An endoplasmic reticulum-targeting signal sequence enhances the immunogenicity of an immunorecessive simian virus 40 large T antigen cytotoxic T-lymphocyte epitope.
An immunological hierarchy among three H-2Db-restricted cytotoxic T lymphocyte (CTL) determinants in simian virus 40 (SV40) large T antigen (Tag) was described previously: determinants I and II/III are immunodominant, whereas determinant V is immunorecessive. To assess the immunogenicity of each determinant individually and define mechanisms that contribute to the immunorecessive nature of determinant V, we constructed a panel of recombinant vaccinia viruses (rVVs) expressing minigenes encoding these determinants in various polypeptide contexts. We found the following. (i) Immunization of mice with an rVV encoding full-length SV40 Tag resulted in priming for CTL responses to determinants I and II/III but not determinant V. (ii) rVVs encoding peptide I or II/III in the cytosol or targeted to the endoplasmic reticulum (ER) were highly antigenic and immunogenic. (iii) rVVs encoding peptide V minigenes were antigenic and immunogenic if the peptide was targeted to the ER, expressed in the cytosol with short flanking sequences, or expressed from within a self-protein, murine dihydrofolate reductase. (iv) Presentation of the nonflanked peptide V (preceded by a Met codon only) could be enhanced by using a potent inhibitor of the proteasome. (v) H-2Db-epitope V peptide complexes decayed more rapidly than complexes containing epitope I or II/III peptides. In brefeldin A blocking experiments, functional epitope V complexes were detected longer on targets expressing ER-targeted epitope V than on targets expressing forms of epitope V dependent on the transporter associated with antigen processing. Therefore, limited formation of relatively unstable cell surface H-2Db complexes most likely contributes to the immunorecessive nature of epitope V within SV40 Tag. Increasing the delivery of epitope V peptide to the major histocompatibility complex class I presentation pathway by ER targeting dramatically enhanced the immunogenicity of epitope V.
Fu
T M
TM
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Mylin
L M
LM
Schell
T D
TD
Bacik
I
I
Russ
G
G
Yewdell
J W
JW
Bennink
J R
JR
Tevethia
S S
SS
D000818:Animals; D017951:Antigen Presentation; D000957:Antigens, Viral, Tumor / Q000276:immunology*; D004721:Endoplasmic Reticulum / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D015398:Signal Transduction / Q000276:immunology; D013539:Simian virus 40 / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
D000957:Antigens, Viral, Tumor; D018984:Epitopes, T-Lymphocyte