Adenoviral Transgene Ubiquitination Enhances Mouse Immunization and Class I Presentation by Human Dendritic Cells

Abstract

Therapeutic vaccination aims at a strong stimulation of antigen-specific CD8⁺ T-cells, so that they differentiate into effectors active in vivo against antigenic targets. Two adenovirus vectors (Ad) encoding two HLA-A*0201-restricted HIV epitope sequences (pol 476 and pol 589) were constructed. The Ad differ by the presence or absence of a ubiquitin monomer sequence (AdUb⁺ and AdUb^-). The effect of transgene product ubiquitination was analyzed on (1) in vivo, the immunization of Ad vaccinated HLA-A*0201 humanized HHD mice and (2) in vitro, the presentation of the transgene encoded peptides by transduced human dendritic cells (DC). In vivo, we found that immunization of humanized HHD mice with AdUb⁺ elicited a transgene product-specific interferon(INF)-γ CD8⁺ T-cell response detectable by enzyme-linked immunospot (ELISPOT), whereas the AdUb^- construction did not. Antigen-specific cytotoxic T lymphocytes (CTL) were also generated in HHD mice immunized with AdUb⁺ and not with AdUb^-. In vitro, using human AdUb⁺-transduced DC, a sizeable expansion of pol 476 and pol 589 tetramer positive CD8⁺ T cells as well as CD8⁺ CTL were obtained in healthy donors. Compared to AdUb^--transduced DC, AdUb⁺-transduced DC triggered a higher number of pol 476-specific IFN-γ-secreting CD8⁺ T cells. In agreement, AdUb⁺ transduced DC, used as target in a ⁵¹Cr-release assay, were more efficiently lysed by peptide-specific CTL than AdUb^--transduced DC. In conclusion, the addition of an ubiquitin sequence to the adenoviral transgene, used as an antigen source, resulted in both in vivo enhanced CD8⁺ T-cell immunogenicity in HHD mice and in vitro increased HLA class I-restricted presentation of encoded peptides by human DC.