Summary CD55 is a protein that protects cells from complement-mediated attack. 791Tgp72 is an antigen which has been used succesfully as a target for both tumour imaging and cancer vaccines. 791Tgp72 has recently been identified as CD55. Quantitative expression of CD55 in the tumour environment was therefore studied. Tumour cells showed a 4-100-fold increase in CD55 cell surface expression when compared to normal cells. Immunohistochemical staining of colorectal tumours also revealed high expression of CD55 in the stroma. To examine the source of this stromal CD55 the ability of both epithelial cells and endothelial cells to produce extracellular CD55 was measured. Tumour cell lines deposit CD55 into their extracellular matrix (ECM) in direct proportion to their cell surface expression. In contrast the ECM from HUVEC cells contained large amounts of CD55 despite expressing low levels of CD55 on their cell surface. Furthermore expression of CD55 on HUVEC cells was increased by exposure to VEGF. Although it remains unclear why CD55 is upregulated in the tumour environment its high level of expression on tumour cells and associated endothelium may explain why it is a good target for both imaging and immunotherapy. © 2001 Cancer Research Campaign http://www.bjcancer.com Keywords: CD55 (DAF), tumour expression; endothelium; stroma; vascular endothelial growth factor (VEGF) 80Received 27 September 1999 Revised 3 February 2000 Accepted 15 March 2000 Correspondence to : LG Durrant British Journal of Cancer (2001) 84(1), 80-86 © 2001 Cancer Research Campaign doi: 10.1054/ bjoc.2000.1570, available online at http://www.idealibrary.com on http://www.bjcancer.com and tumour-conditioned medium or VEGF (10-300 µg ml -1 : Zeneca, Alderley Park, UK) respectively for 48 h prior to harvesting the HUVECs. Tumour-conditioned media was derived from the MDA 231 breast cancer cell line. These were grown to confluence and the media replaced with serum free M199:Hams F12 medium. Following 24 h incubation the resultant conditioned media was filtered for use with the HUVEC. Fresh media was used to culture the control HUVECs. Freshly resected tumours were finely minced and dissociated in collagenase (0.05%; Boehringer Mannheim) and DNase (0.1%; Boehringer Mannheim) for 1 h at 37˚C. Monoclonal antibodiesMonoclonal antibodies 791T/36 (IgG2b anti-791Tgp72;Embleton et al, 1981), BRIC 216 (IgG1 anti-SCR 3 of CD55; Tate et al, 1989), BRIC 220 (IgG1 anti-SCR 1 of CD55; Tate et al, 1989), BRIC 110 (IgG1 anti-SCR 2 of CD55; Spring et al, 1987;Coyne et al, 1992) have been reported previously. BRIC 229 and E4.3 (Sparrow and Mckenzie, 1983) recognize CD59 and CD46 respectively. The BRIC antibodies were purchased from the Blood Group Reference laboratory (Bristol, UK). Normal mouse IgG (Sigma, Dorset, UK) and 708 monoclonal antibody (IgG2b) was used as negative control antibodies. Indirect immunofluorescenceCell lines were incubated with monoclonal antibody for 1 h at 4˚C. Cells were washed twice in fresh media containing 1% FCS and then incubat...

CD59 (protectin), a phosphatidylinositol-anchored glycoprotein, is a member of the cell membrane-bound complement regulatory proteins that inhibits the formation of the terminal membrane attack complex (MAC) of complement. In this study, the expression of CD59 was evaluated in 520 breast carcinomas from patients with a mean follow-up of 87 months. This expression was correlated with clinicopathological features and patient survival. Marked variation in the intensity of CD59 expression, which correlated with histological grade and Nottingham prognostic index (NPI), was found, with higher expression of CD59 found more often in well and moderately differentiated tumours and those of good prognosis (NPI < or = 3.4). In contrast, high grade and poor prognosis (NPI > 5.4) carcinomas significantly demonstrated lack of CD59 expression (p < 0.001). Moreover, it was found that the percentage of CD59-positive cells correlated significantly with patient survival, ie patients with a high percentage of positive cells (>50%) had a better overall survival (p = 0.006). A correlation was also found between the percentage of CD59-positive cells and tumour type and also the development of distant metastases. No association was found between either the intensity or the percentage of cells expressing CD59 and vascular invasion, lymph node stage, tumour size, patient age or menopausal status. In multivariate analysis, CD59 percentage positivity was of independent prognostic significance with grade and lymph node stage. These findings indicate that loss of CD59 may offer a selective advantage for breast cancers, resulting in more aggressive tumours and conferring a poor prognosis for patients.

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Summary Cells from two adenocarcinomas, an adenoma and a metastatic node were isolated in soft agar. Expression of antigens, CEA, Y haptenic blood group and 791T-p72, defined by a range of candidate antibodies for tumour targeting was assessed.All of the cells expressed low levels of CEA but high levels of the Y haptenic blood group antigen although there was enormous inter and intraclonal variation. Of particular interest was the membrane expression of 791T-p72 antigen on all of the dividing tumour cells as previous studies had shown that 791T/36 antibody reacted with tumour stromal elements rather than malignant cell surfaces.The DNA content was abnormal in all of the cells whether they were derived from diploid or aneuploid primary tumours. They all grew readily in athymic mice and at least one monoclonal antibody, 791T/36, localised efficiently within these xenografts.Clonogenic cells therefore expressed the three tumour-associated antigens, several at higher levels than observed in the primary tumour. Monoclonal antibody 'cocktails' should therefore allow antibody mediated drug cytotoxicity to be effective at eradicating rapidly dividing tumour cells.

Cancer vaccines have been shown to stimulate cytotoxic T lymphocyte (CTL) responses in a variety of cancer patients. However, the response is often of low frequency and moderate avidity, and does not result in objective clinical responses. This is related to the target antigens, which are usually over-expressed self-antigens that elicit tolerogenic and regulatory immune responses, resulting in deletion or inactivation of high-avidity T cells. Although moderate-avidity T cells can be efficient killers, tumours are often poor targets as they express a variety of molecules to protect them from cell-mediated immunity. Adoptive transfer of large numbers of high-avidity T cells has been shown to induce regression of bulky disease, proving that immune responses can effectively eradicate tumours. New approaches that target activated dendritic cells in vivo, resulting in cross-presentation of CTL epitopes and release of cytokines that suppress regulatory T cells, have resulted in the production of T cells with sufficient avidity to kill tumour target cells. These approaches in combination with regimes, such as cytokine therapy, chemotherapy or radiotherapy, that modulate effector costimulatory expression on tumour targets may result in more effective second-generation cancer vaccines.

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