Bei R, Kantor J, Kashmiri S V, Schlom J
Laboratory of Tumor Immunology and Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Mol Immunol. 1994 Jul;31(10):771-80. doi: 10.1016/0161-5890(94)90151-1.
Carcinoembryonic antigen (CEA), a glycosylated protein of M(r) 180 kDa, is one of the most widely used human tumor markers. A majority of gastrointestinal cancers as well as breast and nonsmall cell lung carcinomas express CEA. We have previously described a recombinant baculovirus BVCEA-140 expressing the full-length human CEA and a variant, BVCEA-16, that encodes only the NH2-terminal domain, as well as a recombinant (BVNCA) expressing the closely related molecule nonspecific cross-reactive antigen (NCA). We have now compared a panel of 24 anti-CEA and anti-NCA monoclonal antibodies (MAbs) for their ability to bind to these recombinant CEA and NCA proteins, as well as with a new 60 kDa subgenomic form designated BVCEA-60. The epitope mapping studies indicate that all the CEA specific MAbs can recognize BVCEA-140. We also compared the sugar composition of BVCEA-140 to native CEA, using a lectin-linked immunoradiometric assay. The results demonstrated that both the native and recombinant baculovirus CEA contain simple high-mannose carbohydrates as well as biantennary and biantennary hybrid complexes. However, native CEA also contains triantennary and tetraantennary complex sugars, while the recombinant CEA molecule does not. Immunogenicity of the recombinant CEA molecules was demonstrated in mice. ELISA and Western blot analyses were used to determine the cross-reactivity of the anti-CEA sera. Mice immunized with BVCEA-140 elicit antibodies that are reactive to native CEA. When the BVCEA-16 was used as an immunogen, the antisera failed to detect native CEA or BVCEA-140. These studies demonstrate that minor sugar differences exist between native and baculovirus-derived CEA. However, epitope mapping with a panel of 24 anti-CEA MAbs (recognizing at least 10 CEA epitopes) stowed virtual immunologic identity between these two molecules. Moreover, BVCEA-140 appears to be a more potent humoral immunogen in mice than native CEA. These purified recombinant proteins can thus serve as standards in CEA serum assays for the possible detection and characterization of cell-mediated immune responses to CEA and as a potential source of immunogen (primary or for boosting) for active specific immunotherapy protocols of human carcinomas.
癌胚抗原（CEA）是一种分子量为180 kDa的糖蛋白，是应用最为广泛的人类肿瘤标志物之一。大多数胃肠道癌以及乳腺癌和非小细胞肺癌都表达CEA。我们之前曾描述过一种表达全长人CEA的重组杆状病毒BVCEA - 140、一种仅编码NH2末端结构域的变体BVCEA - 16，以及一种表达密切相关分子非特异性交叉反应抗原（NCA）的重组体（BVNCA）。我们现在比较了一组24种抗CEA和抗NCA单克隆抗体（MAb）与这些重组CEA和NCA蛋白以及一种新的60 kDa亚基因组形式（命名为BVCEA - 60）的结合能力。表位定位研究表明，所有CEA特异性单克隆抗体都能识别BVCEA - 140。我们还使用凝集素连接免疫放射分析比较了BVCEA - 140与天然CEA的糖组成。结果表明，天然和重组杆状病毒CEA都含有简单的高甘露糖碳水化合物以及双天线和双天线杂合复合物。然而，天然CEA还含有三天线和四天线复合糖，而重组CEA分子则没有。重组CEA分子在小鼠体内表现出免疫原性。采用ELISA和Western印迹分析来确定抗CEA血清的交叉反应性。用BVCEA - 140免疫的小鼠产生的抗体与天然CEA有反应。当使用BVCEA - 16作为免疫原时，抗血清未能检测到天然CEA或BVCEA - 140。这些研究表明，天然CEA和杆状病毒衍生的CEA之间存在微小的糖差异。然而，用一组24种抗CEA单克隆抗体（识别至少10个CEA表位）进行的表位定位显示这两种分子在免疫学上几乎完全相同。此外，BVCEA - 140在小鼠体内似乎比天然CEA更具强效的体液免疫原性。因此，这些纯化的重组蛋白可作为CEA血清检测的标准品，用于可能的细胞介导的针对CEA免疫反应的检测和表征，也可作为人类癌症主动特异性免疫治疗方案的免疫原（初次或加强）潜在来源。
