INSERTION SIGNAL SEQUENCE FUSED TO MINIMAL PEPTIDES ELICITS SPECIFIC CD8-CELL RESPONSES AND PROLONGS SURVIVAL OF THYMOMA-BEARING MICE( T)

CD8(+) T-lymphocytes (T-CD8+) recognize minimal peptides of 8-10 resid ues which are the products of intracellularly processed proteins and a re presented at the cell surface by major histocompatibility complex c lass I molecules. An important step in this process is the translocati on of processed proteins from the cytosol across the endoplasmic retic ulum membrane, mediated by transporter associated with antigen-process ing proteins or alternatively by endoplasmic reticulum-insertion signa l sequences located at the NH2-terminus of the precursor molecules. We report here that the addition of an endoplasmic reticulum-insertion s ignal sequence at the NH2-terminus of T-CD8+ epitopes from chicken ova lbumin (amino acids 257-264) or a naturally occurring tumor antigen ex pressed by the murine mastocytoma P815 (P1A amino acids 35-43) signifi cantly enhanced the priming of specific T-CD8+ in vivo. The signal seq uence did not enhance peptide immunogenicity by merely increasing the hydrophobicity of the peptide, since ovalbumin amino acids 257-264 pep tide with the signal sequence at its COOH-terminus did not demonstrate enhanced efficacy. The signal sequence did not act as a helper epitop e, since T-CD8+ responses were not diminished in class II-deficient tr ansgenic mice or in mice depleted of CD4(+) T-cells in vivo. Important ly, a single immunization with the fusion peptide significantly prolon ged survival of mice challenged with E.G7OVA, a thymoma transfected wi th the complementary DNA of chicken ovalbumin.