Bryce Anderson, Kemais Ehlers, Deborah Johnson, and Stephen Persaud, Brigham Young University
Life Sciences
Antigen presenting cells digest and display foreign proteins from infected cells on the major histocompatibility complex (MHC) that is recognized by T cells via their T cell receptor (TCR). LLO56 and LLO118 are CD4+ helper T cells with TCRs specific for the same Listeria monocytogenes epitope. Despite differing by only 15 amino acids, these TCRs have dramatically different primary and secondary responses to infection. TCRs have very low affinity for peptide MHC. We determined to generate high affinity T cell receptors to test if T cell activation would be improved. We reasoned that the single chain LLO118 and LLO56 TCRs (Vβ2-linker-Vα2) could be subjected to directed evolution to generate mutants that are more stable and then used as a template for engineering high affinity T cell receptors. Single chain LLO118 and LLO56 were fused to the yeast surface protein Aga-2 and error prone PCR was used to generate mutagenic libraries. Stabilized single chain TCRs (scTCRs) were selected for using biotinylated Vβ2 and Vα2 antibodies and anti-biotin beads. First generation clones with increased stability compared to wild type were isolated for both LLO118 and LLO56. A second mutagenic library using the first generation mutants as templates was produced and the most stable clones were selected after temperature denaturation, permitting isolation of clones with increased stability. We are currently engineering high affinity T cell receptors by generating affinity libraries using site directed mutagenesis of the CDR3 regions. These libraries are sorted for their ability to bind to MHC tetramers and individual clones are tested using flow cytometry. Generation of pathogen specific high affinity TCRs will increase our understanding of how T cells are activated and could also provide infection specific diagnostics and therapeutics.