Abstract 1500: Modulation of recombinant vaccinia virus vector immunogenicity

Recombinant poxviruses expressing tumor associated antigens (TAAs) are evaluated since 20 years as immunogenic vaccine vector in clinical trials. Possible limitation to recombinant viral vector is due to either prior systemic immunity to poxviruses or immunodominance of viral antigens which may reduce the induction of immune response against weaker tumor antigens. To address this issue, we developed a recombinant Vaccinia virus expressing HSV type I protein ICP47. This protein down-regulates MHC class-I antigen presentation by blocking the transporter associated with antigen processing (TAP), which translocates peptides, generated by proteasomal protein degradation, into the endoplasmic reticulum for loading onto MHC class I molecule. Herpes simplex virus (HSV) US12 gene, coding for infected cell protein 47 (ICP47) was introduced into wild type vaccinia virus and into a r.VV expressing MART-1/Melan-A 27–35 HLA-A201 endoplasmic reticulum (ER)-targeted epitope. Following infection with non-replicating recombinant virus, effect of ICP47 expression on cell surface MHC-class-I, MHC class-II and co-stimulatory molecules was characterized by antibody staining and FACS analysis. Human T-lymphocytes were stimulated in vitro with autologous CD14+ cells infected with r.VV-US12, r.VV-Mart-US12 or control virus. Responsiveness of specific CD8+ and CD4+ to viral proteins and recombinant epitopes were monitored by MHC-multimer staining and interferon gamma (IFNg) expression analysis. Cells infected with HSV-US12-r.VV, demonstrated a decreased ability of presenting MHC class-I antigens to CD8+ T cells whereas MHC-class-II restricted presentation to CD4+ T cells remained unaffected. Co-expression of ER-Melan-A/Mart-1 26–35 appeared to partially compensate for the ICP47 related surface MHC class-I molecule down-regulation and preserve a strong capacity to induce CTL response against the TAA derived peptide. Thus, viral vectors expressing ICP47 confirmed a diminished TAP-dependant processing of endogenous class-I restricted epitopes while the immunogenic potential of recombinant epitopes directly targeted to the ER was enhanced. Such reagents could become of high relevance especially in multiple-boost vaccine protocol required in cancer immunotherapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1500.