Peptide engineering allows cytotoxic T-cell vaccination against human papilloma virus tumour antigen, E6.

Major histocompatibility complex (MHC) class I allele-specific binding motifs have proved useful in predicting cytotoxic T-cell epitopes from immunogenic proteins. In a search of the E6 protein from human papilloma virus type 16 utilizing the Kb binding motif, we discovered four potential binding peptides. One peptide, E6.1 (sequence 50-57, YDFAFRDL), was poor in its ability to stabilize empty Kb on RMA-S cells, with a t1/2 = 33 min versus 30 min for empty Kb. This peptide subsequently proved to be non-immunogenic upon mouse in vivo vaccination. It was hypothesized that an isoleucine for aspartate substitution at position 2 would improve Kb stabilization kinetics and therefore immunogenic potential. The engineered peptide E6.1 I2 increased the Kb t1/2 to 100 min and was immunogenic upon in vivo vaccination. Cytolytic T lymphocytes (CTL) raised with the E6.1 I2 peptide responded to cells pulsed with either the wild-type peptide or the engineered peptide, implying a blindness to the substitution. More striking, these CTL also lysed a syngeneic cell line transfected with the E6 gene, implying that the E6.1 peptide was processed and presented. These data demonstrate that subimmunogenic peptides can be engineered to improve binding kinetics, which in turn improves immunogenicity. Provided that poor binding peptides are processed, the induction threshold for CTL activation can be achieved with engineered peptides, thus allowing for the kill of wild-type target cells. This approach may prove relevant to the design of subunit vaccines to virally induced tumours.