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Calcium signaling on Jurkat T cells induced by microbeads coated with novel peptide ligands specific to human CD3ε.

CD3ε is expressed on T lymphocytes as a part of the T cell receptor (TCR)-CD3 complex. Together with other CD3 molecules, CD3ε is responsible for the activation of T cells via transducing the event of antigen recognition by the TCR into intracellular signaling cascades. The present study first aims to identify a novel peptide ligand that binds to human CD3ε in a specific manner and to perform an initial evaluation of its biological efficacy on the human T cell line, Jurkat cells. We screened a phage-display peptide library against human CD3ε using a subtractive biopanning process, from which we identified 13 phage clones displaying unique peptide sequences. One dominant phage clone displaying the 7 amino acid sequence of WSLGYTG, which occupied 90% of tested plaques (18 out of 20) after the 5th round of biopanning, demonstrated a superior binding behavior to other clones in the binding assays against recombinant CD3ε on microbeads or Jurkat cells. The synthesized peptide also showed specific binding to Jurkat cells in a dose-dependent manner but not to B cell lymphoma line, 2PK3 cells. Molecular modeling and docking simulation confirmed that the selected peptide ligand in an energetically stable conformation binds to a pocket of CD3ε that is not hidden by either CD3γ or CD3δ. Lastly, magnetic microbeads conjugated with the synthesized peptide ligands showed a weak but specific association with Jurkat cells and induced the calcium flux, a hallmark indication of proximal T cell receptor signaling, which gave rise to an enhancement of IL-2 section and cell proliferation. The novel peptide ligand and its various multivalent forms have a great potential in applications related to T cell biology and T cell immunotherapy.