MHC class II epitope nesting modulates dendritic cell function and improves generation of antigen-specific CD4 helper T cells1

CD4 T helper cells are critical to the development of coordinated immune responses to infections and tumors. T helper cells are activated through interactions of the TCR with MHC class II complexed with peptide. T cell activation is dependent on the density of MHC peptide complexes as well as the duration of interaction of the TCR with antigen presenting cells. In this study, we sought to determine whether MHC class II peptides could be modified with amino acid sequences that facilitated uptake and presentation with the goal of improving T helper cell activation in vitro and in vivo. A model epitope derived from the murine folate receptor alpha, a self and tumor antigen, was modified at its carboxy terminus with the invariant chain derived Ii-Key peptide and at its amino terminus with a peptide that enhances uptake of antigen by antigen presenting cells. Modification of peptide resulted in enhanced generation of high avidity murine folate receptor alpha T cells that persisted in vivo and homed to sites of antigen deposition. The nesting approach was epitope and species independent and specifically excluded expansion of CD4 regulatory T cells. The resulting T helper cells were therapeutic, enhanced in vivo helper activity, and had an increased ability to resist tolerizing immune microenvironments. In addition to improved immunoadjuvants, this epitope modification strategy may be useful for enhancing ex vivo and in vivo generation of T helper cells for preventing and treating diseases.