An Endoplasmic Reticulum-Targeting Signal Sequence Enhances the Immunogenicity of an Immunorecessive Simian Virus 40 Large T Antigen Cytotoxic T-Lymphocyte Epitope

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An immunological hierarchy among three H-2D(b)-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-2D(b)-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-2D(b) 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., Mylin, L. M., Schell, T. D., Bacik, I., Russ, G., Yewdell, J. W., Bennink, J. R., & Tevethia, S. S. (1998). An endoplasmic reticulum-targeting signal sequence enhances the immunogenicity of an immunorecessive simian virus 40 large t antigen cytotoxic t-lymphocyte epitope. Journal of Virology, 72(2), 1469–1481. https://doi.org/10.1128/JVI.72.2.1469-1481.1998

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