Restricted Distribution In Normal Tissues Research Articles

Molecular cloning of fibroblast activation protein alpha, a member of the serine protease family selectively expressed in stromal fibroblasts of epithelial cancers.

The human fibroblast activation protein alpha (FAP alpha) is a M(r) 95,000 cell surface antigen selectively expressed in reactive stromal fibroblasts of epithelial cancers, granulation tissue of healing wounds, and malignant cells of bone and soft tissue sarcomas. Normal adult tissues are generally FAP alpha-, but some fetal mesenchymal tissues transiently express the molecule. Because of its restricted normal tissue distribution and abundant expression in the stroma of over 90% of breast, colorectal, and lung carcinomas, FAP alpha is under clinical evaluation as a target for immunodetection and immunotherapy of epithelial cancers. In the present study, we have isolated a full-length cDNA for FAP alpha through expression cloning in COS-1 cells. The FAP alpha cDNA codes for a type II integral membrane protein with a large extracellular domain, transmembrane segment, and short cytoplasmic tail. FAP alpha shows 48% amino acid sequence identity to the T-cell activation antigen CD26, a membrane-bound protein with dipeptidyl peptidase IV (DPPIV) activity; however, unlike FAP alpha, CD26 is widely expressed in normal tissues. Three catalytic domains shared by DPPIV homologues in different species and by other serine proteases are conserved in FAP alpha. Immunochemical analysis of COS-1 cells coexpressing FAP alpha and CD26 revealed that the two molecules form heteromeric cell surface complexes, suggesting that a previously identified FAP alpha-associated M(r) 105,000 protein of cultured fibroblasts and growth factor-stimulated melanocytes, FAP beta, is identical to CD26. In vivo coexpression of FAP alpha and CD26 is found in reactive fibroblasts of healing wounds but not in tumor stromal fibroblasts or sarcomas (FAP alpha +/CD26-). The putative serine protease activity of FAP alpha and its in vivo induction pattern may indicate a role for this molecule in the control of fibroblast growth or epithelial-mesenchymal interactions during development, tissue repair, and epithelial carcinogenesis.

Cytokines as adjuvants: effect on the immunogenicity of NeuAc alpha 2-6GalNAc alpha-O-Ser/Thr (sialyl-Tn).

Sialyl-Tn, defined by monoclonal antibody (MAb) B72.3, shows restricted normal-tissue distribution but is expressed in a wide variety of carcinomas. To analyze the immunogenicity of sialyl-Tn, mice were immunized with ovine submaxillary mucin (OSM) in combination with monophosphoryl lipid A (MPLA), liposomes, or adjuvants that activate macrophages (rIL-1, rIFN-gamma, rM-CSF, IL-1-derived peptides) or T cells (rIL-2). The level and specificity of the immune response were analyzed by ELISA. rIL-1 and rIFN-gamma induced a very high and specific antibody response, whereas the effect of rM-CSF was dose-dependent: at a low dose it induced a high-level specific antibody response and at the high dose level it induced a polyclonal non-specific response. These results indicate that cytokines are powerful adjuvants which modulate both the magnitude and specificity of the immune response. More studies are necessary to determine the optimal doses in animal models and in active specific immunotherapy of patients with cancer.

A 72 kD trophoblast glycoprotein defined by a monoclonal antibody.

A novel trophoblast cell surface antigen has been defined by a monoclonal antibody 5T4, raised following immunisation with wheat germ agglutinin (WGA) purified glycoproteins from deoxycholate (DOC) solubilised human syncytiotrophoblast plasma membrane (StMPM). The distribution of the antigen was determined by indirect immunoperoxidase staining of sections of normal organ and placental tissues as well as immunofluorescence and radiobinding assays with a wide variety of cell lines representing differing normal and tumour cell types. In frozen sections of normal full term placenta, 5T4 is strongly expressed only by the syncytiotrophoblast, some extravillous cytotrophoblast and the amniotic epithelium. The 5T4 antigen is apparently not expressed by any maternal component of the placenta nor is it detected in adult liver, lung, bronchus, heart, testis, ovary, brain, or muscle. The antigen is apparently expressed by several specialised epithelia. Immunoprecipitation of radiolabelled StMPM indicated that 5T4 molecules are glycoproteins of mol. wt of approximately 72 kD on SDS-PAGE. 5T4 antigen is selectively expressed by diverse tumour cell lines, including those of developmental origin. The molecular characteristics, relatively restricted normal tissue distribution and expression by certain tumour cell types make this antigen worthy of future study for use as a diagnostic marker of malignancy.