereas the Fab'-RFB4 bound 1.2 to 3.5 times more strongly than the Fab' fragments prepared from the other antibodies. Thus, the potent cytotoxic activity of the RFB4-As appears to derive, in part, from their superior binding affinity. Prior studies have shown that UV22-I and HD6 cross-react with certain normal human tissues lacking cells of B-cell lineage, whereas UV22-2 and RFB4 are B-cell-specific. This fact, together with its superior potency as an IT-A, suggests that RFB4 is the antibody of choice for preparing Fab'-As or IgG-As for in vivo therapy of human B-cell leukemias and lymphomas.
针对人类B细胞抗原CD22的含蓖麻毒素A链免疫毒素（IT-As）由4种单克隆抗体（MAbs）或其Fab'片段制备而成：RFB4、HD6、UV22-I和UV22-2。检测了这些免疫毒素对伯基特淋巴瘤细胞系Daudi、前B细胞白血病细胞系NALM-6和骨髓瘤细胞系ARH-77细胞的杀伤能力。Daudi细胞高表达CD22，而NALM-6和ARH-77细胞低表达CD22。IgG-RFB4-A对所有这3种细胞系都具有高毒性；它在浓度为1.2×10⁻¹² M时可杀死50%的Daudi细胞，在浓度为1.5至2.1×10⁻¹¹ M时可杀死50%的NALM-6和ARH-77细胞。IgG-RFB4-A对Daudi细胞的毒性比由其他3种CD22单克隆抗体制备的IgG-As高10至30倍，比蓖麻毒素本身高10倍。由4种CD22抗体的Fab'片段构建的IT-As对Daudi细胞的毒性比其对应的IgG-A低2至5倍。Fab'-RFB4-A对Daudi细胞的毒性是蓖麻毒素的两倍，而其他Fab'-As的毒性比蓖麻毒素低约7倍。对放射性碘化抗体与Daudi细胞结合的Scatchard分析表明，完整的RFB4抗体的结合力比其他抗体强3至10倍，而Fab'-RFB4的结合力比由其他抗体制备的Fab'片段强1.2至3.5倍。因此，RFB4-As的强大细胞毒活性似乎部分源于其卓越的结合亲和力。先前的研究表明，UV22-I和HD6与某些缺乏B细胞系细胞的正常人组织发生交叉反应，而UV22-2和RFB4是B细胞特异性的。这一事实，连同其作为IT-A的卓越效力，表明RFB4是制备用于人类B细胞白血病和淋巴瘤体内治疗的Fab'-As或IgG-As的首选抗体。
