Cd8 T‐cell recognition of human 5T4 oncofetal antigen

Abstract

The 5T4 oncofetal antigen is expressed by a wide variety of human carcinomas, including colorectal, ovarian and gastric carcinomas. The restricted expression of 5T4 on tumor tissues as well as its implication in tumor progression and bad prognosis makes 5T4 a promising new candidate for immunotherapy. An MVA vaccine encoding 5T4 antigen has been successfully evaluated in preclinical studies in a murine tumor model. Here, we report the generation of human CD8 T cells specific for the 5T4 antigen by stimulation with autologous monocyte derived DC infected with a replication defective adenovirus encoding the 5T4 cDNA (Ad5T4). Analysis of several donors confirms a repertoire of such CD8 responses. In a parallel approach, incorporating the results of proteasome-mediated digestion of 5T4 derived 35-mer peptides and the potential high affinity epitopes predicted by a computer-based algorithm, we identified 8 putative HLA-A*0201-presented CD8 MHC class I epitopes of 5T4 antigen. Two of these generated specific CD8 T cells after restimulation with peptide loaded autologous DC and assay by cytotoxicity and IFNc ELISPOT. Moreover these particular peptide generated T cells recognized naturally 5T4 positive tumor cells only if they expressed HLA-A*0201 as judged by IFNc ELISPOT or ELISA. Also, HLA-A*0201 CD8 T cells recognized these peptides in a DC-Ad5T4 polyclonal response. In conclusion, there is a repertoire of CD8 T cell recognition of 5T4 in normal human donors and some candidate HLA-A*0201 epitopes have been identified. ' 2006 Wiley-Liss, Inc.Key words: 5T4 oncofetal antigen; dendritic cells; adenovirus; proteasome; CD8 T cells There are several types of human tumor-associated antigens (TAAs), which are being exploited as targets for developing immunotherapies against malignant tumors. 1-4 Such antigens include, over or selectively expressed normal molecules (differentiation, oncofetal antigens), viral-and tumor-specific antigens, including mutated products (sometimes functional in the transformed state). Human 5T4 is a 72 kDa cell surface oncofetal antigen defined by a monoclonal antibody raised against wheat germ agglutinin-glycoproteins isolated from human syncytiotrophoblast microvillus plasma membranes. 5,6 The 5T4 antigen is highly expressed in trophoblast, but shows relatively limited expression in other normal tissues. 7 In contrast, the 5T4 antigen is upregulated in a wide variety of human carcinomas, including colorectal, gastric and ovarian carcinomas, where it is associated with poor clinical outcome. [8][9][10][11][12] The restricted expression of 5T4 antigen on tumor tissues as well as its association with tumor progression makes it a promising new candidate for immunotherapy. Several approaches to developing immunotherapies against this target are under development. Thus, we are harnessing the tumor cell surface expression of 5T4, by using antibodies to targeted drugs and/ or activation of effectors 13,14 or retargeting using chimeric immune receptors of polyclonal T-cell populations. 15,16 Our work in...

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