Peptide-specific cytotoxic T lymphocytes fail to recognize MAGE-A1+ or Her-2/neu+ tumor cell lines

Purpose: The majority of tumor-associated antigens are derived from nonmutated self proteins. Little is currently understood about the existence and nature of self-reactive T cells that recognize these antigens in healthy volunteers or cancer patients. Here we try to establish culture conditions to expand Her-2/neu- and MAGE-A1-specific T cells from the blood of healthy donors. Material and Methods: Unseparated peripheral blood mononuclear cells of HLA-A*0201(+) healthy donors were stimulated using the well characterized tumorantigens Her-2/neu(369-377) and MAGE-A1(278-296) for in vitro immunization. The influence of different peptide concentrations loaded on autologous antigen-presenting cells on the phenotype and function of the established T cell lines was elucidated. After repetitive stimulations T cells were assayed for peptide specificity as well as tumor recognition in cytotoxicity tests. Results: Using in vitro immunization protocols it was possible to stimulate tumor antigen-specific cytotoxic T lymphocytes from the blood of healthy donors. This was supported by lower peptide concentrations. However, MAGE-A1(278-296)-specific T cells failed to react with a panel of HLA-A*0201(+)/MAGE-A1(+) tumor cells. Her-2/neu(369-377)-specific T cells were able to lyse HLAA*0201(+)/Her-2/neu(+) tumor cell lines after additional exogeneous peptide-loading. Conclusion: T cell responses toward peptides derived from tumor antigens can be easily generated in vitro. However, their antigen specificity did not necessarily reflect the lytic capacity towards antigen-expressing tumor cells. "Artificially" high concentrations of peptide presumably cause the expansion of low-avidity T cells which fail to respond to tumor cells with suboptimal antigen presentation. In contrast, cytotoxic T cells generated with low concentrations of peptide were demonstrated to be superior in peptide as well as in tumor recognition. Optimizing the conditions to expand self-reacting (tumor-specific) T cells in vitro is of relevance for the effectiveness of adoptive therapies.