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J. Exp. Med.,
Volume 189, Number 5, March 1, 1999 811-820
By


From the * Department of Pathology and Kaplan Comprehensive Cancer Center, New York University
Medical Center, New York 10016; and the Unmutated tumor antigens are chosen as primary candidates for tumor vaccine because of their
expression on multiple lineages of tumors. A critical issue is whether unmutated tumor antigens are expressed in normal cells, and if so, whether such expression imposes special restrictions on
cytotoxic T lymphocyte (CTL) responses. In this study, we use a transgenic approach to study
the development and effector function of T cells specific for P1A, a prototypical unmutated tumor antigen. We report here that although P1A is expressed at low levels in normal tissues, including lymphoid tissues, the P1A-specific transgenic T cells develop normally and remain
highly responsive to the P1A antigen. The fact that transgenic expression of P1A antigen in the
thymus induces T cell clonal deletion demonstrates that normal hematopoietic cells can process
and present the P1A antigen and that P1A-specific T cells are susceptible to clonal deletion. By
inference, P1A-specific T cells must have escaped clonal deletion due to low expression of P1A
in the thymus. Interestingly, despite the fact that an overwhelming majority of T cells in the T
cell receptor for antigen (TCR)-transgenic mice are specific for P1A, these mice are no more
resistant to a P1A-expressing plasmocytoma than nontransgenic littermates. Moreover, when
the same TCR-transgenic mice were challenged simultaneously with B7-1+ and B7-1
Department of Pathology and Comprehensive Cancer
Center, Ohio State University Medical Center, Columbus, Ohio 43210
tumors, only B7-1+ tumors were rejected. Therefore, even though P1A can be a tumor rejection
antigen, the effector function of P1A-specific CTL is restrained in vivo. These results have important implications for the strategy of tumor immunotherapy.
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