Long-term alloreactive T cell lines and clones express a limited T cell receptor repertoire

Alloreactive T cells recognize either determinants of the intact donor MHC molecules displayed on the surface of transplanted-cells or peptide fragments of donor antigens associated with self-MHC molecules by means of their T cell receptors (TCR). To investigate the relationship between the TCR beta chain structure and allorecognition, we established and characterized four long-term T cell lines and seven T cell clones derived following a mixed lymphocyte reaction (MLR) between fully histoincompatible DA (RT1a) and LEW (RT1(1)) rat lymph node cells. These DA anti-LEW T cells were phenotypically CD4+, CD8-, alpha beta TCR+ and produced interferon-gamma but not IL-4, consistent with being Th1 CD4+ T cells. As might be expected, these cells were not significantly cytotoxic and did not display suppressor activity. Analysis of the TCR beta chain gene structure revealed a very restricted repertoire in both long-term lines and clones. The TCRBV6S1 gene was present in 15/21 of the alloreactive T cell mRNA transcripts but only 1/12 of unstimulated DA splenic TCR mRNA transcripts (p = 0.0018). Similarly, the TCRBJ2S1 gene was also used frequently in the alloreactive transcripts (17/21) but in only 2/12 unstimulated splenic transcripts (p = 0.0013). Furthermore, all 15 of the alloreactive TCRBV6S1 transcripts had a distinctive four amino acid N region motif not present in any of the unstimulated TCR transcripts (p = 0.0003). These experiments reveal a distinct homogeneity amongst stable allogeneic T cells in culture. If these results reflect the situation in vivo, the possibility exists that specific immunotherapy may be successful in preventing allograft rejection.