CD55 is over-expressed in the tumour environment

CD55 is a protein that protects cells from complement-mediated attack. 791T gp72 is an antigen which has been used succesfully as a target for both tum our imaging and cancer vaccines. 791Tgp72 has recently been identified as C D55. Quantitative expression of CD55 in the tumour environment was therefor e studied. Tumour cells showed a 4-100-fold increase in CD55 cell surface e xpression when compared to normal cells. Immunohistochemical staining of co lorectal tumours also revealed high expression of CD55 in the stroma. To ex amine the source of this stromal CD55 the ability of both epithelial cells and endothelial cells to produce extracellular CD55 was measured. Tumour ce ll lines deposit CD55 into their extracellular matrix (ECM) in direct propo rtion to their cell surface expression. In contrast the ECM from HUVEC cell s contained large amounts of CD55 despite expressing low levels of CD55 on their cell surface. Furthermore expression of CD55 on HUVEC cells was incre ased by exposure to VEGF. Although it remains unclear why CD55 is upregulat ed in the tumour environment its high level of expression on tumour cells a nd associated endothelium may explain why it is a good target for both imag ing and immunotherapy. (C) 2001 Cancer Research Campaign http://www.bjcance r.com.