Department of Immunology, Medical Center Utrecht, Utrecht, the Netherlands.
Haematologica. 2010 Dec;95(12):2063-71. doi: 10.3324/haematol.2010.025783. Epub 2010 Sep 17.
Incorporation of the chimeric CD20 monoclonal antibody rituximab in the treatment schedule of patients with non-Hodgkin's lymphoma has significantly improved outcome. Despite this success, about half of the patients do not respond to treatment or suffer from a relapse and additional therapy is required. A low CD20-expression level may in part be responsible for resistance against rituximab. We therefore investigated whether the CD20-expression level related resistance to rituximab could be overcome by a new group of CD20 mAbs (HuMab-7D8 and ofatumumab) targeting a unique membrane-proximal epitope on the CD20 molecule.
By retroviral transduction of the CD20 gene into CD20-negative cells and clonal selection of transduced cells a system was developed in which the CD20-expression level is the only variable. These CD20 transduced cells were used to study the impact of rituximab and HuMab-7D8 mediated complement-dependent cytotoxicity. To study the in vivo efficacy of these mAbs an in vivo imaging system was generated by retroviral expression of the luciferase gene in the CD20-positive cells.
We show that HuMab-7D8 efficiently killed CD20(low) cells that are not susceptible to rituximab-induced killing in vitro. In a mouse xenograft model, we observed a comparable increase in survival time between HuMab-7D8 and rituximab-treated mice. Most significantly, however, HuMab-7D8 eradicated all CD20-expressing cells both in the periphery as well as in the bone marrow whereas after rituximab treatment CD20(low) cells survived.
Cells that are insensitive to in vitro and in vivo killing by rituximab as the result of their low CD20-expression profile may be efficiently killed by an antibody against the membrane-proximal epitope on CD20. Such antibodies should, therefore, be explored to overcome rituximab resistance in the clinic.
嵌合型 CD20 单克隆抗体利妥昔单抗的加入显著改善了非霍奇金淋巴瘤患者的治疗效果。尽管取得了这一成功，但仍有约一半的患者对治疗无反应或复发，需要额外的治疗。CD20 表达水平低可能是部分患者对利妥昔单抗产生耐药的原因。因此，我们研究了针对 CD20 分子膜近端表位的新型 CD20 mAb（HuMab-7D8 和奥法木单抗）是否可以克服 CD20 表达水平相关的利妥昔单抗耐药性。
通过逆转录病毒转导 CD20 基因进入 CD20 阴性细胞，并对转导细胞进行克隆选择，建立了一种 CD20 表达水平为唯一变量的系统。这些 CD20 转导细胞用于研究利妥昔单抗和 HuMab-7D8 介导的补体依赖性细胞毒性的影响。为了研究这些 mAb 的体内疗效，通过在 CD20 阳性细胞中逆转录病毒表达荧光素酶基因，生成了一种体内成像系统。
我们证明 HuMab-7D8 可以有效杀伤体外对利妥昔单抗诱导杀伤不敏感的 CD20(low)细胞。在小鼠异种移植模型中，我们观察到 HuMab-7D8 治疗组和利妥昔单抗治疗组的生存时间均有类似的延长。最重要的是，HuMab-7D8 可以清除外周血和骨髓中的所有 CD20 表达细胞，而利妥昔单抗治疗后 CD20(low)细胞存活。
由于 CD20 表达水平低而对利妥昔单抗的体外和体内杀伤不敏感的细胞可以被针对 CD20 膜近端表位的抗体有效杀伤。因此，这类抗体应该在临床上探索，以克服利妥昔单抗耐药性。
