de Palazzo I G, Gercel-Taylor C, Kitson J, Weiner L M
Department of Medical Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111.
Cancer Res. 1990 Nov 15;50(22):7123-8.
Murine monoclonal antibody therapy of human cancer rarely induces clinical responses. Antibody-induced cellular infiltrates rarely accumulate at sites of tumor, even in clinically responding lesions. Thus, the ability of these antibodies to promote host effector cell-mediated lysis of tumor via antibody-dependent cellular cytotoxicity (ADCC) has not been harnessed by existing treatment approaches. One potential explanation is that ADCC requires binding of antibody Fc domains to cellular Fc gamma receptors, and therapeutically administered murine antibodies must compete with vast excesses of human IgG for Fc gamma receptor occupancy. Chemically linked antibody heteroconjugates that bind selected target and effector cell structures via distinct Fab portions can mediate lysis of malignant cells in vitro in the presence of human serum. This approach addresses a potentially major obstacle to antibody therapy. Production of bispecific monoclonal antibodies with similar specificities and superior in vivo biodistribution characteristics would thus have potential clinical applications. We have prepared and purified a bispecific, monovalent monoclonal antibody and evaluated its in vitro effects. The IgG1-secreting hybridoma line 3G8 (alpha-human Fc gamma R III) was fused with the hybridoma line CA19-9, which produces an IgG1 antibody that binds to a glycoprotein shed by gastrointestinal cancers. Multiple clones with bispecific binding properties were identified. CA19-9 x 3G8 clonal supernatants and purified antibody, but not the parent antibodies, efficiently mediated specific in vitro lysis of cells of the SW948 line by human large granular lymphocytes (LGLs). Human serum-resistant target cell lysis augmentation at low effector:target ratios was seen using picogram amounts of antibody. In contrast, the IgG2 alpha variant of CA19-9, which also promotes ADCC by LGLs, was unable to augment lysis of SW948 cells when effectors were preincubated with human serum. This bispecific, monovalent monoclonal antibody is an efficient promoter of the anti-tumor effects of LGLs in physiological concentrations of human serum. In vivo models that evaluate treatment efficacy and promotion of inflammatory tumor infiltrates by bispecific monoclonal antibodies are required to assess the therapeutic potential of these novel constructs.
鼠单克隆抗体治疗人类癌症很少能引发临床反应。抗体诱导的细胞浸润很少在肿瘤部位积聚，即使在有临床反应的病灶中也是如此。因此，现有治疗方法尚未利用这些抗体通过抗体依赖性细胞毒性（ADCC）促进宿主效应细胞介导的肿瘤细胞裂解的能力。一种可能的解释是，ADCC需要抗体Fc结构域与细胞Fcγ受体结合，而治疗性施用的鼠抗体必须与大量过量的人IgG竞争Fcγ受体的占据。通过不同的Fab部分结合选定的靶细胞和效应细胞结构的化学连接抗体异源缀合物可以在人血清存在的情况下在体外介导恶性细胞的裂解。这种方法解决了抗体治疗的一个潜在主要障碍。因此，生产具有相似特异性和优异体内生物分布特征的双特异性单克隆抗体将具有潜在的临床应用价值。我们制备并纯化了一种双特异性单价单克隆抗体，并评估了其体外效应。分泌IgG1的杂交瘤细胞系3G8（α-人FcγR III）与杂交瘤细胞系CA19-9融合，后者产生一种与胃肠道癌脱落的糖蛋白结合的IgG1抗体。鉴定出多个具有双特异性结合特性的克隆。CA19-9×3G8克隆上清液和纯化抗体，而非亲本抗体，能有效地介导人大颗粒淋巴细胞（LGL）对SW948细胞系细胞的特异性体外裂解。使用皮克量的抗体可观察到在低效应细胞：靶细胞比例下对人血清抗性靶细胞裂解的增强作用。相比之下，同样能促进LGL介导ADCC的CA19-9的IgG2α变体，在效应细胞与人血清预孵育时无法增强SW948细胞的裂解。这种双特异性单价单克隆抗体在生理浓度的人血清中是LGL抗肿瘤效应的有效促进剂。需要体内模型来评估双特异性单克隆抗体的治疗效果以及促进炎性肿瘤浸润的能力，以评估这些新型构建体的治疗潜力。
