Targeting EpCAM by a Bispecific Trifunctional Antibody Exerts Profound Cytotoxic Efficacy in Germ Cell Tumor Cell Lines

Outcome in high-risk patients with refractory or relapsed germ cell tumours (GCT) remains poor. Novel strategies enhancing therapeutic efficacy whilst limiting therapeutic burden are warranted, yet immunotherapy approaches geared towards activating endogenous antitumor responses have not been successful thus far. Redirection of cytotoxic effector cells by bispecific antibodies represents a promising approach in this setting. We demonstrate that the Epithelial Cell Adhesion Molecule (EpCAM) is broadly expressed in GCT cell lines of different histologic origin including seminoma, choriocarcinoma (CHC), and embryonal carcinoma (EC). In these GCT lines of variable EpCAM surface expression, targeting T cells by the prototypic bispecific EpCAM/CD3-antibody (bAb) Catumaxomab together with natural killer (NK) cell engagement via the Fc domain promotes profound cytotoxicity across a broad range of antibody dilutions. In contrast, tumor cell lysis mediated by either immune cell subset alone is influenced by surface density of the target antigen. In the CHC line JAR, NK cell-dependent cytotoxicity dominates, which may be attributed to differential surface expression of immunomodulatory proteins such as MHC-I, CD24, and Fas receptors on CHC and EC. In view of redirecting T cell therapymediated by bispecific antibodies, such differences inGCT immunophenotype potentially favoring immune escape are worth further investigation.难治性或复发性生殖细胞肿瘤（germ cell tumours, GCT）高危患者的预后仍欠佳。亟需开发既能提升治疗疗效、又能减轻治疗负担的新型策略，但迄今为止，旨在激活内源性抗肿瘤免疫应答的免疫治疗方案尚未取得成功。双特异性抗体（bispecific antibodies）介导的细胞毒性效应细胞重定向策略，在此类临床场景中展现出良好的应用前景。我们证实，上皮细胞黏附分子（Epithelial Cell Adhesion Molecule, EpCAM）在多种组织学起源的生殖细胞肿瘤细胞系中广泛表达，包括精原细胞瘤（seminoma）、绒毛膜癌（choriocarcinoma, CHC）以及胚胎癌（embryonal carcinoma, EC）。在这些表面EpCAM表达水平各异的生殖细胞肿瘤细胞系中，通过原型双特异性EpCAM/CD3抗体（bispecific EpCAM/CD3-antibody, bAb）卡妥索单抗（Catumaxomab）靶向T细胞，并借助Fc结构域介导自然杀伤（natural killer, NK）细胞结合，可在较宽的抗体稀释浓度范围内引发显著的细胞毒性效应。与之相反，仅单一种类免疫细胞亚群介导的肿瘤细胞裂解效果，会受到靶抗原表面密度的影响。在绒毛膜癌JAR细胞系中，依赖自然杀伤细胞的细胞毒性效应占主导地位，这可能与绒毛膜癌与胚胎癌表面免疫调节蛋白（如主要组织相容性复合体I类（Major Histocompatibility Complex I, MHC-I）、CD24及Fas受体）的表达差异有关。鉴于双特异性抗体介导的T细胞重定向治疗的应用前景，这类可能促进免疫逃逸的生殖细胞肿瘤免疫表型差异，值得开展进一步研究。