Br. Minev et al., INSERTION SIGNAL SEQUENCE FUSED TO MINIMAL PEPTIDES ELICITS SPECIFIC CD8-CELL RESPONSES AND PROLONGS SURVIVAL OF THYMOMA-BEARING MICE( T), Cancer research, 54(15), 1994, pp. 4155-4161
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.