Modjtahedi H, Eccles S, Sandle J, Box G, Titley J, Dean C
Section of Immunology, Institute of Cancer Research, Sutton, Surrey, United Kingdom.
Cancer Res. 1994 Apr 1;54(7):1695-701.
We have carried out an immunohistochemical investigation of xenografts of epidermal growth factor receptor (EGFR)-overexpressing tumors that have been induced to regress by treatment with rat monoclonal antibodies (mAbs) to the human EGFR [ICR16 (IgG2a), ICR62 (IgG2b), and ICR64 (IgG1)]. When mice bearing xenografts of the HN5 squamous cell carcinoma were treated for 5 days with mAb ICR62 or ICR16, the antibodies were found to be localized uniformly on the tumor cell membranes. However, the foci of tumor cells that remained following treatment with ICR62 were smaller than with ICR16 and the former showed a more pronounced host mononuclear cell infiltrate. Examination of the few tumors that had not regressed completely and were still present as static nodules 77 days following the final treatment with anti-EGFR mAbs revealed significant levels of therapeutic mAb in the nonviable areas of the tumors. The microscopic areas of apparently viable tumor cells that did not stain when only secondary antibody was used stained positive when the sections were treated first with an anti-EGFR antibody. This suggests that loss of the target antigen was not a significant factor and that these residual cells might be eradicated by further treatment with mAb. Furthermore, the finding of keratinized areas in the tumors undergoing regression suggested that the carcinoma cells had undergone terminal differentiation following exposure to antibody. This possibility was supported by the finding that treatment of HN5 cells in vitro with mAbs ICR16, ICR62, or ICR64 resulted in the accumulation of cells in the G0-G1 phases of the cell cycle and expression of the terminal differentiation markers involucrin and cytokeratin 10. We found no evidence of apoptosis in such cells. We conclude that antibodies which block the binding of EGF and transforming growth factor alpha to the EGFR can inhibit the growth of EGFR-overexpressing tumors by directing terminal differentiation and that a further therapeutic benefit may be obtained via immunological mechanisms with rat IgG2b mAbs such as ICR62.
我们对表皮生长因子受体（EGFR）过表达肿瘤的异种移植进行了免疫组织化学研究，这些肿瘤已通过用针对人EGFR的大鼠单克隆抗体（mAb）[ICR16（IgG2a）、ICR62（IgG2b）和ICR64（IgG1）]治疗而消退。当用mAb ICR62或ICR16对携带HN5鳞状细胞癌异种移植的小鼠进行5天治疗时，发现抗体均匀地定位在肿瘤细胞膜上。然而，用ICR62治疗后残留的肿瘤细胞灶比用ICR16治疗后的更小，并且前者显示出更明显的宿主单核细胞浸润。在用抗EGFR mAb进行最后一次治疗77天后，对少数未完全消退且仍以静止结节形式存在的肿瘤进行检查，发现在肿瘤的无活力区域有显著水平的治疗性mAb。当仅使用二抗时未染色的明显存活肿瘤细胞的微观区域，在用抗EGFR抗体预处理切片后呈阳性染色。这表明靶抗原的丢失不是一个重要因素，并且这些残留细胞可能通过进一步用mAb治疗而被根除。此外，在消退的肿瘤中发现角化区域表明癌细胞在接触抗体后经历了终末分化。用mAb ICR16、ICR62或ICR64体外处理HN5细胞导致细胞在细胞周期的G0 - G1期积累以及终末分化标志物内披蛋白和细胞角蛋白10表达，这一发现支持了这种可能性。我们在这些细胞中未发现凋亡的证据。我们得出结论，阻断表皮生长因子（EGF）和转化生长因子α与EGFR结合的抗体可通过引导终末分化来抑制EGFR过表达肿瘤的生长，并且通过大鼠IgG2b mAb如ICR62的免疫机制可能获得进一步的治疗益处。
