Cytotoxic T Lymphocytes to An Unmutated Tumor Rejection Antigen P1A: Normal Development but Restrained Effector Function In Vivo

Abstract

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− 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.

The development and functions of CD4+ T cells expressing a transgenic TCR specific for an MHC-I-restricted tumor antigenic epitope

“…Transgenic mice expressing a TCR specific for the H-2L d -restricted P1A tumor antigen peptide (P1A [35][36][37][38][39][40][41][42][43] : LPYLGWLVF) in the BALB/c background have been described previously 12 and backcrossed with the DBA/2 background for more than 10 generations. Heterozygous male transgenic mice were crossed with female DBA/2 mice (Vitalriver Experimental Animal Company, Beijing, China) for breeding.…”

“…13 Although P1A is expressed at low levels in normal tissues, including lymphoid tissues, the P1A-specific TCR (Va8.3/ Vb1)-transgenic CD8 1 T cells develop normally in P1A tumor antigen-specific TCR (P1ATCR)-transgenic mice and remain highly responsive to the P1A antigen. 12 Most of CD4 1 T cells also express the MHC-I-restricted transgenic TCR, but the L d /P1A tetramer could only stain the transgenic CD8 1 T cells, not CD4 1 T cells. 7 In our study, more than a half of the CD4 1 T cells from P1ATCR-transgenic DBA/2 mice could be stained by an L d /P1A dimer when the amount of dimer for staining was increased to three-to fourfold of the usual dose.…”

“…[10][11][12] An H-2L drestricted dominant epitope was identified as P1A [35][36][37][38][39][40][41][42][43] nonapeptide (LPYLGWLVF). 13 Although P1A is expressed at low levels in normal tissues, including lymphoid tissues, the P1A-specific TCR (Va8.3/ Vb1)-transgenic CD8 1 T cells develop normally in P1A tumor antigen-specific TCR (P1ATCR)-transgenic mice and remain highly responsive to the P1A antigen.…”

Ectopic T cell receptor expression causes B cell immunodeficiency in transgenic mice

“…TCR transgenic mice have been instrumental for studying T cell development [1][2][3], autoimmune diseases [4,5], and immunity to pathogen-and tumor-derived antigens [6,7]. Several strategies have been employed to develop transgenic mice, including the use of T-cellspecific and -nonspecific enhancing elements in the transgenes.…”

“…Specifically, Kouskoff et al [9] engineered cassette vectors containing TCR variable regions, obtained by PCR from cDNA or genomic DNA, inserted into the TCR gene loci. These cassette vectors contain many, if not all, of the important TCR regulatory elements and efficiently drive transgene expression in T cells [6,10,11]. However, TCR transgenes integrate randomly into DNA and can disrupt a gene at the site of integration.…”