Molecular characterization of T cell receptors and non-MHC restricted T cell receptor binding peptides

Abstract

T cells recognize antigenic peptides presented by MHC molecules on antigen presenting cells (APC) through T cell receptors (TCRs). Since TCRs are very similar to antibodies in structure and genetics, TCRs might have the potential to bind free antigens as antibodies do. Here, peptides which bound TCRs irrespective of MHC molecules have been identified by screening "one-bead one-peptide" combinatorial libraries. Peptides: VRENAR, RTGNYV, GKMHFK, KDAVKR and RKPQAI bound recombinant Jurkat single chain T cell receptors (scTcrs). GKMHFK, KDAVKR and RKPQAI were also specific for natural TCRs on the Jurkat cell surface. Molecular modeling implies that Glu96 in the CDR3 loop of TCR alpha chain is a candidate for the peptide interaction site. However, TCR-binding peptides did not induce biological effects on parental Jurkat cells. To extend this study to a biologically relevant system, diabetogenic T cells involved in insulin-dependent diabetes mellitus (IDDM) have been characterized. GAD(524-543) responding T cells showed restricted TCR variable gene usage, which utilized preferentially Vα17 and Vβ12. Three domain single chain T cell receptors (3D scTcr) were constructed as tools to investigate potential therapies for IDDM and to identify peptides which bind to TCR without association of MHC molecules. Functional analysis has demonstrated that GAD(524-543)-specific scTcrs retained the ability to bind GAD(524-543)/IAg7 complex. This work shows that recombinant scTcrs can bind cognate peptide presented by MHC molecules, therefore they can be used as substitutes for natural TCRs in screening "one-bead one-peptide" combinatorial libraries to identify TCR-binding peptide.